Shashank Shekhar
email: shashank.shekhar@laas.fr

Anthony Favier
email: anthony.favier@laas.fr

Rachid Alami
email: rachid.alami@laas.fr

Madalina Croitoru
email: madalina.croitoru@lirmm.fr

A Knowledge Rich Task Planning Framework for Human-Robot Collaboration

Keywords: Collaborative planning, Knowledge reasoning, Inference, Theory of Mind (ToM), Human-aware task planning

In this paper, we position ourselves within the context of collaborative planning. Drawing upon our recent research, we introduce a novel, knowledge rich task planning framework that represents and reasons and effectively addresses agents' first-order false beliefs to solving a task planning problem with a shared goal. Our contributions to this work are as follows: First, to enhance the reasoning abilities of an existing framework, an intuitive observability model for situation assessment is addressed, and for that, an improved knowledge modeling is considered. This effectively captures agents' predictable false beliefs and motivates us to exploit the power of off-the-shelf knowledge reasoners. Second, a new planning approach that incorporates this improved encoding. And, to show the effectiveness of our planner and present our initial findings and proof of concept, we conduct a thorough use case analysis.

Introduction

Human-robot collaboration/interaction (HRC/I) is a current research focus due to the growing number of robot-assisted applications [START_REF] Selvaggio | Autonomy in physical human-robot interaction: A brief survey[END_REF]. Collaborative robots add clear value to real-world domains like household [START_REF] Unhelkar | Decision-Making for Bidirectional Communication in Sequential Human-Robot Collaborative Tasks[END_REF], workshops [START_REF] Unhelkar | Human-aware robotic assistant for collaborative assembly: Integrating human motion prediction with planning in time[END_REF], or medical facilities [START_REF] Jacob | Collaboration with a robotic scrub nurse[END_REF].

In this work, we address a task planning problem where humans and robots jointly achieve a shared goal. For seamless human-robot collaboration, we believe that it is essential not to restrict human behaviors and, hence, consider humans as uncontrollable agents [START_REF] Cirillo | A Human-Aware Robot Task Planner[END_REF]. Our focus is on developing a planning framework that generates collaborative behaviors for an autonomous robot while anticipating the possible human behaviors and being congruent to humans' choices. Frameworks that support such requirements, in general, include HAT-P/EHDA [START_REF] Buisan | HATP/EHDA: A Robot Task Planner Anticipating and Eliciting Human Decisions and Actions[END_REF], ADACORL [START_REF] Unhelkar | Semi-Supervised Learning of Decision-Making Models for Human-Robot Collaboration[END_REF] and CommPlan [START_REF] Unhelkar | Decision-Making for Bidirectional Communication in Sequential Human-Robot Collaborative Tasks[END_REF], to cite but a few.

Restricted observability available in the environment often leads agents to form false beliefs about the progress of the task and other agents' beliefs. For instance, an agent may rely on "only believing what they see or can infer" to update or form new beliefs. For the robot to anticipate such situations while planning its behavior to collaborate, it should consider Theory of Mind (ToM) to maintain and manage agents' distinct beliefs.

Our recently proposed planner extends the HATP/EHDA framework and considers the first-order ToM, that is, managing (false) beliefs about the physical world [START_REF] Favier | Anticipating False Beliefs and Planning Pertinent Reactions in Human-Aware Task Planning with Models of Theory of Mind[END_REF]. Roughly, its main idea works as follows: First, the existing problem encoding is enhanced. To be specific, we categorize each environmental property as either observable -meaning its real value can be assessed directly from the environment -or indirectly inferable. In the latter case, the changes in the property's status persist in the environment when an action is executed, but cannot be observed directly. However, an agent can assess this knowledge either as an observer or as an actor, or when they are communicated. Second, to consider restricted observability, we introduce the concept of co-presence and co-location. We formulate the environment such that a collection of discrete places where action manipulation can take place, permitting the enhanced encoding to enable precise action executions, or an agent assessing the value of an environmental property when they are physically situated within a specified place.

The encoding is used in HATP/EHDA as input, modifying the planner to use improved knowledge modeling to handle better the evolution of agents' firstorder (false) beliefs and estimate the actions humans are likely to perform. (Due to space restrictions, we will provide only a high-level description of it.) However, some limitations to the above line of work are: First, the context under which the reasoning works is limited. For example, associating an observable state property directly to a discrete place in the environment is not always intuitive and straightforward and enables sound reasoning. To understand this, consider the following scenario: A robot holding a coffee mug can be assessed from where the robot is currently situated. Moreover, if the robot moves from one place to another, then the condition under which the robot holding the coffee mug can be assessed, also changes implicitly. Or, if a table is moved, then the condition to assess the orientation of blocks on top of it would change implicitly, too. Second, the system's ability to refute a false belief is limited.

In this regard, our contributions to this paper are the following.

1. We first extend and generalize the concepts introduced earlier for observing the value of an environmental property. We provide a new encoding that is much cleaner and intuitive and achieves a sound resolution and refutation. 2. Second, the planning algorithm is improved by incorporating the new encoding for better managing the evolution of agents' predictable (false) beliefs.

To show the efficacy of our planning approach and present our preliminary findings and proof of concept, we conduct a use case analysis.

The Illustrative Example

Consider an adapted version of the scenario appearing in [START_REF] Favier | Anticipating False Beliefs and Planning Pertinent Reactions in Human-Aware Task Planning with Models of Theory of Mind[END_REF]. The scenario includes a pot of water on the stove, while the pasta packet is in the adja-cent room. One sub-task is to pour the pasta into the pot, which can only be done after turning on the stove (results in holding StoveOn) and adding salt to the water (results in SaltIn). Suppose, the robot is responsible for turning on the stove (turn-stove-on), while the human is tasked with fetching the pasta (grab-pasta, however, for that, they need to move to the other room where the pasta packet is kept) and pouring it into the pot (pour-pasta). Both the robot and the human have the capability to add salt (add-salt) to the pot. Humans can be uncontrollable but assumed to be rational, so they can choose to either first add salt, or first fetch the pasta. Next, the robot's actions depend on the human's decision, resulting in the generation of different false beliefs. Such variability in beliefs observed can be precisely attributed to the restricted observability and available human choices within the system. Suppose, when the human is temporarily absent to bring pasta, the robot can act in kitchen. When they return, they can "assess" whether the robot turned on the stove, which is observable. However, the presence of salt (SaltIn) is not directly observable to her. To prevent misunderstandings, a proactive robot needs to anticipate false beliefs held by humans. Here, humans may mistakenly believe that salt is not added to the pasta or be uncertain about it.

The Basic Architecture and Recent Advancements

We provide a brief overview of the HATP/EHDA (human-aware task planning by emulating human decisions and actions) architecture [START_REF] Buisan | HATP/EHDA: A Robot Task Planner Anticipating and Eliciting Human Decisions and Actions[END_REF], building upon previous research, e.g. [START_REF] Alami | Toward Human-Aware Robot Task Planning[END_REF][START_REF] Alili | Planning and plan-execution for humanrobot cooperative task achievement[END_REF][START_REF] De Silva | The HATP hierarchical planner: Formalisation and an initial study of its usability and practicality[END_REF][START_REF] Buisan | A Human-Aware Task Planner Explicitly Reasoning About Human and Robot Decision, Action and Reaction[END_REF]. We also discuss recent advancements that have been made based on its planning framework. (For a better understanding of the basic terminologies, definitions, and planning models, we refer readers to [START_REF] Ghallab | Automated Planning -Theory and Practice[END_REF].)

The HATP/EHDA architecture considers: (1.) distinct capabilities and characteristics of humans and robots, (2.) utilization of human task and/or action models by the robot to inform decision-making, considering human capabilities and environmental dynamics, and (3.) flexibility for humans to choose an action from the available choices, which is congruent to the shared goal.

The HATP/EHDA planning scheme utilizes a two-agent model consisting of a human and a robot, represented as two-agent-HTN (hierarchical task networks) [START_REF] Ghallab | Automated Planning -Theory and Practice[END_REF], adapted as per the requirements. Roughly speaking, each agent has their own initial belief state, action model & methods, and task network. Our focus is on a sequential task to be solved, where both agents have a shared initial task network that needs to be decomposed. Considering perfectly aligned agents' beliefs with the real world to begin with, the classical scheme assumes that the belief state of an agent consists of properties that are either true or false. Assuming the environment is fully observable, the planning scheme uses agents' task/action models and beliefs to decompose their task network into valid primitive components, resulting in an implicitly coordinated plan for the robot within a joint solution policy [START_REF] Buisan | HATP/EHDA: A Robot Task Planner Anticipating and Eliciting Human Decisions and Actions[END_REF]. This policy encompasses both the robot's actions and an estimated policy for the human. For more details, see [START_REF] Favier | Anticipating False Beliefs and Planning Pertinent Reactions in Human-Aware Task Planning with Models of Theory of Mind[END_REF].

A new formalism is proposed to enhance the planning scheme's robustness for estimating human initiatives when dealing with restricted observability. It considers the first-order Theory of Mind for managing agents' (false) belief updates, resulting in improved management of their mental state and enhanced collaboration [START_REF] Favier | Robust Planning for Human-Robot Joint Tasks with Explicit Reasoning on Human Mental State[END_REF]. As we pointed earlier, this scheme addresses the need for a less abstract problem formulation, and conceptualizes place-based situation-assessment models, and hence capturing collaboration nuances more accurately.

An offline planning approach is proposed to detect predictable false beliefs of humans and address them through explicit communication actions if mandatory w.r.t. the goal. It promotes more accurate understanding and alignment between the robot and humans, allowing for minimal communication. Another way, as mentioned in [START_REF] Favier | Anticipating False Beliefs and Planning Pertinent Reactions in Human-Aware Task Planning with Models of Theory of Mind[END_REF], is to delay critical actions, enabling humans to reach a state s.t. the robot's actions become perceivable.

