MSR - Mecànica del Sòls i de les Roques
http://hdl.handle.net/2117/3576
Fri, 06 May 2016 06:07:22 GMT2016-05-06T06:07:22ZThermo-poro-mechanical analysis of landslides: from creeping behaviour to catastrophic failure
http://hdl.handle.net/2117/86648
Thermo-poro-mechanical analysis of landslides: from creeping behaviour to catastrophic failure
Alonso Pérez de Agreda, Eduardo; Zervos, Antonis; Pinyol Puigmartí, Núria Mercè
The scope of the paper encompasses planar and compound sliding motions, which may exhibit creeping behaviour during a certain period but may evolve to a very rapid motion. Thermo-mechanical interactions, at the scale of the sliding surface, are accepted as a critical aspect to explain these motion phases and their relationship. The sliding kinetics and global equilibrium are described at a large scale and the evolving shearing strength at the sliding surface derives from the local analysis of the shearing band and its vicinity. Pore pressures, temperatures and related variables are calculated by resolving a set of balance equations. The paper describes the transition from creeping motions to a rapid event. Results are found in terms of dimensionless numbers. Calculation of the slide evolution requires special numerical techniques described in the paper. Band permeability is found to be the dominant property controlling the triggering of fast motions. The creeping stage and the eventual slide blow-up are intimately linked. This relationship is explored in the paper. The models presented can be readily used to back-analyse relevant case histories or, in principle, even to carry out predictive modelling, provided an adequate calibration is available for the material parameters.
Thu, 05 May 2016 14:08:34 GMThttp://hdl.handle.net/2117/866482016-05-05T14:08:34ZAlonso Pérez de Agreda, EduardoZervos, AntonisPinyol Puigmartí, Núria MercèThe scope of the paper encompasses planar and compound sliding motions, which may exhibit creeping behaviour during a certain period but may evolve to a very rapid motion. Thermo-mechanical interactions, at the scale of the sliding surface, are accepted as a critical aspect to explain these motion phases and their relationship. The sliding kinetics and global equilibrium are described at a large scale and the evolving shearing strength at the sliding surface derives from the local analysis of the shearing band and its vicinity. Pore pressures, temperatures and related variables are calculated by resolving a set of balance equations. The paper describes the transition from creeping motions to a rapid event. Results are found in terms of dimensionless numbers. Calculation of the slide evolution requires special numerical techniques described in the paper. Band permeability is found to be the dominant property controlling the triggering of fast motions. The creeping stage and the eventual slide blow-up are intimately linked. This relationship is explored in the paper. The models presented can be readily used to back-analyse relevant case histories or, in principle, even to carry out predictive modelling, provided an adequate calibration is available for the material parameters.Benchmarking selection of parameter values for the Barcelona basic model
http://hdl.handle.net/2117/86568
Benchmarking selection of parameter values for the Barcelona basic model
D'Onza, Francesca; Wheeler, S. J.; Gallipoli, Domenico; Hofmann, M.; Lloret Cabot, Marti; Lloret Morancho, Antonio; Mancuso, C.; Pereira, J.M.; Romero Morales, Enrique Edgar; Toll, D. G.; Vassallo, R.
Seven teams took part in a benchmarldng exercise on selection of parameter values for the Barcelona Basic Model (BBM) from experimental data on an unsaturated soil. All teams were provided with experimental results from 9 tests performed on a compacted soil in order to determine values for the ten BBM soil constants and an initial value for the hardening parameter. The coordinating team then performed simulations (at stress point level) with the 7 different sets of parameter values, in order to explore the implications of the differences in parameter values and hence to investigate the robustness of existing BBM parameter value selection procedures. The major challenge was found to be selection of values for the constants lambda(0), r, beta, N(0) and p(c) and an initial value for the hardening parameter (p) over bar (0)(0), with the various teams proposing significantly different values for some of these key parameters. A key lesson emerging from the exercise is the importance of choosing a method for selecting values for the parameters beta and p(c) which places the main emphasis on attempting to optimise the match to the experimental spacing of normal compression lines at different values of suction. (C) 2015 Elsevier B.V. All rights reserved.
