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... initial geometry and boundary con- ditions are the same for all simulations and identical to the one described in previous section. Material properties were given in Table 1 except for the re- sidual cohesion (c r ') and the residual friction angle (φ r ') which were changed according to Table 2. Note that simulation number 14 coincides with the case presented above. ...
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... This continuum mechanics model has been widely used in the numerical simulations of actual mountain hazards (Liu et al. 2020) and has also applied to and verified related experiments and engineering cases (Hungr and McDougall 2009;Liu et al. 2016;Ouyang et al. 2017;Ouyang et al. 2013). There are also some other kinds of numerical methods including the discrete element method (DEM) (Bi et al. 2018;Tang et al. 2009), material point method (MPM) (Yerro et al. 2014;Sun et al. 2015), and smoothed particle hydrodynamics (SPH) (Huang et al. 2012;Liang et al. 2019), which are used for simulating dynamics of mountain hazards. In this paper, we plan to use continuum mechanics equations based on the Savage-Hutter model to simulate the dynamic process of landslide induced by particle breakage. ...
Rapid long-runout landslide is a hot topic in the field of landslide researches. Many researchers have proposed different models and hypotheses to explain the superfluidity of long-runout landslides. In this paper, the mechanism of sliding surface weakening caused by particle breakage is studied. Particle breakage can not only cause the excess pore water pressure but also weaken the friction coefficient of the sliding surface. These two factors are both the causes of the superfluidity of the landslide induced by particle breakage. In addition, the evolutions of breakage potential and excess pore water pressure are coupled into landslide dynamic equations to simulate how the particle characteristics such as porosity, crushing hardness, and particle shape influence the landslide fluidity. During sliding process, the numerical results indicate that the breakage potential of sliding surface decreases nonlinearly with time, the excess pore water pressure generated by particle breakage increases first and then decreases nonlinearly, and the effective friction coefficient decreases nonlinearly with time and tends to a residual value.
... The case of the Canelles landslide is revisited in this paper with the purpose of giving a more complete explanation of the observed behaviour, being consistent with the thermal interaction phenomenon. The analysis is carried out by means of the material point method (MPM) (Sulsky and Schreyer 1996;Bardenhagen et al. 2000), which has been selected because of its capabilities to reproduce the entire response of landslides, including static conditions, landslide triggering, and post-failure behaviour Ceccato 2017;Ceccato and Simonini 2016;Soga et al. 2016;Yerro et al. 2015aYerro et al. , 2015bZabala and Alonso 2011). ...
The re-activation of a large (40 Mm ³ ) landslide on the valley slopes of a reservoir motivated a research initiative to estimate the risk of a fast-sliding mass moving into the reservoir. A previous simplified analysis had suggested that a joint consideration of strain rate effects on friction and thermal pressurization phenomena in the sliding surface could provide a rational approach to answer the question raised. The paper describes first the capability of strain rate effects on friction to reproduce long-term creeping records of two real cases. The joint and coupled phenomena of creeping motion and thermal pressurization in shearing bands was incorporated into a material point method computational technique for hydromechanical analysis of porous materials. A representative cross section of the Canelles landslide was then analysed, profiting from previous finite element investigations of the landslide. It was found that a rapid rate of landslide acceleration could be a possibility under extreme external actions. However, it was also found that a moderate strain rate effect on the basal residual friction angle could create conditions that avoid the triggering of a fast motion.
... A computational mesh consisting of tetrahedral elements with 4 material points is used for the computation (Figure 1). The strain softening Mohr-Coulomb constitutive law presented in Yerro et al. (2014) is considered to model the brittle behaviour of the overconsolidated clay. In the calculation procedure, firstly the stresses in the soil are initialised with a K0 value of 2 with a horizontal surface. ...
... It is shown that considering the initialisation of stresses with a more realistic K0, and the modelling of the excavation process the slip failure fits much better the real failure mechanism. Following the idea of Skempton (1964), the concept of the progressive failure has been studied quantitatively with the mobilised shear strength concept introduced in Yerro et al. (2014) which is a measure of the intensity of shear in a certain point. ...
The material point method (MPM) is an advanced particle-based method that combines Eulerian and Lagrangian descriptions of the media to describe the dynamic behaviour of the continuum. The novelty of the method is the capability to deal with large deformations avoiding problems of mesh tangling typical from finite elements. MPM has a good potential to examine the conditions leading to slope failure but, also, it is capable of following in time the evolution of the unstable mass determining its final run-out, which is a key variable to evaluate the consequences of instability. In this work, the MPM is used to analyse the Selborne experiment, which was a landslide induced by water recharge in saturated soils. Excavation is simulated and results show the evolution of a progressive failure and final displacements similar to those observed in the field. Moreover, using the same geometry and material properties of the Selborne experiment a parametric study is performed to understand the influence of the initial stresses on the generated slip surface and the post-failure behaviour. The Mohr-Coulomb strain softening model is used to simulate the soil brittleness. This work contributes to the validation of the method and proves its functionality by modelling a real slope failure.
... It has been extensively validated for quasi-static and dynamic problems in geomechanics, see e.g. [25,27,31,42,50,51]. The finite element discretization adopted in this study uses low order tetrahedral elements. ...
... It has been extensively validated for quasi-static and dynamic problems in geomechanics, see e.g. [25,27,31,42,50,51]. The finite element discretization adopted in this study uses low order tetrahedral elements. ...