Improved Problem Encoding

We consider two types of agents. First is GT, which stands for ground truth, an omnipresent (virtual) agent that cannot achieve any task, however, it immediately knows all the effects when an action is applied. The second type refers to real agents, e.g., a robot. Real agents can have false beliefs, which means their beliefs about the world may diverge from the GT 's beliefs. Moreover, no real-world uncertainty is considered w.r.t. agents' beliefs.

An environmental property is Boolean type, and is augmented by an argument, ?a -agent (e.g., Human/Robot), which is also its first argument. It represents that the agent believes that this property holds true given it is contained in the agent's beliefs. In this work, we restrict ourselves to those properties that are directly observable in the environment, while relying on the existing concepts with some minor updates required, for managing beliefs w.r.t. the facts that are indirectly inferable. To manage appropriate dynamics of the world, we augment the parameter list of relevant state properties which are observable with an argument ?p -Places (at the end of its parameter list). However, for those that are observable but associating them directly to a place is not intuitive to the domain modeler, e.g., StoveOn is a property of a stove and can be assessed from where it is currently situated, we use a different strategy to cater to them.

With a lifted (primitive) action schema, we specify how it is only modeled to affect the beliefs of the GT agent, in principle, focusing on observable state properties.

:action turn-stove-on (?a -agent ?st -stove ?k -kitchen)

:precondition (and (not(= GT ?a))(at ?a ?a ?k)(stoveAt ?a ?st ?k) ...) :effect (and (stoveOn GT ?st) ...)

Real agents assess available information systematically from the environment, and for that, we include the following in our problem specification:

Language & Interpretation: Informally, to assess the value of a property, an agent needs to respect certain condition(s). Of course, a condition could be that the agent is co-located, as supported by the existing system. However, inspired by the work in [START_REF] Baget | Graal: A toolkit for query answering with existential rules[END_REF], we generalize this idea and specify rules for knowledge reasoning to capture more complex contexts. For one observable property (representing the consequent), conditions for assessing its value are "formulated" in the antecedent of a knowledge rule. Formally, a rule is of the form p(a 1 , x, y), q(x) → s(y, b 1 ), which also means that ∀x∀y(p(a 1 , x, y), q(x) → s(y, b 1 )), where x and y are free variables, and p, q and s are names. a 1 and b 1 are constants.

For example, when an agent is situated at the stove's location, it will acknowledge the current status of StoveOn. A corresponding rule to it is, R1: ∀s∀k∀a(stoveAt(a, s, k), stoveon(GT, s), at(a, a, k) → stoveon(a, s). Note that the GT's beliefs play a key role here. Similarly, we can write other important rules for our example domain: R2: ∀a 1 ∀k(at(GT, a 1 , k) → at(a 1 , a 1 , k)), R3: ∀a 1 ∀a 2 ∀k(at(GT, a 1 , k), at(a 2 , a 2 , k) → at(a 2 , a 1 , k)), and R4: ∀a∀s(¬stoveat(GT, s, kitchen), at(a, a, kitchen) → ¬stoveat(a, s, kitchen)). It treats the stove as a mobile object, which alters the context to also evaluate the status of StoveOn along with determining its current location.

Page restrictions allow us to offer a concise overview only, reserving detailed semantics for future research. In rules, it is important to note that the implications must not be contraposed. Anything that cannot be evaluated as true is considered false for agents. Our focus on stratified rule sets avoids potential issues related to unsafe negation usage and ambiguity in interpretation [START_REF] Apt | Towards a Theory of Declarative Knowledge[END_REF][START_REF] Thiébaux | In Defense of PDDL Axioms[END_REF].

Incorporating New Encoding for Planning

We adapt our planning mechanism presented in [START_REF] Favier | Anticipating False Beliefs and Planning Pertinent Reactions in Human-Aware Task Planning with Models of Theory of Mind[END_REF], to assess new encoding's effectiveness. It assumes that the robot's beliefs never deviate from GT's beliefs, and hence essentially two distinct belief states are handled by the scheme.

Two questions arise at this point: First, how does the state transition occur during planning and how are the agents' (false) beliefs updated? Second, how are the relevant false beliefs detected and addressed? We rely on the existing mechanism to address the second question and how beliefs are updated when agents do indirect inference. Our main focus will be to address how the new observability model is incorporated into the planning workflow.

Once an action is executed, such as the human moving to the kitchen, the process of situation assessment is initiated to evaluate the environment from the perspectives of individual agents. Here, our approach diverges from current methods. Instead of directly matching the co-location of agents with state properties and assessing the latter's values, we invoke an external reasoner to deduce such knowledge. Using the agent's beliefs, the reasoner verifies the formula that captures the context specified (in the rules) to deduce new knowledge or to refute a fact that humans believe but is no longer true in the robot's beliefs. This departure from the existing encoding allows us to remove the hardcoded context within an action. For instance, if the human moves from one room to another, carrying the pasta packet that was initially in the room, the new location for assessing the packet switches to the kitchen. Moreover, we needed to hardcode it within each action that updates the place of an agent in the environment. However, with the new encoding, if the robot sees the human in the kitchen, then given the domain rules, it can assess whether the human is holding the pasta packet, by their presence in the kitchen.

Acknowledgments. This work has been partially financed by Défi Clé "Robotique Centrée sur l'Humain" supported by Région Occitanie and the Artificial and Natural Intelligence Toulouse Institute (ANITI).


Agustín Molinero Guerra

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

Yong He

Pierre Delage

Nadia Mokni

Anh Minh

Anh Minh Tang

Patrick Aimedieu

Michel Bornert

Frédéric Bernier

Characterization of water retention, compressibility and swelling properties of a pellet/powder bentonite mixture

Keywords: pellet/powder bentonite mixture, laboratory testing, initial heterogeneity, water retention, swelling, compressibility

ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

The design of most deep geological repositories for high level radioactive wastes (HLW) is based on the multi-barrier concept which involves the natural host rock and engineered barriers [START_REF] Sellin | The use of clay as an engineered barrier in radioactivewaste management -a review[END_REF]. In this design concept, bentonite-based materials are used to construct buffers, backfills and seal plugs of disposal galleries and access shafts to ensure isolation of the waste from the environment. In particular, mixtures made up of bentonite powder and pellets are considered as a promising candidate sealing material because of its particular properties. In addition to their low permeability, high swelling capacity and high radionuclide migration retardation properties, the pellet/powder mixture exhibits operational advantages in terms of emplacement and avoids the formation of technological gaps between the host rock and the seal plug. Once installed in the repository, the pellet/powder mixture will undergo both hydraulic and mechanical loadings: infiltration of host rock pore water and mechanical confinement imposed by the surrounding rocks. In this context, to ensure the stability of the storage structure, thus the safety of the disposal system, it is of paramount importance to well understand the hydro-mechanical behavior of unsaturated bentonite pellet/powder mixture. For this purpose, the French Institute for Radiation Protection and Nuclear Safety (IRSN) launched the SEALEX project, which consisted of a series of in situ experiments in the Underground Research Laboratory (URL) in Tournemire, France [START_REF] Mokni | Hydro-mechanical analysis of SEALEX in situ tests-Impact of technological gaps on long term performance of repository seals[END_REF][START_REF] Mokni | Analysis of hydro-mechanical behaviourbehavior of compacted bentonite/sand mixture using a double structure formulation[END_REF]. This project aimed at investigating the long-term hydraulic performance of sealing systems in normal and critical scenarios, with different sealing plug configurations (pre-compacted or field compacted sand/bentonite mixtures, pellet/powder bentonite mixtures). In parallel to the in situ experiments, mock-up tests were also carried out on compacted sand/bentonite blocks [START_REF] Wang | Experimental study on the swelling behaviour of bentonite/claystone mixture[END_REF][START_REF] Saba | Investigation of the swelling behaviour of compacted bentonite-sand mixture by mock-up tests[END_REF][START_REF] Mokni | Analysis of hydro-mechanical behaviourbehavior of compacted bentonite/sand mixture using a double structure formulation[END_REF]. The swelling pressure of compacted sand/bentonite blocks was also determined by Wang et al. (2013a). The results confirmed the dominating role of the block dry density, identified by many researchers [START_REF] Börgesson | Modelling of the physical behaviour of clay barriers close to water saturation[END_REF][START_REF] Dixon | Swelling and hydraulic properties of bentonites from Japan, Canada and the USA[END_REF][START_REF] Lloret | Mechanical behaviour of heavily compacted bentonite under high suction changes[END_REF][START_REF] Villar | MX-80 Bentonite. Thermo-Hydro-Mechanical Characterization Performed at CIEMAT in the Context of Prototype Project[END_REF][START_REF] Gens | Hydro mechanical Behavior of a Heterogenous Compacted Soil: Experimental Observations and Modelling[END_REF][START_REF] Villar | Basal spacings of smectite in compacted bentonite[END_REF][START_REF] Schanz | Swelling pressure characteristics of compacted Chinese Gaomiaozi bentonite GMZ01[END_REF]. Further examination showed that sand in the mixture did not contribute to the swelling pressure; it was the dry density of bentonite contained in the mixture that defined the final swelling pressure of the sand/bentonite mixture [START_REF] Wang | Experimental study on the swelling behaviour of bentonite/claystone mixture[END_REF][START_REF] Saba | Investigation of the swelling behaviour of compacted bentonite-sand mixture by mock-up tests[END_REF], in agreement with the results obtained by previous researchers (e.g. [START_REF] Villar | Hydraulic properties of montmorillonite-quartz and saponitequartz mixtures[END_REF][START_REF] Karnland | Sealing ability of Wyoming bentonite pellets foreseen as buffer material -laboratory results[END_REF]. The well-established relationship between final swelling pressure and bentonite dry density constituted a helpful tool in interpreting the field observation in the SEALEX project (Wang et al., 2013a).

