Use of generalized material point method (GIMP) to simulate shallow wedge penetration

This paper investigates a numerical solution of a semi-infinite mass of soil being penetrated by a smooth and rigid wedge. Traditional methods such as the finite element method (FEM) meet some difficulties when large strains are involved. Hence the generalized material point method (GIMP) is used to simulate the penetration process, as a first approximation to study other problems involving large strains in geotechnical engineering. The GIMP includes many attractive features in solving engineering problems involving large deformations. Its formulation is shortly described and then an analytical solution is compared with numerical results for different depths of penetration. The results show that the method describes qualitative and quantitatively the phenomenon of penetration. Some differences comparing numerical and analytical results are attributed to artificial roughness introduced by the geometric discretization. Other reasons could be explained by the scheme of integration used in the constitutive law and time stepping, specifically during the transition between elastic and plastic behavior in the constitutive model adopted

An assessment of the material point method for modelling large scale run-out processes in landslides

This paper demonstrates the predictive capabilities of a numerical model based on continuum mechanics for the simulation of run-out processes during landslides. It assesses a particle-based method that takes advantage of a double Lagrangian-Eulerian discretization and known as the material point method (MPM). Attention is given to the post-failure behaviour and, in particular, to the computation of important quantities such as run-out distance, maximum velocity and energy release. The MPM is a step forward in computational solid mechanics and has the potential to simulate large deformations such as those occurring during landslides. A validation is conducted based on simulations of two case studies of different scales, namely the Tokai-Hokuriku expressway failure in Japan and the Vajont landslide in Italy. The results show a very good agreement with field and other numerical observations

Multimodal reliability analysis of 3D slopes with a genetic algorithm

This paper presents a genetic algorithm (GA) to solve the multimodal optimisation problem resulting from 3D slopes prone to multiple regions of failure. A probabilistic approach is taken by using the first-order reliability method (FORM) to approximate the probability of failure. The 3D Bishop method is selected but can be replaced as appropriate. Since 3D analyses have higher computational costs than 2D simulations, we demonstrate that the FORM approach is very practical to large-scale geotechnical problems compared to alternatives such as Monte Carlo simulations (MCS). Furthermore, we show that the GA optimiser can obtain reliability indices and find critical failure regions that would not be found by the MCS easily. These characteristics are demonstrated by some simple test cases and the more complex topography of the Mount St. Helens in the USA

An assessment of statistically based relationships between critical state parameters

Reliability-based design (RBD) has been proved effective in the application of probability theory to research and practice in geotechnical engineering. However, the limited field and laboratory information makes it difficult to build robust predictions. This note shows some statistical relationships that may help with additional information in this area. Descriptive statistics are performed in the note followed by demonstrations of the close relationship between deformabilty parameters. The strong correlation between the slope of the critical state line and the earth pressure coefficient at rest is found. The applicability of the statistical relationships is also examined using RBD. Numerical analysis of oedometer tests demonstrates how RBD can consider the influence of the uncertainty of the critical state parameters

Considerations on the experimental calibration of the fall cone test

The fall cone test is widely used in soil mechanics to determine the liquid limit of fine-grained soils as an aid to soil classification. The test can also be used to obtain the undrained shear strength of a fine-grained soil, based on the "cone factor," K. Reports from different authors show K values ranging from 0.4-1.33. Differences are mostly attributed to the cone surface roughness. This article presents a reinterpretation of several experimental observations available in the literature. It is observed that besides the cone roughness, testing methods have a clear influence when calibrating the fall cone for determining the undrained shear strength of materials with low and very low consistency. The results show that existing K reports should be extrapolated with care. Finally, we propose a series of recommendations and good practices for future calibrations

Dielectric spectroscopy of artificial faeces for smouldering applications

Our objective is to develop an analysis concept in order to measure the in situ estimation of state parameter, such as water content, during smouldering of waste and sand mixtures. High frequency electromagnetic (HF EM) method presents a high potential for the quantitative estimation of state parameter in porous media. However, it provides indirect measurement: the major challenge is to derive robust relationship between the performed measured permittivity and the parameter under interest. Thus, laboratory measurement of dielectric properties of waste and sand mixtures under controlled boundary are urgently needed. In this preliminary study, the relative effective complex permittivity of artificial faeces was studied over the 50°MHz-3°GHz frequency range with network analyzer technique in combination with homemade open ended coaxial method. In a first step, the effect of water content on dielectric properties was investigated. The results have shown an important dispersion for the imaginary part which can be related to interface process and a systematic increase of the permittivity with water content. In a second step, a shrinking test was monitored with the homemade probe. The relative complex permittivity shows a nonlinear evolution with gravimetric water content and show marked transitions during the decrease of water content. The results of combined investigations have shown the potential of HF EM techniques for quantitative monitoring of the hydraulic state of waste and sand mixtures during smouldering combustion