COLLECTIONS

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• Reply to Comments on “Unsaturated soils: From constitutive modelling to numerical algorithms” by Daichao Sheng, Antonio Gens, Delwyn G. Fredlund and Scott W. Sloan

  D. Sheng, A. Gens, D. Fredlund, S. Sloan

  Computers and Geotechnics (2009). Vol. 36 (6), pp. 1100

  
  

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• Identification of bonded clay parameters in SBPM tests: a numerical study

  N. González, M. Arroyo, A. Gens

  Soils and Formulation (2009). Vol. 49 (3), pp. 329-340

  
  

  Abstract

  A bonded elasto-plastic soil model is adopted to simulate self-boring pressuremeter tests. Calibration of the model with results from several natural clays identifies a meaningful parameter range for the simulations. Then a systematic sensitivity analysis of the loading SBPM test curve is carried out with an infinite cylindrical cavity analogue, focusing on the variables and parameters that are specific to the bonded material. This analysis reveals that the effects of mechanical overconsolidation and bonding on the pressuremeter loading curves are very similar. Unloading and strain-holding phases of the test show a greater capability to separate mechanical overconsolidation from bonding. The limited effects of finite pressuremeter length and partial drainage on the simulated curves do not change those conclusions.

  Abstract
  A bonded elasto-plastic soil model is adopted to simulate self-boring pressuremeter tests. Calibration of the model with results from several natural clays identifies [...]

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• Tunnelling and swelling in triassic sulphate–bearing rocks: part I: case studies from Baden–Württemberg

  I. Berdugo, E. Alonso, E. Romero, A. Gens

  Epsilon (2009). Vol. 12, pp. 13-37

  
  

  Abstract

  Cases of swelling in tunnels excavated through Triassic sulphate-bearing rocks from the Gipskeuper and the Anhydritgruppe are presented and discussed in this series of papers in order to gain a better understanding of the expansive phenomena in these materials and to identify the most relevant ones. Part I deals with main features of swelling in tunnels and alternative supports designs for their control an mitigation, as well as with the phenomenology of swelling in tunnels from Baden-Württemberg (Germany) excavated through the Gipskeuper.

  Abstract
  Cases of swelling in tunnels excavated through Triassic sulphate-bearing rocks from the Gipskeuper and the Anhydritgruppe are presented and discussed in this series of papers [...]

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• Tunnelling and swelling in triassic sulphate-bearing rocks: part II: case studies from Jura Mountains

  I. Berdugo, E. Alonso, E. Romero, A. Gens

  Epsilon (2009). Vol. 12, pp. 39-53

  
  

  Abstract

  Part II of this series of paper deals with the phenomenology of swelling in tunnels from Jura Mountains (Switzerland) excavated through the Gipskeuper and the Anhydritgruppe. The main features of expansions observed in the presented case studies are summarized and the performance of resisting and yielding support systems is compared. Evidences presented in this series of papers indicate that the transformation of anhydrite into gypsum is not a reasonable explanation for long-term expansive phenomena occurring in sulphate-bearing rocks. It is suggested that these phenomena are strongly related to rock degradation due to both tunneling induced drainage towards the bottom of excavations and tunneling induced ventilation.

  Abstract
  Part II of this series of paper deals with the phenomenology of swelling in tunnels from Jura Mountains (Switzerland) excavated through the Gipskeuper and the Anhydritgruppe. [...]

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• A full-scale in situ heating test for high-level nuclear waste disposal: observations, analysis and interpretation

  A. Gens, M. Sanchez, L. Guimarães, E. Alonso

  Geotechnique (2009). Vol. 59 (4), pp. 377-399

  
  

  Abstract

  The paper describes the performance, observations and interpretation of a large-scale in situ heating test that simulates a disposal concept for heat-emitting, high-level nuclear waste. In the experiment, heaters are emplaced in the axis of a tunnel excavated in granite to simulate the heat production of radioactive waste. The test is fully instrumented, and attention is focused on the thermo-hydro-mechanical (THM) behaviour of the near-field region constituted by the compacted bentonite barrier surrounding the heater and the immediately adjacent rock. Interpretation of the test is assisted by the performance of a coupled numerical analysis based on a formulation that incorporates the relevant THM phenomena. Initial and boundary conditions for the analysis as well as material parameters are determined from an extensive programme of field and laboratory experiments. The paper presents and discusses the thermal, hydraulic and mechanical observations in the bentonite barrier and in the host rock. Special attention is paid to the progress of hydration in the barrier, to the effects of heating and vapour transport, and to the development of swelling pressures in the barrier. After five years of heating, one of the heaters was switched off and the experiment was partially dismantled, allowing the final state of the barrier to be observed directly. The numerical analysis performed has proved able to represent the progress of the experiment very satisfactorily. In addition, predictions concerning the final state of the clay barrier are very close to the observations obtained during dismantling. The performance and analysis of the in situ test have significantly enhanced the understanding of a complex THM problem and have proved the capability of the numerical formulation to provide adequate predictive capacity

  Abstract
  The paper describes the performance, observations and interpretation of a large-scale in situ heating test that simulates a disposal concept for heat-emitting, high-level [...]