As opposed to the compacted bentonite-based blocks, the pellet/powder bentonite mixture has been scarcely investigated in the laboratory. [START_REF] Hoffmann | Hydro-mechanical behaviour of bentonite pellet mixtures[END_REF] performed different tests on mixtures of different-size pellets of Febex bentonite at different dry densities considered within the Engineered Barrier (EB) project. An important finding was the progressive decrease of water permeability induced by the clogging of the large inter-pellet pores due to granule swelling and the development of both swelling strain and pressure upon wetting. [START_REF] Imbert | Hydro-mechanical response of a bentonite pellets/powder mixture upon infiltration[END_REF] investigated the hydro-mechanical behavior of a 50/50 FoCa bentonite pellet/powder mixture by a series of infiltration tests. They concluded that the mixture became homogeneous with a swelling pressure equal to that of a bentonite powder compacted at the same dry density once full saturation was reached.

In this study, the water retention capacity and the swelling and compressibility properties of a 80/20 pellet/powder MX80 bentonite mixture were investigated. Firstly, the water retention curve (WRC) was determined by following a wetting path under constant-volume conditions using a specially designed cell with vapor exchange allowed in all directions. This curve was compared to that of a single pellet of bentonite swelling under free swelling conditions.

Secondly, a series of suction controlled oedometer tests were performed to investigate the compressibility properties of the mixture. The swelling behavior of the mixture after following a wetting-drying path was also studied in oedometer. Finally, the swelling pressure was investigated using both constant-volume and swell-consolidation methods. Emphasis was put on the size of samples due to the strong heterogeneous nature of the material with large pellets.

The results obtained allowed the main hydro-mechanical properties of the bentonite pellets/powder mixture used in the SEALEX project to be characterized, providing relevant parameters for the numerical analysis of the field infiltration experiments involving this mixture.

Materials and methods

Materials

The investigated material was a mixture of pellet/powder of MX80 bentonite at a proportion of 80/20 in dry mass. The MX80 bentonite came from Wyoming, USA, and had a smectite content of 80%, other non-clayey inclusions being quartz, calcite and pyrite. The cation exchange capacity (CEC) was 98 meq/100g, with Na + as major exchangeable cation, with a value of 52 meq/100g (1.2 meq/100g for K + , 10 meq/100g for Mg 2+ and 37 meq/100g for Ca 2+ ). The liquid limit was 560%, the plastic limit was 62% and the unit mass of solid was 2.77 Mg/m 3 [START_REF] Saba | Investigation of the swelling behaviour of compacted bentonite-sand mixture by mock-up tests[END_REF].

Pellets were produced in the Laviosa-MPC company by instantaneously compacting MX80 bentonite in a mould of 7 mm in diameter and 7 mm in height. A zoom on a single pellet is shown in Figure 1. The fabrication water content was w = 6.0 ± 1.0% and the dry density was ρ d = 2.06 ± 0.06 Mg/m 3 , corresponding to a void ratio e = 0.30 ± 0.07. The pellets were stored in the laboratory in a hermetic plastic box at 20°C. The initial suction (s = 135 ± 3 MPa) was measured in the laboratory with a chilled mirror dew point hygrometer (Decagon WP4C), at an initial water content w = 7.2 ± 1.0% (determined after oven-drying at 105°C), slightly higher than the fabrication one due to the water adoption from air after fabrication [START_REF] Molinero-Guerra | In-depth characterisation of a mixture composed of powder/pellets MX80 bentonite[END_REF]. Note that the WP4C measures corresponded to total suction, including the osmotic suction.

The MX80 bentonite powder was produced by crushing pellets just after their fabrication. The maximum size of grains was 2 mm and the portion of the grains smaller than 80 µm was 5%.

An initial water content of 3.2 ± 1.0% was found in the laboratory by oven-drying at 105°C for 24 h, corresponding to an initial suction s = 191 MPa (measured with WP4C). This water content was quite low compared to the fabrication water content (6.0 ± 1.0%), suggesting loss of some water during the pellets crushing operation. More details about the initial state of the material can be found in Molinero [START_REF] Molinero-Guerra | In-depth characterisation of a mixture composed of powder/pellets MX80 bentonite[END_REF].

Sample preparation

All the results presented in this study were obtained by performing laboratory tests on the pellet/powder bentonite mixture. The mixture was prepared by following the first protocol presented in Molinero [START_REF] Molinero-Guerra | In-depth characterisation of a mixture composed of powder/pellets MX80 bentonite[END_REF] to obtain a relatively homogeneous pellet/powder distribution. It consisted in filling the cell by packets corresponding to one layer of pellets spread over the base of the cylinder, with the corresponding amount of powder, respecting the proportion of 80-pellets/20-powder. The global dry initial density of the mixture thus prepared was 1.49 Mg/m 3 .

In order to better understand the initial pellet/powder distribution, microfocus X-ray computed tomography observations were made on the mixture at its initial state. A vertical slice is presented in Figure 2. The dimensions of the observed sample were 120 mm in height and 60 mm in diameter. It appears that even though a special protocol was followed, it was difficult to perfectly control the homogeneity of the sample. Indeed, the grains of powder were not uniformly distributed within the sample, and inter-pellet voids could be clearly identified. The sample, placed between two porous stones, presented larger inter-pellet voids close to the top porous stone and no grains of powder were observed in this zone. Therefore, this material was characterized by a strong heterogeneity at its initial state, which is an important aspect to take into account while further analyzing the global hydro-mechanical behavior of the sample. This initial heterogeneity was investigated in depth by Molinero [START_REF] Molinero-Guerra | In-depth characterisation of a mixture composed of powder/pellets MX80 bentonite[END_REF].

The samples used for the present study were prepared in the same manner, but with a height of 35 mm. This height corresponded to 5 times the height of a single pellet and it was believed that such dimensions constituted a representative volume of the pellet/powder mixture. This ratio of sample size to maximum grain size was also adopted by [START_REF] Duong | Effects of fines and water contents on the mechanical behavior of interlayer soil in ancient railway sub-structure[END_REF] when investigating the mechanical behavior of a mixture of coarse and fine soils.

Experimental methods

Water retention properties

The water retention curve (WRC) of the pellet/powder bentonite mixture under constantvolume conditions was determined on samples of 50 mm in diameter. A special device presented in Figure 3 was designed for this purpose. The pellet/powder mixture was placed into a rigid stainless steel cell that was designed to allow vapor exchanges not only through the two metallic porous disks on both top and bottom of the sample, but also through a cylindrical porous disk on the lateral surface of the sample. This design was expected to significantly accelerate the hydration of the sample by vapor equilibrium technique, essential for lowpermeability materials like the studied swelling MX80 bentonite. The mass of sample was regularly measured. In a standard fashion, equilibrium was considered once the mass changes became insignificant. For each pellet/powder mixture, once equilibrium was reached, three measures were performed for both the water content by oven drying and the suction with WP4C.

The mean values were considered in the further analyses.

In parallel, the water retention curve under free swelling conditions for a single pellet of bentonite was obtained. To this end, pellets were hydrated under several values of suction from their initial state by vapor equilibrium technique. For the pellet/powder mixture, zero suction was applied by injecting deionized water into the cell under a low pressure corresponding to a water column height of about 200 mm.

Compressibility properties -suction controlled oedometer tests

Controlled suction oedometer compression tests were performed on samples of 35 mm in height and 50 mm in diameter by circulating vapor at controlled relative humidity through the base of the sample as shown in Figure 4 (tests SCO1, SCO2 and SCO3 presented in Table 1). In order to investigate the mechanical behavior of the mixture in a relatively large range of load, a high pressure oedometer was used allowing application of vertical stresses as high as 50 MPa [START_REF] Marcial | On the high stress compression of bentonites[END_REF]. This oedometer was previously calibrated using a force transducer in order to ensure the accuracy of the imposed pressures. As opposed to other suction values, zero suction was imposed by circulating deionized water. Vertical displacement was monitored using a digital micrometer (accuracy ± 0.001 mm). The temperature in the laboratory was controlled at 20 ± 0.5°C during the experiments. Time was allowed until swelling stabilized under the imposed value of suction and a low vertical stress of 0.1 MPa. The stabilization was considered when the vertical displacement was lower than 0.01 mm for, at least, 8 h. It is worth noting this criterion was defined based on the French Standard AFNOR (1995) for oedometer compression test. The real swelling stabilization might take much longer time. Three tests were carried out under three different suctions (0 MPa, 9 MPa and 138 MPa). The test at 138 MPa suction (SCO1) was performed without imposing the suction, assuming that the suction changes during loading-unloading were negligible. In this case, the test was performed at constant water content. This assumption was supported by the results of [START_REF] Gens | Effect of structure on the volumetric behaviour of a compacted soil[END_REF] who measured the suctions of a soil compacted under three different stresses and observed that on the dry side of optimum the soil suction was almost the same, suggesting that inter-aggregate macro-pores were dry. Similarly, in this study, the macro-pores of the pellets/powder mixture could be considered as dry at a suction as high as 138 MPa. Thus, it is assumed that compression decreased the macro-pores but not the suction of the mixture.

Loadings were performed in steps from 0.1 MPa. A new load equal to the double of the previous one was applied (except the last loading step for sample SCO1) when the change of the vertical displacement became insignificant (< 0.01mm for 8 h according to AFNOR, 1995). The maximums loads were 12.8 MPa for SCO2, SCO3 and SCO4 and 18 MPa for SCO1 because of the higher stiffness of this latter due to its higher suction. After the loading process, unloadings were performed in steps down to different load values.

