Güldemann, Tom. 2008. Quotative indexes in African languages: A synchronic and diachronic survey. Berlin: Mouton de Gruyter. (Empirical Approaches to Language Typology 34). ISBN 978-3-11-018590-4 The book under review provides a thorough construction-oriented synchronic and diachronic investigation of quotative indexes in a representative sample of 39 African languages. The study is typologically and theoretically well-informed and offers a good of deal of thoughtprovoking findings and insightful generalizations of general interest, well beyond the Africanist readership whose attention the title may attract most. The book also contains a wealth of language-specific data and analyses, both synchronic and diachronic. These data and analyses will be relevant not only to the specialists in the respective languages and language families, who could profit a lot from the new perspective on the data they may already be familiar with, but also to a readership attentive to issues of cross-linguistic diversity and language change.

A QUOTATIVE INDEX is defined as "a segmentally discrete linguistic expression which is used by the reporter for the orientation of the audience to signal in his/her discourse the occurrence of an adjacent representation of reported discourse" (p. 11). Reported discourse is understood broadly and also includes "texts that were never actually uttered like so-called 'internal speech', or in general any representation of cognitive acts or states" (p. 7). The study focuses especially on quotative indexes marking direct reported discourse, as in (1), that is, the kind of reported discourse where "the formal interference of the reporter is maximally restricted" (p. The generic speech verb say forms the nuclear part of the quotative index in (1). The quotative index in (1) also includes a reference to the SPEAKER, viz. he, and the ADDRESSEE, viz. to me (p. 7). Note that say in (1) is not conventionalized in the function of introducing an adjacent representation of reported discourse, i.e. a quote. That is, as such it does not fulfill the "quote-orienting or quote-pointing function" (p. 134). However, quotative indexes can also contain dedicated QUOTE-ORIENTERS, or simply QUOTATIVES, which share the feature of reference to an utterance with speech verbs, such as say, while at the same time functionally differing from the latter in being conventionalized in relation to reported discourse. That is, either they are not used in other contexts at all or they lack (fully or partially) the feature of reference to an utterance when no representation of reported discourse is adjacent. For instance, consider be like in English, as in (2), as an example of such a quotative.

(2) And he's like, "That's great!" Chapter 1 presents the object of the study and major research questions, as well as theoretical and methodological foundations. In Chapters 2 ("The internal structure of quotative indexes") and 3 ("Quotative indexes and their linguistic context"), Güldemann (henceforth TG) proposes a (morpho)syntactic typology of quotative indexes and of quotatives. The two major parameters used for the classification of quotative indexes are: (i) whether the construction involved is a clause and how complex it is (detailed in 3 below), and (ii) the position of the quotative index with respect to the quote (detailed in 4).

(3) The syntactic structure of quotative indexes (i) monoclausal (ii) monoclausal bipartite (iii) biclausal (bipartite) (iv) non-clausal (4) The position of the quotative index with respect to the quote (i) preposed (ii) postposed (iii) circumposed (iv) intraposed (v) combination involving intra-quote A secondary parameter classifies monopartite quotative indexes (monoclausal and nonclausal) in terms of their primary semantic orientation, viz. quote-oriented vs. (in the case of monoclausal quotative indexes) event-oriented (pp. 153-154) or (in the case of non-clausal ones) participant-oriented (pp. 160-161). This parameter is not applied in Appendix 1 where major types of quotative indexes in the sample languages are presented. Various combinations of the two major parameters are possible within a given language. Interestingly, none of the 39 languages of TG's sample has all the four syntactic constructional types of quotative indexes summarized in (3) above.

Quotatives as the nuclear parts of quotative indexes are first of all classified syntactically as to whether they are predicative or nonpredicative. One of the major results of Chapters 2 and 3 is the finding that quotative indexes are often based on elements other than speech verbs, "suggesting that they are more than simple predicative assertions about a speech event" (p. 2). Morphosyntactically, predicative quotatives may behave as regular verbs and are then classified as QUOTATIVE VERBS (p. 13). Those predicative quotatives that do not fully qualify for the status of verb in a given language are referred to as QUOTATIVE PREDICATORS (p. 15). Nonpredicative quotatives do not show any properties characteristic of verbs in a given language. In its general outline TG's classification of quotatives is very appealing, although I found certain aspects of its presentation somewhat confusing. A figure summarizing all the types of quotatives, comparable to the one provided on p. 516 for the classification of quotative indexes, would have been helpful. For instance, the term QUOTATIVE MARKER, defined as a "grammaticalized function word which is normally adjacent to the quote" "in addition to a predicate" appears to be introduced on p. 14 as a type of a nonpredicative quotative. However, on p. 15, quotative markers are referred to as a "more general category" of which the predicative quotatives, viz. quotative predicators and quotative verbs, "can be [functionally] conceptualized as special subtypes". Again on p. 14, the notion of quotative marker is exemplified by introducing the concept of QUOTATIVE COMPLEMENTIZERS, which are quotative markers occurring when a quote is in a relation of complementation with a clausal quotative index. Later in the text, however, the label "quotative/complementizer" is usually used rather than "quotative complementizer". As becomes clear from the discussion in Sections 3.1 and 3.4, the reason behind TG's avoidance of the latter label is that there is, as he convincingly argues, hardly any evidence for the widespread view that the representation of a reported discourse is the object complement of a higher clause (and respectively, that any verb used to build a quotative index is transitive). It would have been more consistent then to use a term like QUOTATIVE CLAUSE LINKING MARKER to indicate that the relation of a quote to the adjacent clause-level quotative index is not that of complementation but of some type of clause linking. See, for instance, [START_REF] Idiatov | Person-number agreement on clause linking markers in Mande[END_REF] where I tried out the present classification on data from Mande languages.1 Alternatively, as the relevant data may not always be present in the primary sources, the need to distinguish between complementation and clause linking in such a typological survey could have been avoided by using a more general term, such as QUOTATIVE CLAUSE RELATOR, that is a syntactic or morphological element marking a relation between two clauses such that one clause is a quotative index and the other is a quote. Finally, I would also propose to confine the term QUOTATIVE MARKER to the leftover category of nonpredicative quotatives that relate the quote to a non-clausal quotative index (cf. Idiatov 2010 for an illustration on the example of Mande languages).

Chapters 4 to 7 focus on the diachrony of quotative indexes and quotatives, investigating both their variable sources and the recurrent further developments that they undergo themselves. Thus, Chapter 4 provides an overview of previous research on the etymology of quotatives, where speech verbs have figured particularly prominently as presumably the most natural source of quotatives. TG is quite critical of this line of analysis and he subjects it to a thorough scrutiny taking the oft-cited case of Yoruba to illustrate his point. He argues that a better understanding of the history of quotative constructions can be achieved if they are analyzed as a particular case of "mimesis constructions", as suggested by their recurrent synchronic properties examined in Chapters 2 and 3. Mimetic expressions directly enact a state of affairs rather than describe it. Besides reported discourse, they comprise "representational gesture, ideophones, and non-linguistic sound imitation" (p. 275). Chapter 5 reveals a much more varied range of sources of quotatives than just speech verbs, as summarized in (5), and demonstrates that the alternative, mimesis perspective straightforwardly accounts for the data observed.

(5) The diverse origins of nuclear elements of quotative indexes (i) generic speech verbs (e.g., 'say', 'tell') (ii) generic verbs of equation, inchoativity and action (e.g., 'be(come)', 'do, make', 'go') (iii) markers of similarity and manner (e.g., 'like', 'as', 'thus', 'so') (iv) quote-referring pronominals and deictics (e.g., 'this', 'that') (v) foregrounding devices and presentationals (e.g., 'it is', 'there is') (vi) pronominals referring to the speaker TG warns against "overgeneralizing the speech-verb channel" of the origin of quotatives (p. 267) and deplores that argumentation in the literature on the history of quotatives is often "reduced to purely theoretical consideration of crosslinguistic precedents" instead of "a careful reconstruction" (p. 269). However, in the ardour of his legitimate critique, he sometimes falls prey to the same pitfall of overgeneralization but in favour of the "channels" other than speech verbs. Thus, I believe this is the case with Mandinka and Gola quotatives which TG, somewhat unfortunately for his otherwise quite convincing argument, takes as exemplar cases to illustrate his point (pp. 344-345, 418-422).

In Mandinka the quotative kó can function as a quotative predicator and a quotative clause linking marker (cf. Idiatov 2010:849). On the basis of the observation that "the similative marker 'like' has the same phonetic form" and the same form "also appears in the complex conjunction kó níŋ 'as if'" (where níŋ is 'if, when; and, with'), TG comes to conclusion that "it is reasonable to view the similative marker as the source for the quotative index" (pp. 344-345), against the commonly accepted view that the similative kó 'like, as' comes from a quotative construction such as í sí à fó kó (2SG POTENTIAL 3SG QUOTATIVE) 'you would say; like, as' (Creissels 1983:188) or rather simply í kó (2SG QUOTATIVE) 'you [would] say; like, as'. Even though TG does admit (p. 422) that the traditional account "has a certain amount of plausibility", he argues that "it still remains unclear where the quotative verb is to have come from" (p. 421). However, neither of the two hypotheses is convincing here. To begin with, in many other lects within the Manding dialect continuum of which Mandinka is the westernmost variety, the similative is only formed as a quotative index with the obligatory 2SG pronoun í representing the speaker, as in Bamana í kó (2SG QUOTATIVE) or í n'à fɔ́ (2SG FUT:3SG say). From the point of view of Manding phonotactics, once the construction í kó is conventionalized and its original morphological makeup blurred by frequent use, the loss of í would be absolutely natural (cf. Idiatov 2010:858). Furthermore, the same kind of similative uses of structurally identical quotative constructions based on quotatives of various origins and undergoing similar conventionalization and formal reduction are well attested elsewhere in Mande, as in Kpelle yɛɣɛ́ (or simply yɛ) '2SG:QUOTATIVE; like, as' (Westermann & Melzian 1930:69) or Tura yé 'as, like', originally a 2SG form of the quotative (cf. Idiatov 2010:852-853).2 At the same time, no quotative extenstions of originally similative markers, comparable to be like in English, as in (2) above, have been reported in Mande. Finally, the Mandinka quotative kó has clear cognates in Mande that have nothing to do with simile or mimesis but with speech, such as the speech verbs kù (PFV)/ kùɛ (IPFV) '(vi) speak, talk' in Jeli, kó '(vt) say' in Soninke and kúmá 'speak, talk; speech, words' in development whereby […] a specialized and complex QI [Quotative Index] became reduced in substance to a one-word sign that was then reanalyzed as an adposition 'like'" (p. 422). Another clear example of such a development outside of Africa that comes to mind is Ukranian mov. The similative meaning 'like, as' of mov is clearly derivative of its quotative use as is suggested by the fact that mov is a truncation of a form of the speech verb movyty/movljaty 'to speak, say'. Note that a related form movljav (lit.: 'he spoke, said') is used only as a quotative (or an attenuator 'so to speak'). The same is true of the cognate Russian form mol.

