Eva Leotz-Gartziandiao

Véronique Tatryo

Patrick Carlier

SAMPLING AND ANALYSIS OF POLYCYCLIC AROMATIC HYDROCARBONS (PAH) AND OXYGENATED PAH IN DIESEL EXHAUST AND AMBIENT AIR

Keywords:

Polycyclic Aromatic Hydrocarbons (PAH) and their oxygenated derivatives occur in particles or in the vapour phase in the atmosphere. Some of these compounds, particularly the PAH, are known as strong carcinogens and/or mutagens. Emissions from diesel engines are an important source of these contaminants in urban air. In this work, the chemical composition of diesel particles was studied from two different perspectives: the gaz/particule partitioning and the different size fractions of these compounds. A dilution tunnel, with a diesel car connected, was built for the purpose of this study. Measurements were carried out near a motorway in Paris for comparison to the tunnel test results. The results show, firstly, that the gaseous phase of the PAH is predominant (up to 20 times) with respect to the particulate phase, and that the PAH and their derivatives are mainly adsorbed in the very fine particulate fraction (for particle size under 0.4 urn). Secondly, the oxygenated PAH, neglected in the majority of previous studies, are predominant with respect to the PAH.

INTRODUCTION

Several epidemiological studies indicate that mortalities and morbidities can be correlated to the concentrations of atmospheric aerosols [1,2] and short term health effects (respiratory problems, asthme incidents...) have been reported too [START_REF]Société française de santé publique : La pollution atmosphérique d'origine automobile et la santé publique[END_REF]. These problems are normally associated with very fine particles (diameter < 2 or 3 urn)

In urban air 50 to 80 % of fine particles come from traffic sources. In France, diesel engines account for 30 % of the total traffic. In 1995 the French motor industry estimated that 87 % of these particles came from diesel vehicles, 12 % came from gasoline vehicles without catalysed engines and 1 % came from vehicles with catalysed engines.

The Diesel exhaust is a complex mixture of gases, vapours and particulate matter that is the result of the incomplete combustion of diesel fuel and lubricants. In general 10 % to 40 % of the particle phase consists of organic compounds extractable by solvents. These extracts include PAH and many oxygenated PAH. Several of these compounds are found distributed between both the gaseous and particulate phases [4,5,6].

Diesel particles are very small (average diameter near 0.2 urn), they have a respirable size, and once they are inhaled, they can reach the pulmonary alveoli, carrying with them any adsorbed organic compounds. This can provoke respiratory problems as well as mutagenic or genotoxic effects. There is a wider knowledge of the toxicity of PAH e.g., BaP, than there is for oxygenated PAH, for which complete toxicological data is not yet available.

For a comprehensive assessment of the health risks of diesel emissions it is necessary to have a good understanding of their chemical identity, atmospheric concentrations, the distribution between the particulate and gaseous phases, and also their biological activity.

DIESEL PARTICLES

The particle phase of diesel emissions consists of aggregates of spherical carbonaceous particles (about 0.2 um in mass median aerodynamic diameter), upon which significant amounts of highmolecular-weight organic compounds are adsorbed when the hot engine exhaust cools down to ambient temperature (figure 1). The particles in diesel emissions are unique, because they have large surface areas allowing the adsorption of organic compounds.

Solids (SOL)

Vapor Phase - 10 to 40 % of the diesel particulate mass is normally due to organic compounds which include high-molecular-weight hydrocarbons and semi-volatile hydrocarbons.

The organic compounds present in diesel particles can be classified into three groups:

-aliphatic hydrocarbons: alkanes, alkenes ... -aromatic hydrocarbons: polycyclic aromatic hydrocarbons (PAH) -polar hydrocarbons: oxygenated and nitrated PAH, dicarboxylics acids, alcanoic acids... [7]. The distribution of these compounds between the gas and particle (adsorbed) phases depends on the physico-chemical properties, e.g. ambient temperature and humidity.

Diesel particles have been classified as "probably carcinogenic" in humans by the « Centre International de Recherche sur le Cancer (CIRC) » and the US EPA (Environmental Protection Agency) and several hydrocarbons present in these particles are or are suspected to be carcinogenic and/or mutagenic (e.g. BaP, BaA, DBahA, nitro-PY, fluorenone).

After inhalation these compounds can be absorbed by the organism and mutations in humans can be induced by them. Therefore, they could conceivably play a role in both genotoxic and non-genotoxic carcinogenesis [START_REF]Diesel exhaust : a critical analysis of emissions, exposure, and health effects[END_REF][START_REF] Nielsen | [END_REF].

Our work was focused on two aspects:

-characterization of organic compounds in the diesel particles in a dilution tunnel, both in the particle and the gas phases and in different size fractions, with special emphasis on oxygenated PAH. -the collection of atmospheric particles during a test campaign in the neighbourhood of Porte d'Auteuil in Paris to compare their composition with the results obtained with the particles collected in the dilution tunnel experiments.

EXPERIMENTAL

3.1. Choice of the organic compounds. They were chosen because they are known to be : molecular markers for diesel emissions, toxic or suspected toxic substances and photochemically active. We chose: -aromatic hydrocarbons : 17 HAP from EPA Method TO-13: NAP, ACE, AC, FLN, PHE, ANT, FL, PY, B(a)A, CHR, B(e)P, B(b)F, B(k)F, B(a)P, DB(ah)A, B(ghi)P, IP -polar hydrocarbons : 1-napthaldehyde, fluorenone, anthraquinone, phenanthrene-9-carboxaldehyde 3.2. Sampling methods Samples of diesel particles were collected by using two différents apparatus :

-A High Volume Sampler (HVS) inspired on the PS-1 (General Metal Works Inc.) built in our laboratory. Particles were collected on a 10.16 cm diameter quartz fiber filter and the gas phase compounds were collected in two cylindrical plugs of polyurethane foam (PUF) located downstream of the filter. The flow rate was approximately 17 Nm 3 /h.

-And a 6-stage cascade impactor (Andersen) in order to separate particles according to their aerodynamic size. Quartz fiber filters were used. The différents stages of the impactor were separated in four granulometrics groups to minimize the analytical work : > 4.2 urn (A), 1.3-4.2 urn (group B), 0.4-1.3 (am (group C) and <0.4 um (group D or final stage). The flow rate was about 33 Nm/h.

After air sampling the PUF and the filters were wrapped in aluminium foils and stored at 4 °C. They were always analysed within 48 h.

Analytical methods

All samples (filters and PUF) were Soxhlet extracted with dichloromethane for 24 hours. The extracts were concentrated under a current of nitrogen and transferred into hexane. The samples were cleaned up on a alumina-silicagel column containing 1 g alumina (5 % water) and 1 g silicagel (5 % water). 1 ml of hexane containing the extract was added to the top of the column and the PAH were eluted with 4 ml of dichloromethane:hexane (20:80) mixture and the oxygenated PAH were eluted with 4 ml of methanol: dichloromethane (20:80) mixture.

The PAH were analyzed using a HPLC with fluorescence/UV detection and GC-MS apparatus. The oxygenated PAH were analyzed using a GC-FID and GC-MS apparatus.

Quantification was performed from the GC and HPLC profiles using representative hydrocarbons as external standards. Recovery rates of the analytical method and blanks were calculated for all the hydrocarbons studied and the results were corrected according to them.

The detection limit was 1 ng/m 3 for the oxygenated PAH and 0.01 ng/m 3 for the PAH [10].

THE DILUTION TUNNEL

We built a dilution tunnel which was connected to a diesel car. With this tunnel it was possible:

-to use a standard car -to efficiently dilute the exhaust gases and to obtain an homogeneous mixture between exhaust gases and ambient air (which is filtered later on). -to reproduce the chemical and physical phenomena (like reactions, and the adsorption of the compounds on the particles) -to monitor temperature, humidity and compounds like NO X and CO 2 -to connect the HVS and the impactor Stainless steel was used for the tunnel and quartz wool permitted thermal insulation (figure 3).

The flow in the tunnel was optimised for the different samplers to allow collection under isokinetic conditions. 154 Nm 3 /h and 126 Nm /h for the HVS and the impactor, respectively.

Blank runs were carried out in the air dilution with the two apparatus. For oxygenated PAH the results were under detection limits. For PAH, the results for NAP, FL and PHE were between 1 and 6 ng/m 3 and for the others they were under detection limits.

RESULTS AND DISCUSSION

5.1.Characterization of organic composition of diesel particles

For this study The « Institut Français du Pétrole, IFP » supplied a car and a reference fuel. Real time determinations of temperature, humidity, carbon dioxide (CO 2 ) and oxides of nitrogen (NO X ) were carried out in the dilution tunnel. Each sample was obtained during 5 minutes at 30 °C with the HVS and the impactor and each experiment was carried out three times. A good repeatability of the experiments was observed.

All the organic compounds studied were found in the diesel exhaust (gas and particulate). The n-alkanes and a complex mixture of branched and cyclic hydrocarbons was found in each sample.

Table 1 show the concentrations of PAH in gas and particle phases. PHE, FL and PY were the major constituent, these compounds are characteristic molecular markers for diesel exhaust components [START_REF] Masclet | Physico-Chemical behavior of atmospheric pollutant[END_REF]. The concentration of NAP in the gas phase was high. In the three experiments the gaseous fraction was predominant with respect to the particulate phase (Figure 2). Up to 15 times more predominant for the PAH between FLN and FL. The importance of sampling the gas phase was demonstrated. • particles g gas ' FIGURE 2. The percentage distribution of each PAH between the gas and particle phases.

4 series of diagnostic PAH ratios were defined (the particle phase was only used) for comparison with the ones corresponding to diesel source inputs [START_REF] Aceves | [END_REF][START_REF] Rosell I Mêlé | report of the Institut Quimic de Sarria[END_REF]. In Table 2 The results obtained for the oxygenated PAH are shown in Figure 3, for both the gas and particulate phases. The naphtaldehyde was the major component in the two phases. Contrary to what we saw for the PAH, the concentration of oxygenated PAH in the particle phase was greater than that of the gas phase. This is because the volatility of these compounds is less than that of the PAH. The results obtained showed that there is a bigger proportion of oxygenated PAH than PAH in the particulate phase. For the compounds studied, the sum of concentrations of the 4 oxygenated PAH was 30 times greater than the sum of the concentrations of the 17 PAH This shows that the importance of these compounds has been under estimated as they have been neglected in the majority of previous studies.