Swelling properties

Three tests, SCO3, SCO4 and CV1 presented in Table 1, were performed in order to study the swelling properties of the pellet/powder bentonite mixture. Both the constant-volume and swell-consolidation methods were applied to determine the swelling pressure. To apply the constant-volume method, a constant volume cell was used, which included three parts: (i) the bottom part which contained a porous stone and a drainage system; (ii) the middle cell (70 mm in inner diameter) which prevented any radial swelling, with two air outlets; (iii) the top part including a total pressure sensor for monitoring the axial swelling pressure. The water inlet was connected to a water reservoir placed at the same height of the cell, flooding the pellet/powder mixture from the bottom. The saturation water used was a synthetic water (see Table 2 for the receipt of preparation), which has the same chemical composition as the pore water of the Callovo-Oxfordian claystone in the underground research laboratory of the French agency for radioactive waste management (ANDRA) in Bure, France. In the swell-consolidation method, the sample was hydrated under a low vertical load of 0.1 MPa until full swelling was achieved.

Then, it was compressed following a standard consolidation test procedure. The pressure needed to compress the specimen back to its initial volume was defined as the swelling pressure of the material [START_REF] Basma | Laboratory assessment of swelling pressure of expansive soils[END_REF]Abdullah andMhaidib, 1998, 1999;[START_REF] Agus | An Experimental study on hydro-mechanical characteristics of com-pacted bentonite-sand mixtures[END_REF][START_REF] Wang | Experimental study on the swelling behaviour of bentonite/claystone mixture[END_REF].

Experimental results

Water retention curve

Figure 5 displays the evolution of water content with time for the pellet/powder mixture equilibrated at different suctions. The special cell designed allowed the samples to reach water content stabilisation quite quickly. This was because with the specially designed cell (Figure 3), the sample was completely surrounded by porous stones, which accelerated the vapor exchange process. For all imposed suctions, the water content was stabilized after 30 days of hydration, except for 4 MPa and 82 MPa. For s = 4 MPa, some technical problems occurred during the test, and a constant water content value was found after 80 days. It is suspected that, at this low suction, the hydration system failed after a certain time due to water condensation in the pipes -cleaning intervention was necessary to solve the problem. The slight temperature fluctuations of ± 0.5°C in the laboratory during the experiments could cause this condensation.

For suction s = 82 MPa, it seems that water content was constant after 30 days; nevertheless, it continued increasing slightly up to 90 days. For this value of suction, several problems were found during wetting in the hydration system (blockage of the vapor circulation system) and regular interventions were needed. It could be considered that this technique ran well for suctions higher than or equal to 9 MPa. For lower suctions, problems related to condensation in the pipes could be significant in the relatively long tests (more than 80 days). These problems are to be solved in further studies, by placing the main system in water with temperature control for example.

The water retention curves under constant (pellet/powder mixture) and free swelling conditions (single pellet) for a wetting path are presented in Figure 6 in terms of water content versus suction. It appeared that pellet and mixture had comparable water retention capacities when suction was higher than 4 MPa, suggesting that the suction was governed by the micro-pores within the pellets or powder grains. In addition, in the case of the mixture, the existing macropores can accommodate the swelling of the clay particles. This is in agreement with the results obtained by Yahia-Aissa et al. ( 2001) on compacted Foca 7 clay. It seems that the mixture had a lower water retention capacity under constant-volume conditions for suctions lower than 4 MPa, since its water content at zero suction was 34.3%. This indicated the restriction effect on the clay particles swelling, thus the water retention capacity. More data are needed in this range of suction to confirm this conclusion. Figure 7 presents the suctions measured by WP4C versus the imposed values by either vapor equilibrium technique (for non-zero suctions) or injecting deionized water (for zero suction) for the pellet/powder mixture. Some differences were found between the measured suction after equilibrium and the imposed value by vapor equilibrium technique, in particular for zero suction. This could be due to the stress release while dismantling the specimen, which led the suction to increase within the mixture. This effect appeared more pronounced in the case of zero suction due to the highest swelling pressure developed, which enhanced the stress release effect. [START_REF] Pintado | Assessment of the use of the vapour equilibrium technique in controlled-suction tests[END_REF] concluded that, with the vapor equilibrium technique, it was difficult to reach the same suction distribution inside the sample. From Figure 7, it appears that the suction imposed and the suction measured were almost the same, indicating that in our case the uniform suction distribution was reached thanks to the additional air flow through the lateral surface. This shows the performance of the designed device.

Controlled suction compression tests (SCO1, SCO2 and SCO3)

Figure 8 presents the evolution of volumetric strain with time for tests SCO1, SCO2 and SCO3.

The test at 138 MPa of suction was performed without imposing suction. It was carried out at constant water content conditions. As mentioned before, the suction can be reasonably considered as constant in this test.

In test SCO3, the pellet/powder mixture was hydrated under 0.1 MPa by injecting deionized water to impose zero suction. Equilibrium was reached after 1272 h (53 days), with a value of 21% of volumetric strain, corresponding to a void ratio of e = 1.25. The volumetric strain at equilibrium was higher than the value obtained by [START_REF] Wang | Experimental study on the swelling behaviour of bentonite/claystone mixture[END_REF] for compacted bentonite/sand mixture: 18% (e = 0.97). This could be explained by the higher swelling capacity of the pellet/powder mixture without sand. In test SCO2 for 9 MPa suction applied by vapor equilibrium technique, equilibrium was achieved after 1032 h (43 days), with a volumetric strain of 9% (e = 1.02). A constant-volumetric strain was reached between 320 h and 430 h. This is due to a problem in the hydration system that needed a cleaning intervention. After 430 h, the specimen continued swelling until reaching equilibrium. In test SCO1, no suction was imposed as 138 MPa corresponded to the initial state of the pellet/powder mixture; a period of 5 days was considered prior to loading in this case.

Once equilibrium was reached, the samples were submitted to loading/unloading at constant suctions. For SCO3 (zero suction), on the whole, the evolution of volumetric strain in each loading step showed typical consolidation features of fine-grained soils, in particular under high loads. On the contrary, for SCO1 (138 suction) and SCO2 (9 MPa suction), the evolution curves were rather characterized by the presence of almost instantaneous volumetric strains after each loading. It was thus suspected that when suction was higher than 9 MPa, it was rather the pellets/grains arrangement or crushing that governed the volume change behavior of the mixture.

Test SCO4 was designed to study the volume change behavior upon wetting/drying in oedometer. In this case, the pellet/power mixture was submitted to a wetting-drying cycle at a constant vertical stress of 0.1 MPa. In the first phase, the specimen was hydrated by injecting deionized water during 1248 h (52 days) to reach equilibrium at zero suction (comparable to the 1272 h for test SCO3). A volumetric strain of 23% (e = 1.28) was found at equilibrium. Then, a suction of 262 MPa was imposed to the mixture. The volumetric strain decreased drastically, reaching a value of 5% (e = 0.87) after 1375 h (57.3 days). A final value of 3% (e = 0.84) was observed after 2311 h (96.3 days).

Once equilibrated at the imposed suctions, the pellet/powder mixtures were submitted to compression at constant suctions. The results are displayed in Figure 9 in terms of void ratio with respect to vertical stress. The initial void ratio values were different due to the different swellings under different suctions. In a standard fashion, the compression curves were characterized by an initial linear part with low compressibility (that could be considered as the pseudo-elastic domain) followed by a second part with higher compressibility (that could be considered as the plastic domain). Finally, the third part, corresponding to the unloading, exhibited the same trend as the elastic domain, as only elastic deformations were expected. For test SCO3 where zero suction was applied, the unloading path could also be considered as bilinear.

The swelling pressure of the pellet/powder mixture could be determined by the swellconsolidation method using the results from test SCO3. As it was explained previously, the swelling pressure of the material corresponded to the vertical stress needed to compress the sample to its initial volume. The obtained value was

MPa (e = 0.859). 𝜎 𝑠 = 7.1

Swelling under constant-volume conditions (CV1)

The swelling behavior of the pellet/powder bentonite mixture under constant-volume conditions was investigated by following the evolution of the axial swelling pressure during hydration (CV1 in Table 1). The results are displayed in Figure 10. Two rates of increase of axial swelling pressure could be distinguished from the beginning of the hydration process: the first one corresponded to a period from the beginning of the hydration up to 20 days, when swelling pressure reached 0.43 MPa. Then, the pressure continued increasing at a different rate, until 45 days of hydration. At this moment, the swelling pressure reached 0.8 MPa. Afterwards, a slight increase was observed, finally reaching 0.87 MPa after 440 days. Nevertheless, the swelling pressure continued increasing, which means that the sample was not completely stabilized, even though the rate of increase was quite low compared to those observed before.

The value of pressure observed after 440 days (0.87 MPa) was significantly lower than the value obtained by applying the swell-consolidation method on the consolidation curve (7.1 MPa).

