SUMMARYSimulation of large deformation and post-failure of geomaterial in the framework of smoothed particle hydrodynamics (SPH) are presented in this study. The Drucker-Prager model with associated and non-associated plastic flow rules is implemented into the SPH code to describe elastic-plastic soil behavior. In contrast to previous work on SPH for solids, where the hydrostatic pressure is often estimated from density by an equation of state, this study proposes to calculate the hydrostatic pressure of soil directly from constitutive models. Results obtained in this paper show that the original SPH method, which has been successfully applied to a vast range of problems, is unable to directly solve elastic-plastic flows of soil because of the so-called SPH tensile instability. This numerical instability may result in unrealistic fracture and particles clustering in SPH simulation. For non-cohesive soil, the instability is not serious and can be completely removed by using a tension cracking treatment from soil constitutive model and thereby give realistic soil behavior. However, the serious tensile instability that is found in SPH application for cohesive soil requires a special treatment to overcome this problem. In this paper, an artificial stress method is applied to remove the SPH numerical instability in cohesive soil. A number of numerical tests are carried out to check the capability of SPH in the current application. Numerical results are then compared with experimental and finite element method solutions. The good agreement obtained from these comparisons suggests that SPH can be extended to general geotechnical problems.

Most slope stability analyses have employed limit equilibrium methods (LEMs) or the finite-element method (FEM) as the standard approach. However, slope instability is often accompanied by discontinuous failure of the soil, which cannot be modelled by either LEMs or FEM. To overcome this limitation, this paper presents an extension of the smoothed particle hydrodynamics (SPH) method to evaluate the stability of a slope, and to simulate the post-failure behaviour of soil. For the slope stability analysis, the shear strength reduction technique with a modified failure criterion for distinguishing convergent from non-convergent solutions is applied to estimate the safety factor of a slope, and the critical slip surface is determined from a contour plot of accumulated plastic strain. To take the pore water pressure into account, a new SPH formulation for soil motion is developed. It is suggested that this equation can be applied to further developments of SPH for saturated soil. As an application of the proposed method, several smoothed particle slope stability analyses and corresponding slope failure simulations are presented, and compared with other solutions. The results show good agreements with other methods in terms of the safety factor and the critical slip surface. As compared with such traditional methods, however, an advantage of SPH is that it can simulate large deformation and post-failure of soil, and can thereby treat a wide range of applications in computational geomechanics, especially those that include large deformation and failure of geomaterials.La plupart des analyses de stabilité des pentes emploient, comme méthodes standards, des méthodes d'équilibre limite et la méthodes aux éléments finis. Toutefois, l'instabilité des pentes s'accompagne fréquemment d'une rupture discontinue du terrain, qui ne peut être modélisée avec les méthodes d'équilibre limite ou aux éléments finis. Pour résoudre ce problème, la présente communication se penche sur une extension de la méthode de l'hydrodynamique par particules adoucies [smoothed particle hydrodynamics (SPH)] pour évaluer la stabilité d'une pente et simuler le comportement de post-rupture du sol. Pour la stabilité de la pente, on emploie la technique de réduction de la résistance au cisaillement, en ajoutant un critère de rupture' modifié pour distinguer les solutions convergentes des solutions non convergentes, afin d'estimer le facteur de sécurité de la pente, et on détermine une surface de glissement critique sur la base d'un tracé des déformations plastiques accumulées. Afin de tenir compte de la pression interstitielle, on a développé une nouvelle formulation SPH pour le mouvement du sol. On propose que cette équation pourrait être appliquée pour des développements ultérieurs du SPH pour des sols saturés. A titre d'application de la méthode proposée, plusieurs analyses de la stabilité de pentes, par la methode SPH, et leurs simulations correspondantes de la rupture de pentes, sont présentées et comparées avec d'autres solutions. Les résultats démont...

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The inter-particle force due to meniscus at a contact point of soil particles is derived and then the relationship between suction and apparent cohesion is numerically obtained based on some probabilistic consideration on the soil particle size. A new slope stability analysis is proposed to analyze the stability of Shirasu slopes , in which Janbu method is applied to the slope failure caused by heavy rainfall. In the proposed stability analysis the change in apparent cohesion with the change in water content due to rainfall can be taken into account. The current safety factor can be calculated by a personal computer when the data on total amount and intensity of rainfalls are obtained in the real time.

Fig. 1. Mechanism of rainfall-induced slope failures 955SOILS AND FOUNDATIONS Vol. 50,No. 6,[955][956][957][958][959][960][961][962][963][964] Dec. ABSTRACTThe many recent slope failures due to heavy rainfall have been accompanied by signiˆcant loss of life, and massive damage to infrastructures and heritage. Many studies have been done to investigate the mechanism of rainfall-induced slope failures and establish a prevention system for slope disasters. In this paper, the state-of-the-art research works on slope failures due to rainfall published in the journal of Soils and Foundations (S&F) during the latest 50 years are reviewed and summarized. This report is written with the perspective that knowledge of unsaturated soil mechanics is necessary to elucidate the mechanism of rainfall-induced slope failure.

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Granular flows play an important role in many industrial processes. To optimize these processes, it is necessary to simulate the flow accurately. However, due to the complexity of the granular flows, there is no generally accepted theory or computational method at the present. This paper presents a new numerical approach based on the smoothed particle hydrodynamics method (SPH) to simulate granular materials, which are assumed to be elasto-plastic. Herein, the Drucker-Prager model with non-associated plastic flow rule was employed to describe elasto-plastic behavior of granular flows, and the accuracy of SPH approximation of governing equation is improved by adopting a procedure to renormalize the kernel derivative. Application of SPH to simulate granular flow in a silo was presented after a validation of SPH with experiment. It is shown that the current SPH model can capture overall behavior of granular flows.