The same PAH and oxygenated PAH were identified with the impactor. The concentration of oxygenated PAH was greater than that of PAH again, and the results obtained showed, that all the studied compounds (PAH and oxygenated PAH) are mainly found in the very fine particulate fraction (for particle size under 0. This fraction can reach the pulmonary alveoli, which enhaces the risk of introducing the organic compounds, present in these particles, into the organism.

Table 2 summarises the toxicological data of studied compounds [START_REF] Sax's | [END_REF]. Extensive toxicological data are available for PAH which is not the case for oxygenated PAH, particularly for phenanthrene-9carboxaldehyde. A few toxicological data are available for them with respect to the evaluation of the air quality.

Paris campaign

To complete the tunnel dilution tests, measurements were carried out near a motorway for a week (Paris-Porte d'Auteuil). A HVS was used to collect the gas and particle phases for PAH and oxygenated PAH.

2 series of 12 h samplings (day and night) for 5 days were performed. The CO, NO, NO 2 , traffic and carbon data were obtained during the same period. A good correlation between CO, NO, trafic and the PAH and oxygenated PAH maxima was observed, and the concentration of these compounds was high in the day samplers.

We systematically observed, a predominance of the gaseous fraction with respect to the particulate phase, up to 10 to 20 times more predominant for PAH between FLN and FL (Fig 5) and a higher concentration of oxygenated PAH than PAH in the particulate phase, by a factor of almost 10 (Fig 6). It is important to recall again that some of the oxygenated PAH family are mutagenic, but current toxicological knowledge is poor. We observed too the contribution of different sources of samples: vehicular emissions (diesel and gasoline) and natural emissions (measurements were carried out in spring near the « Bois de Boulogne »).

The percentage distribution of PAH in diesel as determinated by the test results is shown in Fig 7 and they are compared to those previously found in gasoline [START_REF] Miguel | [END_REF]. Comparing the profiles of fig 7 with those of fig 8, a good correlation is observed, however, it can be noted that the contribution of both fuel types appears to be similar.

CONCLUSION

The analysis of each sample of diesel exhaust showed that besides PAH and oxygenated PAH, the organic fraction also contained n-alkanes and an unresolved complex mixture (UCM) of hydrocarbons. These compounds are characteristic of petroleum residues and vehicular exhaust.

PAH and oxygenated PAH were identified in both the gaseous and particulate phases ant the results show the extent of the distribution between the two phases. In both the field and tunnel experiments it was observed that the PAH were predominantly found in the gaseous phase rather than in the particulate phase.

The work, therefore, highlights the importance of the sampling the gaseous phase, something which has been often neglected in previous studies.

Determination of the size distribution of diesel particles showed that the organic compounds were mainly adsorbed onto the very fine particulate fraction (< 0.4 urn). Particles of this size can reach the pulmonary alveoli carrying with them any adsorbed organics species such as PAH or oxygenated PAH.

In fact, oxygenated PAH were found to be present at greater concentrations than the PAH in the particulate phase. In the tunnel experiments up to 30 times more oxygenated PAH than PAH were found while the factor for ambient air was about 10. This factor is surely under estimated and very few toxicological data exist for these compounds. Given the high concentrations found, further studies are required for investigating these compounds in ambient air.

Finally, the field studies clearly show the contribution of traffic sources to the urban aerosol. However, the lack of supplementary information inhibits the possibility of recognising the exact contribution of diesel to urban aerosols. Nevertheless, the results observed show the same trends as those seen in the tunnel experiments with respect to the importance of sampling the gaseous phase for organics compounds as

FIGURE 3 .

 3 FIGURE 3. Concentration of the gaseous and particulate phases of the oxygenated PAH in diesel exhaust (the mean of three values).

  4 urn) Fig 4.

FIGURE 4 .

 4 FIGURE 4. Concentration of PAH in the different size partitions in diesel exhaust.

FIGURE 5 .FIGURE 6 .

 56 FIGURE 5. A day concentrations of PAH in Porte d'Auteuil (Paris)

Fig 8 FIGURE 7 .s S 1 FIGURE 8 .

 8718 FIGURE 7. Comparison of diesel (results from the dilution tunnel) and gasoline (results from littérature) PAH profils

TABLE 1 .

 1 Concentration of the gaseous and particulate phases of PAH in diesel exhaust (the mean of three values).

		Particle	Gas
		(ng/m3)	(ng/m3)
	NAP	0.26	149.19
	ACE	0.00	11.18
	AC	0.00	7.25
	FLN	0.18	13.79
	PHE	2.14	36.47
	ANT	0.30	12.07
	FL	0.10	7.86
	PY	0.93	3.81
	B(a)A	0.32	0.60
	CHR	0.11	0.40
	B(e)P	0.04	0.00
	B(b)F	0.04	0.06
	B(k)F	0.02	0.00
	B(a)P	0.04	0.00
	DB(ah)A	0.03	0.00
	B(ghi)P	0.06	0.00
	IP	0.04	0.00

TABLE 2 .

 2 a good correlation with the available data in the previous studies is shown. Source imputs correlation ratios for this study and the previous studies.

		Filter 1	Filter 2	Filter 3	Diesel	Gasoline
					[12,13]	[12,13]
	PHE/(PHE+ANT)	0.87	0.88	0.88	-	0.77
	FL/(FL+PY)	0.1	0	0.16	-	0.43
	BeP/(BeP+BaP)	0.59	0.46	0.5	0.44	0.53
	IP/(IP+BghiP)	0.44	0.39	0.44	0.46	0.18

TABLE 2 .

 2 Toxicological data of PAH and Oxygenated PAH studied in this work[START_REF] Sax's | [END_REF]

	PAH	Toxkity		Matagettity	Reported in
	Nnphtalène	Moderate	Not confirmed		EPA-TSCA
	Àcénapblhyïène	Moderate		Established	EPA-TSCA
	Acénaphtfténe	Moderate		Established	EPA-TSCA
	Fluorène	Weak		Established	EPA-TSCA, IARC
	Phénanthrène	Moderate		Established	EPA-TSCA, IARC
	Anthracene	Moderate		Established	EPA-TSCA, IARC
	Ftuoranfliène	Moderate	Not confirmed	Established *	EPA-TSCA, IARC
	Pvrène	Moderate	Not confirmed	Established *	EPA-TSCA, IARC
	Benzo(«)anflira	Poison	Confirmed	Established *	EPA-TSCA, IARC
	cène
	Chrysène		Confirmed	Established *	EPA-TSCA, IARC
	Benza(fa)fliioran		Confirmed	Established	IARC
	tbêne
	Benzo(k>fluoran		Confirmed	Established	IARC
	tbèae
	Bettiû(â)pyrènc	Poison	Confirmed	Established *	EPA-TSCA, IARC
	Be»zô(e>|*yrèfte		Not confirmed	Established *	IARC
	lndenû(J,23-		Confirmed	Established	EPA-TSCA, IARC
	cct)pyrène
	Benzo(g,h,t^péry		Not confirmed	Established	IARC
	lêne
	Dibenzo{a,h)auf	Poison	Confirmed	Established *	EPA-TSCA, IARC
	hracène
	1-	Moderate			EPA-TSCA
	haphthaldehydè
	Fluorenone		Not confirmed		EPA-TSCA
	Antliraqttinone	Moderate		Established	EPA-TSCA
	* Human mutagen
	IARC : International Agency for Research on Cancer
	EPA-TSCA : Environmental Protection Agency-Toxic Substances Control Act

ACKNOWLEDGEMENT This work was supported by French Ministry of Territorial Planning and Environment under contracts 24/96 and 19/97 and by Ademe-Primequal Program under contract 96 66 012, and carried out in collaboration with IFP (Institut Français du Pétrole). The authors would like to express their gratitude to Mrs. Nathalie Bocquet, Mrs. Maryse Marlière, Mrs. Claudine Viley and Mr. Bruno Triart for their technical assistance.

well as the predominance of oxygenated PAH in the particulate phase.


Guymarlair Ineris
email: guy.marlair@ineris.fr

Experimental Approach of the Fire Hazard in Closed Spaces Laboratory and Full-scale Tests by

This presentation is intended to open technical discussions at the workshop devoted to fire testing and modelling with regard to the specificity of the fire hazard in various enclosures that are liable to drive the fire scenario (tunnels, warehouses, technical rooms, underground structures). More particularly, the paper outlines INERIS views on the role that can be played by fire tests, from lab-scale to real scale, at the light of a brief historical review and from its own experience. The purpose is illustrated by a number of examples where INERIS has contributed to analyse or solve fire problems, evaluate fire protection systems or potential consequences to the environment or more generally understand related phenomena that can be encountered in closed structures. Eventually, the paper stresses the opportunity and advantages from conjugated use of testing and modelling techniques.

Large scale and small scale tests : some historical issues

From a general point of view, it is worth to notice that major fundamental progress in the past decades in the understanding of the fire physics have been obtained through experimentations of various kinds. In comparison, the development of mathematical models and related computer codes, although started as early as in the 70's, have only gained substantial interest together with the sharp increase in the power of microprocessors, related decrease of computation time and with the delivery of user-friendly softwares dedicated to fire engineering and fire hazard analysis, say, since the mid 80's. As stated very clearly by Hirano et al [START_REF] Hirano | Fire spread phenomena : the role of observation in experiment[END_REF] iterative experiments and related observations are fundamental steps of any scientific research, in order to generate ideas, validate first order analysis of fire problems like fire spread. Eventually, the experimental approach support mathematical development of the expected final operational tools that one wish to use to make accurate or conservative predictions of confined structures at the design level.

