Key Engineering Materials Vols. 340-341

Abstract: Soil nailing, developed from the New Austrian Tunnelling Method, has been widely used in many countries and regions in the world since the 1970’s. This technique is used to stabilize in situ soil mass by installing a large number of closely spaced unstressed inclusions into the soil mass to increase its strength and stability. Since the mid 1970’s, several design methods have been proposed based on laboratory and field tests. Among the design criteria in these methods, the pull-out resistance of a soil nail is a key parameter that controls the stability assessment of soil nail structure. In the previous investigations, the soil dilatancy was found to be an important factor that influences the soil nail pull-out resistance especially for drill-and-grout soil nails. In order to study the influence of soil dilatancy on soil nail pull-out resistance, laboratory pull-out tests and numerical parametric studies have been carried out for soil nails in Completely Decomposed Granite (CDG) fill. The results show that the soil dilatancy has a significant influence on the soil nail pull-out resistance.

Abstract: This paper presents a theoretical study of failure modes in sand-like granular materials under general triaxial stress conditions based on a hypoplastic model and a bifurcation analysis. The well developed constitutive model contains the void ratio as a state variable which allows the pressure and density dependent behaviour of the granular materials to be described with a single set of state-independent constitutive parameters. Based on this model a shear bifurcation condition is derived. Loading along various stress paths that can be achieved with a true triaxial test apparatus are simulated numerically. Either localized failure or uniform diffuse failure in granular samples may occur, which is determined based on whether the shear bifurcation condition is met. Effects of confining pressure and initial density are discussed.

Abstract: One small-scale physical model test on the PVD (Prefabricated Vertical Drain) treated Hong Kong marine clay was simulated using finite element method (FEM) in this study. A User MATerial (UMAT) subroutine describing an Elastic Visco-Plastic (EVP) constitutive model was developed and incorporated into one commercial finite element code ABAQUS. A degressive permeability of the PVD strip was included to consider variations of its permeability during the consolidation process. The UMAT and the adopted reducing technique were demonstrated to be effective by good agreement between the observed consolidation settlement and excess pore water pressures and the simulated ones.

Abstract: In this paper the interface behavior between an infinite strip of a granular mate- rial and a rough boundary under plane shearing is numerically investigated using a micro-polar continuum approach. Particular attention is paid to the influence of a fluctuation of micro-polar boundary conditions along the interface on the evolution of shear strain localization within the granular material. The mechanical behavior of the cohesionless granular material is described with a micro-polar hypoplastic model. The evolution equations for the stress and the couple stress are non-linear tensor valued functions which model inelastic behavior. The investigations show that the micro-polar boundary conditions have a strong influence on the location and thickness of the zone of strain localization when relative displacements within the interface are excluded.

Abstract: Anisotropic visco-plastic constitutive model and generalized pore pressure are incorporated in the equation between irreversible downwards velocity and visco-plastic strain rate. The solution to velocity is obtained and by use of it the progressively destructurated deformation of partially saturated natural soil in slopes is analyzed to investigate the influence of anisotropy, viscosity, degrees of structure and destructuration, and partial saturation. The solutions are verified by use of the observed field behavior of a natural slope.

Abstract: According to unified strength parameters obtained from unified strength theory, the slope of critical state line is modified to reflect critical states of different geomaterials under general stress states. Yield function that can consider the effect of the third deviatoricic invariant is proposed, and an elasto-plastic constitutive model is established by adopting non-associated flow rules; furthermore, methods of overcoming singular points on the yield surface are discussed. The proposed model is verified by true triaxial tests of clay, and results show that the model can well predict stress-strain relationships.

Abstract: A practical elastoplastic constitutive model for granular materials is presented. And the model is suitable for description of the material behaviour for a wide range of stresses, including those sufficient to cause particle crushing. With a limited number of model parameters, the model can predict the confining-pressure dependent stress-strain relation and shear strength of granular materials in three-dimensional stresses, especially of variation of shear strength and dilatancy characteristics due to particle crushing under high confining pressure. The model parameters, which have clear physical meanings, can be determined from the results of isotropic compression test and conventional triaxial compression tests. The model performance is demonstrated for triaxial compression tests of a sand for a wide range of the confining-pressure from 0.2MPa to 8.0MPa.

Abstract: Analysis of dynamic behavior of soil-structure interaction (SSI) is a complicated problem due to the complexities of soil behaviors and dynamic analysis. It is difficult to solve SSI with analytical methods. However, numerical methods with highly developed computer technique are efficient. Based on the advanced nonlinear finite element analysis software MSC.Marc, SSI on loess ground is studied. An approach for the application of MSC.Marc in SSI analysis is presented and an example is given. Hyperbolic soil constitutive relationship and viscous boundary conditions are adopted in the soil model. Moreover, contact between the embedded columns and the adjacent soil is considered. Response spectrum analysis of the result is carried out. Some conclusions about the seismic response of soil-structure system under different soil stiffness and different soil-layer thickness conditions are given. A new way of analyzing SSI for loess ground is provided.

Abstract: For conventional reinforced soil, the reinforcements are put horizontally in the soil. A new concept of soil reinforced with three-dimensional elements was proposed. In 3D reinforced soil, besides conventional horizontal reinforcements, some vertical and 3D reinforcements can also be laid in the soil. The triaxial tests on sand reinforced with 3D reinforcement were carried out. From the experimental results, the differences of stress-strain relationship and shear strength between horizontal reinforced sand and 3D reinforced one were analyzed. The experimental results show that 3D reinforcement not only increases its cohesion, the angle of internal friction has been increased greatly, especially with 3D elements on both sides. Based on experimental results, a retaining structure reinforced with 3D reinforcements was analyzed by the finite element method. The stress distribution and interaction between 3D elements and soil were studied. The plastic zone and stability analysis of the retaining structure reinforced with 3D reinforcements were investigated by finite element method by shear strength reduction technique.

Abstract: We propose a thermo-hydro-mechanically coupled finite element analysis method for clay with a thermo-elasto-viscoplastic model. The volume changes in soil particles and pore fluids are introduced into the analysis method. The instability of the problem is studied and a numerical simulation of the thermal consolidation is presented using the newly developed analysis method. It was confirmed that the analysis method can reproduce the thermal consolidation phenomenon well.