Mandinka itself (from *kó-má 'speech/talk-do', where the verb 'do' on which this compound is based has been lost in Mandinka), as well as the nouns góó/wóó 'voice' in Looma and wʊʊ̀ 'voice, speech, language; issue, matter' in Tura.

Gola, as described by Westermann (1921:45, 150, 161, 175), has a person-inflected quotative whose stem is yaa and two similative markers 'like', viz. mãã, which is the 2SG form of the quotative ('you say') similarly to the Mande languages mentioned above, and yaa, which has "the same form" as the quotative stem and also makes part of two manner deictics yáe 'so, like this' and yɛí 'so, like that' (pp. 420-421). On the basis of this, TG concludes that the similative yaa is the source of the quotative yaa. Several objections can be made here. To begin with, the similative yaa and the quotative yaa seem to have different tones. Thus, although [START_REF] Westermann | Die Gola-Sprache in Liberia: Grammatik[END_REF] marks tones only on some words and also leaves the tones of the two forms unmarked, the high tone marked on the aforementioned manner deictics yáe and yɛí which are based on the similative suggest that the tone of the similative is also high, viz. yáá, whereas the tone of the quotative is in all probability low, viz. yàà, as suggested for instance by the 3SG form of the quotative wààŋ found in Fachner (1990:41-43). Second, both the quotative and the similative look very much like a relatively recent borrowing from a Southwestern Mande language, in all probability Kpelle, as is already hinted at by Westermann (1921:45) himself with respect to the quotative. Thus, the Liberian variety of Kpelle described by [START_REF] Westermann | The Kpelle language in Liberia: Grammatical outline, colloquial sentences and vocabulary[END_REF] has yɛɣɛ́ (or simply yɛ) '2SG:QUOTATIVE', also used as 'like, as', and yɛ/ɲɛ/yɛɣɛ/ɲɛɣɛ̀ '3SG:QUOTATIVE ' (1930:22, 69). The variation y-/ɲin the 3SG form of the quotative points to the pronominals of the socalled "absolute" series whose vowel is a (1930:15, 69), such as the 3SG forms yà/ɲà, so that the older forms of the quotative were presumably yáɣɛ́ and yàɣɛ/ɲàɣɛ̀ respectively, 3 which in Gola apparently contracted to yáá and yàà.

Chapter 6 deals mostly with various kinds of non-quotative functions that quotative indexes may develop, as summarized in (6). The "absolute" pronominals are used in equational and presentative constructions, as well as for emphasis in some other constructions (cf. Westermann & Melzian 1930:15-16). In other Southwestern Mande languages, such as Mende, it is rather the pronominals of the "basic"/perfective series (comparable to the Kpelle "past" pronominals, as found in Westermann & Melzian 1930:4) that have been involved in quotative formation. See Idiatov (2010:854-855) on the origins of the quotative stem ɣɛ.

(ix) reason-clause linkage (x) condition-clause linkage (xi) multipurpose subordination Chapter 7 considers various elements that have often been claimed in the literature to go back to quotative indexes but that, TG argues, are at best independent parallel developments from a common source, or just altogether unrelated, (7).

(7) Elements frequently misclassified as developments of quotative indexes (i) "auxiliary-foregrounding complex": multipurpose auxiliaries, dummy predicatives, and inflection-type markers, as well as predication and clause operator (ii) functions in nominal morphosyntax: nominal identification, listing, and coordination markers, as well as multipurpose relational grams Chapter 8 provides a summary of the findings and a concise overview of the typology of quotative indexes proposed in the study, and discusses some possible questions for further research. The end material accompanying the book includes two appendices, one with the data on the major types of quotative indexes found in the sample languages and one with quotative and generic speech verbs attested in the sample languages, a list of references, as well as language, author and subject indexes.

As is somewhat inevitable with studies of such scale, different readers may happen to regret this or that issue having been overlooked or find it not having been treated properly. I have already brought up some of my own grievances above and would like to add a couple of minor remarks by way of a conclusion. However, they should not disguise my overall high appreciation of the quality of the research and writing involved in the study under review.

One point that I feel TG could have made much more explicit is that (fully in accordance with the constructional approach he takes) in a given language, the same quotative form can happen to be construed in more than one way depending on the construction it enters (cf. examples from Mande in Idiatov 2010). He is clearly aware of this fact but at some places he seems to have been distracted by the identity of form, as when on pp. 123, 134 he analyzes the clause-linking use of the quotative kó in Mandinka as a case of "[quotative] verb copy" of the quotative verb kó, even though elsewhere, as on p. 344, he keeps these two functions of the form kó distinct. Finally, one minor parameter that can be added to the typology of quotatives concerns the possible importance of lexical semantic distinctions of various kinds between different quotatives in a given language. For instance, in Soninke (Western Mande; Mali), there are four different quotative verbs. The choice between them depends on honorificity status of the speaker of the reported discourse, with one of the four verbs being a default quotative verb that can be applied to anyone (cf. Idiatov 2010:838 for references and examples).

  [He said to me,] QUOTATIVE INDEX ["Come back tomorrow!"] REPORTED DISCOURSE (= QUOTE)

( 6 )

 6 Functional extensions of quotative indexes (p. 522) (i) naming (ii) reported evidence (iii) illocution reinforcement (and possibly other speech act modifiers) (iv) simile (relevant for similatives and manner-clause linkage)

In Mande, the word order together with the way transitivity is obligatory manifested within a clause unambiguously exclude a complementation interpretation.

In this respect, compare TG's observation that he has "not found a single clear case of the historical


Nouha Omrane

Adeline Nazarenko

Sylvie Szulman

From Linguistics to Ontologies The Role of Named Entities in the Conceptualisation Process

Keywords: Ontology design, named entity, conceptualisation

Ontologies that have been built from texts can be associated with lexical information that is crucial for the semantic annotation of texts and all semantic search tasks. However, the entire pocess of building ontologies from texts cannot be fully automated and it is important to guide the knowledge engineer during the building process. This paper presents an enriched version of TERMINAE, which is a text-based methodology for ontology design. It combines a fact-based approach of modeling with the more traditional concept-centric one. We show that named entities can be used to enrich an existing ontology and to bootstrap the acquisition process. In other words, named entities are used for the conceptualisation of ontologies and not only for their population. This approach is illustrated on two use-cases based on policy documents and evaluated by measuring the Precision and Recall of the resulting ontologies with respect to pre-existing ontologies independently built by domain experts.

INTRODUCTION

As defined by [START_REF] Studer | Knowledge Engineering: Principles and Methods[END_REF], an ontology is a formal, explicit specification of a shared conceptualisation. Specialized texts are rich sources of information and they are more widely available and exploitable than domain experts who often do not have much time for interviews and are hardly conscious of their own knowledge. Another advantage of building ontologies from texts concerns the future exploitation of the ontology. If the ontology is to be used to annotate documents, for information retrieval or document indexing, it is important to link documents to ontologies and this can be done by recycling the information captured in text-based acquisition.

This paper shows how two types of domain specific textual units -terms and named entities, extracted from texts using natural language processing (NLP) tools -can help the design of ontologies and more specifically their conceptualisation. Beside methods relying on the terminological analysis of texts for the building of ontological models (Terminological Box, or T-Box, in Description Logic), many works have tried to exploit named entity recognition for the population of these ontologies (Assertional Box, or A-Box) [START_REF] Maynard | NLP techniques for term extraction and ontology population[END_REF]. However, we argue that named entities are also worth consid-ering for conceptualisation and that taking these textual entities into account yields to improve T-Boxes (hereafter ontologies).

The TERMINAE methodology [START_REF] Aussenac-Gilles | The terminae method and platform for ontology engineering from texts[END_REF] is enhanced by taking named entities into account in addition to terms 1 . In this paper we focus on the creation of concepts and instances. Many of our conclusions can be extended to the creation of properties and instance properties, but this point is not developed here.

The resulting methodology is illustrated in the context of business rules and policy modeling, where knowledge engineers have to design ontologies, which are then used as conceptual vocabularies for the annotation of source documents and the design of business rules.

Section 2 presents the current approaches in textbased ontology building. Although named entities and terms are traditionally given distinct roles, Section 3 explains that terms and named entities can be exploited in a unified way and shows how the TER- MINAE methodology has been enriched with the output of named entity recognition tools. Section 4 illustrates the approach on two use-cases. The last section evaluates our approach.