In France, we often refer to the fire disaster of the Bazar de la Charité that occurred in Paris at the end of last century (where 129 people died) as being the starting point for the implementation of reaction-to fire tests to evaluate the fire performance of linings, floor and ceilings coverings that are allowed to be used in places of public assembly. A more comprehensive review performed by V. Babrauskas has identified the first " recognized " fire test (e.g. being supported by accurate specifications) to be the one in use in the US Marine to evaluate fire performance of wood used in ship construction [START_REF] Babrauskas | From Bunsen burner to heat release rate calorimeter[END_REF] . The most common use devoted in the early times to small-scale fire tests was the ranking of test materials from the empirical appraisal of one single or a few criteria that relate to the global fire behaviour (for instance ignitability, fire spread, smoke index, time to ignition...). hi parallel, the very severe risk of fire and explosion and related potential damage in coal mines have been studied by all concerned industrial countries through extensive large-scale experiments, generally performed in wind tunnels or other experimental galleries. Basically, large-scale tests have been used in the field to learn the consequences of a fire scenario from a real simulation, or verify by observation and measurements major fire safety issues whereas current knowledge was unable to understand, even less predict, on a scientific basis all the results obtained and analyse them in terms of physical laws or models. Later, other large-scale multipurpose facilities were built or retrofitted for fire testing use by various fire research or technical centres such as FMRC, BFRL (a division of the NIST), or Underwriters Laboratories in the USA, FRS in the UK, SP in Sweden. More specific equipment of that kind also exist in France, for instance to study the fire hazard in the nuclear industry [START_REF] Malet | Fire Fighting Procedures and Estimation of Fire Consequences in Nuclear Plants[END_REF] or for the certification of fire extinguishers. They often present the configuration of large burn halls where for instance storage commodities may be tested and are generally provided with large-scale heat release rate measurement tools. Extensive use of such facilities have resulted in a basic classification of storage commodities and have also greatly contributed to the improvement of sprinkler systems. Recent experimental investigations using such burn halls deal with the interaction of sprinkler systems with other fire protection devices such as smoke vents and draft curtains [START_REF] Grattan | Large-scale tests of sprinkler, vent, draft curtain interaction[END_REF] . In France, IPSN is operating specific concrete enclosures for fire safety studies regarding the French nuclear power plants [START_REF] Malet | Fire Fighting Procedures and Estimation of Fire Consequences in Nuclear Plants[END_REF] . Historically speaking, the major advantage of the large-scale experimental approach was the ability of observing the fire phenomena (smoke movement for instance) and measuring basic parameters characterising the overall fire behaviour (or fire suppression process) at a realistic scale in such a condition that no extrapolation step is needed, because the interaction with the structure or the confinement involved in the fire scenario studied was reproduced at 1:1 scale.

It shall be stated that fire dynamics which relates to uncontrolled combustion process, remains until now a very complex topic that will justify for still many years the use of pertinent experiments in a number of cases in spite of the progress accomplished by fire zone and CFD models. This will be true in particular, when the fire problem to be coped with relates to complex enclosures or when the main fire hazard deals with chemical issues (e.g. source terms characterisation of toxicants or pollutants produced in fire plumes, that is often a basic requirement for adequate introduction of input data in computer codes).

At the time, due to such considerations, the assessment of the overall performance of smoke venting systems in heavy traffic underground structures is generally performed or at least checked by in-situ calibrated fire tests. Figure 1 illustrates a fire test recently performed by INERIS which took place in a complex underground roadway located in Paris aiming at such a goal. In the field, interactive processes between pertinent use of CFD and experimental validations at various scales become more and more efficient.

As an example of this, a recent thesis work has outlined the mutual interest of CFD calculations and use of pertinent 1:20 scale tunnel section mock-up designed adequately to perform investigation on the same subject [START_REF] Megret | rapport de thèse : "Etude expérimentale de la propagation des fumées d'incendie en tunnels pour différents systèmes de ventilation[END_REF] . A further example of a complex confinement where the experimental approach was considered a fundamental step of the risk assessment process was the Channel Tunnel. Coping with the fire hazard inside the single and double deck carriages of the Shuttle to be in use in the Trans-Manche fix link had led to the building and operation at INERIS of a full scale mock-up of a wagon carrying real cars. The mock-up was used to perform real fire scenarios for the evaluation of emergency procedures and related fire protection systems performance. More recently, a collaborative study involving contributions of CETu, Scetauroute, SAPRR and INERIS focused on system under development to drain safely flammable accidental spills for use in road tunnels [START_REF] Lacroix | Full-Size Testing of Drainage Systems for Burning Liquids in Road Tunnels[END_REF] . The work has comprised a validation step performed by use of a full scale prototype of the drainage system tested with real fire scenarios in the Mont-la-ville explosion and fire testing field also belonging to the institute.

Although less directly informative in comparison to large-scale, small-scale fire tests have been developed extensively from early times for purposes such as quality control, fire performance evaluation or approval of various materials (by reference to a standard or a specification in some designated areas e.g. building construction, electrical devices, transportation systems...). Low costs remain the major advantage of these series of tests , very numerous, but however very often suffering from empirical design and use. Indeed, many of them have capabilities basically limited to ranking of materials in terms of fire performance regarding a single criteria (e.g. ignitability, flammability, smoke obscuration, fire toxicity, flame spread,...). However, with the emergence of modern techniques for the measurement of heat release, a very important fire parameter, some new lab-scale tests have emerged, with much more potential for powerful applications such as the cone calorimeter (ISO 5660), the OSU calorimeter (ASTM E906 ; FAR part 21 and 121 ; NFPA 263) and the FMRC Lab-Scale Flammability Apparatus (proposed standards ASTM E5 Z6880Z and NFPA 278). Scientific publications of works based on the use of those apparatuses have largely confirmed that statement. The Single Burning Item (SBI) apparatus newly proposed to serve as the main fire test in the European will also allow the measurement of the rate of heat release.

Eventually, adequate validation work of lab-scale testing protocols by comparison with largescale tests results is very often a requirement to promote technological breakthroughs in fire problem evaluations at lab-scale [START_REF] Newman | Technological Breakthroughs in Material Flammability Evaluations[END_REF] .

INERIS fire testing facilities and related instructive experimental works

Similarly to the general trend mentioned in the historical review, INERIS started to learn the explosion and related fire risk in mines preferably by use of large testing galleries and wind tunnels.

In particular, the Institute has studied a variety of fire problems related to confined fires by use of its 600 m [START_REF] Malet | Fire Fighting Procedures and Estimation of Fire Consequences in Nuclear Plants[END_REF] fire gallery (see figure 2) commissioned in 1982, still in operation today in parallel with more recently built experimental facilities such as the 80 m 3 enclosure and the INERIS lab-scale fire calorimeter, based on the FMRC lab-scale flammability apparatus. The potential applications of the whole set of test equipment are very numerous, and current applications do not restrict any longer to the mine safety background. hi 1996, INERIS has overviewed the use of its fire gallery to qualify well ventilated chemical fires that may occur in warehouses where free burning quickly becomes the dominating process [START_REF] Marlair | A Review of Large-scale Fire Testing Focusing on the Fire Behaviour of Chemicals[END_REF] . Thanks to funds coming from the French Ministry of the Environment and some other international technical and financial supports (International Isocyanate Institute, EU DGXII [START_REF] Marlair | The Commercially Important Di-Isocyanates in Fire Conditions[END_REF] ), the characterisation of the thermal and chemical parameters of the fire behaviour of a series of products, such as pesticides, fertilizers, or some commercially-important chemicals, like TDI or MDI has been achieved. Some fire safety issues of a high rise warehouse containing pharmaceutical products and related materials were also determined [START_REF] Cwiklinski | L'essai en grand : une méthode réaliste d'évaluation du risque incendie[END_REF] . Other major examples of pertinent applications of the equipment was the experimental work carried out in support of the revision of the ventilation equipment of the RATP, the company operating the Underground in Paris [START_REF] Lodel | Le Cerchar étudie le comportement au feu d'une installation de ventilation de la RATP[END_REF] , or a customised fire resistance test carried out in collaboration with CTICM to qualify the fire resistance properties of a newly designed irrigated curtain made of mineral woven fabric. The system had proven to perform like an unusual but efficient movable fire door now in operation in a very large exhibition hall in Paris [START_REF] Mohamed | Le mur coupe-feu irrigué et le système d'évacuation du public et entrée d'air[END_REF] Other example of use in relation with the fire problem in closed spaces deal with the sizing of the pressure conditions that should prevail for the suitable operation of a safety refuge in the French tunnel of Puymorens [START_REF] Casale | Dimensionnement aéraulique des refuges incendie du tunnel de Puymorens[END_REF] or the experimental approach at full-scale of the fire behaviour of Christmas trees decorated with artificial snow in confined areas such as town halls, schools (see figure 3). INERIS is also using a 80 m 3 (movable to a 100 m 3 ) enclosure (4 m x 4.5 m x 4 m) to perform tests involving fire scenarios under control of ventilation, which may be a common situation in some closed spaces depending on the fire spread rate and the size of burning items. The initial use of this concrete building was the validation at 1:1 scale (enclosure + combustible materials) of a non propagating fire scenario from one cable tray (catching a fire) to another cable tray located on the opposite wall, a configuration representative of a cable room of a nuclear power plant.

F ;&

At the lab-scale, INERIS commissioned in 1997 a fire calorimeter based on the FMRC Flammability apparatus, according to fruitful collaborations initiated in the early 90's with the inventor of the equipment still working at FMRC and the French user of the equipment Rhône-Poulenc Industries. The equipment has been implemented at the Institute as a major step of an on-going research programme aiming at learning and assessing the associated risks of chemical fires controlled by ventilation. However, this equipment is in fact capable of testing materials and products on the full range of ventilation conditions, by adjusting the airflow rate coming in the quartz tube physically delimiting the combustion area. Various scaling techniques involving the external heat flux and the O2 content of the inlet flow as controlling parameters are in use to simulate large-scale fires or develop predictions applying for large-scale. Tables 1 and2 list some a few characteristics of this test rig and figure 3 gives of picture of it. The equipment has already revealed very relevant for the identification of specific confined fire phenomenology such as drastic enhancement of non thermal damage in case studies of storage of cellulose nitrate films, or when organophosphorous compounds undergo decomposition in fire conditions [START_REF] Marlair | Experimental Evaluation of the Fire Hazard of Organophosphorous Insecticides by Use of Various Test Methods[END_REF] . It may also serve as a screening method for ranking the materials with respect to their ability to produce dioxines in fire conditions [START_REF] Adam | Soot Generation in Fires : An important Parameter for Accurate Calculation of Heat Release[END_REF] . Repeatability of experimental data obtained by use of this apparatus is really excellent in all cases.

Apparatus design

Eventually, INERIS will soon commission a cold modular mock-up able to address fire problems by use of similarity laws. Thanks to appropriate construction, the new cold mock-up will have the ability to treat fire dispersion problems in both conventional enclosures (rooms) or tunnel configurations at different scales. The design and construction of the equipment are important milestones of a research project regarding the simulation of fires in complex underground structures.

Discussion and conclusive comments

Technical progress in fire science and computer technology, conjugated to new requirements in matter of fire safety levels have now led to new trends in the design and use of fire test equipment and related use. Small-scale testing have achieved new capabilities in the field of certification and characterisation of the fire behaviour of products and materials, although scaling laws required to extrapolate the results to real fire scenario are still under development for many applications. Among them, the so-called Tewarson Apparatus in France (Lab-scale FMRC Flammability Apparatus) seems to our opinion the one presenting the more versatile capabilities, particularly with regard to underventilation of fires which often prevail in closed structures 22723 .

