Numerical Simulation of the Rainfall Infiltration on Unsaturated Soil Slope Considering a Seepage Flow
S.Kimoto, F.Oka and E.Garcia
ABSTRACT: Frequent failures of river embankments have occurred in the world due to heavy rains. Heavy rainfalls bring about an increase of the ground water level within the soil as well as a rise in the water level of the rivers. As a result, embankments have been failed due to the rainfall infiltration and the generation of seepage flow. A series of two-dimensional numerical analyses of river embankments are carried out using a seepage-deformation coupled method for unsaturated soil. The mechanism of the surface deformation and the strain localization on these soil structures are discussed mainly with respect to the water permeability of the soils. Results obtained by the simulations show that the deformation of the embankments significantly depends on the water permeability of the soil and it is localized on the slope surface at the river sides. The larger the saturated water permeability of the soil, the larger the velocity of the seepage flow and the larger the deformation on the surface of the river embankments. Additionally, numerical simulations of a field experiment are used to show that, the method adopted here, can effectively be used to study the practical seepage deformation coupled problems on unsaturated soils.
Seismic Response of Gravity-Cantilever Retaining Wall Backfilled with Shredded Tire
N. Ravichandran and E. L. Huggins
ABSTRACT: Using shredded tires as an alternative backfill material for retaining walls is an effective method for recycling a common and abundant waste material. In this paper, the engineering properties of the shredded tire from various sources were compiled; retaining walls were designed for static and seismic conditions using the mean properties following LRFD method and compared with that of conventional granular material. The performance of retaining wall backfilled with shredded tires was then investigated by applying design earthquake acceleration-time histories using advanced finite element software and compared with that of sand backfill. In addition, a detailed parametric study was conducted to quantify the effect of variations in shredded tire properties and earthquake loadings. Results show that the shredded tire backfill significantly reduces the wall tip deflection and maximum shear force and bending moment along the wall. Parametric studies on the shredded tire properties determined that cohesion has the greatest effect on the shear force and wall tip deflection. The friction angle showed the most influence on the bending moment in the wall. Quantitative and qualitative analysis of wall response with variations in shredded tire properties provide guidelines for the design of walls to be backfilled with shredded tires and for the selection of backfill materials.
Numerical modeling of lateral response of long flexible piles in sand
Md. Iftekharuzzaman and Bipul C Hawlader
ABSTRACT: The behavior of a steel pipe pile in sand subjected to lateral load is examined by finite element (FE) analysis. Threedimensional finite element analyses are performed for pure lateral load applied at 0.3m above the ground surface. The FE analyses are performed using the commercially available software package ABAQUS/Standard. The sand around the pile is modeled using a modified form of Mohr-Coulomb soil constitutive model. The modification involves the variation of mobilized angle of internal friction and dilation angle with plastic shear strain. The nonlinear variation of elastic modulus with mean effective stress is also considered in the present FE analyses. These important features of soil constitutive model have been implemented in ABAQUS/Standard using a user subroutine. Numerical analyses are also performed by using the LPILE software, which is based on the p-y curve. The FE and LPILE results are compared with the results of a full-scale test. It is shown that the FE analysis with modified Mohr-Coulomb soil model can successfully simulate better the response of a pile under lateral load. Comparing the numerical results with the full-scale test results some limitations of the p-y curve method are highlighted.
A New Sampling Algorithm in Particle Filter for Geotechnical Analysis
T. Shuku, S. Nishimura, K. Fujisawa and A. Murakami
ABSTRACT: This paper discusses the applicability of the particle filter (PF) algorithms to geotechnical analysis through some numerical tests. Although several types of the PF algorithms have been proposed so far, this study focuses on three typical PF algorithms: sequential importance resampling (SIR), sequential importance sampling (SIS), and merging particle filter (MPF). First, a geotechnical parameter is identified using the three algorithms in both total stress and soil-water coupled analyses, and the effectiveness of each algorithm is investigated. The test results clarify that (1)SIS can be applied to non-Markov dynamics such as elasto-plastic problems, but degeneration problems are often encountered, and (2)MPF can avoid the degeneration problems, but it cannot be applied to non-Markov dynamics. To overcome the dilemma, an algorithm which can treat non-Markov dynamics and solve the degeneration problems is newly proposed. The proposed algorithm is applied to an element test, and the performance is demonstrated experimentally.