Wed, 04 May 2016 12:51:48 GMThttp://hdl.handle.net/2117/865682016-05-04T12:51:48ZD'Onza, FrancescaWheeler, S. J.Gallipoli, DomenicoHofmann, M.Lloret Cabot, MartiLloret Morancho, AntonioMancuso, C.Pereira, J.M.Romero Morales, Enrique EdgarToll, D. G.Vassallo, R.Seven teams took part in a benchmarldng exercise on selection of parameter values for the Barcelona Basic Model (BBM) from experimental data on an unsaturated soil. All teams were provided with experimental results from 9 tests performed on a compacted soil in order to determine values for the ten BBM soil constants and an initial value for the hardening parameter. The coordinating team then performed simulations (at stress point level) with the 7 different sets of parameter values, in order to explore the implications of the differences in parameter values and hence to investigate the robustness of existing BBM parameter value selection procedures. The major challenge was found to be selection of values for the constants lambda(0), r, beta, N(0) and p(c) and an initial value for the hardening parameter (p) over bar (0)(0), with the various teams proposing significantly different values for some of these key parameters. A key lesson emerging from the exercise is the importance of choosing a method for selecting values for the parameters beta and p(c) which places the main emphasis on attempting to optimise the match to the experimental spacing of normal compression lines at different values of suction. (C) 2015 Elsevier B.V. All rights reserved.A sequential algorithm for feed-forward neural networks with optimal coefficients and interacting frequencies
http://hdl.handle.net/2117/85824
A sequential algorithm for feed-forward neural networks with optimal coefficients and interacting frequencies
Romero Merino, Enrique; Alquézar Mancho, René
An algorithm for sequential approximation with optimal coefficients and interacting frequencies (SAOCIF) for feed-forward neural networks is presented. SAOCIF combines two key ideas. The first one is the optimization of the coefficients (the linear part of the approximation). The second one is the strategy to choose the frequencies (the non-linear weights), taking into account the interactions with the previously selected ones. The resulting method combines the locality of sequential approximations, where only one frequency is found at every step, with the globality of non-sequential methods, where every frequency interacts with the others. The idea behind SAOCIF can be theoretically extended to general Hilbert spaces. Experimental results show a very satisfactory performance.
Mon, 18 Apr 2016 14:53:10 GMThttp://hdl.handle.net/2117/858242016-04-18T14:53:10ZRomero Merino, EnriqueAlquézar Mancho, RenéAn algorithm for sequential approximation with optimal coefficients and interacting frequencies (SAOCIF) for feed-forward neural networks is presented. SAOCIF combines two key ideas. The first one is the optimization of the coefficients (the linear part of the approximation). The second one is the strategy to choose the frequencies (the non-linear weights), taking into account the interactions with the previously selected ones. The resulting method combines the locality of sequential approximations, where only one frequency is found at every step, with the globality of non-sequential methods, where every frequency interacts with the others. The idea behind SAOCIF can be theoretically extended to general Hilbert spaces. Experimental results show a very satisfactory performance.Run-out of landslides in brittle soils: an MPM anlysis
http://hdl.handle.net/2117/85083
Run-out of landslides in brittle soils: an MPM anlysis
Yerro Colom, Alba; Alonso Pérez de Agreda, Eduardo; Pinyol Puigmartí, Núria Mercè
In this paper a slope stability problem due to an increase of the pore pressure is analysed by means of the material point method (MPM). A strain softening model is implemented and the progressive failure is examined in terms of mobilized shear strain. A parametric study is performed varying the strength decay but maintaining a common peak envelope. The influence of the brittleness of the material, evaluated in
terms of the brittleness index (IB) proposed by Bishop (1967), in run-out and velocity of unstable slopes is examined. The initiation of motion in the defined slope is observed for values of IB>0.5 and a well correlation between run-outs and brittleness is found. It can be concluded that MPM is able to simulate both the initiation of the failure and the post-failure stages.
Fri, 01 Apr 2016 15:13:03 GMThttp://hdl.handle.net/2117/850832016-04-01T15:13:03ZYerro Colom, AlbaAlonso Pérez de Agreda, EduardoPinyol Puigmartí, Núria MercèIn this paper a slope stability problem due to an increase of the pore pressure is analysed by means of the material point method (MPM). A strain softening model is implemented and the progressive failure is examined in terms of mobilized shear strain. A parametric study is performed varying the strength decay but maintaining a common peak envelope. The influence of the brittleness of the material, evaluated in
terms of the brittleness index (IB) proposed by Bishop (1967), in run-out and velocity of unstable slopes is examined. The initiation of motion in the defined slope is observed for values of IB>0.5 and a well correlation between run-outs and brittleness is found. It can be concluded that MPM is able to simulate both the initiation of the failure and the post-failure stages.The material point method for unsaturated soils
http://hdl.handle.net/2117/85081
The material point method for unsaturated soils
Yerro Colom, Alba; Alonso Pérez de Agreda, Eduardo; Pinyol Puigmartí, Núria Mercè
The paper describes a three-phase single-point material point method formulation of coupled flow (water and air) for hydro-mechanical analysis of geotechnical problems involving unsaturated soils. The governing balance and dynamic momentum equations are discretised and adapted to material point method characteristics: an Eulerian computational mesh and a Lagrangian analysis of material points. General mathematical expressions for the terms of the set of governing equations are given. A suction-dependent elastoplastic Mohr-Coulomb model, expressed in terms of net stress and suction variables is implemented. The instability of a slope subjected to rain infiltration, inspired from a real case, is solved and discussed. The model shows the development of the initial failure surface in a region of deviatoric strain localisation, the evolution of stress and suction states in some characteristic locations, the progressive large strain deformation of the slope and the dynamics of the motion characterised by the history of displacement, velocity and acceleration of the unstable mass.