It looks however surprising that use of CFD calculations seems to be until now very rarely used to understand more finely what happens in well established lab-scale fire testing equipment or in the design phase of new ones. INERIS is currently exploring this technique to increase the detailed knowledge of the operation conditions of the Tewarson apparatus in the framework of the ADELFI project, a European 'ESPRIT' programme. Large-scale tests using fixed equipment such wind tunnels, large burn halls or room fire tests, as well as in-situ experimentation are very important tools, although leading to more expensive procedures in comparison to lab-scale. Today, they are keeping their interest in a variety of cases, and will remain of high added value for the supply of validation sets of data for the development of the models and related codes running on computers as well as for the engineering of fire safety devices. They may also support conveniently the analysis of special fire hazards in closed spaces. New series of adequately conducted tests are also required to validate new physical submodels that still have to be introduced in CFD models to treat major fire related phenomena (e.g. near field air entrainment, smoke production, emission factors of fire products, fuel mass flowrates...) in a suitable manner for accurate prediction of the fire threat in close spaces. In that field, pertinent lab-scale mock-ups developed in agreement with similitude laws may help also in the extent that boundary conditions are more easily monitored at small scale than at large-scale.

Due to this background, the existing set of fire testing facilities at INERIS seems to be very competitive with regard to the fire hazard assessment in closed spaces. At large-scale, the fire gallery will address adequately well ventilated fire scenarios in tunnels and the 80 m enclosure will be more appropriate when fuel rich conditions are liable to occur in closed spaces. Besides, the INERIS fire calorimeter (of Tewarson type) is suitable to bring valuable contribution to the study of both cases by simple modification of the controlling parameters, hi addition, INERIS has been increasing its capabilities in fire modelling. The expected issue is improved efficiency in the use of the mentioned testing devices as well as the development and the improvement of modelling tools suitable for the evaluation of fire scenarios pertaining to confined hazardous spaces [START_REF] Ruffin | Numerical simulation of locomotive fires in the Lyon-Turin tunnel[END_REF] . The French Ministry of the Environment has recently supported that general policy by bringing his financial support to the development of a comprehensive 3-years programme aiming at developing a comprehensive methodology for the study of fires and related environmental impacts in warehouses. The programme will largely rely on computational simulations associated to pertinent testing. Experimental investigation by use of a cold mock-up and numerical simulation are also very tightly associated in another on-going project conducted at INERIS. The main aim of the project deals with the development of a coupling technique between ID numerical computation of fluid flows in complex networks (with many branches, ventilators...) and 3D computation (by means of CFD codes) in some particular areas of the network where a fire takes place for instance. This latter project is also granted by National fund.

Literature

figure 2 :

 2 figure 2 : picture of the INERIS fire gallery and related equipment

figure 3 :

 3 figure 3 : Annular ignition source (alcohol) used in a series of full scale fire tests on Christmas trees (1998) performed in the INERIS fire gallery, vertical section

figure 4 :

 4 figure 4 : view of a fire test by use of the liNERIS lab-scale calorimeter (plastic sample)

table 1 :

 1 Some characteristics of the INERIS lab-scale fire calorimeter (Tewarson Apparatus).

		Main features
	basic design features	FMRC lab-scale flammability apparatus
	test sample, physical state	solid (even powders), liquid or gas
	test sample size	in the order of 10 cm or 50 g
	inlet flow (usual range : 0-200 1/min)	air, any mixture of O 2 /N 2 , mixture O 2 /Ar
	outlet flow	usual range : 50 to 300 Nm 3 /h
	external heat flux	0-65 kW/m 2 by infrared heaters with quartz lamps
	ignition device	Pilot flame and spark ignitor
	Basic measurements and related calculations
	weight loss rate	weighing sensor range 0 -125 g
	heat release rate	both O 2 consumption and CDG techniques 18
	on-line gas analysis capabilities	O 2 , CO, CO2, NO, NO 2 , HCt, SO 2 , HCN, HC1,
		H 2 O vap , NH 3
	other (optional) chemical measurements	e.g. NH 3 , aldehydes, ketones, nitriles
	smoke density	optical measurement of extinction coefficient at 3
		different wavelengths
	flame temperature	thermocouple K
	combustion gases temperature and convected heat	thermocouple K
	yields of combustion products	for all measured product, as a function of the
		equivalence ratio (e.g. ventilation factor)
	outlet gas flow	averaging Pitot tube
	flammability parameters 19	Thermal Response Parameter (TRP), Fire
		Propagation Index (FPI), Critical Heat Flux
		(CHF) according to FM standards

table 2 :

 2 measurements and related calculated data on the INERIS fire calorimeter

figure 1 : in-situ evaluation of the fire plume interaction with the smoke venting system in an underground roadway (source term : twin pools of heptane, heat release around 5.2 MW)


F Vinkler

J Rpiguet

Analysis of the long-term stability of an ancient room and abandoned pillar mine -Impact of the water level

Analysis of the long-term stability of an ancient room and abandoned pillar mine -Impact of the water level

Fabrice Vinkler, Jack-Pierre Piguet

INTRODUCTION

During the last three years, the surface of the iron basin in Lorraine (France) subsided straight above several recently flooded mines, after the water pumping ceased. Studies were therefore iaunched to examine the role the mine water rise plays in these instabilities. Several cities located straight above abandoned mine areas with characteristics similar to that of already subsided sites have initiated studies in order to locate, evaluate, and possibly prevent the hazards.

This articie focuses on an ancient mine, which is 100 m deep. and has been exploited on two leveis separated by a 5 m thick intercalary layer. The data proceeding frorn three boreholes allowed mechanical characterizations. Based on the analysis of the geometry and of these characterizations, experts located the possible unstable areas. and advised of preventive actions. They do not conclude to any major long-term hazard, but emphasize on further research to be made conceming the hydromechanical behavior of the rocks, and the preventive monitoring of microseismical events precursory to a possible subsidence.

This numerical study has several goals. First it aims at confinning the long-term stability diagnostic expressed by the experts, and predicting the short and long-term failure zones. Then it seeks to evaluate the respective impact on failure. on the one hand of the long-term strength reduction, on the other hand of stress variations during the water level rise. Finally several instability scenarios, considered äs possible by the experts, have been studied: locally below average mechanical properties or potentially dangerous geometry (especially bad superimposition of the pillars in the two seams).

HYDROMECHANICAL INTERACTIONS IN THE MINES

The hydromechanical interactions around undermined areas are characterized by three phenomena:

• local permeability changes, äs a consequence of excavation-induced fracturing and aperture changes related to the stress Variation; • hydraulic pressure changes, related to the water table decline during exploitation, then rise after the pumping ceases; • mechanical properties change (particulariy compression and tension strengths) äs a function of the Saturation degree.

2.-Stress variations related to the water level rise

Terzaghi's classical law (valid in porous media) states that the pore pressure increase results in a reduction of the effective stress by the same amount, thus in a rise of the local failure risks.

In fractured rock masses with a highiy impermeable matrix, the pore pressure increase has the effect

Spontaneous collapse

Very rare phenomenon characterized by a sudden extended vertical glide of the overburden occurring in very precise geological and exploitation conditions. A stiff layer of the overburden bends then fails, resulting in the brutal and simultaneous collapse of the pillars. The bending proceeds either from water seepage through the overburden, and the setting of a water load upon the stiff layer [START_REF] Maury | Effondrements spontanes-Synthese d'observations et possibilite de mecanisme initiateur par mise en Charge hydraulique[END_REF], or from the long-term strength reduction of the pillars that sustain the roof [START_REF] Tincelin | La prise en compte de l'eau et la prevision des exhaures en mines et carrieres[END_REF] Formation of a sinkhole Shallow mine (<50m) • f Less cohesive rocks (marls) or sands Figure 2. Room and pillar mines. Impact of a change in their hydraulic environment on their stability For each rock type, a series of physical and mechanical tests was undertaken, which gave the average values (table l ) of the properties, äs well äs their variability. Note that the testing did not allow the monitoring of Stresses and strains after peak-strength was reached.

The intercalary marls may constitute the weakest point of the mine, considering their clay content, particular position, and the variability of their prop-erties. Despite the presence of clay, the tests do not show any creep-related differed deformation. On the other hand, they develop a swelling pressure up to 0.5 MPa, which most certainly proceeds from the chemical reaction of pyrite. Furtherrnore the rnechanical properties do not differ from those of the other facies. The experts theretbre estimated that the hazards usually associated with the intercalary marls in the iron mines seem unlikely here. Parameters for the long-term failure criterion:

Mechanical properties

K 1.LT -K I,ST ~Z~( l) (2)
TPLT=<PST-10°

where: R t , R g , R " c (Pa) and (p respectively refer lo the peak strenglh, the elastic limit, the tensile strength, the cohesion and the friction angle of the rock In order to account for the dehumidification, creep, fatigue... of the rocks, long-term failure criteria must be devised. Frorn the results of Wiid ( 1970), it appears that, for wet dolerite, the point of crack initiation (R E , also elastic limit), is a better measure of the ultimate strength.

The pre-failure behavior in the different mechanical modeis used is always linear elasticity. The failure criterion is also always Mohr-Coulomb's.

The first Option set gave the choice between including the average properties coming from the tests, or decreasing them by one Standard deviation, particularly to take into account the spatial variability of the data.

To simulate the post-failure behavior of the rocks, unknown since not monitored during the tests, two options were tested: • strain-softening (Fig. 5). The parameters were estimated according to the bibliography. Tests carried out in our laboratory and [START_REF] Bieniawski | Propagation of brittle fracture in rock[END_REF] show a ratio between residual and peak-cohesion varying from 0.25 (sandstone, gabbro) to 0.7 (coal). We retained an intermediate value, 0.4. The friction angle decreases by 5°; • perfect plasticity.

Choice o/ a numerical model

Several reasons expiain why FLAC-2D was chosen to run the modeis: • a porous medium model is fit for little fractured rocks; • the use of the effective stress to simuiate hydromechanical coupiing is in adequacy with the behavior of the rocks: R, R,/10

Strength criteria: "'"''"" in eiasticity "" -for a plastic deformation Ep = 2,5 10' 3 for a plastic deformation E p • 5.IO'3

Figure 5. Strain-softening model.

