http://hdl.handle.net/2117/3576 2013-06-20T09:16:27Z http://hdl.handle.net/2117/15045 Title: Analysis of the excavation of a deep drift in a tertiary clay Authors: Vaunat, Jean; Gens Solé, Antonio; de Vasconcelos, R.; Li, X.-L. Abstract: This paper tackles the issues related to the excavation of a horizontal gallery carried out in Boom clay, a tertiary clay that hosts the Underground Laboratory of the Belgium Nuclear Agency (SCK-CEN). The gallery is 85 m long, 5 m wide and connects one of the laboratory access shafts to a horizontal drift drilled from the second access shaft. Displacement and pore water pressure sensors installed from both gallery ends allowed for a detailed monitoring of the hydro-mechanical response of the clay rock before, during and after gallery excavation. A striking feature of the response concerns the strong changes measured in pore water pressure at distances as large as 60m from the excavation front. To explore and discriminate the mechanisms controlling such pore pressure changes, 2D axisymmetric Finite Element hydro-mechanical calculations have been carried out. An elastoplastic constitutive law based on Mohr-Coulomb criterion has been considered for the material. Several types of analyses have been performed: a) material and stress state are isotropic; b) material is isotropic but stress state is orthotropic and, c) material and stress state are orthotropic. Results allow for explaining the field measurements and identifying the key variables that control the clay response around the drift. 2012-02-09T18:38:38Z http://hdl.handle.net/2117/15044 Title: Modelling the behaviour of structured London Clay Authors: González, N.A.; Gens Solé, Antonio; Arroyo Alvarez de Toledo, Marcos; Rouainia, Mohamed Abstract: The paper presents a constitutive modelling of the London clay based on the detailed laboratory knowledge gathered about London clay structure (Hight et al, 2007; Gasparre et al, 2007; Gasparre & Coop, 2008). Modelling was performed using a structured kinematic hardening soil model based on Rouainia & Wood (2000). It was found that a smooth elasto-plastic transition was required to avoid a spurious stiffness degradation response. Consequently, the initial model was modified following a procedure similar to that suggested by Grammatikopoulou et al. (2006). Parameters associated with soil structure and state variables for each lithological sub-unit of the London clay are presented. A good prediction of stress-strain, strength and stiffness behaviour in the small strain range is obtained in spite of the complex behaviour observed in laboratory. The significantly different mechanical behaviours of the lithological sub-units, arising from differences in structure, are adequately reproduced. 2012-02-09T18:35:01Z http://hdl.handle.net/2117/15043 Title: Coupled analysis of double porosity swelling clays Authors: Gens Solé, Antonio; Guimarães, Leonardo do N; Sánchez, Marcelo; Valleján, Beatriz Abstract: The understanding of the coupled behaviour of highly active swelling clays is better achieved considering two structural levels and their interactions in the context of a double-porosity model. Hydraulic equilibrium between the two porosity levels is not assumed. Applications to hydration swelling tests of bentonite powderpellets mixtures and to the chemomechanical behaviour of bentonites are presented. 2012-02-09T18:30:46Z http://hdl.handle.net/2117/14937 Title: Numerical implementation of an elastoplastic model for unsaturated soils Authors: González, Nubia; Gens Solé, Antonio Abstract: This paper describes some issues related to the numerical implementation of a constitutive model for unsaturated soils based on the BBM [1]. The focus of the paper is on the stress variables used and on the numerical algorithms adopted. Conventional stress variable approach (net stress and suction) as well as the approach that takes into account the degree of saturation (Bishop’s stress and suction) are examined. To solve the constitutive stress–strain equations, two stress integration procedures have been implemented, an explicit stress integration scheme with automatic substepping and error control techniques [2] and a fully implicit stress integration scheme based on the Backward-Euler algorithm with substepping [3]. Their performances during the integration of the constitutive laws are compared. 2012-02-03T18:55:55Z http://hdl.handle.net/2117/14935 Title: Smoothing of yield surfaces and a reformulation of multi-surface plasticity Authors: Gesto Beiroa, José Manuel; Gens Solé, Antonio; Vaunat, Jean Abstract: In this work we describe a procedure for the smoothing of non-regular yield surfaces and plastic potential functions. We also present several application examples corresponding to different well-known cases. Moreover, we show that a multi-surface plasticity model can be reduced to a model with a single yield surface by using the same smoothing procedure. 2012-02-03T18:49:51Z http://hdl.handle.net/2117/14934 Title: Generalized plasticity for geomaterials with double structure Authors: Gens Solé, Antonio; Sánchez, Marcelo; Valleján, Beatriz Abstract: The paper presents a double structure constitutive model based on a generalized plasticity formalism. The behaviour of macrostructure, microstructure and their interactions are described. A coupled hydromechanical formulation is then presented that assumes no hydraulic equilibrium between structural levels. Constitutive law and formulation are applied to the simulation of the behaviour during hydration of a heterogeneous mixture of bentonite powder and bentonite pellets. A satisfactory reproduction of observed behaviour is achieved. 