Fri, 01 Apr 2016 15:05:01 GMThttp://hdl.handle.net/2117/850812016-04-01T15:05:01ZYerro Colom, AlbaAlonso Pérez de Agreda, EduardoPinyol Puigmartí, Núria MercèThe paper describes a three-phase single-point material point method formulation of coupled flow (water and air) for hydro-mechanical analysis of geotechnical problems involving unsaturated soils. The governing balance and dynamic momentum equations are discretised and adapted to material point method characteristics: an Eulerian computational mesh and a Lagrangian analysis of material points. General mathematical expressions for the terms of the set of governing equations are given. A suction-dependent elastoplastic Mohr-Coulomb model, expressed in terms of net stress and suction variables is implemented. The instability of a slope subjected to rain infiltration, inspired from a real case, is solved and discussed. The model shows the development of the initial failure surface in a region of deviatoric strain localisation, the evolution of stress and suction states in some characteristic locations, the progressive large strain deformation of the slope and the dynamics of the motion characterised by the history of displacement, velocity and acceleration of the unstable mass.Patterns of cracking in soils due to drying and wetting cycles
http://hdl.handle.net/2117/85063
Patterns of cracking in soils due to drying and wetting cycles
Ledesma Villalba, Alberto; Cordero Arias, Josbel Andreina; Cuadrado Cabello, Agustín; Prat Catalán, Pere
There is a well reported evidence of cracking in clayey or silty soils when drying. Shrinkage in the soil mass and also boundary conditions generate a nonhomogeneous stress state locally producing tensile stresses and eventually cracking. This process has been analysed in detail by several authors. However, the evolution of such cracks due to further relative humidity changes (i.e. wetting and drying again) has been rarely considered in the reported experiments. This paper describes a particular type of experiments developed in an environmental chamber with a cylindrical soil specimen 80 cm in diameter and 10 cm in height, of Barcelona silty clay. Relative humidity was imposed in the chamber by controlling the flows of dry and wet air applied, whereas the main soil and chamber variables were recorded (temperature, suction, water content). A cycle of desiccation, wetting and further desiccation was considered and the paper describes the evolution of the cracking pattern during this process. It is shown that the pattern of cracks changes dramatically when cycles of relative humidity are imposed. In particular, soil cracking increases when soil is wetted after a dry period. An explanation of this behaviour based on Unsaturated Soil Mechanics concepts is also presented in the paper.
Fri, 01 Apr 2016 13:02:04 GMThttp://hdl.handle.net/2117/850632016-04-01T13:02:04ZLedesma Villalba, AlbertoCordero Arias, Josbel AndreinaCuadrado Cabello, AgustínPrat Catalán, PereThere is a well reported evidence of cracking in clayey or silty soils when drying. Shrinkage in the soil mass and also boundary conditions generate a nonhomogeneous stress state locally producing tensile stresses and eventually cracking. This process has been analysed in detail by several authors. However, the evolution of such cracks due to further relative humidity changes (i.e. wetting and drying again) has been rarely considered in the reported experiments. This paper describes a particular type of experiments developed in an environmental chamber with a cylindrical soil specimen 80 cm in diameter and 10 cm in height, of Barcelona silty clay. Relative humidity was imposed in the chamber by controlling the flows of dry and wet air applied, whereas the main soil and chamber variables were recorded (temperature, suction, water content). A cycle of desiccation, wetting and further desiccation was considered and the paper describes the evolution of the cracking pattern during this process. It is shown that the pattern of cracks changes dramatically when cycles of relative humidity are imposed. In particular, soil cracking increases when soil is wetted after a dry period. An explanation of this behaviour based on Unsaturated Soil Mechanics concepts is also presented in the paper.Anisotropic features on the thermal conductivity of a deep argillaceous formation
http://hdl.handle.net/2117/84575
Anisotropic features on the thermal conductivity of a deep argillaceous formation
Romero Morales, Enrique Edgar; Sau Valenzuela, Núria; Lima, Analice; Van Baelen, H; Sillen, X.; Li, Xiang Ling
An experimental study on Ypresian clays – one of the potential deep and sedimentary clay formations in Belgium for the geological disposal of heat-emitting radioactive waste – has been undertaken to systematically study anisotropic features on the thermal conductivity using a setup with thermal flux measurement. A careful pre-conditioning protocol before the thermal tests has been followed to ensure a very high degree of saturation and the closure of fissures/gaps along bedding planes. Thermal conductivity data with this improved pre-conditioning protocol allowed obtaining results consistent with the values reported when using back-analysis in a constant volume cell with fully saturated material.