TEXT-BASED APPROACHES TO ONTOLOGY BUILDING

Text-based ontology building methods differ on the degree of automaticity they claim to achieve and in the kind of textual elements they rely on (words, terms and named entities2 ).

Towards semi-automatic methods Distributional approaches rely on the hypothesis that clustering words on the basis of their contextual distribution yields to semantic classes that can then be interpreted as concept. This approach has proved to be more reliable on specialized acquisition corpora and is often referred as "ontology learning", but it can hardly be considered as automatic. In the OntoLp plug-in of the Protege ontology editor, human intervention is required for filtering out words and words semantic clusters [START_REF] Lopes | Automatic extraction of composite terms for construction of ontologies: an experiment in the health care area[END_REF]. Text2Onto [START_REF] Cimiano | Text2onto -a framework for ontology learning and data-driven change discovery[END_REF] exploits various NLP tools to build a draft ontology but the resulting ontology needs to be manually edited by the knowledge engineer afterwards [START_REF] Wang | Towards semiautomatic ontology building supported by large-scale knowledge acquisition[END_REF]. Systems like ASIUM [START_REF] Faure | Knowledge acquisition of predicate argument structures from technical texts using machine learning: the system asium[END_REF] or Doodle-OWL [START_REF] Morita | Doddle-owl: Interactive domain ontology development with open source software in java[END_REF] directly implement ontology design as an incremental or interactive process. Even if word similarities seem to be helpful in the modeling process, word classes are seldom directly exploitable as ontological concepts.

Terminological

Approach Among humancentered approaches, the importance of domain terminology for the building of domain specific knowledge is acknowledged for years [START_REF] Meyer | Towards a new generation of terminological resources : an experiment in building a terminological knowledge base[END_REF][START_REF] Aussenac-Gilles | How can knowledge acquisition benefit from terminology[END_REF] and TERMINAE methodology relies on a terminological analysis. Terminology is often defined as the body of words or terms relating to a particular subject, field of activity or branch of knowledge3 . If we consider that each domain of knowledge has its specific sublanguage(s), the terms form the vocabulary associated to such a sublanguage. A term is often a multi-lexical unit rather than a simple word since compounds usually have a more precise, more specialized and less ambiguous meaning than words. Another important property of terms is their relative stability. Even if a term may have variant forms, this variability is lower than for plain words which can often substitute for other words or phrases.

These domain specific and stable textual units are useful for ontology building but termhood cannot be defined on purely linguistic or statistical ground. Linguistic and surface clues help to restrict the set of candidate terms but the final selection requires human expertise and a general understanding of the domain.

The Role of Named Entities Named entities are another type of domain specific textual units. They have a referential meaning and refer to well identified domain entities.

Although various types of mentions refer to defined entities (proper names as "American Airlines", pronouns like "it" and definite descriptions such as "this company") (LDC, 2004), we focus on proper names that are easier to identify in documents. Named entity recognition (NER) tools have been designed to locate proper names in texts (persons, locations and organisations but also temporal expressions or mesure units) and to associate a semantic type to them (e.g. PERSON, LOCATION) [START_REF] Nadeau | A survey of named entity recognition and classification[END_REF].

Named entities are traditionally exploited in ontology engineering but for populating the instance level of ontologies rather than for their conceptual structuring. [START_REF] Magnini | Ontology population from textual mentions: Task definition and benchmark[END_REF][START_REF] Giuliano | Instance-based ontology population exploiting named-entity substitution[END_REF] try to (semi-)automatically enrich the knowledge base (A-Box) associated to a given ontology by discovering new concept instances. Recognising a named entity of type T yields to the creation of an instance of the concept T .

A COMBINED METHOD FOR BUILDING ONTOLOGIES FROM TEXTS

Assuming that texts do not contain all useful information and that ontology design depends on the application for which the ontology is to be used, TER- MINAE proposes an an interactive approach where the knowledge engineer relies on domain specific textual units to model an ontology (Section 3.1). Whereas terms are traditionally used in conceptual design and named entities for ontology population, we argue that both types of textual units can be exploited for the conceptualisation (Section 3.2) and its bootstrapping (Section 3.3). This approach is embodied in a new version of TERMINAE tool (developed as an eclipse application and available as a NeonToolkit plugin).

TERMINAE Layered Approach

The TERMINAE method decomposes the building process into three main steps -the extraction, normalisation and formalisation (or ontological) steps. The overall process is represented on Figure 1 4 . At each level, the knowledge engineer has to select the relevant items and organise them. This process is helped by the previous terminological analysis of the text which is automatic (step 1), and by the guidelines of the method embodied in the interfaces of TERMINAE (steps 2 and 3). At the terminological level, the knowledge engineer identifies the textual units of the acquisition corpus that seem to be relevant for the domain and usecase to model. This step relies on NLP tools known as term extractors and named entity recognition tools 5 , but the knowledge engineer has to rework manually the results to rule out ill-formed units, filter out the irrelevant ones and cluster variants or synonyms under a single canonical representative. Only a rough analysis is usually done at that level but the selection and clustering go on during the next building step.

At the termino-conceptual level, the list of relevant textual units is normalised into a network of termino-concepts structured by the BT/NT (broader than/ narrower than) links. Each group of synonymous terms must be clustered and associated to a unique termino-concept. Ambiguous terms must be disambiguated in such a way that each relevant meaning is represented as a distinct termino-concept.

The third building step formalises the network of termino-concepts into an ontology. Several important questions regarding the concept/instance/property distinction and the inheritance hierarchy must be tackled at the conceptual level. 4 We focus hereon the upper level of the figure. 5 In the reported experiments, YaTeA term extractor (http://search.cpan.org/ thhamon/Lingua-YaTeA-0.5) and ANNIE NER tool (http://gate.ac.uk/sale/tao/splitch6.html#chap:annie) have been used.

In TERMINAE, the correspondence between the levels is established through the creation of terminological and termino-conceptual forms (see Section 3.2). The termino-conceptual network can be exported as a SKOS file6 ). The conceptual level is realized within Neon Toolkit Ontology editor7 which is plugged in our tool.

Named Entities Conceptualisation

The core task of ontology building is the conceptualisation step that consists in choosing, structuring and defining the conceptual elements of the domain model. The introduction of named entities at the terminological level raises the question of their role in the conceptualisation process, which mainly relies on the knowledge engineer's understanding of the domain and aimed application.

Our approach differs from the works on ontology population which tend to automatically derive the ontological types of conceptual elements (instances vs. concepts) out of their linguistic type (named entities vs. concepts). TERMINAE allows to link any type of conceptual elements to any type of textual unit through the termino-concepts (terms and named entities to termino-concepts and termino-concepts to concepts, instances or conceptual relations), as shown on Figure 1. The distinction between the T-Box and the A-Box levels does not exists at the terminoconceptual level. The relevant linguistic units have to be linked to termino-concepts or termino-conceptual relations at the termino-conceptual level. The conceptualisation choices come after, in the transition from the termino-conceptual level to the ontological one.

The first conceptualisation step is handled in TER- MINAE through the creation of terminological forms for any textual unit that is considered as relevant for the domain to model. A terminological form describes the properties of a term or named entity and associates it to one or several termino-concepts, one for each relevant meaning. Figure 2 presents the form of Sapphire, the textual unit that had been selected in the list on the left side8 . The lexical information indicates whether it has been extracted as a term, a named entity or both. By browsing the list of its occurrences, the knowledge engineer decides whether this unit is an important one or not (selection) and how many of its meanings are relevant for the usecase (ambiguity analysis). For each relevant meaning, a termino-concept is created, the knowledge en- The case of named entities is specific c they are associated to a semantic type by NER tools (PERSON in the case of Sapphire). This semantic type may also be relevant for the domain to model. As they have no linguistic counterpart, semantic types are represented directly at the termino-conceptual level with no occurrence attached to them even if they remain associated to their named entities as the fathers of the corresponding termino-concepts (see the hierarchical list of termino-concepts on the left side of Figure 3). The terminological form of the named entity Sapphire is thus associated with the termino-concepts Sapphire and Person, the latter being built from the semantic type PERSON given by the NER tool.

Bootstraping Conceptualisation

Mining long lists of terms, named entities, terminoconcepts or concepts is difficult. The broad-first search is not practicable as the terminological analysis cannot be completed without a view of the intended ontology. Conceptualisation rather relies in a deep-first search strategy but the problem is to choose the textual units and concepts to start with for bootstrapping the conceptualisation process.

We propose here a fact-based approach. Starting with the named entities that are expected to refer to core domain specific entities leads to createx the concepts the named entity belong to, the relations they hold and more generally to model what is said about them (in the same sentences or textual areas).

EXPERIMENTS

We consider two use-cases dealing with regulations (loyalty program, EU directives). The resulting ontologies are to be used for the modeling and formalization of the rules that are expressed in written policies. The final rule bases and underlying ontologies are intended to be used in Business Rule Management Systems in the FP7 ONTORULE project. These experiments show that the named entities are important to take into account even in texts that do not contain a lot of them .

The ontology building scenario differs in the two experiments reported below. In the first one, the named entities are exploited to enrich an ontology that we had previously built on the basis of terms only. The second experiment shows how useful named entities are for bootstrapping the conceptualisation.

Airline use-case

In the first experiment, the ontology is built out of a document explaining the mileage policy of American Airlines (AA) to customers (5 744 words).

Having built an initial ontology from of a list of 973 terms, we considered the 67 named entities identified in the corpus and some of them appeared as highly relevant for the domain.