2012-02-03T18:43:04Z http://hdl.handle.net/2117/14933 Title: A structured constitutive model for simulating the behaviour of an overconsolidated bonded clay Authors: González, Nubia; Gens Solé, Antonio; Arroyo Alvarez de Toledo, Marcos; Rouainia, Mohamed Abstract: The paper presents some improvements in the formulation of a kinematic hardening constitutive soil model incorporating structure initially proposed for soft clays. For the modelling of overconsolidated bonded clay the elastic formulation was deemed more important. Two different alternatives, one purely empirically based the other with a background in thermodynamics were implemented. It was also found that a smooth elasto-plastic transition was required to avoid a spurious stiffness degradation response. Consequently, the hardening modulus formulation of the model was modified. The paper presents some results from a parametric analysis of the triaxial drained response of a material tailored to mimic London clay. The results chosen do not show a major difference between the chosen alternative elastic formulations, although both do improve the original model response. On the other hand the importance of ensuring a smooth elasto-plastic transition is clearly highlighted. 2012-02-03T18:37:44Z http://hdl.handle.net/2117/14539 Title: El túnel de Lilla Authors: Alonso Pérez de Agreda, Eduardo; Ramon Tarragona, Anna Abstract: Las arcillas sulfatadas pueden experimentar fenómenos expansivos graves como consecuencia de excavaciones. La intensidad del comportamiento expansivo observado en estos materiales es mayor que en otras rocas y suelos expansivos libres de sulfatos. En la mayoría de casos la funcionalidad y estabilidad de los túneles se ven afectadas. Investigaciones de campo y ensayos de laboratorio muestran que, en general, el desarrollo de deformaciones y altas presiones en rocas sulfatadas está asociado al crecimiento de cristales de yeso en discontinuidades. El crecimiento de cristales de yeso es una consecuencia de la sobresaturación del agua del macizo en sulfatos. Los datos de campo que avalan esta interpretación tienen un ejemplo sobresaliente en el túnel de Lilla (Tarragona), que ha sufrido graves problemas de hinchamiento tras su construcción. Aunque el fenómeno de hinchamiento en túneles que atraviesan materiales yesíferos se ha descrito y analizado cualitativamente a menudo, la predicción de deformaciones y presiones de hinchamiento sigue siendo una tarea difícil. En el presente trabajo se ha desarrollado un modelo de cálculo hidro-mecánico acoplado que permite predecir hinchamientos en excavaciones en arcillas sulfatadas durante la etapa de diseño. Se concluye con una descripción del diseño de la sección resistente del túnel de Lilla, a partir de datos de campo de presiones experimentadas por el revestimiento en secciones de prueba. 2012-01-13T18:14:41Z http://hdl.handle.net/2117/13298 Title: Evaluation of self-combustion risk in tire derived aggregate fills Authors: Arroyo Alvarez de Toledo, Marcos; San Martin, Ignacio; Olivella Pastallé, Sebastià; Saaltink, Maarten Willem Abstract: Lightweight tire derived aggregate (TDA) fills are a proven recycling outlet for waste tires, requiring relatively low cost waste processing and being competitively priced against other lightweight fill alternatives. However its value has been marred as several TDA fills have self-combusted during the early applications of this technique. An empirical review of these cases led to prescriptive guidelines from the ASTM aimed at avoiding this problem. This approach has been successful in avoiding further incidents of self-combustion. However, at present there remains no rational method available to quantify selfcombustion risk in TDA fills. This means that it is not clear which aspects of the ASTM guidelines are essential and which are accessory. This hinders the practical use of TDA fills despite their inherent advantages as lightweight fill. Here a quantitative approach to self-combustion risk evaluation is developed and illustrated with a parametric analysis of an embankment case. This is later particularized to model a reported field self-combustion case. The approach is based on the available experimental observations and incorporates well-tested methodological (ISO corrosion evaluation) and theoretical tools (finite element analysis of coupled heat and mass flow). The results obtained offer clear insights into the critical aspects of the problem, allowing already some meaningful recommendations for guideline revision. 2011-09-22T11:22:54Z http://hdl.handle.net/2117/13278 Title: An insight into the water retention properties of compacted clayey soils Authors: Romero Morales, Enrique Edgar; Della Vecchia, G.; Jommi, Cristina Abstract: Experimental data from different testing methodologies on different compacted clayey soils, with dominant bimodal pore size distribution, are presented and analysed, to provide a comprehensive picture of the evolution of the aggregated fabric along hydraulic and mechanical paths. Fabric changes are analysed both from the porous network viewpoint, by means of careful mercury intrusion porosimetry investigation, and from the soil skeleton viewpoint, by quantifying swelling and shrinkage of the aggregates in an environmental scanning electron microscopy study. The consequences of the aggregated fabric evolution on the water retention properties of compacted soils are analysed and discussed. A new model for water retention domain is proposed, which introduces a dependence of the intra-aggregate pore volume on water content. The model succeeds in tracking correctly the evolution of the hydraulic state of the different soils investigated along generalised hydromechanical paths. The proposed approach brings to light coupling between intra-aggregate and inter-aggregate pores in the retention properties of compacted clayey soils. Dependence of the air entry and the air occlusion values on swelling and shrinking of aggregates, besides void ratio, is introduced and discussed. 