Wed, 16 Mar 2016 19:30:08 GMThttp://hdl.handle.net/2117/845752016-03-16T19:30:08ZRomero Morales, Enrique EdgarSau Valenzuela, NúriaLima, AnaliceVan Baelen, HSillen, X.Li, Xiang LingAn experimental study on Ypresian clays – one of the potential deep and sedimentary clay formations in Belgium for the geological disposal of heat-emitting radioactive waste – has been undertaken to systematically study anisotropic features on the thermal conductivity using a setup with thermal flux measurement. A careful pre-conditioning protocol before the thermal tests has been followed to ensure a very high degree of saturation and the closure of fissures/gaps along bedding planes. Thermal conductivity data with this improved pre-conditioning protocol allowed obtaining results consistent with the values reported when using back-analysis in a constant volume cell with fully saturated material.Drying cracks in soils: current advances and challenges
http://hdl.handle.net/2117/84574
Drying cracks in soils: current advances and challenges
Romero Morales, Enrique Edgar; Sanchez, Marcelo; Kim, Sewon; Guimarães, Leonardo do N; Zielinski, Marcin; Atique, Alvis; Manzoli, Osvaldo
This paper presents some current advances and challenges related to the behavior of soil subjected to drying and the consequent formation and propagation of cracks in the soil mass. Typical geotechnical problems associated with the presence of desiccation cracks in soils are also discussed. A new experimental technique based on a 3D laser scanner is presented in detail. The main components of the setup are introduced, as well as the methodology adopted to interpret the data gathered from the scanning of soil samples. The application of this technique to study the drying process of a real soil used as fill embankment in Indonesia is presented. The paper also presents a numerical technique recently developed to model the formation and propagation of drying cracks in soils. The main aspects of the proposed methodology and its applications to the simulation of drying plate experiments are discussed in this contribution. Both, experimental and numerical techniques appear as very appropriate and promising to study the behavior of soils subjected to drying process.
Wed, 16 Mar 2016 19:21:21 GMThttp://hdl.handle.net/2117/845742016-03-16T19:21:21ZRomero Morales, Enrique EdgarSanchez, MarceloKim, SewonGuimarães, Leonardo do NZielinski, MarcinAtique, AlvisManzoli, OsvaldoThis paper presents some current advances and challenges related to the behavior of soil subjected to drying and the consequent formation and propagation of cracks in the soil mass. Typical geotechnical problems associated with the presence of desiccation cracks in soils are also discussed. A new experimental technique based on a 3D laser scanner is presented in detail. The main components of the setup are introduced, as well as the methodology adopted to interpret the data gathered from the scanning of soil samples. The application of this technique to study the drying process of a real soil used as fill embankment in Indonesia is presented. The paper also presents a numerical technique recently developed to model the formation and propagation of drying cracks in soils. The main aspects of the proposed methodology and its applications to the simulation of drying plate experiments are discussed in this contribution. Both, experimental and numerical techniques appear as very appropriate and promising to study the behavior of soils subjected to drying process.Gas migration and coupled hydro-mechanical issues in claystones for radioactive waste disposal at great depth
http://hdl.handle.net/2117/84565
Gas migration and coupled hydro-mechanical issues in claystones for radioactive waste disposal at great depth
Romero Morales, Enrique Edgar; González Blanco, Laura; Marschall, Paul
The hydro-mechanical behaviour of shales is becoming an important issue in current energy-related geomechanical investigations, such as CO2 sequestration, extraction of gas shale and nuclear waste geological storage. Within this last context, an experimental study of two deep claystone formations from a Mesozoic sequence in Northern Switzerland (Opalinus Clay and ‘Brauner Dogger’), considered as candidate host rocks in the Swiss program for deep geological disposal of radioactive waste, has been performed. The experimental program intends to characterise their hydro-mechanical behaviour and to analyse gas migration issues by paying particular attention to the volume change response of these initially water saturated materials along gas injection and dissipation process.