For instance, Central America refers to a specific type of airports that plays a specific role in the attribution of miles. The underlying notion had not showed up in our initial term analysis but the named entity list has brought it to light and we finally modelled it as a concept in the ontology (with various airports as instances). The named entities referring to airline compagnies (e.g. Japan airways) were modelled as instances of the concept AAdvantage Airline Participant that we had already created from the term AAdvantage participant (airline compagnies participating in the "AAdvantage" program). The semantic type ORGANIZATION lead us to create a concept Organization as a father concept of AAdvantage Airline Participant. The named entity analysis also revealed the importance of Sapphire and Ruby which had initially been considered as noisy terms but actually refer to customer categories.

Detecting these named entities allowed us to better understand the airline policy underlying domain and lead us to revise the initial ontology. The final one contains 137 domain concepts.

Regulation use-case

The Regulation use-case is based on EU directives describing policies on seat belt control procedures (3 704 words).

We started modeling the domain by considering the named entities having PERSON, DATE, PERCENT and UNKNOWN as semantic types 9 and by exploring their contexts 10 as shown on Figure 4. Bootstrapping the conceptualisation starting with the selected named entities (1st iteration) helped identifying relevant domain terms during the first regulation browsing. For instance, the names of the tests (e.g. Calibration Test) used to check the conformance of seat belts are emphasised. Named entities of PER- CENT type help the knowledge engineer to detect im-9 A quick analysis showed that the named entities of other semantic types (ORGANISATION and LOCATION) were not relevant for the domain to model and the aimed application. 10 The occurrence and the two surrounding sentences.

portant properties of domain concepts (mainly testing conditions). The UNKOWN named entities often correspond to specific elements of the vocabulary of safety belt procedures such as categories of vehicles (M1, N1 ) or specific belt positions (Point A, Point C ).

In all, we created 53 domain concepts during the bootstrapping step.

EVALUATION

We compare the ontologies built for each use-case with those that were previously built by an expert who did not start from texts (hereafter "expert ontologies"). The comparison is based on the labels of concepts or termino-concepts. We use Precision and Recall 11 measures to evaluate the resulting ontologies with respect to the pre-existing ones.

For each use-case, we created a draft ontology, through a single iteration of the whole building process. The goal is to evaluate the role of named entities either for enriching a term-based ontology (Airline use-case) or in the bootstrapping strategy (Regulation use-case).

In the Airline use-case, we compare a first ontology built without taking named entities into account and a revised version enriched with named entities with respect to the expert one. There is no major difference between the first and enriched versions of the ontology (from 0.828 to 0.830 for Precision and from 0.675 to 0.720 for Recall ), due to the small number of named entities. However, taking the named entities into account has lead to re-structure the first ontology (11.5% of the existing concepts have been redefined), enrich it (the revised version is 40% larger) and populate it (45 instances have been added). In all, 60% of the named entities have been introduced in the ontology in a way or another.

The Regulation use-case presents a high Precision (0.742) but a low Recall (0.393): the ontology contains mainly relevant domain concepts but only partially covers the domain described by the expert. The concepts that are missing in our ontology belong either to the core level of the ontology or to specific sub-types of existing concepts (e.g. categories of vehicles). The former ones are concepts that are not directly expressed in texts. Detecting the latter would require a finer-grained analysis and additional iterations of the conceptualisation process, but most of the related terms occur in the contexts of the mentions of existing concepts.

11 P = number of relevant termino-concepts RTC number of termino-concepts TC R = number of relevant termino-concepts RTC number of concepts in the expert ontology C Both use-cases show that named entities help the detection of relevant domain concepts. Since the list of named entities extracted is much smaller than the list of terms (more than 10 times smaller in our usecases), it is interesting to rely on named entities as a starting step, even if the list of textual units must then be further explored to enrich the draft ontologies based on named entities.

CONCLUSION

This paper shows how text-based ontology building methods can be enriched by taking specific textual units into account -named entities as well as terms -and explains how named entities can be used in the conceptualisation task. We show that they can be used either to enrich an ontology (building new concepts, their properties, re-structuring and populating existing concepts) or for bootstrapping the conceptualisation step and identifying relevant domain terms.

This combined approach, which is implemented in the new TERMINAE tool, is illustrated on two usecases. Even if named entities are not as numerous in policies as in press articles for instance, they are important to take into account in the conceptualisation process because they point out critical domain elements that are important to integrate in a conceptual model.

Figure 1 :

 1 Figure 1: Abstracting a conceptual model out of text: the TERMIANE layered approach.

Figure 2 :

 2 Figure 2: Terminological form of the named entity Sapphire

Figure 3 :

 3 Figure 3: Termino-concept Sapphire

Figure 4 :

 4 Figure4: Exploration strategy. Starting with a given named entity (NE i ), the knowledge engineer analyses the surrounding terms (T i1 to T in ) during a 1st iteration before further exploring the list of terms during additional iterations.

The corresponding TERMINAE tool has been improved accordingly (http://www-lipn.univ-paris13.fr/ szulman/logi) but we focus on the methodological aspects here.

Much work has also been done for relation extraction, but, as mentioned above, we do not focus on properties here.

Cf. Collins Dictionary.

http://www.w3.org/2004/02/skos/

http://neon-toolkit.org/wiki/Main Page

Sapphire is a specific category of travellers in the Airline use-case (see Section 4).

ACKNOWLEDGMENTS

This work was realised as part of the FP7 231875 ONTORULE project (http://ontorule-project.eu). We are grateful to American Airline who is the owner of one of our working corpora.


Nouha Omrane
email: nouha.omrane@lipn.univ-paris13.fr

Adeline Nazarenko
email: adeline.nazarenko@lipn.univ-paris13.fr

Sylvie Szulman
email: sylvie.szulman@lipn.univ-paris13.fr

Combining terms and named entities for modeling domain ontologies from texts

Keywords: Ontology acquisition from texts, terms, named entities, conceptualization

Building ontologies from plain texts is still a research issue. This process cannot be fully automated but natural language processing and methodological guidelines can help the knowledge engineer's task. In this paper we present terminae and show through the analysis of three different experiments on policy documents how the initial terminological approach can be guided by taking named entities into account.

INTRODUCTION

Specialized texts are rich sources of information and they are more widely available than domain experts who often do not have much time for interviews and are hardly conscious of their own knowledge. There exist two main text-based approaches for designing ontologies.

The first "ontology learning" approach [START_REF] Lopes | Automatic extraction of composite terms for construction of ontologies: an experiment in the health care area[END_REF] relies on distributional analysis of large acquisition corpora. It is considered as an automatic one, even if the resulting ontology needs to be manually edited afterwards. The second approach is based on the terminological analysis [START_REF] Cimiano | Ontology Learning and Population from Text: Algorithms, Evaluation and Applications[END_REF] of the text. It is less automated than the previous one but is useful for applications where ontologies need to be carefully designed. This work is part of a project aiming at modeling business rules expressed in written policies. In this context, where domain ontologies are used as conceptual vocabularies for the writing of the rules of various use cases, the terminological approach is prefered given the typical size of policies (medium size specialised corpora) 1 and the expected qual-0 This work was realized as part of the FP7 231875 ON-TORULE project. We thank American Airline and Arcelor-Mittal who are the owners of our working corpora. 1 Typically, from 5 to 500 thousands of words ity of the ontologies. In the terminological approach, terms of a domain form the domain specific vocabulary and, as such, serve as a bootstrap for ontology design. Named entities are another type of domain specific textual units that refer to well identified domain entities. They are traditionally exploited in ontology engineering but for populating the instance level of existing ontologies. The originality of the proposed method comes from the fact that it exploits both types of textual units to bootstrap the conceptualization process itself. Our approach is a terminological fact-based one that is embodied in a revised version of terminae tool [START_REF] Aussenac-Gilles | The TERMINAE Method and Platform for Ontology Engineering from texts[END_REF], which now takes named entities into account in addition to terms. Section 2 explains that terms and named entities can be exploited in a unified way and shows how the terminae methodology has been enriched with the output of named entity recognition rules. The last section presents three different experiments exploiting named entities in the ontology building process.

A COMBINED METHOD FOR BUILDING ONTOLOGIES FROM TEXTS

The terminae text-based acquisition method decomposes the acquisition process into three main levels -the terminological, termino-ontological and conceptual (or ontological) levels -which are built on top of each other, the corpus playing the role of ground level. The transition from text to ontology must actually be mediated. Ontologies cannot be "extracted" as such from texts, because conceptual models (or ontologies) and texts are different in nature. At each level, the knowledge engineer has to select the relevant items and to organise them. This process is helped by the previous terminological analysis of the text, which is automatic, and guided by the method embodied in the interfaces of terminae tool. The overall process is represented on Figure 1. In this paper, we focus on the upper part of it. At the linguis- tic level, the user has to extract from the acquisition corpus the textual units that seem to be relevant for the domain and use case to model. This step relies on NLP tools known as "term extractors", as well as "named entity recognizers" that extract named entities and their semantic types. The user has to revise the extracted elements and to turn the list of relevant units into a list of termino-concepts. In that process, the linguistic output is normalised, which is a way to abstract the future domain model from the textual wording and linguistics. The third acquisition step of Terminae methodology consists in formalising the list or network of termino-concepts into an ontology. The core task of ontology acquisition is the conceptualization step that consists in choosing, structuring and defining the conceptual elements of the domain model. In this step, named entities are generally neglected. On the contrary, we consider these textual units and their semantic types from the beginning of the conceptualization phase in the same way as we do for the terms. It is not because they are identified as named entities by NLP tools that they must necessary be turned into instances. In some cases the named entities might model concepts. The underlying modeling choices depend on the corpus and use case that are considered.

The next section illustrates the various bootstrapping approaches in the context of policy taking into account the specificities of policy documents in which passages expressing rules deserve specific attention.