Discussion

The swell-consolidation and constant-volume method revealed different values of swelling pressure: the swell-consolidation method provided 7.1 MPa, whereas a value of 0.87 MPa was found with the constant-volume method. This was common results and [START_REF] Wang | Experimental study on the swelling behaviour of bentonite/claystone mixture[END_REF] explained that by the coupling between the microstructure deformation and the macrostructure deformation, combined to the effect of friction. [START_REF] Cui | An Insight into the Unloading/reloading Loops on the Compression Curve of Natural Stiff Clays[END_REF] carried out oedometer tests with loading/unloading/reloading on natural stiff Ypresian clays (YPClay). They concluded that each unloading/reloading curve could be satisfactorily considered as bi-linear with a small and a larger slope separated by a threshold vertical stress. This stress was found, through hydrations tests under constant volume conditions, to be the swelling pressure corresponding to the void ratio just before the unloading or reloading. By applying this approach to the pellet/powder mixture at zero suction (SCO3), with the consideration of the unloading path as bilinear, a swelling pressure of 4.2 MPa (threshold vertical stress) would be obtained, corresponding to a void ratio e = 0.72 (dry density ρ d = 1.61 Mg/m 3 ). This value was comparable with that estimated by the method of [START_REF] Wang | Experimental study on the swelling behaviour of bentonite/claystone mixture[END_REF]: a value of 4.15 MPa of swelling pressure was found at a dry density of 1.49 Mg/m 3 . This showed that the true swelling pressure of the mixture should be lower than that determined by the swell-consolidation method, because the value would correspond to the point separating the two parts of unloading curve, thus below the consolidation curve.

Further analysis of the swelling pressure evolution with time displayed in Figure 10 revealed the processes governing the structural changes of the pellet/powder mixture while wetting. At the very beginning of the test with wetting from the bottom, the observed swelling pressure and the corresponding rate of increase were due to the pellets located at the top of the sample, where the suction was still high. After a period of 20 days, a second rate of increase higher than the first one was observed. The reason was that water has arrived to pellets or powder grains located at the top of the sample at this state; thus, the involved pellets and powder grains started swelling and the pressure increased accordingly. It was suspected that all inter-pellet/grain voids were filled with swollen bentonite after 40 days of hydration, as the rate of increase of swelling pressure decreased. However, the rate was not equal to zero, meaning that the specimen was not homogeneous. Taking into account the relationship proposed by Wang et al. (2013a) between the swelling pressure and the dry density of bentonite, a final value of 4.15 MPa of swelling pressure was found. Obviously, the swelling pressure of 0.87 MPa obtained by the constant method was quite far from this value. Molinero Guerra et al. ( 2018) performed an infiltration test on the same mixture with the same global dry density (1.49 Mg/m 3 ) using a metallic column (60 mm in diameter and 120 mm in height) equipped with a force transducer for the axial swelling pressure measurement and several total pressure transducers for the radial swelling pressure measurements at different positions (20 mm, 40 mm, 60 mm, 80 mm and 100 mm from the bottom of sample). Water infiltration was allowed from both the top and the bottom of sample. They observed an axial swelling pressure of 2.5 MPa after 845-day infiltration, also lower than the expected value (4.15 MPa). The radial pressures at 20 mm, 40 mm, 60 mm, 80 mm were almost the same, around 4 MPa. By contrast, the value at 100 mm was lower, around 3 MPa. In addition, the swelling pressures were developed mainly during the first 100 days, the variations after 100 days appearing negligible. They attributed the difference between the radial swelling pressures by the heterogeneity of the sample: a higher swelling pressure was expected at a position where the local dry density was greater. They explained the lower axial pressure by the effect of friction between the sample and the column wall, as also identified by [START_REF] Saba | Investigation of the swelling behaviour of compacted bentonite-sand mixture by mock-up tests[END_REF]. Indeed, the expected sample homogenization process implied the local movements of bentonite particles. Thus, the wall friction could be mobilized even in constant-volume condition. The results obtained in this study showed that even for a sample of 35 mm height, the effect of cell wall friction was significant, hampering or slowing down the sample homogenization process.

The results from test SCO4 allowed the reversibility of swelling of the pellet/powder mixture to be investigated. After wetting under zero suction, the sample was dried by imposing s = 262 MPa. The results showed a drastic decrease of volumetric strain, reaching a final value of 3%. This suggested that plastic swelling strain occurred upon wetting under zero suction, as shown in Figure 11. This was probably due to pellets fissuring upon wetting. [START_REF] Wang | Investigation of the hydro-mechanical behaviour of compacted bentonite/sand mixture based on the BExM model[END_REF] also reported the fissuring phenomenon for compacted bentonite/sand mixture upon wetting.

Compared to test SCO3, a slightly higher volumetric strain was reached in test SCO4, suggesting a certain effect of the pellet/powder distribution that is specific for each sample. The final points of tests SCO1, SCO2 and SCO3 appeared well aligned, defining a wetting line. This line was below the drying line estimated from test SCO4. The difference between the two lines was larger at higher suction.

The evolution of the yield stress with suction is presented in Figure 12, together with the values obtained by [START_REF] Marcial | Comportement hydromécanique et microstructural des matériaux de barrière ouvragée[END_REF] and [START_REF] Wang | Investigation of the hydro-mechanical behaviour of compacted bentonite/sand mixture based on the BExM model[END_REF] for compacted bentonite with initial void ratio of 0.559 and compacted bentonite/sand mixture with initial void ratio of 0.635, respectively. A good coincidence was observed for compacted bentonite and the pellet/powder mixture at zero suction. For other values of suction, in a standard fashion, the yield stress increased as suction increased. However, this phenomenon was not clear for the pellet/powder mixture: a much lower yield stress value was obtained. A possible explanation is as follows:

for non-zero suctions, the pellet/powder mixture did not completely lose its initial granular mixture; thus, the deformations were essentially governed by the rearrangement and possible crushing of pellets while loading. These deformations were of plastic nature. However, in the case of zero suction, the mixture entirely lost its granular structure; thus, the volume change behavior was comparable to that of a common compacted bentonite. This observation was supported by analyzing the evolution of volumetric strain with time: at 138 MPa and 9 MPa of suctions, the volumetric strains decreased almost instantaneously while loading; however, at zero suction, the decrease rate of volumetric strain was clearly lower than those observed at other suctions, because the pellets lost their granular structure in that case.

Conclusion

The water retention, compressibility and swelling properties of a 80-pellet/20-powder bentonite mixture were investigated through the water retention tests under free (pellet) and constantvolume (mixture) conditions, the suction controlled oedometer tests and the hydraulic tests on samples at a dry density of 1.49 Mg/m 3 .

The new cell designed for the WRC determination under constant-volume condition allowed the vapor exchange in all directions, which significantly accelerated the hydration process. Similar water retention properties were observed for pellet/powder mixture under constantvolume condition and single pellet under free swelling condition at suction higher than 4 MPa, indicating that the suction was mainly controlled by the micro-pores inside the pellets or powder grains, and the swell of clay particles was accommodated by existing macro-pores in the mixture. On the contrary, at lower suctions, constant-volume condition defined a lower water retention capacity, showing the restriction effect on clay particles swelling and thus their hydration. Note that more tests are needed to complete the data in the range of suctions lower than 4 MPa.

The investigation of the compressibility properties revealed lower values of yield stress than the common bentonite mixtures, except for the specimen hydrated at zero suction. This is due to the granular structure in the case of non-zero suction where the volume change behavior was suspected to be governed by the rearrangement and crushing of pellets, and the loss of the granular structure in the case of zero suction.

The irreversibility of the volumetric strain was evidenced by imposing a wetting-drying cycle to the pellet/powder mixture under constant loading. This was probably due to the pellets/grains fissuring upon wetting.

Different swelling pressure values were obtained by applying different methods. A higher swelling pressure was obtained with the swell-consolidation method. Further analysis based on the method proposed by [START_REF] Cui | An Insight into the Unloading/reloading Loops on the Compression Curve of Natural Stiff Clays[END_REF] showed that the swell-consolidation systematically overestimates the swelling pressure because for a given density the swelling pressure must be lower than the corresponding pressure on the consolidation curve: the swelling pressure corresponded to the point separating the two parts of unloading curve, thus below the consolidation curve. Nevertheless, the swelling pressure determined by the constant-volume method seemed quite low (0.87 MPa) with respect to the expected one (4.15 MPa). This could be attributed to the effect of cell wall friction because the expected sample homogenization process implied the local movements of bentonite particles, thereby mobilizing the cell wall friction even in constant-volume condition and with a sample of limited height (35 mm). The cell wall friction would hamper or slow down the sample homogenization process. Table 1. Test program for investigating the compressibility and swelling properties of pellet/powder bentonite mixture Table 2. Receipt for preparing the synthetic water. Figure 12. Yield stress versus suction for compacted bentonite with initial void ratio of 0.559 [START_REF] Marcial | Comportement hydromécanique et microstructural des matériaux de barrière ouvragée[END_REF], compacted bentonite/sand mixture with initial void ratio of 0.635 [START_REF] Wang | Investigation of the hydro-mechanical behaviour of compacted bentonite/sand mixture based on the BExM model[END_REF] and pellet/powder mixture with initial void ratio of 0.859 (present work). Figure 12. Yield stress versus suction for compacted bentonite with initial void ratio of 0.559 [START_REF] Marcial | Comportement hydromécanique et microstructural des matériaux de barrière ouvragée[END_REF], compacted bentonite/sand mixture with initial void ratio of 0.635 [START_REF] Wang | Investigation of the hydro-mechanical behaviour of compacted bentonite/sand mixture based on the BExM model[END_REF] and pellet/powder mixture with initial void ratio of 0.859 (present work).

List of Tables

List of Figures

Figure 1 .

 1 Figure 1. Pellet at its initial state.

Figure 2 .

 2 Figure 2. Vertical slice on the investigated pellet/powder bentonite mixture obtained by µ-CT observations -Resolution: 50 µm/voxel.

Figure 3 .

 3 Figure 3. Schematic view of the special cell designed for determining the water retention curve under constant-volume conditions.

Figure 4 .

 4 Figure 4. Experimental setup for suction-controlled oedometer tests.

Figure 5 .

 5 Figure 5. Evolution of water content with time for the pellet/powder bentonite mixture submitted to different suctions under constant-volume conditions.