This paper presents numerical simulations of Cone Penetration Test (CPT) in water-saturated soft soils taking into account pore pressure dissipation during installation. Besides modelling interaction between soil skeleton and pore fluid, the problem involves large soil deformations in the vicinity of the penetrometer, soil–structure interaction, and complex non-linear response of soil. This makes such simulations challenging. Depending on the soil’s permeability and compressibility, undrained, partially drained or drained conditions might occur. Partially drained conditions are commonly encountered in soils such as silts and sand–clay mixtures. However, this is often neglected in CPT interpretation, which may lead to inaccurate estimates of soil properties. This paper aims at improving the understanding of the penetration process in different drainage conditions through advanced numerical analyses. A two-phase Material Point Method is applied to simulate large soil deformations and generation and dissipation of excess pore pressures during penetration. The constitutive behaviour of soil is modelled with the Modified Cam Clay model. Numerical results are compared with experimental data showing good agreement.
Many natural hazards involve large deformations of unsaturated soils, e.g. rainfall-induced landslides, embankment collapses due to wetting, seepage-induced instabilities of dams and levees, etc. The study of these phenomena requires accounting for the complex hydro-mechanical interactions between solid skeleton and pore fluids and modeling large deformations to predict the post-failure behaviour, which poses significant computational challenges. In recent years, several hydro-mechanical coupled MPM formulations were developed to model saturated and unsaturated soils. These approaches are slightly different in terms of governing equations, integration schemes and have been implemented in different MPM software; thus, they benefit from various computational features. The purpose of this paper is to present an overview of the available MPM approaches to model unsaturated soils discussing differences and similarities of the formulations and their impact on the results under different conditions in a range of geotechnical applications. In addition, the effect of partially saturated conditions on the critical time step in explicit numerical integration schemes is studied for the first time. Different analytical expressions are derived and compared with the numerical results.
The piezocone penetration test (CPTU) is commonly used to identify a soil’s profile and estimate its material properties. Depending on the soil type, ranging from clay to sand, undrained, partially drained, or drained conditions may occur during cone penetration. In silt and sand–clay mixtures, the CPTU penetration is characterized by partially drained conditions, which are often neglected in data interpretation. The effect of drainage on CPTU measurements has been mainly studied experimentally. Numerical analyses are rare because taking into account large soil deformations, soil–water and soil–structure interactions, and nonlinear soil behavior is still a challenging task. This paper presents and discusses numerical simulations of CPTU in saturated soils with the two-phase material point method. Soil behavior is described with the modified cam clay model. This study investigates the effects of pore pressure dissipation during penetration, cone roughness, and horizontal stress state, comparing the results with experimental data. The paper discusses the effect of neglecting partial drainage in deriving the shear strength parameters for silty soils and suggests a procedure to estimate the consolidation coefficient for performing CPTU at different penetration rates.
Read More: http://ascelibrary.org/doi/full/10.1061/(ASCE)GT.1943-5606.0001550
Landslides and slope instabilities represent one of the most important problems in geotechnics causing significant damages around the world every year. Understanding the mechanics of the whole deformation process is of particular importance for risk assessment. First, it is important to determine what areas may be susceptible to landsliding. In addition, it is essential to estimate the travelled distance and the velocity of the unstable mass in order to prevent severe damage. The need to develop solution schemes capable of simulating failure initiation as well as post-failure dynamics is also required in most geotechnical
analyses. For instance the design of dams, tunnels, pipes or foundations.
The numerical modelling of such events presents several challenges due to the complexity of simulating large deformations and real soil behaviour. In addition, coupled formulations are needed to model solid-fluid interaction in saturated and unsaturated soils.
Traditional geotechnical analysis, such as Limit Equilibrium Methods (LEM) and the well-known standard lagrangian Finite Element Methods (FEM) are very useful to study the failure initiation, but they provide limited information on the post-failure behaviour. In order to overcome such difficulties, modern numerical approaches are being developed. This is the case of the Material Point Method (MPM), which offers an interesting alternative. MPM discretises the media into a set of lagrangian material points which move
attached to the material carrying the soil properties. Governing equations are solved incrementally at the nodes of a computational grid that remains fixed through the calculation. This dual description of the media is capable of modelling large deformations and prevents mesh tangling.
This thesis focusses on studying brittle failures and slope instabilities, from static conditions to run-out by means of the MPM framework. It is proved to be a very useful tool to analyse relevant aspects for the interpretation of landslides such as the development of progressive failure mechanism, the role played by internal shearing in compound slides, and the effect of brittleness on the onset of failure and run-out. The MPM is successfully applied to solve several slope instability problems caused by pore pressure changes. First, the Selborne slope experiment is simulated. This case, well identified with laboratory data, has been an opportunity to perform a validation of the MPM formulation, since a good agreement is obtained between numerical results and experimental data. In a second example, a simplified geometry of the Vajont landslide is analysed. It has shown that a kinematically admissible failure mechanism requires internal degradation of the mobilised mass controlled by the geometry of the basal sliding surface. In a third analysis, a parametric study varying peak and residual strength is presented, and run-out is found to be directly related with brittleness index.
Moreover, a step forward in the application of MPM to solve multi-phase problems in porous media has been achieved. A coupled 3-phase 1-point MPM formulation is derived and implemented in a software code in order to model problems involving large deformations in unsaturated soils. In this way, the interaction of three different phases (solid, liquid and gas) is taken into account within each material point. This approach
is validated with a benchmark problem and it is applied to study the behaviour of an embankment slope instability induced by heavy rain.
Finally, two constitutive models are derived and implemented: a brittle model with strain softening for saturated soils, and a Mohr-Coulomb elastoplastic model for unsaturated materials formulated in terms of net stress and suction.