EXPERIMENTATIONS

We consider three use-cases, each one dealing with a specific type of regulations (loyalty program, decision process, rules of a game). The resulting ontologies are to be used for the modeling and formalization of the rules that are expressed in written policies. The acquisition scenario is not the same in the three experiments reported below. In the first one, the named entities are exploited to enrich an ontology that we had previously built on the basis of terms only. The second case aimed at adding linguistic information to an existing ontology and at enriching it with information coming from the acquisition corpus. In the third experiment, the named entities are realy used to bootstrap the conceptualization. Even if the policy corpora do not contain numerous named entities, the three experiments show that the named entities are important to take into account.

In the first experiment, the ontology is built out of a document of American Airlines (5, 300 words), which explains mileage policy to customers. In this use case, taking the named entities into account yields to enrich and partially populate the ontology. Compared to the initial ontology of 130 concepts, 7 new concepts and 45 instances have been added. 15 of the existing concepts have also been redefined. Except for cities which were not interesting for the use case, all the named entities (76) have been introduced in the ontology in some way. The second use-case deals with the galvanization process and the rules dealing with the assignement of a product (coil)(3, 562 words) : depending on various quality criteria, a coil can be assigned to the order (delivered to the customer), repaired or thrown away. We started modeling the domain from an existing core ontology of 12 concepts. The goal was to associate textual units to existing concepts2 and to enrich the structure of the ontology with entities which have been found in the text. We exploited the 663 terms and 105 named entities respectively extracted by YaTeA3 and Gate4 . Taking named entities into account helped to understand the details of the assignement process and to identify the relevant conceptual properties. In the third experiment, we had no preexisting information and we exploited the named entities to bootstrap the conceptualization process, in a fact-oriented approach. We started with a French "Rules of Golf" corpus5 (112,898 words) which describes the rules and conditions according to which a golf player must replay, loose points or quit the game. YaTeA and Gate respectively extracted 3, 711 terms and 350 named entities. In this use case where the term list were too long to be studied in detail, the analysis started with named entities which underlined some core domain elements and was progressively extended to the related terms and their interrelations. These three experiments aimed at building ontologies out of written policies. Named entity recognizers bring into light textual units that are not identified as terms but which nevertheless refer to crucial domain elements and guide the conceptualization work. Even if the "populating" hypothesis does not hold -named entities can be modeled as concepts as well as instances -, named entities favour a fact-oriented approach, which counterbalance purely terminological analyses.

CONCLUSION

This paper shows how text-based ontology acquisition methods can be enriched by taking all types of domain specific textual units into account, named entities as well as terms, and explains how named entities can be used in the conceptualization task. This combined approach, which is implemented in the terminae tool, is illustrated on three different experiments that all aim at building ontologies for the modeling of rules. The written policies do not have as many named entities as press articles for instances, but we have shown that they support a fact-based modeling approach that is complementary to the terminological one, which is more concept-oriented. Even when they are represented as instances at the conceptual level, named entities point out critical domain specific elements that are important to integrate in the conceptual structure in a form or another.

Figure 1 :

 1 Figure 1: Abstracting a conceptual model out of text: the layered approach.

for the further semantic annotation of additional documents

http://search.cpan.org/%7Ethhamon/Lingua-YaTeA-0.5/

http://gate.ac.uk/

This public document is available on http://www.ffgolf.org/


Qiong Wang

Anh Minh Tang

Prof Yu-Jun Cui
email: yujun.cui@enpc.fr

Pierre Delage

Behrouz Gatmiri

Experimental study on the swelling behaviour of bentonite/claystone mixture

Keywords: bentonite/claystone mixture, swelling pressure, water chemistry effect, long term behaviour, final density, correlation

A mixture of the MX80 bentonite and the Callovo-Oxfordian (COx) claystone were investigated by carrying out a series of experiments including determination of the swelling pressure of compacted samples by constant-volume method, pre-swell method, zero-swell method and swell-consolidation method. Distilled water, synthetic water and humidity controlled vapour were employed for hydration.

Results show that upon wetting the swelling pressure increases with decreasing suction; however, there are no obvious effects of synthetic water chemistry and hydration procedure on the swelling behaviour in both short and long terms. For the same initial dry density, the swelling pressure decreases with increasing pre-swell strain; whereas there is a well defined logarithmic relation between the swelling pressure and final dry density of the sample regardless of the initial dry densities and the experimental methods. It was also found that swelling pressure depends on the loading-wetting conditions as a consequence of the different microstructure changes occurred in different conditions. Furthermore, it was attempted to elaborate a general relationship between the swelling pressure and the final dry density for various reference bentonites.

INTRODUCTION

Deep geological repository is being considered for high-level radioactive waste (HLW) in several countries such as China, Belgium, France, Germany, Japan, Sweden, etc. In most cases, compacted bentonite-based materials are chosen as sealing/buffer materials thanks to their low permeability, high swelling and high radionuclide retardation capacities [START_REF] Pusch | Highly compacted sodium bentonite for isolating rock-deposited radioactive waste products[END_REF][START_REF] Yong | Formulation of backfill material for a nuclear fuel waste disposal vault[END_REF][START_REF] Villar | Influence of dry density and water content on the swelling of a compacted bentonite[END_REF].

Once the repository is closed and local groundwater conditions are re-established, the water in the host rock formation will move to the repository. The bentonite-based material absorbs water and swells, filling the technical voids as the gaps between the bentonite bricks themselves, between the canister and the bricks, between bricks and the host rock, as well as the fractures in the host rock due to excavation. After that, the subsequent swelling is restrained by the host rock and swelling pressure develops.

From a mechanical point of view, in order to ensure the stability of the system, the swelling pressure must be lower than the in situ minor stress: 7 MPa in the Underground Research Laboratory (URL) of Bure site, France (Delege et al., 2010;Tang et al., 2011a); 3-4 MPa at Tournemire site, France [START_REF] Barnichon | Sealing Experiments at the Tournemire URL. Towards convergence of technical nuclear safety practices in Europe[END_REF] and 4-5 MPa at Mol site, Belgium [START_REF] Li | Design and Development of the Large Scale In-situ PRACLAY Heater Test and Horizontal HLW Disposal Gallery Seal Test in Belgian URL Hades[END_REF], etc. As the compacted bentonite-based material is a key component of a repository system, it governs the overall behaviour of the whole system. Hence, a proper understanding of how the compacted bentonite-based material behaves during hydration process is essential for the assessment of the short and long term performance of the repository system.

The behavior of compacted bentonite-based material upon wetting has been widely investigated, in terms of swelling properties [START_REF] Pusch | Mineral-water interactions and their influence on the physical behavior of highly compacted Na bentonite[END_REF][START_REF] Komine | Experimental study on swelling characteristics of compacted bentonite[END_REF][START_REF] Kröhn | Results and interpretation of bentonite resaturation experiments with liquid water and water vapour[END_REF], 2004a;[START_REF] Delage | The relationship between suction and swelling properties in a heavily compacted unsaturated clay[END_REF][START_REF] Agus | Swelling pressures and wetting-drying curves of a highly compacted bentonite-sand mixture[END_REF][START_REF] Komine | Swelling characteristics of bentonites in artificial seawater[END_REF]; hydraulic behaviour under saturated state [START_REF] Kenney | Hydraulic conductivity of compacted bentonite-sand mixtures[END_REF][START_REF] Dixon | Hydraulic conductivity of clays in confined tests under low hydraulic gradients[END_REF]Komine, 2004b;) and unsaturated state [START_REF] Borgesson | Water flow and swelling pressure in non-saturated bentonite-based clay barriers[END_REF][START_REF] Borgesson | Thermo-hydro-mechanical characterisation of a bentonite-based buffer material by laboratory tests and numerical back analyses[END_REF][START_REF] Kröhn | Results and interpretation of bentonite resaturation experiments with liquid water and water vapour[END_REF]Lemaire el al., 2004;[START_REF] Loiseau | The gradient effect on the water flow through a compacted swelling soil[END_REF][START_REF] Cui | Determining the unsaturated hydraulic conductivity of a compacted sand-bentonite mixture under constant-volume and free-swell conditions[END_REF]. There are also many studies on the effect of temperature [START_REF] Komine | Thermal influence on compacted bentonite for nuclear waste disposal[END_REF][START_REF] Romero | Temperature effects on the hydraulic behaviour of an unsaturated clay[END_REF][START_REF] Villar | Influence of temperature on the hydro-mechanical behaviour of a compacted bentonite[END_REF][START_REF] Tang | Controlling suction by the vapour equilibrium technique at different temperatures and its application in determining the water retention properties of MX80 clay[END_REF][START_REF] Tang | A new isotropic cell for studying the thermo-mechanical behavior of unsaturated expansive soil[END_REF]Tang et al., 2008a;[START_REF] Tang | Modelling the thermo-mechanical behaviour of compacted expansive clays[END_REF] and water chemistry of the saturating fluid (Pusch 2001a, Karland et al., 2005;[START_REF] Suzuki | In situ observations of the swelling of bentonite aggregates in NaCl solution[END_REF][START_REF] Komine | Swelling characteristics of bentonites in artificial seawater[END_REF] on the hydro-mechanical (HM) behaviour.