Figure 6 .

 6 Figure 6. Water retention properties under free swelling conditions and constant-volume conditions.

Figure 7 .

 7 Figure 7. Imposed suctions by vapour equilibrium technique versus measured suction after equilibrium for the pellet/powder bentonite mixture.

Figure 8 .

 8 Figure 8. Evolution of the volumetric strain with time in the oedometer tests SCO1, SCO2 and SCO3.

Figure 9 .

 9 Figure 9. Void ratio versus vertical stress for tests SCO1, SCO2 and SCO3.

Figure 10 .

 10 Figure 10. Evolution of axial swelling pressure with time in test CV1.

Figure 11 .

 11 Figure 11. Volumetric strains measured at different suctions after equilibrium at the imposed suction for the different tests.

Figure 1 .

 1 Figure 1. Pellet at its initial state.

Figure 2 .

 2 Figure 2. Vertical slice on the investigated pellet/powder bentonite mixture obtained by µ-CT observations -Resolution: 50 µm/voxel.

Figure 3 .

 3 Figure 3. Schematic view of the special cell designed for determining the water retention curve under constant-volume conditions.

Figure 4 .

 4 Figure 4. Experimental setup for suction-controlled oedometer tests.

Figure 5 .

 5 Figure 5. Evolution of water content with time for the pellet/powder bentonite mixture submitted to different suctions under constant-volume conditions.

Figure 6 .

 6 Figure 6. Water retention properties under free swelling conditions and constant-volume conditions.

Figure 7 .

 7 Figure 7. Imposed suctions by vapour equilibrium technique versus measured suction after equilibrium for the pellet/powder bentonite mixture.

Figure 8 .

 8 Figure 8. Evolution of the volumetric strain with time in the oedometer tests SCO1, SCO2 and SCO3.

Figure 9 .

 9 Figure 9. Void ratio versus vertical stress for tests SCO1, SCO2 and SCO3.

Figure 10 .

 10 Figure 10. Evolution of axial swelling pressure with time in test CV1.

Figure 11 .

 11 Figure 11. Volumetric strains measured at different suctions after equilibrium at the imposed suction for the different tests.


Simon Dawes

Neoliberalism Studies and Media Studies

This short article provides an overview of the various theoretical and methodological approaches to analysing neoliberalism, paying particular attention to political-economic and governmental approaches (and the extent to which they can be contrasted or combined), and argues for a more theoretically-and methodologically-informed, interdisciplinary critique of neoliberalism in media studies. In emphasising the heterogeneity of approaches to studying an object such as neoliberalism, as well as the differences in how those approaches are deployed in different "studies", it will thus also argue for the applicability of such concerns to research in multiple disciplines in other countries (such as France) as well.

A danger with reflections on the pertinence and applicability of "studies" to French academic disciplines is that it can over-emphasise the Anglo-Saxon otherness of such approaches, and fall into the trap of suggesting something homogenous about what is a wide variety of domains of research, within which there are multiple methodological and theoretical debates. Indeed, the interdisciplinarity and internationalism of such approaches supposedly necessitates an ongoing dialogue between local-national and disciplinary contexts, on the one hand, and wider debates and literatures on the other.

The burgeoning field of critical neoliberalism studies, for instance, has emerged principally from the research of geographers and urban studies scholars, and has involved writing the history and genealogy of international neoliberal thought-collectives, as well as critiquing the process of neoliberalization in various geographical areas, industrial sectors, public policies and aspects of everyday life. Rich and nuanced debate on how to do so has not, however, been as prominent in other fields, such as critical media studies, where research has hitherto tended to employ the term 'neoliberalism' as little more than a term of rebuke. This short article will provide an overview of the various theoretical and methodological approaches to analysing neoliberalism, paying particular attention to political-economic and governmental approaches (and the extent to which they can be contrasted or combined), and argue for a more theoretically-and methodologically-informed, interdisciplinary critique of neoliberalism in media studies. In emphasising the heterogeneity of approaches to studying an object such as neoliberalism, as well as the differences in how those approaches are deployed in different "studies", it will thus also argue for the applicability of such concerns to research in multiple disciplines in other countries as well.

Neoliberalism

References to neoliberalism in Anglophone scholarly research are commonplace, and have increased exponentially over the past couple of decades. While the first handful of citations to articles featuring the term 'neoliberalism' (or 'neo-liberalism') occurred in only 1992, there

were over 200 a year by the end of the 1990s, almost a 1000 a year by 2005, over 4000 a year in 2010, and almost 10,000 a year in 2015 (Web of Science, 2016). Such interest seems unlikely to subside in the foreseeable future. Prompted by the dramatic onset of the global financial crisis (2008-ongoing), which was purportedly the result of neoliberal logic, and the subsequent intensification of the familiar policies of 'regulatory restraint, privatisation, rolling tax cuts, and public-sector austerity' through an even more relentless focus on 'growth restoration, deficit reduction and budgetary restraint' (Peck, 2013: 3-5), there has also recently been an abundance of public debate on the efficacy, validity and legitimacy of neoliberal policies. Even researchers at the IMF have begun to question the logic and efficacy of neoliberal policies [START_REF] Ostry | Neoliberalism: Oversold?[END_REF]. Despite (or perhaps because of) such promiscuity, however, the term itself has often been dismissed as a concept of the politically and economically illiterate [START_REF] Phelan | It's Neoliberalism, Stupid': New Zealand media and the NZME-Fairfax merger[END_REF], particularly by those on the right accused of being neoliberal. Within the social sciences and humanities too, it has more recently been acknowledged that the term has been prone to inflation (Peck, 2013: 17), and for some it has become an 'overblown' concept [START_REF] Collier | Neoliberalism as Big Leviathan, or…? A Response to Wacquant and Hilgers[END_REF]) that tends to be applied (in an invariably disapproving way) to pretty much anything today (Allison & Piot, 2011: 5).

Although occurrences of 'neoliberalism' abound in media scholarship (and further afield), authors rarely explain what is meant by the term, assuming instead a commonsensically shared understanding of the negative affect on public life it evokes. When greater specification is provided, neoliberalism's essential features are 'variously described, but always include' (Ferguson, 2009: 170): consumer choice (Harvey, 2007 :42); private ownership and property rights, free trade, free markets, privatisation, and state withdrawal from social provision (Harvey, 2007: 2); deregulation, the restriction of state intervention, opposition to collectivism, emphasis on individual responsibility and a belief that economic growth leads to development (Hilgers, 2011: 352); valorisation of private enterprise over the state, tariff elimination, currency deregulation and enterprise models that run the state like a business (Peck, 2008); a logic of 'DIP (deregulation, individualisation, privatisation)' (Bauman & Rovirosa-Madrazo, 2010: 52); as well as an emphasis on the entrepreneurial self; and the social scientist's particular bugbear regarding Thatcher's claim that there is 'no such thing as society' (Mirowski, 2013). Emphasis is also placed on the encroachment of market relations into domains previously considered exempt, and on the opportunities such encroachment provides for particular individuals and corporations to not only extend and diversify their commercial media empires, but even to ultimately influence the political process (Harvey, 2007: 34). More broadly, neoliberalism is seen as the reinvention of the classical liberal tradition, expanded to encompass the whole of human existence, whereby the market stands as the ultimate arbiter of truth, and where freedom is recoded to mean anything the market allows (Mirowski, 2013). Other uses of 'neoliberalism' see it as shorthand for a new era of capitalism in more speculative times, or as an abstract and external causal force, often little more than a 'sloppy synonym' for capitalism or the world economy and its inequalities (Ferguson, 2009: 171).

While its meaning, its history and even its existence have now been debated at length in disciplines such as geography, urban studies and sociology, the richness of the theoretical and methodological debate surrounding neoliberalism has been, until recently, conspicuously absent from the Anglophone literature on media, cultural and communications studies. Despite rare acknowledgments that references to neoliberalism require greater nuance (Hesmondhalgh, 2005), even rarer engagements with neoliberal literature itself (O'Malley & Jones, 2009), and occasional warnings that the 'intuitive' focus on a big picture narrative of global neoliberal trends risks privileging similarities in privatisation and liberalisation over 'diverging accents' in their implementation [START_REF] Parthasarathi | Deciphering Chindia: Two Accents of Media Governance[END_REF], most accounts have limited themselves to the ways in which 'neoliberal ideology' (Hall, 2011;[START_REF] Harvey | A Brief History of Neoliberalism[END_REF] is combined with other ideologies in policy and regulation. Such work has tended to avoid, however, critical engagement with the theoretical perspective it draws on, to ignore competing approaches, and to see neoliberalism not only as a unitary ideology imposed from outside or above, but often as little more than a 'bogeyman' to be denounced [START_REF] Collier | Neoliberalism as Big Leviathan, or…? A Response to Wacquant and Hilgers[END_REF][START_REF] Gane | The Governmentalities of Neoliberalism: Panopticism, Post-Panopticism and Beyond[END_REF].

In contrast, recent contributions towards a burgeoning field of neoliberalism studies [START_REF] Burgin | The Great Persuasion: Reinvening Free Markets since the Depression[END_REF][START_REF] Davies | The Limits of Neoliberalism: Authority, Sovereignty and the Logic of Competition[END_REF][START_REF] Jones | Masters of the Universe: Hayek, Friedman, and the Birth of Neoliberal Politics[END_REF]Mirowski & Plehwe, 2009;[START_REF] Peck | Constructions of Neoliberal Reason[END_REF] deal not only with the contradictory ways in which these elements combine with other policies, and the contextual differences in their application from one country to another, but with the history of liberal and neoliberal thought, and an engagement with the political-economic debates within liberalism and neoliberalism. This literature, engaging critically with both the Marxist approach of Stuart Hall and David Harvey, which constructs neoliberalism as an ideology, and that of [START_REF] Foucault | The Contradictions of Media Power[END_REF], which sees it instead as a form of governmentality, as well as a more discursive and processual approach [START_REF] Peck | Explaining (with) Neoliberalism', Territory[END_REF][START_REF] Springer | Neoliberalism as discourse: between Foucauldian political economy and Marxian poststructuralism[END_REF], which aims to bridge the gap between the other approaches, suggests a longer and more detailed history than tends to be assumed, and provides a corrective to accounts of neoliberalism framed in terms of laisser-faire or individualisation. It also turns our attention to a more nuanced appreciation of the changing role of both the state and the market.