• it is possible to experiment several mechanical and geometrical modeis, and to compare them on the basis of the extent of the failure zone. It was decided to use a two-dimensional model to save time and improve the grid precision. However, the rooms parallel to the model brought about a problem. It was solved by increasing the density of the gridpoints just above the pillars, so that the stress in the pillars is equal to that caiculated by the "tributary area" model.

The comparisons between difierent modeis are made in terms of failure zone extension. As any plastic area was considered äs in failure, the failure zones were identified when plotting the plastic points.

Caiculations stages

FLAC-2D was chosen to run the modeis, äs it is adapted to the modeling of porous media with t'ew fractures. The command CONFIG GW was used to explicitly simulate the water table rise. Rocks were given either strain-softening or Mohr-Coulomb plasticity model, depending on the assumptions.

The caleulations has been divided into three stages, which can also be subdivided:

• initial state after exploitation. Rocks have shorttemi mechanical behavior. The water table is l m below the mine wall. The Saturation degree of the rocks above water table is set to 95 % in order to account for the near-saturation of the rocks due to capillarity (Fig. l); • adoption of löng-term failure criteria; • progressive rise of the water table. The final level is set to 20 m below the surface (regional level).

The mine water rise causes effective stress lowering in all flooded rocks. but also a mareinal ad-ditional load brought about by water entering into the rock masses (the Saturation degree increases from 95 % to 100 % in the resaturated rocks).

MODEL RESULTS

4.l Basic case

The basic case features the basic geometry (Fig. 3) and a mechanical behavior based on average properties and strain softening after rock failure (Fig. 4).

Figure 6 shows the evolution of the failure zone during the caiculation stages.

A failure zone progressively develops at the roof of the upper rooms. The central gridpoints undergo tensile failure while the others undergo shear failure. The wide extent of the failure zone proceeds from the weak cohesion and tensile strength of the micaceous marls and from the pore pressure increase. The plastic deformation can reach several percent, thus lowering the failure criteria (impact of the strain softening law adopted) and furthering the failure zone extent.

The grey seam progressively fails in shear, while the red seam much less. äs a consequence of more favorable long-term strength. In this geometry, the intercalary marls are fairlv stable.

The vertical stress in the pillars (Fig. 7) is conform to that caiculated by the "tributary area" model: they vary on the center of the pillar from -3.03 to -3.29 MPa (compressive stress are negative). Shear stress develops at the angles of the rooms, äs well äs tensile stress at the roofs of the upper room. The intercalary layer, between the rooms, undergoes weak horizontal and vertical stress. The principal stress is horizontal.

As an effect of the pore pressure increase, most gridpoints in the marlic facies have tensile minor principa] stress at the final stage of the caiculation, the stress varying from 0.2 to 0.5 MPa, which stays below the tensile strength, ranging from 0.6 to 1.7 MPa depending on the facies but are still considerable. Furthcrmore, observation of the induced plastic deformations in this geometrical configuration and others shows that the strength reduction has a more preponderant impact on failure development than the pore pressure increase.

Reduction by one Standard deviation of the mechanical properties

Under these conditions, the Mohr circles representative of the stresses in the intercalary marls in the pillars systematically intersect the failure criterion (Fig. 8a). On the other hand, the failure zones around the rooms only increase a little compared to the basic case. But should these conditions be met, the scale of the failure zone would be sufficient to bring about a global collapse. Nonetheless the persistence, on the scale of the model (22 m), of well-below average properties has been denied by the tests. since specimens collected very near from one another often displayed a great variability in their characteristics. This model only shows that intercalary marl areas with locally weak properties may ultimately collapse. A model where the intercalary marls had stochastically distributed properties showed that these local failures do not result in global instability. Another model was also built, with properties reduced by one Standard deviation in one pillar and stochastically distributed properties in the others. The caiculations showed that the collapse of the first pillar did not have any consequence on the stability of the adjacent ones. The only result would be a local instability.

Post-failure behavior: perfect plasticity

The introduction of perfect plasticity äs post-failure behavior involves a notable reduction of the failure zone, particularly at the roof of the upper room (Fig. 8b). The huge reduction of the tensile strength in the strain softening law actually contributes mostly to the extension of this failure zone. As this feature is legitimate, it is therefore more coherent and safer to use the strain softening law, even with estimated parameters. Appropriate tests are planned later to provide for precise characterizations of the post-failure rock behaviors.

Collapse of the intercalary layer between two rooms

This geometry (Fig. 4a) did not prove to be dangerous. It causes a minor extension of the failure zone in the intercalary marls, and very limited consequences on the failure zones around the adjacent rooms.

Contrary to what the experts feared, the intercalary marls are stiff enough not to be squeezed between the two iron seams, after the intercalary layer between two rooms has collapsed. This event, should it occur (äs the caiculations made above do not show it äs granted, it could only be an isolated event), would not lead to any consequence in terms of overall stability.

Transition wne between a two-level and a onelevel exploitation

The failure zones around the rooms are very little affected in this configuration (Fig. 4b). In effect, in the transition zone the Stresses ränge between those calculated in a two-level and a one-level exploitation.

Consequently any locally specific increase of the failure zones is impossible in this configuration.

Superimposition shift of the pillars in the two exploited levels

All the observations have shown that the instability hazards increase with the superimposition drift (Fig. 4c). It is therefore usefui to study the impact of different values of the drift on the overall stability, and to deduce the maximum admissible drift. The failure zone around the rooms greatly increases with the superimposition drift. Not very different to that in the basic case for a l m or 2 m drift (Fig. 9), a dangerous Situation develops for a 3 m drift.

The intercalary layer begins then to undergo failures in traction, likely to result in its collapse. Note however that FLAC cannot conclude whether the "failure zone" information means development of a fracture network or the utter collapse of the zone in question. Nevertheless in this present case the failure mode (tension) of the intercalary marls means a final collapse is more likely. Moreover this conclusion promotes a safer analysis.

3 m Superimposition drift and depth of the intercalary layer reduced to 4 m

This even more unfavorable configuration has been used to analyze the consequences of a collapse of the intercalary layer.

The collapse of a unique intercalary layer results in a significant extension of the failure zone in the surrounding pillars (Fig. lOa). Moreover, the failure zones around the adjacent rooms increases slightly, which may also trigger the collapse of their already disturbed intercalary layers. If however the collapse remains an isolated event, the induced failure zone cannot endanger the overall stability.

The long-term global collapse of all the intercalary layers between the rooms represents a very pessimistic but plausible assumption. These events could occur äs a chain reaction but also progressively and individually. Even in these extreme conditions, the pillars remain stable, despite an increase in the induced failure zone.

Conclusions on this case

The different caiculations allowed locating the weak points in the mine. These are first the grey seam and the micaceous maris. The weak longtenn tension strength assigned to the micaceous marls leads to the formation of a tension failure zone at the roof of the upper rooms, which can be seen äs the initiation of a sinkhole. As noted before-1 I ! 1 1 1 1 I 1 1 ! 1 ' ::::::•::::::: hand, FLAC is not well adapted to the analysis of the fonnation of sinkholes through roof failure. But no sinkholes has ever been known to have reached the surface from 100 m [START_REF] Piguet | Affaissements et deformations au-dessus des exploitations minieres : mecanismes. consequences et facteurs influents[END_REF], so this scenario would be highiy improbable.

J •: -jB FE J 1 1 1 M 1 "• -n i 1
The intercalary marls represent the other weak point. The areas with well below average strength may locally fail at long-term äs a mere consequence of the state of stress in the pillars, but without consequence on the overall stability.

The state of stress that develops in the intercalary layer between two rooms can lead it to collapse if locally the pillars in the two exploited seams are not exactiy superimposed, and the drift exceeds 3 m. However even if this event occurs between severai adjacent rooms, the global stability is not affected.

To sum up, in the studied mine failure zones should develop at long term, particularly in the roof of the upper rooms and in the pillars of the lower rooms. The extension of the failure zones varies, depending on the geometric configuration of the mine, and if the mechanical properties locally fall below average. In some extreme configurations, the intercalary layer between two rooms collapses. But the overall stability is never affected.

GENERAL CONCLUSION

The mine water rise in the ancient room and abandoned pillar mines brings about two phenomena un-favorable to their long-term stability : the pore pressure increase and the strength reduction of the rocks, to which the resaturation, the fatigue, the creep and/or chemical reactions contribute.

The numerical analysis ailowed locating the weakness zones in the rock masses and the foreseeable failure mechanisms involved. It also contributed to test easily alternative geometries and mechanical properties. The use of a two-dimensional model led to moderate caiculation times in each configuration (about l h).

The choice of mechanical properties and above all the long-term strength reduction have been shown to have a great influence on the extension of the failure zones. In the present case, no instability can be foreseen in whichever geometricai configuration, and whatever mechanical properties are used. Still in more critical cases a precise characterization of the long-term properties would be necessary, in order to properly evaluate the instability hazards. The emphasis should be put on the detennination by specific tests of the real long-term properties, and a fair knowledge of their spatial variability.

  Figure 3. Basic geometry ot' the model.

4. 2 Figure 8 .Figure 7 .

 287 Figure 8. Failure zones after introduetion of the long-term strengths and pore pressure increase-Basic geometry, different mechanical behaviors

  Figure 9. Extension of the failure zone -2 m and 3 m superimposit i on drift of the pillars in the two exploited seams.