For the swelling properties, it has been found that the swelling pressure determined in the laboratory can be affected by the experimental methods [START_REF] Sridharan | Swelling pressure of clays[END_REF]Tang el al., 2011b). Normally, different methods give different values of swelling pressure due to the difference in the loading and wetting conditions in each method [START_REF] Abdullah | Prediction of swelling potential of an expansive shale[END_REF][START_REF] Abdullah | Swelling behaviour of expansive shales from the middle region of Saudi Arabia[END_REF]. In addition, the swelling properties depend on the initial dry density and water content of the soil specimen. The higher the initial dry density, the higher the swelling pressure or the higher the swelling strain; the swelling strain decreases with increasing initial water content, but the swelling pressure seems not to be affected by the initial water content [START_REF] Komine | Experimental study on swelling characteristics of compacted bentonite[END_REF][START_REF] Villar | Influence of dry density and water content on the swelling of a compacted bentonite[END_REF]. The swelling properties can be also affected by the chemical composition of the saturating fluid: the swelling capacity of the bentonite decreases with the increase in salinity of saturating fluid, although this influence becomes less significant for higher densities [START_REF] Pusch | Swelling pressure of highly compacted bentonite[END_REF]Sugita et al., 2003;[START_REF] Karnland | Bentonite swelling pressure in NaCl solutions-Experimentally determined data and model calculations[END_REF][START_REF] Castellanos | Chemical impact on the hydro-mechanical behaviour of high-density febex bentonite[END_REF][START_REF] Siddiqua | Evaluation of the impact of pore fluid chemistry on the hydromechanical behaviour of clay-based sealing materials[END_REF]. Moreover, studies on the aging effects on the swelling behavior show that the swelling potential may decrease with time due to the rearrangement of clay particles with time (Nalzeny et al., 1967;[START_REF] Day | Swell-shrink behaviour of expansive compacted clay[END_REF][START_REF] Subba Rao | Effect of aging on swelling and swell-shrink behaviour of a compacted expansive soil[END_REF][START_REF] Delage | Ageing effects in a compacted bentonite: a microstructure approach[END_REF].

Very often, bentonite/sand mixtures are considered for the reasons of good control of swelling pressure, large thermal conductivity and a better mechanical resistance. In France, the mixture of bentonite and crushed Callovo-Oxfordian (COx) claystone excavated from the Bure site of the ANDRA URL (-490 m, North-eastern France) was proposed as a possible sealing and backfill material. This choice has several advantages: (i) it is more economical by using local excavated claystone; (ii) the negative impacts on the environment is reduced by recycling the excavated material;

(iii) there is better compatibility of mineralogical and chemical compositions with host rock, allowing reduction of complex physico-chemical interaction with the host rock [START_REF]Référentiel des matériaux d'un stockage de déchets à haute activité et à vie longue -Tome 4: Les matériaux à base d'argilites excavées et remaniées[END_REF]Tang et al., 2011a;Tang et al., 2011b). On the other hand, unlike relatively inert sand, claystone contains clay minerals and interaction between claystone and bentonite may occur, affecting the hydro-mechanical behaviour of the compacted mixture. Moreover, this interaction can be of long term. Particular attention should be paid to this aspect.

This study focuses on the swelling properties of the mixture MX80 bentonite/crushed Cox claystone. A series of swelling tests were performed under constant temperature (20±1°C). The influences of water chemistry, hydration procedure and duration, pre-existing technical void and loading-wetting paths on the swelling pressure of compacted samples were investigated. Emphasis was put on the relationship between the swelling pressure and the dry density of bentonite.

MATERIALS AND METHODS

Materials

The commercial MX80 bentonite from Wyoming, USA, was used. Table 1 lists its physical parameters. It appears that the proportion of montmorillonite is dominant in the bentonite (92 %); it has an average specific gravity of 2.76, a liquid limit of 520%, and a plastic limit of 42%. The grain size distribution determined by sedimentation in Figure 1 shows that 84% grains are smaller than 2 µm (clay fraction).

Callovo-Oxfordian (COx) claystone taken from the Bure site of the ANDRA URL was studied. It contains 40-45% clay minerals (mainly interstratified minerals illite-smectite), 20-30% carbonates and 20-30% quartz and feldspar [START_REF] Hoteit | Geological radioactive waste disposal project in franceconceptual model of a deep geological formation and underground research laboratory in Meuse Haute-Marne site[END_REF][START_REF] Lebon | French underground research laboratory of Meuse, Haute-Marne THM aspects of argillite formation[END_REF][START_REF] Zhang | Experimental study of the hydro-mechanical behaviour of the Callovo-Oxfordian argillite[END_REF]. The specific gravity is 2.70.

The excavated claystone was air-dried (w = 2.64%) and crushed to powder. The grain size distribution determined by sedimentation is presented in Figure 1. It confirms that 40% grains are clays (< 2 µm).

Both distilled water and synthetic water having the same chemical composition as the site water (see Table 2) were used.

Samples preparation

All the tests in this study were performed on samples of compacted bentonite/claystone mixture with a bentonite content of 70 % in dry mass. Bentonite and claystone powders with the initial water contents of 11.8 % and 2.64 % respectively, were used for the samples preparation. Their grain size distributions were determined by sieving and are presented in Figure 1.

Samples were statically compacted in an oedometer cell (38 or 70 mm in internal diameter) at a controlled rate of 0.05 mm/min. A load transducer was used for axial force monitoring, and a micrometer dial gauge was used for axial displacement monitoring. After compaction, the specimen was carefully transferred into the hydration cell (with the same diameter as the oedometer cell) by connecting the bottom of the two cells together. This procedure allows the lateral stress released without significant increase in sample diameter.

Experimental methods

Various methods were used to determine the swelling pressure upon wetting. The stress paths of these methods are presented in Figure 2.

For the "constant-volume" method (stress path OA), the devices presented in Figure 3 and Figure 4 were used. The constant-volume cell includes three parts (Figure 3, Tang et al., 2011b): [START_REF] Abdullah | Swelling behaviour of expansive shales from the middle region of Saudi Arabia[END_REF] the bottom part containing a porous stone and a drainage system; (2) the middle cell (70 mm inner diameter) used to prevent radial swelling, with two air outlets; (3) the top part incorporating a total pressure sensor to monitor the swelling pressure. Figure 4 presents the setup used to control the suction in the soil sample using the vapour equilibrium technique (see [START_REF] Delage | The relationship between suction and swelling properties in a heavily compacted unsaturated clay[END_REF] for more details). When flooding the soil sample, this system was removed and the water inlet was connected to a water reservoir.

For the "pre-swell" method (stress path OBB′), the sample was first allowed to swell freely in the axial direction to a certain value (Point B, noted as "pre-swell"), then the piston was fixed permitting the generation of swelling pressure that was monitored by the load transducer. This method was used to investigate the effect of pre-existing technical voids (simulated by the pre-swell allowed in the tests) on the swelling pressure.

For the "zero-swell" and "swell-consolidation" methods, the equipment employed was a conventional oedometer [START_REF] Basma | Laboratory assessment of swelling pressure of expansive soils[END_REF][START_REF] Nagaraj | Critical Evaluation of Determining Swelling Pressure by Swell-Load Method and Constant Volume Method[END_REF]. Firstly, a low initial load of 0.1 MPa was exerted on the specimen prior to water flooding. As the specimen wetted up it attempted to swell. When the swell exceeded 10 µm (equivalent to 0.1%), additional pressure was added in small increment to bring the volume of soil specimen back to its initial value [START_REF] Basma | Laboratory assessment of swelling pressure of expansive soils[END_REF][START_REF] Abdullah | Prediction of swelling potential of an expansive shale[END_REF][START_REF] Abdullah | Swelling behaviour of expansive shales from the middle region of Saudi Arabia[END_REF][START_REF] Attom | Changes in clay swelling and shear strength properties with different sample preparation techniques[END_REF]. This operation was repeated until the specimen ceased to swell (OCC′ in Figure 2). The swelling pressure was defined as the stress under which no more swelling strain was observed.

The "swell-consolidation" method consists of re-saturating the soil under a low vertical pressure of 0.1 MPa until full swell was achieved. After swell completion, standard consolidation test was conducted. The pressure required to compress the specimen back to its original void ratio is defined as the swelling pressure [START_REF] Basma | Laboratory assessment of swelling pressure of expansive soils[END_REF][START_REF] Abdullah | Prediction of swelling potential of an expansive shale[END_REF][START_REF] Abdullah | Swelling behaviour of expansive shales from the middle region of Saudi Arabia[END_REF][START_REF] Agus | An Experimental study on hydro-mechanical characteristics of compacted bentonite-sand mixtures[END_REF]. The corresponding stress path ODD′ is shown in Figure 2. In this path, point D also represents the maximum swelling strain of the sample.

The experimental programme is shown in Table 3. Three tests were performed using the constant-volume method to study the effect of water chemistry and the hydration procedure (CV01, CV02 and CV03). Distilled water and synthetic water was used in test CV01 and CV02, respectively. In test CV03, three suctions (57 MPa, 38 MPa and 12.6 MPa) were first applied step by step using vapor equilibrium technique (as shown in Figure 4), prior to distilled water flooding in the last stage.

Four tests were performed by pre-swell method to study the influence of pre-existing technical voids on the swelling pressure (PS01 -PS04). Different pre-swells were allowed before measurement of the swelling pressure. Note that for test PS04 the sample was allowed to swell freely to reach the maximum pre-swell strain.

Two other tests were conducted using zero-swell method (ZSO1) and swell-consolidation method (SCO1), respectively, for analyzing the influence of loading-wetting paths followed in different experimental methods.