Although such debates have been for the most part unacknowledged in English-language media studies, I suggest that Des Freedman (2014), Terry Flew (2012;2014;[START_REF] Flew | Foucault, Weber, Neoliberalism and the Politics of Governmentality[END_REF] and Sean [START_REF] Phelan | Neoliberalism, Media and the Political[END_REF] can be considered as exemplars, respectively, of political-economic, governmental and discourse approaches within media and communications research, and this article will now turn to each of these in turn.

Neoliberal Ideology

Critiques of neoliberal trends in media policy and regulation tend to refer understandably to (geographer) David Harvey's seminal contribution (2007), and to Stuart Hall's successive (cultural studies) analyses of UK neoliberalization from Thatcher, through Blair, to Cameron (1988, 2003[START_REF] Allison | Editors' Notes[END_REF]. Unfortunately, such announcements demonstrate little critical engagement with Harvey's and Hall's approach, and limited awareness of the wider array of perspectives on neoliberalism. Both Hall and Harvey (see also [START_REF] Duménil | Michel Foucault's The Birth of Biopolitics and contemporary neo-liberalism debates[END_REF] portray neoliberalism as an ideological and hegemonic project (Hall, 2011: 728;[START_REF] Harvey | A Brief History of Neoliberalism[END_REF] 3) to disembed capital from the constraints of Keynesian interventionism (Harvey, 2007: 11), and to oversee 'the shift of power and wealth back to the already rich and powerful' (Hall, 2011: 721;Harvey, 2007: 42). Hall's neo-Gramscian account highlights Thatcherism's contradictory strategy of balancing ideological anti-statism with state-centrist interventions, thus providing an admirably nuanced account of hegemony that refuses to reduce Thatcherism to a simple phenomenon of ideological class interests. However, it makes the ideological impulse of Thatcherism of 'considerable importance' (Barry et al, 1996: 11), while refusing to acknowledge neoliberalism itself as anything other than an ideological project.

Heavily influenced by the ideological critique of media regulation (in the work of Nicholas [START_REF] Garnham | Capitalism and Communication: Global Culture and the Economics of Information[END_REF]Graham Murdock, 1993) and neoliberalism [START_REF] Harvey | A Brief History of Neoliberalism[END_REF], Des Freedman, for example, has emphasised that media policy and regulation need to be understood in terms of political acts and ideological influences (Freedman, 2008: 13), rather than as a disinterested process that is impartially applied in the public interest (Freedman, 2008: 2), focusing our attention on the informal and relatively invisible influence of corporate lobbying as much as official policymaking processes (Freedman, 2008: 12). Although such an approach sees neoliberalism as aversion to state intervention in markets (Freedman, 2008: 11), it sees debate less in terms of a regulated market versus a free market, and more in terms of a distinction between regulation that is either in the public interest or for private interests (Freedman, 2008: 17). Freedman's engagement with those alternative approaches that have emphasised the contradictory, historically-specific and ongoing nature of neoliberalization ultimately concludes that, despite such contradictions and theoretical nuance, neoliberalism remains fundamentally connected to a limited set of core ideas; namely, free markets, individual rights, personal choice, small government and minimal regulation (Freedman, 2008: 25;36). He warns, however, that in providing long lists of its negative aspects, or in treating it as shorthand for marketisation, neoliberalism is 'flattened and homogenised', to the extent that it comes to be little more than an 'umbrella term for all that is wrong with a more commercialised society', simultaneously dehistoricising the process (by suggesting that market obsession is only a recent phenomenon) and marginalising the tensions and competing interests at the heart of neoliberal projects (Freedman, 2008: 37-38).

Nevertheless, Freedman maintains that a singular conception of neoliberalism that foregrounds its links with increasing social inequality remains both useful and necessary (Freedman, 2008: 46), and recommends understanding neoliberalism instead (Freedman, 2008: 41) as a range of discourses that legitimate the market and delegitimate the social (Couldry, 2006), with the aim of transforming the balance of forces so as to facilitate capital accumulation [START_REF] Harvey | A Brief History of Neoliberalism[END_REF]. He maintains that while appreciating varieties of neoliberalization and acknowledging the nuances of neoliberal thought is a useful area of research, it remains limited compared to research that develops a sense of what links such variation and nuance together, approaching neoliberalism instead as a purposeful political project with an overarching commitment to private over public institutions and interests (Freedman, 2008: 223-224).

Freedman's emphasis on 'critique' echoes similar calls to counter a perceived tendency in contemporary cultural studies and media studies to read Stuart Hall's work on identity and representation selectively, at the expense of his emphasis on ideology critique [START_REF] Downey | Ideology critique: the challenge for media studies[END_REF]. Such calls distance a 'critical' version of cultural/media studies from an alternative relativist approach that has also tended to draw more on (an equally selective reading of) Foucault, leading to an insular case of 'Foucault-phobia' (Dawes, 2016b) amongst critical scholars that makes them reluctant to embrace Foucauldian critiques of neoliberalism that have developed in other disciplines.

At the same time, the 'critical' tendency to use 'neoliberalism' a little too loosely and freely, seeing it as a Leviathan [START_REF] Collier | Neoliberalism as Big Leviathan, or…? A Response to Wacquant and Hilgers[END_REF] that immerses itself everywhere, and denouncing it wholesale without really engaging it as an object of study in its own right, has been located within a broader weakness of the Left to reduce politics to negation and resistance, to the extent that it is often 'anti-everything' but rarely 'pro-something' (Ferguson, 2009: 167). There are theoretical and methodological weaknesses to a structural and moralistic approach that ignores debates and developments beyond broadcasting studies; a self-defeating consequence of which may be to also undermine the political efficacy of such critique [START_REF] Dawes | British Broadcasting and the public-private dichotomy: Neoliberalism, citizenship, and the public sphere[END_REF]. In contrast, others have warned against fetishising neoliberalism as an ideology, representing it as a caricature of liberalism (Mirowski & Plehwe, 2009: 433), or reducing it to (neoclassical) economics (Mirowski & Plehwe, 2009: 421), when it should instead be seen as a multidisciplinary concern with theories and practices of the state (Mirowski & Plehwe, 2009: 427) and market.

Neoliberal Governmentality

For Terry Flew, for instance, the term's use has become 'sloppy'. It is "routinely invoked to explain everything from the rise of Bollywood themed weddings to competitive cooking shows to university departmental restructurings" and the propensity to "lapse into a kind of conspiracy theory is readily apparent" (Flew, in Dawes, 2016a). He has criticised the tendency of many scholars to use the term as a conceptual trash-can, "…into which anything and everything can be dumped, as long as it is done with suitable moral vehemence", and written about the need to "rescue' the concept from the most vocal moral critics of markets and economic discourse, whom he accuses of producing functionalist and instrumentalist accounts of the state.

In recent years (2012; 2014; 2015b), he has been focusing on Foucault's lectures on neoliberalism, and engaging with the theoretical debates on how best to understand neoliberalism. Foucault's lectures at the College de France in 1978-79, published in English in 2008 as The Birth of Biopolitics, were very important in giving the concept of neoliberalism some analytical rigour. Rather than just being an abuse term, that critical humanities scholars came to do to denounce anything to do with economics and markets, neoliberalism was now being seen as part of an important historical moment, where economists associated with the 'Austrian School' (led by Hayek, and inspired by von Mises and Schumpeter) and the 'Chicago School' (Milton Friedman, George Stigler etc.), as well as the 'Virginia School' of James Buchanan and the 'public choice' theorists, were turning their critique of Keynesian economics and government intervention into markets into a wider set of ideas about the relationship between political economy and social order. For Flew, this shows that talk about neoliberalism has been moving beyond being essentially a rhetorical flourish to appearing as a sound analytical concept grounded in empirical evidence. He argues however, that this kind of approach cannot be combined with the ideological approach. For Flew (in Dawes, 2016a), Foucault pursued a critique of Marxism from the perspective of someone who understood the theory well, and this makes it difficult to synthesise Foucault's work into neo-Marxist theories of hegemony.

Motivated by dissatisfaction with the broadly Marxist reduction of capitalism to economic relations, of ideology to false ideas that serve ruling class interests, and of power to a falsifier and suppressor of 'true' human essence (Miller & Rose, 2008: 2-4), a contrasting sociology of neoliberalism developed throughout the 1990s and 2000s under the banner of 'governmentality studies'. The work of the 'Anglo-Foucauldians' (Barry et al, 1996;Rose, 1999;Miller & Rose, 2008) on the Thatcherite and Reaganite neoliberal assaults on the welfare state focused instead on the governmental rationalities that emerged during the period.