Wed, 16 Mar 2016 18:33:28 GMThttp://hdl.handle.net/2117/845652016-03-16T18:33:28ZRomero Morales, Enrique EdgarGonzález Blanco, LauraMarschall, PaulThe hydro-mechanical behaviour of shales is becoming an important issue in current energy-related geomechanical investigations, such as CO2 sequestration, extraction of gas shale and nuclear waste geological storage. Within this last context, an experimental study of two deep claystone formations from a Mesozoic sequence in Northern Switzerland (Opalinus Clay and ‘Brauner Dogger’), considered as candidate host rocks in the Swiss program for deep geological disposal of radioactive waste, has been performed. The experimental program intends to characterise their hydro-mechanical behaviour and to analyse gas migration issues by paying particular attention to the volume change response of these initially water saturated materials along gas injection and dissipation process.Trends in large-deformation analysis of landslide mass movements with particular emphasis on the material point method
http://hdl.handle.net/2117/84551
Trends in large-deformation analysis of landslide mass movements with particular emphasis on the material point method
Soga, Kenichi; Alonso Pérez de Agreda, Eduardo; Yerro Colom, Alba; Kumar, K.; Bandara, S.
Traditional geotechnical analyses for landslides involve failure prediction (i.e. onset of failure) and the design of structures that can safely withstand the applied loads. The analyses provide limited information on the post-failure behaviour. Modern numerical methods are able to simulate large mass movements and there is an opportunity to utilise such methods to evaluate the risks of catastrophic damage if a landslide occurs. In this paper, various large-deformation analysis methods are introduced and their applicability for solving landslide problems is discussed. Since catastrophic landslides often involve seepage forces, consideration of the coupled behaviour of soil and pore fluid is essential. Two approaches to model soil–pore fluid coupling in large-deformation analysis using the material point method (MPM) are introduced. An example simulation is presented for each approach; one on a model levee failure and the other on a natural cut slope failure (the Selborne experiment conducted by Cooper and co-workers in 1998). In the levee failure case, MPM simulation was able to capture a complex failure mechanism including the development of successive shear bands. The simulation was also able to predict excess pore pressure generation during the failure propagation and the subsequent consolidation stage. The simulations demonstrated the importance of the dilation characteristics of soil as well as changes in geometry for the post-failure behaviour. In the Selborne case, MPM was able to simulate the progressive failure of brittle, overconsolidated clay. The evolution of shear stresses along the failure surface was also captured by the MPM. The changes in the pore pressure and the actual shape of the failure surface were simulated by the MPM. The importance of accurately modelling the shear band within the MPM framework is highlighted.
Wed, 16 Mar 2016 17:53:57 GMThttp://hdl.handle.net/2117/845512016-03-16T17:53:57ZSoga, KenichiAlonso Pérez de Agreda, EduardoYerro Colom, AlbaKumar, K.Bandara, S.Traditional geotechnical analyses for landslides involve failure prediction (i.e. onset of failure) and the design of structures that can safely withstand the applied loads. The analyses provide limited information on the post-failure behaviour. Modern numerical methods are able to simulate large mass movements and there is an opportunity to utilise such methods to evaluate the risks of catastrophic damage if a landslide occurs. In this paper, various large-deformation analysis methods are introduced and their applicability for solving landslide problems is discussed. Since catastrophic landslides often involve seepage forces, consideration of the coupled behaviour of soil and pore fluid is essential. Two approaches to model soil–pore fluid coupling in large-deformation analysis using the material point method (MPM) are introduced. An example simulation is presented for each approach; one on a model levee failure and the other on a natural cut slope failure (the Selborne experiment conducted by Cooper and co-workers in 1998). In the levee failure case, MPM simulation was able to capture a complex failure mechanism including the development of successive shear bands. The simulation was also able to predict excess pore pressure generation during the failure propagation and the subsequent consolidation stage. The simulations demonstrated the importance of the dilation characteristics of soil as well as changes in geometry for the post-failure behaviour. In the Selborne case, MPM was able to simulate the progressive failure of brittle, overconsolidated clay. The evolution of shear stresses along the failure surface was also captured by the MPM. The changes in the pore pressure and the actual shape of the failure surface were simulated by the MPM. The importance of accurately modelling the shear band within the MPM framework is highlighted.