As it can be seen in Table 3, the tests conducted have in general long duration, from 80 h to one year. The results of test CV03 is presented in Figure 6. The initial suction of sample was about 90 MPa (measured by a relative humidity sensor on the soil specimen after the compaction and prior to the installation in the cell). The application of the first suction of 57 MPa resulted in a swelling pressure of 0.57 MPa. Then, the second suction of 38 MPa was applied and the swelling pressure reached 1.43 MPa. With the third suction of 12.6 MPa the swelling pressure increased to 2.61 MPa. The zero suction applied by distilled water led the sample to a maximum value of 4.39 MPa swelling pressure. This value is very close to that from test CV01 (4.30 MPa) and CV02 (4.37 MPa) in which the samples were flooded directly with water. This means there is no kinematic effect on the swelling pressure for the studied mixture. In Figure 8, the whole results from the three tests CV01, CV02 and CV03 during one year are presented. It appears that after a long period of one year, there was just a slight decrease of swelling pressure and the values for the three samples still remain very close (4.23MPa, 4.32MPa and 4.29MPa for test CV01, CV02 and CV03, respectively). This shows a negligible effect of any bentonite-claystone interaction on the swelling pressure.

EXPERIMENTAL RESULTS

The evolution of swelling pressure for the specimens having the same initial dry density of 1.90 Mg/m 3 with different pre-swells is presented in Figure 9. An expected significant decrease of swelling pressure with increasing pre-swell is observed. For the pre-swells of 10, 20 and 25%, the swelling pressures obtained are 5.38, 2.03 and 0.7 MPa, respectively. Note that the maximum swelling strain from test PS04 reaches 43 %.

The results from test SCO1 using the swell-consolidation method are presented in By definition, this value is the swelling pressure by this method.

From the results in Figure 9, the swelling pressure is plotted versus the pre-swell strain in Figure 11. The maximum pre-swell of test PS04 and the swelling strain in SCO1 (swell consolidation method) are also presented in this figure. Note that all specimens had the same initial dry density of 1.90 Mg/m 3 and all flooded with synthetic water. It appears that the result of SCO1 is close to that of PS04 (free swell), showing a good repeatability of the free-swell tests. A linear correlation can be obtained between the swelling strain allowed (ε in %) and the logarithm of swelling pressure (σ s in MPa):

946 . 23 ) ( 32 . 19 + - = s Lg σ ε (Eq.2)
In Figure 12, the swelling pressure determined by the pre-swell method (PS01, PS02, PS03, PS04), constant-volume method (CV02), zero swell method (ZSO1) are plotted in the plane of void ratio/logarithm of vertical stress, together with the consolidation line from test SCO1. Point O and O′ correspond to the initial states of the samples at a dry density of 1.90 Mg/m 3 (PS01, PS02, PS03, PS04 and SCO1) and 1.70 Mg/m 3 (CV02 and ZSO1), respectively. It can be noted that at the same void ratio, the vertical stress of the consolidation curve (SCO1) is slightly higher than the swelling pressure determined by other methods.

Figure 13 shows the measured swelling pressure versus the final dry density of the bentonite/claystone mixture for all the tests. Note that these tests have been performed with two different initial dry densities (ρ di = 1.90 Mg/m 3 for tests PS01, PS02, PS03, PS04, SCO1; and ρ di = 1.70 Mg/m 3 for tests CV02, ZSO1), and using various methods (see Table 3). In spite of this, a unique correlation seems enough to describe the relationship between the swelling pressure σ s (MPa) and the final dry density of the mixture ρ dm (Mg/m 3 ): where ρ m (Mg/m 3 ) is the mixture density; B (%) is the bentonite content (in dry mass) in the mixture; w m is the water content of the mixture; w a is the initial water content of claystone; G sa is the specific gravity of claystone. In this study, w a = 2.64%, B = 70 %, G sa = 2.70.

Using Eq. 4, the results shown in Figure 13 were re-analysed and Figure 15 shows the variations of swelling pressure with the final dry density of bentonite. In the same figure, the results collected from other works on the MX80/sand mixture (Karland et al., 2008) and the pure MX80 bentonite [START_REF] Karnland | Sealing ability of Wyoming bentonite pellets foreseen as buffer material-Laboratory results[END_REF][START_REF] Dixon | Swelling and hydraulic properties of bentonites from Japan, Canada and USA[END_REF] are also presented. A very similar relationship is obtained for the different data sets, showing that the swelling pressure mainly depends on the final dry density of bentonite, sand and claystone being both inactive components in the mixtures for the swelling pressure development.

To further investigate this point, results on other reference bentonites were collected and analysed in the same fashion. Figure 15 shows the variations of swelling pressure with the final dry density of MX80 (from Figure 14), FoCa7 [START_REF] Imbert | Hydro-mechanical response of a bentonite pellets-powder mixture upon infiltration[END_REF], FEBEX [START_REF] Villar | Thermo-hydro-mechanical characterisation of a bentonite from Cabo de Gata. A study applied to the use of bentonite as sealing material in high level radioactive waste repositories[END_REF] and Kunigel V1 [START_REF] Dixon | Swelling and hydraulic properties of bentonites from Japan, Canada and USA[END_REF]. It appears that for each bentonite, there is a unique relationship between the swelling pressure and the final dry density of bentonite. However, the relationships are not the same. A general expression can be proposed:

db s βρ α σ exp × =
Eq.5

where α and β are the two constants.

Table 4 shows the values of α and β for the four bentonites analysed. In the table, the mineralogy of these materials is also presented. The difference of parameters can be related to the different types of clay (i.e. montmorillonite, beidellite and saponite, etc), montmorillonite content and type of exchangeable cations (i.e. calcium or sodium). In general, the swelling capacity of sodium bentonite is higher than that of calcium bentonite; with the same type of exchangeable cations, a larger montmorillonite content leads to a higher swelling pressure.

DISCUSSION

It has been observed that the effect of the chemistry of Bure site water on the swelling pressure is negligible. However, it is generally accepted that the swelling pressure decreases with the increase in salinity of the pore-water, although this decrease becomes less significant in case of high density [START_REF] Karnland | Bentonite swelling pressure in NaCl solutions-Experimentally determined data and model calculations[END_REF][START_REF] Castellanos | Chemical impact on the hydro-mechanical behaviour of high-density febex bentonite[END_REF][START_REF] Siddiqua | Evaluation of the impact of pore fluid chemistry on the hydromechanical behaviour of clay-based sealing materials[END_REF][START_REF] Komine | Swelling characteristics of bentonites in artificial seawater[END_REF]. [START_REF] Castellanos | Chemical impact on the hydro-mechanical behaviour of high-density febex bentonite[END_REF] reported that the swelling pressure of the FEBEX bentonite compacted to a dry density of 1.65 g/cm 3 decreases to almost half its initial value when 2 mol/L CaCl 2 and NaCl/L solutions are used as saturating fluids; At low salinities (0.004 mol/L, granitic water), the swelling pressure of bentonite seems not to be affected by the salinity changes at a dry density ranging from 1.40 to 1.70 Mg/m 3 . It appears that for the studied bentonite/claystone mixture, the high density and the low salinity of synthetic water together resulted in the negligible effect of water chemistry on the swelling pressure. This can be explained by the theory of cations filtration [START_REF] Komine | Swelling characteristics of bentonites in artificial seawater[END_REF]. For high dry density of bentonite-based materials, the distances between the montmorillonite mineral layers being very small, these layers can filter the cations in the solution; on the contrary, in the case of low dry density, the cations in solution can infiltrate easily into the montmorillonite mineral layers due to the larger distances between them, thus affecting the swelling behaviour.

For the sample wetted with suction control (CV03), an exponential function was found between the swelling pressure and the suction applied. This can be explained as follows. As clay samples are exposed to humid water vapour, water molecules first migrate into the open channels and adsorbed on the exposed mineral surface [START_REF] Pusch | The microstructure of MX-80 clay with respect to its bulk physical properties under different environmental conditions[END_REF][START_REF] Arifin | Thermo-hydro-mechanical behavior of compacted bentonite sand mixtures: An Experimental Study[END_REF], then move to elementary clay layers. The number of water molecules absorbed by the clay layers depends on the relative humidity or suction [START_REF] Pusch | The microstructure of MX-80 clay with respect to its bulk physical properties under different environmental conditions[END_REF][START_REF] Saiyouri | Experimental study of swelling in unsaturated compacted clays[END_REF][START_REF] Delage | Some microstructure effects on the behaviour of compacted swelling clays used for engineered barriers[END_REF], and this number of water molecules defines the swelling pressure of the sample. Therefore the swelling pressure is suction or relative humidity dependent. After the sample was flooded with distilled water, the maximum swelling pressure was found close to that obtained by water-flooding the sample directly, indicating the negligible effect of wetting procedure. This phenomenon can be explained by the mechanism identified by [START_REF] Cui | Microstructure changes of a confined swelling soil due to suction controlled hydration Unsaturated soils[END_REF]: when hydrating by decreasing suction (57-38-12.6 MPa) under confined conditions, the size of macro-pores was progressively decreased, whereas the micro-pores remained almost un-affected. The micro-pores started to change only when the water saturation is approached. This suggests that step-wetting by suction control and direct saturation by water flooding may lead to similar final microstructures, thus similar final swelling pressures. [START_REF] Yang | A coupled non-isothermal reactive transport model for long-term geochemical evolution of a HLW repository in clay[END_REF] reported that the mineralogical composition of the bentonite will not be stable under the chemistry fluid infiltration and its properties may degrade over long time periods. Moreover, for the bentonite/claystone mixture used in this study, interaction of claystone with water and bentonite was suspected. This justifies the long swelling tests kept over one year. However, no any significant effects were observed on the swelling pressure. It is possible that one year test is not long enough and this point should be studied further with longer tests, giving the long-term nature of the nuclear waste disposal.