  Figure10. Influence on the failure zone of the collapse of an intercalary layer between two rooms -3-m superimposition drift of the rooms in the two exploited seams, depth of the intercalary layer reduced to 4 m.

of a seasonal rise and lowering of the water table S Rock fatigue Influence of seepage of water from the surface

	Influence of the mine water rise
	• / Rock strength reduction
	S Effective stress lowering and / or pillar confinemenl
	Influence S Same influence äs the groundwater level rise
	• / Simultaneous seasonal variations of pluviometry and frequency of subsidence in
	shallow mines
	Increased floor deformation, risk of floor	Risk of roof failure
	failure	Progression of the failure in the overburden lay-
		ers, depending on their thickness and nature
		Stable collapse bell
		• f Thick overburden
		S Stratified cohesive rocks
	*• Increase of the effective height of the	*» No damage in surface
	pillars, therefore increasing their risk of
	collapse
	Subsidence:
	propagation of the
	collapse to the
	surface
	Example:
	Subsidence events
	in the iron basin of
	Lorraine (France)
	during the water
	level rise

Table l .

 l Average properties of the facies

		Hydraulic properties
	Porosity n	0.15	0.30	0.20	0.30	0.15
	Penneability (10' "m2) l 5 4		5	4	16	6
	Mechanical properties in elasticity
	E (MPa)	6900	12000	8200	10200	6700
		0.15	0.30	0.15	0.30	0.20
	Short-tenn strength properties
	R, (MPa)	17.0 29.0 20.0 25.0	20.2
	R,.S T (MPa)	1.2	2.6	2.5	1.5	2.5
	Csr(MPa)	2.6	5.0	3.8	3.4	4.6
	[PST (MPa)	49	45	36	55	41
	Long-term strength properties
	RE= RC,LT (MPa)	9.2	13.9	13.0	11.6	13.9
		0.6	1.2	1.6	0.7	1.7
	; LT (MPa)	1.4	2.4	2.5	1.6	3.2
	[PLT(MPa)	39	35	26	45	31
	Properties:		Micaceous marls
	^| "Red" seamr		Intercalary marls
	H "Grey" seam		Roof marls


Guy Landrieu

Let's use models in a more reasonable way ! 1

The total cost of implementation of the Jl scenario for EU-15 has been estimated to 64 milliard EURO/year in 2010 by IIASA. To realize the magnitude of that number : the GNP of EU-15 was estimated to 7580 milliards US $ in 1995. So, without considering detailed bases of such evaluations, the total cost of the Jl scenario is in a order of magnitude near to 1% of GNP, or near to the European Union budget... The allocation of efforts and financial burden between european countries is a matter of concern. Such an allocation should aim not only at economic efficiency but also at equity. It should not be only a game of chance even chance can sometimes take the form of random result of a model.

1

Models as simulation tools : helping to visualize the stakes of transboundary pollution policies.

During the two last decades, integrated models like RAINS, AS AM, CASM... have been developed in the background of the discussions of past CLRTAP protocols. These models constitute rich but complex tools and questions are being posed about their use.

The contribution of models for enlightening negotiations

The most important contribution of these models has been a pedagogical one. They have helped people to think about various angles of the transboundary air pollution problem. They have given a language for discussing and visualized links between different aspects in a coherent scheme : listing of possible reductions measures of pollutants emissions and evaluation of their costs, relationship between emission reductions and pollutants concentrations and deposition in Europe in the form of source-receptors matrices, definition of criteria for protecting the ecosystems and potential benefits of action...

The first quantitative use of such models has been as simulation tools in relatively « simple » cases : for example, for a given strategy of reducing SO2 emissions, the model calculate the value of an indicator of potential benefits for ecosystems protection against acidification. Such exercises have been very valuable.

By the development of the sole RAINS model, the same approach is now extended to describing a system taking into account several pollutants (NOx, VOC, NH3, SO2) and several effects (acidification, eutrophication, risks for human health and vegetation resulting from ozone exposure).

The shortcomings of present models

In the new developments of RAINS model, on one hand the posed problem is more complex and in the other hand stakes are higher. Negotiators and other users of the model should be very careful that such a model, though it represents a lot of work and offer an impressive presentation of results, is only a crude representation of reality.

On some importants aspects of the models, there is a chance that the representation deviates significantly from the reality. As examples, one can mention :

-the evaluation of the potential for emission reductions in the future and the corresponding costs : RAINS considers a given economic scenario for each country, with known levels of production or fuel input and fixed technical processes, and evaluates the potential for « end of pipe » emission reduction for each sector of economic activity. Some studies have been made according to a methodology similar to the IIASA approach but with a more detailed analysis of industrial conditions ( 2 ). They conclude that potential for emission reduction are lower than RAINS hypotheses, and that reduction costs increase more rapidly when emissions decrease. On the contrary Finn R. Forsund ( 3 ) remarks that the actual potential for emission reduction is much higher than considered in RAINS, and costs of reduction lower, if one take into account possibilities of input substitution, technological change, and variations in the level of polluting activities that are finally induced by the costs of emission regulations. IF ARE studies show that the final result of such effects on costs curves depends a lot on the specific conditions of each country( 4 ). -the relationship between variations of emissions in one country and variations of pollutants concentrations or depositions in one grid cell (source-receptor matrices) ; as far as we know, no confidence interval has been yet associated to the coefficients of such matrices ; the uncertainty on estimations should be particularly large for NOx/VOC precursors emissions -ozone AOT60 relationship ( 5).

-the level of pollutant deposition that constitutes the actual « critical load » : critical loads relative to acidification can be calculated according to various approach giving significantly different results ; in particular scientists have suggested that actual critical loads for acidification in some regions could be lower than the present figures taken into account in RAINS. On another side, if the noxious effect on some ecosystems of high load of nutrient nitrogen is clear, the impact of more moderate loads, typical of a large part of Europe is difficult to establish and the value of eutrophication critical loads seems controversed.

The result of these uncertainties is that models should be used only for giving general guidance or global evaluation of abatement strategies. The actual significance of results should not be overestimated. In particular, in the absence of in-depth study, one can think that the confidence given to the results should generally diminish when passing from a general view to the details, in particular when considering results at a fine geographical level.

Methodological flaw of using a model as an « optimisation » tool in the present context

As simulation tools, given the pollutants emissions, the models calculate costs and indicators of impacts. Theoretically, models can also be used in a backward mode calculating what should be emissions for achieving fixed targets in terms of impacts or costs. As it can exist in fact an infinite number of solutions to such a problem, generally one may specify additional objectives for arriving at a « best » solution.

During such an exercise, models are used as « optimisation » tools.

Developing the optimisation mode of a model like RAINS is a very exciting challenge from a theoretical point of view and by the mobilization of intelligence ressources of mathematicians and computers scientists. But from a practical point of view, the optimisation mode poses even further the question of the credibility of the results compared to the simulation mode. This is a serious problem because results include, in particular, the allocation of emission threshold between countries, an allocation that has important economic implications.

In addition to the fundamental issue of uncertainty affecting results, there are other questions concerning some choice of modélisation.

Uncertainty affecting the results and mathematical data processing

In the simulation mode, emissions reductions being given, the user can judge the significance of calculated costs if he has read AEA or IFARE studies ; he can also have an idea about credibility of the evaluation of effects if he has seen comparisons of EMEP models with observations and if he has listened discussions about critical loads.

But in the optimisation mode, all the data is handled in a complex way that is totally opaque for the end-user. In some cases, because of a sort of mathematical lever effect, a small change in the input can have drastic effect on the results ( 6). Even if the model user knows uncertainties affecting input data, his intuition can't be of very much help for understanding the significance of numbers presented as output results of the model.

From the above-mentioned uncertainties affecting input, one can only presume that output like « optimal » allocation of emissions between countries have a high level of uncertainty, or in other words that such allocation be less a requirement for environmental and economic efficiency than an effect of random choices in the building of the model.

Therefore from a scientific point of view one should not recommend an operational use of RAINS optimisation results before an in-depth evaluation of the credibility of such results. This is a point that should comes under a quality assurance / quality control chapter ( 7 ) ( 8 ).

This paper examines the RAINS acidification model in the optimisation mode. It points out for example that a variation of 5% in one input data -the acidification critical load of the 20/17 cell of the EMEP grid -can change of 34% an important output result of the optimisation : the 2010 implementation cost that should be beared by the U. K.. For a better appreciation of the significance of that observation, one can notice that the maximum critical load for Sulphur for that grid cell was estimated to 120 eq/ha/an in the 1995 CCE Report and was in the class 200-400 eq/ha/an in the 1997 Report. 7 Leen Hordijk -past chairman of the TFIAM, Integrated assessment models as a basis for air pollution négociations, Proceedings from the 5th International Conference on Acidic deposition : Science and Policy, Gôteborg, 1995(Kluwer, 1996) The fragility of such modélisation inferences is thrown into relief when considering the prudence of some EMEP remarks ( 12).

An alternative approach to the 2010 optimisation should consider the 2010 emissions ceilings as halfway marks towards 2020 or 2030 targets.

For a pragmatic approach

Models like RAINS, used in a simulation mode, are indispensible tools for illustrating the relationship between efforts made for reducing pollutant emissions and environmental benefits. In view of the uncertainties of such representations, it would be desirable that the development of others models with different methodological choices should be continued.

The use of such models in an optimisation mode is quite a different question altogether. Such a practice should be considered more as a research exercise than for his direct operational use. To base decisions having important consequences on the output of a black box would give a technocratic image of environmental policies because : 1) maybe nobody except for a few experts understand in-depth his reactions, 2) some displayed principle are highly questionable, 3) input data are obviously very uncertain.

On the contrary of static models, the real world is evolving continuously. The relative importance of various industries change, new technologies emerge, activities move, human behaviour is transformed... It is therefore not possible to confine the future in any definitive model whatever. A pragmatic and efficient approach to manage environmental change is probably an iterative one, with not too sophisticated prospective analyses but frequent re-examination of prospects and possibilities of new improvements.

Presently the reference scenario (REF) constitutes the first basis of work. However a sort of audit would be very useful for verifying that all countries put really the same content in some words such as « business as usual ». The variations of reference emissions for some countries in successive interim reports of IIASA study is posing a question.

12 cf. D. Simpson and A. Eliassen, ibid.,: « Even the current authors admit that it is possibly dangerous to rely on the results of the EMEP model (any model) to be correct for the year 2010 when emission reductions of order of 80% are being considered ! Thus, the possibility exists that features such as the ozone 'hill' discussed above may be artifacts, due to unavoidable uncertainties connected with, for example, biogenic or man-made emissions, model formulation, or even basic scientific understanding. Thus a global optimisation which relies upon the model results to be accurate at all extremes of its prediction may give a worse answer than a simpler iterative approach which proceeds in small steps with an emphasis on safe strategies at all emissions levels. »

If countries want to go further in environmental protection, considering the large uncertainty affecting evaluations of benefits and costs of environmental protection measures (as often for problems relating to sustainable development), the first direction of work should be to formulate and study common policies. Such common policies could be based on the implementation of specific technical measures or on general emission reduction commitments, taking into account percentage of reduction with regard of a reference year or level of emission per inhabitant.

However, one can easily understand, and models show, that some regions in the centre of Europe, characterized by high densities of population, activities and pollutant emission and being at the confluence of various pollution flows, may justify particular reduction efforts. Studies could be made, country by country, of the effects in terms of costs and benefits of specific supplementary measures by using simulation models.

The resolution of problems caused by locally high densities of emissions should be searched at first at the local level.

  cf. AEA, Review of IIASA cost curves for the reduction of emissions of nitrogen oxides, sulphur dioxide, ammonia and volatile organic compounds, May 1998. The AEA study make an estimation of the « incompressible levels of emission » (MFRs) in U.K.. It gives MFRs figures higher than RAINS evaluations, with differences in the order of 40% for NOx, 60% for VOC and 350% for SO2. F. R. Forsund, Linking RAINS to the economy, Task Force on economic Aspects of Abatement Strategies, 14th session, London 2-4 December 1998.