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• THM-coupled finite element analysis of frozen soil: formulation and application

  S. Nishimura, A. Gens, S. Olivella, R. Jardine

  Géotechnique (2009). Vol. 59 (3), pp. 159-171

  
  

  Abstract

  A fully coupled thermo-hydro-mechanical (THM) finite element (FE) formulation is presented that considers freezing and thawing in water-saturated soils. The formulation considers each thermal, hydraulic and mechanical process, and their various interactions, through fundamental physical laws and models. By employing a combination of ice pressure, liquid pressure and total stress as state variables, a new mechanical model has been developed that encompasses frozen and unfrozen behaviour within a unified effective-stress-based framework. Important frozen soil features such as temperature and porosity dependence of shear strength are captured inherently by the model. Potential applications to geotechnics include analysis of frost heave, foundation stability or mass movements in cold regions. The model's performance is demonstrated with reference to the in situ pipeline frost heave tests conducted by Slusarchuk et al. Detailed consideration is given to FE mesh design, the influence of hydraulic parameters, and the treatment of air/ground interface boundary conditions. The THM simulation is shown to reproduce, with fair accuracy, the observed pipeline heave and the porosity growth driven by water migration.

  Abstract
  A fully coupled thermo-hydro-mechanical (THM) finite element (FE) formulation is presented that considers freezing and thawing in water-saturated soils. The formulation considers [...]

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• Applications of multiphysical geomechanics in underground nuclear waste storage

  A. Gens, B. Garitte, S. Olivella, J. Vaunat

  European Journal of Environmental and Civil Engineering (2009). Vol. 13 (7-8), pp. 937-962

  
  

  Abstract

  Deep geological disposal in suitable host rocks is the favoured strategy for the storage and disposal of heat-emitting high level nuclear waste. A rational design of repositories requires a good understanding of the interacting thermo-hydro-mechanical phenomena that occur in the engineered barrier and adjacent rock. To this end, a multiphysical formulation is described that allows the performance of coupled THM analyses capable of reproducing observed phenomena. The formulation and computer code is applied to the simulation of two large scale tests: a mine-by test involving the excavation of a shaft in an argillaceous rock and a large-scale high- temperature heating test in fractured rock.

  Abstract
  Deep geological disposal in suitable host rocks is the favoured strategy for the storage and disposal of heat-emitting high level nuclear waste. A rational design of repositories [...]

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• Reply to the discussion by Zhang and Lytton on “A new modelling approach for unsaturated soils using independent stress variables”

  D. Sloan, D. Fredlund, A. Gens

  Canadian Geotechnical Journal (2008). Vol. 45 (12), pp. 1784-1787

  
  

  Abstract

  We would like to thank the discussers for their interest in our paper and also for their challenging questions, which show their thorough knowledge on the subject. Their comments have enhanced our understanding of the subject area and hopefully may lead to further constitutive model developments.

  Abstract
  We would like to thank the discussers for their interest in our paper and also for their challenging questions, which show their thorough knowledge on the subject. Their comments [...]

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• Unsaturated soils: from constitutive modelling to numerical algorithms

  D. Sloan, A. Gens, D. Fredlund, S. Sloan

  Computers and Geotechnics (2008). Vol. 35 (6), pp. 810-824

  
  

  Abstract

  This paper presents an overview of constitutive modelling of unsaturated soils and the numerical algorithms for solving the associated boundary value problems. It first discusses alternative stress and strain variables that can be used in constitutive models for unsaturated soils. The paper then discusses the key issues in unsaturated soil modelling and how these issues can be incorporated into an existing model for saturated soils. These key issues include (1) volumetric behaviour associated with saturation or suction changes; (2) strength behaviour associated with saturation and suction changes, and (3) hydraulic behaviour associated with saturation or suction changes. The paper also shows how hysteresis in soil–water characteristics can be incorporated into the elasto-plastic framework, leading to coupled hydro-mechanical models. Finally, the paper demonstrates the derivation of the incremental stress–strain relations for unsaturated soils and discusses briefly the new challenges in implementing these relations into the finite element method.

  Abstract
  This paper presents an overview of constitutive modelling of unsaturated soils and the numerical algorithms for solving the associated boundary value problems. It first discusses [...]

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• Tunnelling and geotechnics: new horizons. Vote of thanks

  R. Mair, A. Gens

  Géotechnique (2008). Vol. 58 (9), pp. 736-736

  
  

  Abstract

  New developments in both the theory and the practice of tunnelling are covered in the lecture. The important relationship between tunnelling and geotechnics is highlighted, and recent advances in research and practice are described, drawing on model studies, theoretical developments and field measurements from case histories from around the world. Simplified plasticity models are presented that can be used by designers to assess ground movements and tunnel lining loads in complex ground conditions. The important role of pilot tunnels and in situ measurements to validate such models, drawing on a case history from Bolu, Turkey, and on other tunnelling projects, is described. Recent technical advances in earth pressure balance tunnelling are considered, illustrated by measurements from the Channel Tunnel Rail Link project, with emphasis on key factors influencing volume loss, such as face pressure, soil conditioning and effective screw conveyor operation. A recent case history in Bologna is described, in which the innovative use of directional drilling to install curved grout tubes was employed for a compensation grouting project in granular soils. Time-dependent ground movements and tunnel lining distortions occurring after tunnelling are discussed, their magnitude depending on the relative permeability of the tunnel lining and soil, the degree of anisotropy of the soil permeability, and the initial pore pressure prior to tunnelling. The effects of tunnelling-induced settlements on pipelines are considered, drawing on centrifuge tests and analytical solutions, and a new design approach is presented, taking into account the reduction of soil stiffness with increasing shear strain as a result of tunnel volume loss. The lecture concludes with a description of a distributed strain sensing technique using fibre optic technology, based on Brillouin optical time domain reflectometry (BOTDR), and its innovative application to field monitoring of a masonry tunnel subjected to new tunnel construction beneath it.

  Abstract
  New developments in both the theory and the practice of tunnelling are covered in the lecture. The important relationship between tunnelling and geotechnics is highlighted, [...]

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