A linear correlation was observed between the pre-swelling strain and the logarithm of swelling pressure for the samples with the same initial dry density. This line defines the limit of swelling potential: the samples at the same initial state followed different stress-volume paths until reached this limit and then no further expansion occurred. This is consistent with the conclusion of [START_REF] Villar | Influence of dry density and water content on the swelling of a compacted bentonite[END_REF] and [START_REF] Siemens | Evaluation of the influence of boundary confinement on the behaviour of unsaturated swelling clay soils[END_REF] who found a similar relationship between swelling strain and swelling pressure. It can be seen that the final state of specimen governed the swelling pressure: for the samples with the same initial state, different pre-swelling strains led to different final dry densities and thus resulted in different swelling pressure. Moreover, a unique relationship was observed between the swelling pressure and the final dry density of the samples whatever the initial dry density, the percentage of pre-swell and the experimental method. This also enhances the conclusion that the final state of the sample controls the swelling pressure. Further analysis showed that the swelling pressure mainly depends on the final dry density of bentonite in the mixture. This observation is in agreement with the conclusion of [START_REF] Lee | Swelling Pressures of a Potential Buffer Material for High-Level Waste Repository[END_REF] and [START_REF] Agus | An Experimental study on hydro-mechanical characteristics of compacted bentonite-sand mixtures[END_REF] who noted that the swelling pressure of bentonite/sand mixtures with different bentonite contents is a function of the final bentonite dry density. This suggests that the swelling mechanism of bentonite-based materials is the same as that of pure bentonites.

At the same void ratio, the swelling pressure determined by different methods was found slightly lower than the vertical stress needed to reach the same void ratio following the swell-reload path (swell-consolidation method). This was in agreement with the results by many other authors [START_REF] Justo | The influence of stress-path in the collapse-swelling of soils at the laboratory[END_REF][START_REF] Sridharan | Swelling pressure of clays[END_REF][START_REF] Basma | Laboratory assessment of swelling pressure of expansive soils[END_REF][START_REF] Abdullah | Prediction of swelling potential of an expansive shale[END_REF][START_REF] Abdullah | Swelling behaviour of expansive shales from the middle region of Saudi Arabia[END_REF][START_REF] Agus | An Experimental study on hydro-mechanical characteristics of compacted bentonite-sand mixtures[END_REF][START_REF] Villar | Investigation of the behaviour of bentonite by means of suction-controlled oedometer tests[END_REF][START_REF] Villar | Influence of dry density and water content on the swelling of a compacted bentonite[END_REF], and can be considered as a consequence of the coupling between the microstructure and macrostructure [START_REF] Gens | A framework for the behaviour of unsaturated expansive clays[END_REF][START_REF] Villar | Investigation of the behaviour of bentonite by means of suction-controlled oedometer tests[END_REF]Sánchez et al., 2005). For the swell-consolidation oedometer test, wetting took place under a low vertical load and the void ratio increased greatly due to the large microstructural changes. In this case, intense breakage of particle aggregates occurs, leading to relatively uniform distribution of the expandable component. A relatively high vertical stress was needed to compensate this large macrostructure deformation. By contrast, smaller microstructure and macrostructure interaction is expected in other methods, with lower stress at full saturation. Furthermore, the relative larger displacement in the swell-consolidation oedometer test would mobilise higher friction and this friction can also contribute to the phenomenon observed.

CONCLUSION

The swelling pressure of bentonite/claystone mixture was determined by different methods. The effects of the water chemistry, the hydration procedure, the pre-existing technical voids and the experimental methods on the swelling pressure were investigated. From the experimental results the following conclusion can be drawn.

There was no obvious effect of water chemistry on the swelling pressure due to the high density and the low salinity of synthetic water.

An exponential function was found between the swelling pressure and the suction applied; no effect of hydration procedure on the final swelling pressure was observed.

The swell-consolidation method gives higher swelling pressure mainly because of the coupling between the microstructure deformation and macrostructure deformation. The effect of friction is also to be considered for this phenomenon.

The swelling pressure of bentonite-based materials mainly depends on the final dry density of the bentonite in the mixture, suggesting that the swelling mechanism of bentonite-based materials is the same as that of pure bentonites. A general relationship between the swelling pressure and the final dry density of various bentonites was proposed, with two parameters depending on the montmorillonite content and the type of exchangeable cations.

From a practical point of view, the relationship elaborated between the swelling pressure and the final bentonite dry density is helpful in designing the sealing/filling buffers with bentonite-based materials: when the initial state of bentonite-based materials and the technical voids are known, the final swelling pressure can be predicted. Moreover, the crushed Cox claystone can be used to form the bentonite/claystone mixture because it behaves as sand. However it should be noted that this conclusion is based on the results from one year tests and further studies with longer tests are needed to gain more confidence on this aspect.

List of Tables

Table 1 Characteristics of MX80 bentonite (Tang et al., 2008) Table 2 Chemical components of the synthetic water Table 3 Test programme Table 4 Montmorillonite content and external cations type of several bentonites

List of Figures

Figure 5

 5 Figure 5 presents the results from tests CV01 and CV02 with distilled water and synthetic water respectively, during the first 100 h. The two curves are very similar, showing negligible effect of water chemistry (in the range considered). With water infiltration, swelling pressure increased first very quickly; after about 20 h the swelling pressure reached a first stability stage. At 32 h, the swelling pressure restarted to increase and it reached a second stability stage at 100 h. The final values are 4.30 MPa and 4.37 MPa for CV01 and CV02, respectively.

Figure 7

 7 Figure 7 presents the relationship between the swelling pressure (σ s in MPa) and the suction (s in MPa), with the values obtained from test CV03. An exponential function can be used to satisfactorily describe this relationship: s s 0178 . 0 10 9908 . 4 -× = σ

Figure 10 .

 10 Figure 10. When wetting up, the sample swelled under a low vertical pressure of 0.1 MPa and the maximum swelling strain reached 41.76%. Further compression gave a normal consolidation curve that allows the determination of the swelling pressure: σ s = 22.20 MPa.

  the swelling pressure of the compacted claystone/bentonite mixture is mainly dependent on the final dry density of the mixture. For a deeper analysis on the role of the bentonite itself in the swelling pressure development of the bentonitebased mixutre, the dry density of bentonite (ρ db ) was considered by assuming that the water content of additives (claystone in this study) kept constant, while the water added during the tests was totally absorbed by bentonite. The volume of bentonite (V b ) is the difference between the total volume (V) and the volume of claystone (soil particles and water inside). The bentonite dry density can be calculated by the

Figure 1 .

 1 Grain size distribution of MX80 bentonite and crushed COx claystone Figure2. Stress path of various experimental methods used to determine the swelling pressure Figure3. Constant-volume cell Figure4. Schematic view of constant volume cell with suction control system Figure5. Evolution of swelling pressure for test CV01 and CV02 during the first 100 h. Figure6. Evolution of swelling pressure for test CV03 during decreasing of suction. Figure7. Swelling pressure versus suction of test CV03 Figure8. Evolution of swelling pressure for tests CV01, CV02, and CV03 for 1 year Figure9. Evolution of swelling pressure with various pre-swells Figure10. Swelling strain versus vertical stress applied for test SCO1 Figure11. Pre-swell versus swelling pressure Figure12. Swelling pressure or vertical pressure versus void ratio of mixture Figure13. Swelling pressure versus finial dry density of bentonite/claystone mixture Figure14. Results of various mixtures using MX80 bentonite -swelling pressure versus final dry density of bentonite Figure15. Swelling pressure versus final dry density of bentonite

Figure 1 .Figure 5 .

 15 Figure 1. Grain size distribution of MX80 bentonite and crushed COx claystone

Figure 6 .

 6 Figure 6. Evolution of swelling pressure for test CV03 during decreasing of suction.

Figure 7 .Figure 8 .Figure 9 .Figure 13 .Figure 15 .

 7891315 Figure 7. Swelling pressure versus suction of test CV03

Table Characteristics

 Characteristics

			of MX80 bentonite (Tang et al., 2008b)
	Montmorillonite (%)		92
	Quartz (%)			3
	w l (%)			520
	w p (%)			42
	I p				478
	ρ s (Mg/m 3 )			2.76
	Table Chemical components of the synthetic water
	Components	NaHCO 3 Na 2 SO 4 NaCl KCl	CaCl 2 .2H 2 O MgCl 2 .6H 2 O SrCl 2 .6H 2 O
	Mass (g)		0.28	2.216	0.615 0.075 1.082	1.356	0.053
	per 1L solution
	Table Test programme
	Test No. Injected water	Method		(Mg/m 3 ) Initial dry density	Duration
	CV01	Distilled		Constant-volume	1.70	1 year
	CV02	Synthetic		Constant-volume	1.70	1 year
	CV03	Vapour and distilled Constant-volume	1.70	1 year
	PS01	Synthetic		Pre-swell ε = 10%	1.90	100 h
	PS02	Synthetic		Pre-swell ε = 20%	1.90	100 h
	PS03	Synthetic		Pre-swell ε = 25%	1.90	100 h
	PS04	Synthetic		Pre-swell ε = max	1.90	80 h
	ZSO1	Synthetic		Zero-swell	1.70	80 h
	SCO1	Synthetic		Swell-consolidation 1.90	4 months

Table 4

 4 Montmorillonite content and external cations type of several bentonites

	Bentonite	α	β	Montmorillonite Content (%)	Type
	MX 80	1.78×10 -4 6.75 75-90	Na
	FEBEX	9.80×10 -5 6.85 92	Ca
	FoCa	7.83×10 -7 9.24 50 Beidellite 50 Kaollite	Ca
	Kunigel V1 3.67×10 -3 3.32 48	Na

Acknowledgements

This work was conducted within the framework of GM2 of the French National Agency for Nuclear Waste Management (ANDRA). The conclusions and the viewpoints presented in the paper are those of the authors and do not necessarily coincide with those of ANDRA. The support from the PHC Cai Yuanpei project (24077QE) and that of the China Scholarship Council (CSC) are also greatly acknowledged.