Comparison of deep foundation systems using 3D finite element analysis employing different modeling techniques
F. Tschuchnigg & H.F. Schweiger
ABSTRACT: Finite element analyses for the deep foundation of the Donau City Towers in Vienna are discussed in this paper. The towers are located very close to each other, thus interaction of the two towers has to be taken into account for the design of the foundation system. The objective of the analysis was twofold, namely to calculate maximum and differential settlements to be expected and optimisation of the layout of the foundation elements. In addition to the foundation concept actually constructed alternative solutions have been studied in a numerical study and the results of this study are presented in this paper. Different techniques for modelling the foundation elements in the numerical model, namely a standard approach using volume elements and the embedded pile concept, are investigated. The latter approach is discussed is some detail before the case study is presented.
Application of a constitutive model for swelling rock to tunnelling
B. Schadlich, T. Marcher and H.F. Schweiger
ABSTRACT: Swelling due to chemical processes is a well-known problem in tunnelling in anhydritic rocks and certain types of claystone. If the swelling rock mass is exposed to water due to tunnel excavation or natural water influx, in anhydritic rocks large deformations of more than 1 m can be observed, which are typically concentrated at the tunnel invert. Estimating swelling deformations and swelling pressures is of paramount importance for the design of durable underground structures in such materials. This paper presents the results of a numerical back analysis of measured swelling deformations with a simple constitutive model, using swelling parameters derived from laboratory swelling tests.
Finite element modelling of seismic liquefaction in soils
V. Galavi, A. Petalas and R.B.J. Brinkgreve
ABSTRACT: Numerical aspects of seismic liquefaction in soils as implemented in the finite element code, PLAXIS, is described in this paper. After description of finite element equations of dynamic problems, three practical dynamic boundary con ditions, namely viscous boundary tractions, tied degrees of freedom and free field elements are reviewed. Possibilities and limitation of each type of boundary condition is highlighted. The formulation of a constitutive model, called as UBC3D-PLM, which describes the mechanical behaviour of soils under cyclic loading is also presented. The model is an extension of the two dimensional UBCSAND model developed at University of British Colombia which utilises isotropic and kinematic hardening rules for primary and secondary yield surfaces to properly take into account accumulation of excess pore water pressure and effect of soil densification during cyclic loading. By means of a simp lified Rowe’s stress-dilatancy theory, the model is capable of modelling liquefaction for different stress paths. It will be presented in this paper how most of the model parameters can be found from the corrected SPT blow count which makes the model easy to use for practical applications. Finally, the model is used for modelling a real boundary value problem and the results are compared with field measurements.
Random Wave-Induced Seabed Responses around Breakwater Heads
Y Zhang, D-S Jeng, Z-W Fu and J Ou
ABSTRACT: Wave-induced pore pressures and effective stresses in a porous seabed around breakwater heads have been recognised as one of the key factors in the design of breakwaters. Unlike previous investigations, which were limited to regular wave loading, this paper investigated random wave-induced seabed responses. Two common wave spectra, B-M and JONSWAP, were used for the simulation of random waves in a model. Based on this poro-elastoplastic model, the influence of random wave parameters, waves and seabed parameters on the pore pressures around breakwater heads were examined and discussed in detail.
Influence of brittle property of cement treated soil on undrained bearing capacity characteristics of the ground
S. Yamada, T. Noda, A. Asaoka and T. Shina
ABSTRACT: In this study, the influence of brittle property of geomaterials on the failure behavior of the ground in an undrained bearing capacity problem was investigated numerically from the standpoint of taking the brittle behavior of cement treated soil as softening behavior of the soil element. The numerical analyses were performed using the soil-water coupled finite deformation analysis code GEOASIA mounted with the SYS Cam-clay model, which describes the soil skeleton structure at work. Cement treated ground and naturally deposited clay ground were modelled and compared, and it was found that they showed widely differing failure processes depending on differing initial conditions. Especially, it was found that when progressive failure in which strain localization region develops due to propagation of material failure occurs, even though the ground is composed of brittle materials such as cement treated soil, those brittle properties do not directly manifest in the load-settlement relationship. Additionally, the investigation revealed that, since every soil element on the slip lines does not reach its peak strength simultaneously when progressive failure occurs, post -peak material properties, i.e. the ratio of residual strength to peak strength and softening rate from peak to residual state, affect the bearing capacity of the ground.