O. Rentz, et al., SO2

emissions reductions strategies based on the concept of critical load ; analysis and improvement of the RAINS integrated assessment model -applied to the case of France,

IFARE, 1992.

Paper prepared for the UNECE Task Force on Integrated Assessment Modelling,

rd meeting, Les Diablerets 10-12 March 1999.

cf. E. P. Weijers, A review of the RAINS Integrated Assessment Modelling, KEMA, May 1998.

Annexe : Quelques citations rappelées en toile de fond de l'exposé ... it is of major importance to face the limitations of the model to be built and to recognize the type of issues/questions that cannot be adressed by and what falls beyond the scope of the model. Although the management of uncertainty within computer models is not sufficient for the full assurance of quality in Integrated Environmental Assessments, it is quite necessary...

Unless there is quality assurance at the quantitative end of the decision process, then at the qualitative end there is no protection against all sorts of subjectivity and caprice.

Jerome R. Ravetz Integrated Environmental Assessment Forum :

developping guidelines for « good practice » ULYSSES Working Paper, EC Joint Research Centre, 1996 Except when standard well validated engineering design models are being used, the one thing it is almost never appropriate to do is to run a big research model and then adopt its output as policy gospel.

The key point to remember is that without thorough and systematic modeling and analysis of the uncertainty of the problem, we can not be sure that the results of a model, especially a very large and complex one, mean anything at all.

M. Granger Morgan and Max Henrion Uncertainty, A Guide to Dealing with Uncertainty

in Quantitative Risk and Policy Analysis, Cambridge University Press, 1990.


J F Masfaraud

Y Vjbeaunoirl

Perrodin

E Thybaud

D Savanne

J F Ferard

ASSESSMENT OF SOIL CONTAMINATION AND ECOTOXÏCITY BY THE USE OF AN ASCENDING FLOW PERCOLATION -BIOASSAY APPROACH

INTRODUCTION

Soil contamination and subsequent ecotoxicity are to be assessed by the use of appropriate methodologies allowing high repeatability and reproducibility. Non-direct methods consist in preparing either lixiviates or percolates which can be analysed for chemical contaminants and whose toxicities on aquatic organisms may be further determined.

During experimental water percolation through soil columns, the movement of water is generally due to natural gravity. Here we proposed a complementary method in which an ascending water flow through the soil column is created. This system was developed in order to minimise boundary flow during percolation, which may result in improving repeatability and reproducibility of the aqueous extraction.

In this work, the ascending flow percolation method was used for studying soils sampled from 2 contaminated sites. The resulting percolates were then tested for contaminant concentrations, ecotoxicity and genGtoxicity.

MATERIALS AND METHODS

Percolation

The percolation apparatus comprised a borosilicated glass column (0 90 mm x 650 mm deep) and a peristaltic pump which delivered pure water at a"continuous flow rate of 2.3 ml / minute. Two soils corresponding to 2 different pollution profiles were studied :

-S m : heavy metals, polychlorobiphenyls (PCBs), adsorbable halogenated organics (AOX) -S iv : polycyclic aromatic hydrocarbons (PAHs) Columns were filled with 5 kg of crushed and 5 mm-sieved soil taking care of damming down the matrix in such a way that successive disks of soils were formed. This procedure was shown to allow a better radial diffusion of water into the experimented matrix. For each soil, 3 columns were prepared in order to permit an evaluation of an inter-column variability. For each column, the 1,2 jxm-fiberglass filtered percolates were entirely collected after 24, 48 or 109 h, i.e. liquid / solid ratios of 0.66, 1.33 and 3 respectively (encoded P 1, P 2 and P 3). Thus, P 1, P 2 and P 3 corresponded to successive fractions and not to cumulative percolates.

Percolate analysis

Percolates were analysed for conductivity, DOC, Zn, Pb, PCBs, AOX (S ni) or naphthalene, fluorene, phenanthrene, chrysene, benzo{a)pyrene, fluoranthene, pyrene (S rv) -Acute toxicity (Microtox™, 24 h-Daphnia magna immobilisation test), chronic toxicity (7 à&y-Ceriodaphnia dubia reproduction test, 72 h-Pseudokirchneriella subcapitata inhibition test) and genotoxicity (Mutatox™) were assessed according to references 1,2,3 (modified version),4 and 5 respectively.

RESULTS

S m percolates

Conductivity, DOC, AOX, Zn and Pb exhibited marked decreases (50-90 %) from percolate P 1 to percolate P 3, with a particular drop between P 1 and P 2. On the contrary, PCB concentrations in the successive percolates remained at similar levels.

The acute toxicity of percolates P 1, P 2 and P 3 were comparable (CE 50 » 3 % in each case) when measured by the Microtox™ assay. With the 24 h-Daphnia magna test, a slight decrease in toxicity was observed : the CE 50 of the P 1, P 2 and P 3 percolates reached 28.3, 36.3 and 46.9 % respectively.

The chronic toxicity of percolates as determined by the 72 h-algae assay and the 7 day-Ceriodaphnia dubia assay was shown to decrease markedly from percolate P 1 to percolates P 2 and P 3. Although some variability occurred between columns for the algae assay, a 10-fold increase in either CI 50 (algae assay) or LOEC (Ceriodaphnia dubia assay) values was observed.

The results from the Mutatox™ assay led to consider the percolates as «genotoxic» or «suspect genotoxic». Nevertheless, the comparison of the P 1, P 2 and P 3 percolates was made difficult since the results depended on the positivity criteria used.

S iv percolates

The P 1, P 2 and P 3 percolates from the S iv soil were analysed for PAHs. Contaminants were extracted from the soil matrix and could be measured all along the experiment from the first percolate (P 1) to the third (P 3). The contaminants exhibited different leaching profiles according to the individual molecules considered. Nevertheless, for most compounds, in particular benzo(a)pyrene and fluoranthene, the highest concentrations were found in the percolate P 2.

No toxicity in the percolates was shown when considered the results from the Microtox™ assay, the Daphnia magna assay and the Ceriodaphnia dubia assay. Only a slight toxicity was observed in the algae assay but no differences between the percolates could be observed. The genotoxicity of the percolates seemed to decrease from P 1 to P 3.

DISCUSSION -CONCLUSION

The S m soil percolates were monitored for several parameters including AOX, Zn, Pb, DOC and PCBs. While some tracer concentrations exhibited a marked decrease between P 1 and P 2/P 3 (AOX, Zn, Pb, DOC), others (PCBs) were approximately similar in the 3 percolates. The leaching profile of the tracers could be compared to the toxicity of the successive percolates P 1, P 2 and P 3 whose toxicities declined as revealed by chronic assays on algae and Ceriodaphnia dubia. On the contrary, acute toxicity tests were not able to detect any change in contaminant load in the successive percolates.

For the PAH-contaminated soil (S iv), a leaching of pollutants was observed in the 3 successive percolates but the resulting concentrations were not sufficient enough to induce a toxicity as revealed by the acute and chronic ecotoxicity assays. The genotoxicity declined from P 1 to P 2 and P 3 percolates which is surprising since the highest concentrations in PAHs, particularly benzo(a)pyrene, a well-known genotoxicant, were measured in the P 2 percolate. This suggested that an unidentified and water soluble genotoxic agent was present initially in the soil.

In both cases, the use of ascending flow column for the assessment of soil contamination and ecotoxicity allowed to study the leaching of contaminants as well as the ecotoxicity of successive percolates. For the 2 soils used in this study, the results concerning chemical analysis or toxicity obtained with the 3 columns were generally reproducible for most of the parameters considered. This demonstrates the usefulness of the proposed approach for the hazard assessment of contaminated sites and the risk assessment for potential soil contaminants.

ACKNOWLEDGEMENTS

The research presented is supported by the « Agence de l'Environnement et de 3a Maîtrise de l'Energie » (ADEME, contract n°97 93 008).


G Senfaute

M Abdul Wahed

J P Piguet

J P Josien

Qualification of the microseismic monitoring technique applied to the risk of colfapse in iron ore mines

Keywords: Microseismic monitoring, collapse, torpedoing, robbing of pillars Dieser Bericht beschreibt die Validation, durch einen in einem aktieven Eisenerzbergwerk durchgeführten Feldtest, der Mikroseismik zum Abhöhren von Brüchen im Gebirge welche anzeichenfür einen der Tagesoberfläche, mikroseismische Signale aufzunehmen, welche durch das nach der gewollten Sprengung bestimmter zur Überwachung von alten, nicht mehr befahrbaren, Kammer-Pfeiler

Experiments carried out in a working iron mine validated the microseismic monitoring technique äs a means of detecting fracture noise emissions regarded äs Signals indicating an incipient collapse.

In the experiment surface recordings were made of the microseismic Signals corresponding to fractures and local collapse phenomena generated at the mine bottom by deliberately destroying pillars. The pillar removal operations and the collapse of the roof were systematically correlated with a series of microseismic events. The experiment served to validate the microseismic monitoring technique äs a means of detecting surface precursors of a collapse, to demonstrate the ejfectiveness of the technique, and to calibrate the principal parameters of a microseismic monitoring System adapted to detection and monitoring in areas where there is a risk of collapse.

Introduction

The iron ore basin in Lorraine extends between the eitles of Luxembourg in the north and Nancy (France) in the south. The iron ore deposit is sedimentary Aalenian and an insertion in the geological series between the Lias and the Jurassic (Tincelin, 1958). This deposit is virtually horizontal with a regulär average slope of 3% and a mean thickness of 30 metres (figure l). The sterile rocks lying above the iron-bearing formation known äs "dead ground" have an average thickness of 150 metres. In the deepest mines in the basin iron ore has been recovered some 250 metres below ground level.

Over the greater part of the deposit, recovery involved removing the roof Supports and collapsing the residual pillars. However beneath sensitive zones (where there were houses and surface infrastructure) partial recovery methods were used : abandoned chambers and pillars, with Islands separated by longwalls. In these areas of partial recovery, collapse phenomena have occurred several times, usually owing to the failure of abandoned pillars (Piguet et al, 1999, Vinkler et al, 1998).