Predominantly an 'Anglo School of Governmentality' building on the work of Nikolas Rose and colleagues, it was based in large part on what were at the time only the scattered availability (occasional interviews and partial notes from his then unpublished lectures of the late-1970s) of Foucault's elaborations on the subject of governmentality (Barry et al, 1996: 7). Of particular importance was Foucault's lecture on 'governmentality' (1 st February 1978), subsequently published in English in The Foucault Effect (Burchell, Gordon & Miller, 1991) and eventually in its proper context as the fourth lecture in Security, Territory, Population (2009). In this lecture, Foucault traced back to the 16 th Century the emergence of the idea of 'government as a general problem', the associated problematisations of concepts such as state, economy and society, and an increasing concern with statistics and calculation as a means of governing the 'conduct of conduct' (Foucault, 1991;Rose, 2000: 315). Arguing that the 'state' is a relatively abstract and unimportant concept, he shifted attention instead to the ways in which 'government', as both internal and external to the 'state', makes possible the redefinition of what is within and outside of the competence of the state; in other words, what is public and what is private (Foucault, 1991: 103). Seeking to understand, without recourse to ideology (Miller & Rose, 2008: 4), intervention into the lives of individuals in 'liberal' societies, which otherwise proclaimed the limits of the state and the privacy of the individual (Miller & Rose, 2008: 1), the Anglo School found in Foucault's approach a more adequate way of capturing the productive, individualising aspects of power that actually make possible a series of positive and tactical interventions, as well as those negative aspects captured by the ideological approach.

Arguing that Hall's ideological critique of Thatcherism, in particular, missed the ethical and technical character of neoliberalism, and the ways in which neoliberalism constructively aligns diverse interests (Barry et al, 1996: 11), the governmentalists shifted theoretical attention away from political philosophy, and towards governmental rationality and the close analysis of mundane techniques and technologies. Although the ethos of public service and the public provision of social welfare no longer play a pivotal role in the neoliberal way of governing social life (Miller & Rose, 2008: 82), governmental analyses suggested that neoliberalism does not necessarily preclude their continued existence in some form. Rather than a rejection of actual failures of central planning, therefore, the neoliberal critique of the welfare state is better appreciated as a critique of the ideals of knowledge and power that such rationalities embody (Miller & Rose, 2008: 81).

Because the governmentality lecture on which much of the early literature was based was more an 'overture of where [Foucault's] researches were going…than a culmination of analyses already undertaken' (Elden, 2007: 29), however, both sympathetic and critical accounts have much to learn from the fuller 'history of [liberal and neoliberal] governmentality' (Elden, 2007: 30) offered by the publication of Foucault's two lecture series on liberalism (2009) and then neoliberalism (2010).

For proponents, the advantage of the governmental over the ideological approach is that it treats the public-private (state-society) dichotomy as an instrument and effect, rather than the basis and limit, of governmental practice, becoming itself an object of study (Lemke, 2001: 201). It also highlights a congruence, rather than a distinction, between individuals and collectivities as moral-responsible and rational-economic actors (Lemke, 2001: 201). Rather than diagnosing a shift from state to society, the state is shown to retain its sovereign form and take on new functions. The reduction in welfare state intervention, therefore, is less a matter of the state losing its powers of regulation, than the reorganisation and restructuring of governmental techniques, and the shifting of competence onto responsible and rational individuals (Lemke, 2001: 201-202).

Neoliberalism as Process and Discourse

According to 'inflationist' political-economic accounts (such as those provided by Hall and Harvey), neoliberalism is an expansive and adaptable ideological project linked to financialised capitalism. The Foucauldian 'sceptics' (such as Collier and Ferguson), on the other hand, emphasise it instead as one of many strands of a complex of individualised governmentalities, and never more than a flexible assemblage of technologies, routines and conducts (Peck, 2013a: 3).

Despite some efforts to bridge the gap between these two approaches (Larner, 2003;Peck, 2004) or to rethink the terms of debate (Brenner et al, 2010;Dean, 2012), constructive dialogue between them has been rare. For some (Collier, 2012: 189), such attempts risk obscuring rather than illuminating neoliberalism, as there are 'unbridgeable methodological differences' between political-economic and governmental approaches. Although Collier acknowledges that the tensions between similarly non-structural approaches can be reconciled, and neoliberalism as an original movement of thought linked to policy programmes that produce hybrid government formations, he maintains that such approaches cannot be reconciled with even the nuanced structural approach of Peck and colleagues (Collier, 2012: 193-194). There remain, he argues, two distinct ways of approaching analysis. Either neoliberalism is specifically linked to particular elements that are then teased out from a jumble of diverse elements, or it is expanded so that the entire ensemble is associated with neoliberalism, in which case it is presumed to have greater significance than and influence upon any other element (Collier, 2012: 189). Methodologically, Collier sees a clear distinction between the approach that insists that heterogeneity and variegation can still be called neoliberal, and that which dispenses with structural explanations that only obfuscate actual processes.

For others [START_REF] Peck | Explaining (with) Neoliberalism', Territory[END_REF], however, although there are significant tensions between the contrasting ontological and epistemological understandings of neoliberalism, there remains scope for dialogue between them (Peck, 2013a: 18). The urban studies scholars, Jamie Peck, Nik Theodore and Neil Brenner have made the most serious attempt to find a compromise between approaches (Collier, 2012: 188), accommodating a fluid and variegated appreciation of contextual difference while maintaining a structural approach that recognises the ways in which local differences and contextually embedded forms are shaped by the 'context of context ' (Brenner et al, 2010). Both approaches have, they argue, questioned 'template' models of neoliberalism that tend to reduce it to a list of explanatory attributes, such as 'privatisation, deregulation and the limited state', though neither alarmist presumptions of a singular and global monolith, nor ambivalent or agnostic accounts of diverse techniques that share no more than a 'family resemblance', offer a satisfactory account of neoliberalism (Peck, 2013a: 15). Rather, 'theoretically informed, and informing, empirical work' is required for the refinement of understandings of neoliberalization (Peck, 2013a: 19).

For geographer Simon Springer, the distinction made between ideological and governmental approaches is ultimately a false dichotomy, and approaching neoliberalism as discourse helps to recognise its variegated nature and transcend this impasse.

A discourse approach moves our theorizations forward through an understanding that neoliberalism is neither built from the 'top-down', as in Marxian understandings of ideological hegemony, nor from the 'bottom-up', as in poststructuralist notions of governmentality. Rather, neoliberalism is instead recognized as a mutable, inconsistent, and variegated process that circulates through the discourses it constructs, justifies, and defends (Springer, 2012: 135) Following Jamie Peck's and Simon Springer's recognition of neoliberalism as a variegated process, rejecting the false dichotomy between Marxist and Foucauldian approaches to neoliberalism, and emphasising the relational logic of the social, Sean Phelan (2014) develops his own discourse-based account of neoliberalism in the context of media studies. This approach builds on the work of Laclau (and Mouffe) on the idea of the 'political' as much as their approach to discourse theory, and mobilises Bourdieu's field theory as a sociological and theoretical supplement to Laclau. His approach is also indebted, to a lesser extent, to Glynos and Howarth's particular version of discourse theory, as well as their privileging of logics, the work of Billig on banal rhetoric, and of Couldry on media rituals.

Instead of over-relying on a reified version of neoliberalism, Phelan argues, it is more productive to see neoliberalism as a series of constitutive, discursive logics; in particular those of market determinism, commodification, individualization, competition, and self-interest.

Rather than replacing, or being imposed, he contends, these neoliberal logics are dialectically internalised and contextually, didactically and hegemonically articulated with other political, social and fantasmatic logics. Consequently, the task of media researchers is to identify not so much the ways in which neoliberal doctrine is reproduced in media content, but how the neoliberalization of a journalistic habitus is primarily performative and always mediated [START_REF] Phelan | Liberalism and Neoliberalism[END_REF].

A focus on process also allows us to look at the longer-term history of the influence of neoliberal thought on media policy. In my own research, for instance, I have focused on the increasing importance of the concepts of 'competition' and 'choice' in British broadcasting policy in the decades leading up to the 1980s and the point at which scholars normally identify a neoliberal turn in policy, and connected them to dialogues that policymakers had with neoliberal think-tanks and lobbyists as part of the consultation process in developing policy [START_REF] Dawes | British Broadcasting and the public-private dichotomy: Neoliberalism, citizenship, and the public sphere[END_REF], while others have analysed the internalisation of neoliberal discourse and perspectives within an ostensibly public service broadcasting working environment [START_REF] Born | Uncertain Vision: Birt, Dyke and the Reinvention of the BBC[END_REF].

Conclusion

While Freedman insists on the importance of retaining the term 'neoliberalism' and of a Marxist-informed critique of neoliberal ideology, Flew criticises the overblown and reductive use of the term and favours instead a Foucauldian-inspired reading of neoliberal governmentality. Despite their differences, both these authors reflect the position (exemplified by Stephen Collier, 2012) that the two paradigms cannot be reconciled. Phelan, on the other hand, follows Jamie [START_REF] Peck | Explaining (with) Neoliberalism', Territory[END_REF] in seeking a way of bridging the gap between distinct theoretical and methodological approaches. A more reflexive and comparative form of media research [START_REF] Flew | Global Media and National Policies: The Return of the State[END_REF] and a focus on neoliberalism as a mediated as well as variegated process [START_REF] Phelan | Neoliberalism and Media[END_REF], as well as of media power as a material and relational property (Freedman, 2014), can make not only a more effective critique of neoliberalized media; additionally, such media research into neoliberalism can, in turn, make a valuable contribution to its critique in other disciplines.

Drawing on these recent engagements in Anglophone media studies with those debates that have taken place in other disciplines, this article has argued for a rapprochement between these approaches, for a more self-reflexive engagement with neoliberalism as an object of analysis, and for a consideration of the necessity of engaging with neoliberalism as a mediated process rather than a unitary ideology. Ultimately, it represents a call for British media studies to be as interdisciplinary as it claims to be, and for the applicability of critical media and neoliberal studies to disciplines and domains of research beyond the Anglophone world.