2011-09-21T10:00:40Z http://hdl.handle.net/2117/13273 Title: Benchmark of experimental techniques for measuring and controlling suction Authors: Muñoz, Juan Jorge; Tarantino, A; Gallipoli, Domenico; Augarde, C. E.; Gennaro, V. de; Gómez, R.; Laloui, L.; Mancuso, C.; El Mountassir, G.; Wheeler, S. J.; Tombolato, S.; Toll, D. G.; Rojas Arias, Juan Carlos; Raveendiraraj, A.; Romero Morales, Enrique Edgar; Pisoni, G.; Peron, H.; Pereira, J.-M. Abstract: The paper presents a benchmarking study carried out within the ‘Mechanics of Unsaturated Soils for Engineering’ (MUSE) network aimed at comparing different techniques for measurement and control of suction. Techniques tested by the eight ‘Mechanics of Unsaturated Soils for Engineering’ research teams include axis-translation (pressure plate and suction-controlled oedometer), highcapacity tensiometer and osmotic technique. The soil used in the exercise was a mixture of uniform sand, sodium bentonite (active clay) and kaolinite (non-active clay), which were all commercially available. Samples were prepared by one team and distributed to all other teams. They were normally consolidated from slurry under one-dimensional conditions (consolidometer) to a given vertical stress. The water retention characteristics of the initially saturated specimens were investigated along the main drying path. Specimens were de-saturated by applying suction through the liquid phase when using an axis-translation technique or osmotic method and de-saturated by air-drying, when suction was measured using igh-capacity tensiometers. In general, the same technique was tested by at least two teams. The water retention curves obtained using the different techniques are compared and discrepancies are discussed in the paper. 2011-09-20T12:42:58Z http://hdl.handle.net/2117/12894 Title: CO2 injection in deep saline sloping aquifers through a vertical well Authors: Vilarrasa Riaño, Víctor; Olivella Pastallé, Sebastià; Carrera Ramírez, Jesús 2011-07-08T07:24:18Z http://hdl.handle.net/2117/12628 Title: Cone penetration tests in a virtual calibration chamber Authors: Arroyo Alvarez de Toledo, Marcos; Butlanska, Joanna; Gens Solé, Antonio; Calvetti, Francesco; Jamiolkowski, Michael Abstract: A virtual calibration chamber was built using a threedimensional model based on the discrete-element method. The chamber was then filled with a scaled granular equivalent of Ticino sand, the material properties of which were selected by curve-fitting triaxial tests. Cone penetration tests were then performed under different initial densities and isotropic stresses. Penetration resistance in the virtual calibration chamber was affected by the same cone/chamber size effect that affects physical calibration chambers and was corrected accordingly. The corrected cone resistance obtained from the virtual calibration chamber cone penetration tests shows good quantitative agreement with correlations that summarise previous physical results. 2011-05-20T12:41:23Z http://hdl.handle.net/2117/12414 Title: Evaluation of the susceptibility to failure of rocky slopes based on the SMR index Authors: Corominas Dulcet, Jordi; Mavrouli, Olga Christina 2011-04-21T15:17:55Z http://hdl.handle.net/2117/12189 Title: Influence of cracking in the desiccation process of clay soils Authors: Levatti, Hector Ulises; Prat Catalán, Pere; Ledesma Villalba, Alberto Abstract: It is well known that clayey soils undergoing desiccation tend to shrink and eventually crack. Analysis of the behaviour and influence of cracks in these types of soils is very important in several engineering fields such as mine tailing dams, long-term radioactive waste storage, impervious core of earth dams, and in any situation where clay is used as a barrier to fluid flow. Loss of humidity and cracking changes the permeability of such barriers that may no longer work properly and pose potentially high risks to property and lives. This paper presents an analysis of cracking during drying of soils using a computer code de-veloped within the framework of the finite element and finite differences methods. A study of the influence of crack initiation and propagation in the desiccation process is also undertaken, with a comparative analysis of the phenomenon both with and without crack generation that allows some preliminary conclusions about the desiccation problem. The computer code has been implemented within the MatLab environment. The formulation is based on the principles of the unsaturated soil mechanics and the mechanics of a continuum medium. The partial differential equations that govern the problem are solved using the finite element (Galerkin) method in space and the finite differences method, using the Crank-Nicholson scheme, in time. Further developments of the code will include fracture mechanics principles to simulate crack propagation. 2011-03-31T14:10:14Z