The microseismic monitoring technique is used today in a number of different situations: to study seismic phenomena induced by activities in working mines (Senfaute et al, 1994(Senfaute et al, , 1997(Senfaute et al, and 1999)), the injection of fluids, geothermal phenomena (Moriya H., Niitsuma H., 1996), the recovery of gas and oil, and the surveillance of Underground storage facüities or sensitive installations. As regards abandoned iron mines exposed to the risk of sudden and unexpected collapse affecting the surface, there has hitherto been no means of predicting or detecting these phenomena.

For this reason we undertook a research program with the objective of validating the microseismic monitoring technique to detect the noise emitted during the fracturing that constituted the first signs of incipient collapse (failure of pillars in the mine, then of the surrounding roof, and finally of the overburden). The technique was validated by means of an experiment carried out in the last working iron mine with the support of ARBED's mine. The experiment involved surface recordings of the Signals corresponding to the fracturing and local collapses generated deliberately at mine bottom by destroying (torpedoing) pillars.

Description of the mine and the microseismic monitoring System

The usual method of mining iron in Lorraine was to separate the deposit into panels which in tum were divided into pillars, i.e., into parallelepiped blocks of the order of 10 metres in size.

In cases of total recovery, the dimensions of these pillars were gradually reduced and they were then removed with explosives. This Operation known äs "robbing pillars" led to the collapse of the roof of the strata known äs "caving".

Whenever it was considered necessary to protect the infrastructure on the surface (towns, roads, railways, etc.) the methods was then either to leave the pillars in place (the so-called "abandoned pillars" method) or to limit the dimensions of the panels (the method known äs "Islands"). In the latter case, the collapse height of the roof is less the smaller the size of the panel. In the Arbed mines, experience shows that the collapse cone reaches a height of about 6 metres above an island 25 metres in length.

The geometry of the mining unit monitored by the microseismic technique is shown on figure 2. In this unit, the width of the Islands is 40 metres, the strips between the Islands are 30 metres wide and the mining height is 4 metres. The microseismic monitoring Station was installed at the surface, in a borehole 30 metres in depth and about 300 metres from the mining operations.

The microseismic Station is a three-directional unit consisting of sensors of the accelerometer type with a pass band of 2 to 2300 Hz and a sensitivity of 500 mV/g. The Signals are fed to a local Computer with a sampling frequency of 10 kHz (figure 3).

lUUcroseismic events recorded

The microseismic Station on the surface was left switched on for 34 days during the operations of removing roof supports and the torpedoing of pillars at mine bottom. During this period 260 microseismic events were recorded. These were classified into three types:

• Class l : Events associated with blasting.

• Class 2: Events associated with fractures in the caving of the immediate roof. • Class 3: Events associated with fractures away from the roof caving.

The events in class l were identified by the time at which blasting took place. The events in class 2 were identified by the time at which the localised slip or collapse occurred, following the torpedoing of the pillars. Experience showed that collapse might be immediate or take place a few hours or a few days arter the shot was fired. The third class of events were relatively isolated incidents. They occurred at times other than those at which blasting took place to remove roof supports or for plotting purposes äs well äs roof collapse.

Microseismic events associated with blasting

All the blasting done during mining operations located 300 metres from the seismic Station was systematically recorded by the seismic monitoring system.

The Signals recorded were of very high amplitude, leading to Signal Saturation. The signal frequency is about 200 Hz with peaks of up to 500 Hz.

Other blasts located about 600 metres from the monitoring Station were also recorded. The maximum frequency of these events is lower (under 100 Hz) than the frequency of the events recorded during blasts located at 300 metres from the monitoring Station. Finally, blasts some 900 metres from the monitoring Station were not detected by the System. Figure 4 shows examples of seismic Signals and of the frequency spectrum of the events recorded.

Microseismic events associated with fractures in the caving

The collapse of the roof following the torpedoing of pillars A and B (see figure 3) generated 66 microseismic events. These events were characterised by their arrival in bursts, i.e., a number of events recorded in a short period of time. The signature of the Signals and the spectral content of these events are appreciably different from those associated with blasting. They are very short events with maximum frequency peaks between 400 and 500 Hz (figure 5).

^M^^t^M^WwF igure 5:

Examples of seismic Signals recorded during the collapse of the roof. The dijference with the signature of the seismic events associated with blasting can be clearly seen (see figure 4)

Collapse following the torpedoing of pillar A

The area left unsupported by the torpedoing of pillar A is about 500 m 2 . E the height of the collapse cones is assumed to be of the order of 6 metres, the volume of collapsed material is estimated at about 2800 m 3 . A series of microseismic events was recorded in the minute following the final blast, corresponding to the removal of the pillar. Observations made at mine bottom confirmed the immediate collapse following the torpedo shot making it possible to correlate the microseismic events recorded with the rockbursts generated by the advent of collapse.

Collapse following the torpedoing of pillar B

The area left unsupported by the torpedoing of pillar B is of the order of 625 m 2 , the configuration of this pillar being different from that of pillar A. Pillar B is about 6 metres from a pillar already torpedoed. This configuration means that the dimensions of the collapse cone of this pillar are greater than those associated with pillar A. This new collapse cone added to the collapse cone of the neighbouring pillar. The volume of the collapse cone during torpedoing of pillar B was estimated directiy on the spot at about 3000 m 3 .

At the moment when pillar B was torpedoed, no microseismic event (apart from the blasts) was recorded. Observations at mine bottom confirmed that there was no collapse after the blasts torpedoing the pillar. Further shots were fired 24 hours later, without immediate collapse. A burst of events was recorded 7 hours after these torpedo shots (20 microseismic events in 40 minutes). Verification at mine bottom showed that these events were concomitant with part of the roof collapse. However observations showed that the collapse was not complete. A further burst of events, greater man the previous one (40 events in an hour) was recorded 16 hours after this first collapse. Checks at mine bottom showed that these events were associated with the occurrence of a second collapse. Following this second burst of events, no other events were recorded and the collapse ceased spreading.

Microseismic events associated with fractures away from the roof collapse

These events were characterised in that they were all recorded at times other man those of the blasting and roof collapses. These events did not occur in bursts, but were isolated in time and could arrive at any time, including during the night. The signature and spectral content are similar to the events associated with collapses. These events were interpreted äs being subsequent adjustments in the rock in the vicinity of the mined zone (failures of the roof or pillars).

Sensitivity of the monitoring System to the seismic events recorded

In view of the frequency ränge of the events occurring at mine bottom and that of the sensors installed to record them, it appeared that no blasting event taking place at more than 900 metres away was detected by the experimental monitoring Station. However every blast taking place at a distance within 600 metres was detected by the seismic Station. Also, fractures occurring in the mined strata at a distance of about 300 metres from the seismic monitoring Station tripped the System and recorded interpretable seismic signals. For this reason the sensitivity radius of the System was fixed at 400 metres äs a first approximation.

Conclusions

The operations to remove roof supports at mine bottom and in particular the fracturing äs the roof collapsed were unambiguously correlated with a characteristic series of microseismic events recorded by a 3-directional seismic Station on the surface. The microseismic events associated with fractures in the roof collapse are very short events with maximum frequency peaks between 400 and 500 Hz.

Other events, producing signals similar to those of the collapse of the roof but more isolated in time were interpreted äs later adjustments within the rock.

The experiment made it possible to validate the microseismic monitoring technique äs a way of detecting precursor signs of the collapse process before the phenomenon produces surface effects, to demonstrate the effectiveness of the technique and to calibrate the principal Parameters of a microseismic monitoring System adapted to the detection and surveillance of zones exposed to the risk of collapse in the Lorraine iron ore basin.

The System was applied for the first time at the towns of Joeuf and Homecourt. The subsoil of these towns is entirely undermined by mine workings that are now abandoned. A continuous microseismic monitoring system was installed on this site and on the basis of the results from these preliminary qualification tests, a warning procedure has been set up.

Figure 2 :Figure 3 :

 23 Figure l: Simplified geological section of the Lorraine iron ore basin

Figure 4 :

 4 Figure 4: Examples of seismic Signals and frequency spectra recorded during blasting operations some 300 metres from the seismic monitoring Station on the surface.

  Table l below shows all the recordings made throughout the period of microseismic monitoring.

	Class l	Class 2	Class 3
	Events	Seismic events:	Seismic events
	associated with	fractures in	fractures away
	blasting	caving	from caving
	26	66	168
	Table l: Total microseismic events recorded
	during the monitoring period

Acknowledgements

The authors wish to thank the LORMINES and ARBED companies and the Ministry for Industry for their generous funding of this experiment. We offer our particular thanks to the management and staff of ARBED's Terres Rouges mine for their support during our research on the site.

Bibliographie

Moriya H., Niitsuma H.;(1996), Doublet analyses for characterizing regional structures in three-component microseismic measurement.


E valuation of gas emission from closed mines su rfa ce to atmosphere

AIMSANDPRINCIPLESOFTHEMETHOD

For concentrated emissions or when gas builds up in a confined space, simple measurements of gas con" centrations in the atmosphere can be sufficientto de" tect and evaluate the hazards. I he dimensions of the chamber and the operating parameters of the method were optimised at the de"

I

( 0\

sign stage on a test rig ^figure t_) using known gas f I o ws. / \ t this stage it w a s also possible to determine the influence on the results of the measuring system itself, the nature of the soil, the wind and many other factors, so that due allowance could be made in the calcul ati o n s. on May 14 th 1996 and entitled "Measurement of gas flows through surfaces").

Fan Chamber

Soil

LJLJJBJLJLJ

+

CQ Emission Flowmeter

TYPICAL APPLICATIONS

I he method has been applied in a operational m a n " ner for diagnostics and appraisals at a number of sites [old mines, waste dumps, landfills, and so onj.

  d e d f o r d e t e c t i n g , q u a n t i f y i n g a n d q u a l i f y i n g g a s d i s c h a r g e s , b u t c a n a l s o be a p p l i e d t o v e r i f y t h e e f f e c t i v e " n e s s of t h e p r e v e n t i v e m e a n s u s e d f o r r e d u c i n g e m i s s i o n s [ s e a l i n g o p e r a t i o n s , g a s d r a i n a g e , etc.J . I he m e t h o d h a s a l r e a d y b e e n a p p l i e d i n an o p e r a t i o n a l m a n n e r f o r d i a g n o s i s a n d a p p r a i s a l on a n u m b e r o f s i t e s [ o l d m i n e s , l a n d f i l l s , etc.J .

  Figure!. INERISflu x chamber diagram.

Figure iL ,

 iL Figure iL, LJiagram of test rig for chamber valid at ion.

  Figure O. IVIeasu ring of firedamp emission on the sur" face of a closed coal mine.