Haruyuki Yamamoto

An Elastoplastic Model for Granular Materials Exhibiting Particle Crushing

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.

Study on Strength Characteristics of Reinforced Soil by Cement and Bamboo Chips

Soft ground with low bearing capacities is found to large areas in the world. In order to increase the bearing capacity of soft ground and to decreases settlement, some methods were developed for improving the mechanical properties of ground. As a stiffener of soil improvement, bamboo chips were used in this study. Bamboo is one of the fastest-growing plants on Earth and with a large distribution around the world. As a natural material, it is even better for environment and has excellently mechanical characteristic. The bamboo chips were mixed into the test specimen as a stiffener of soil improvement. Unconfined compression test were performed with test specimen, then mechanical characteristics of reinforced soil by cement and bamboo chips were investigated. From the test results, the strength and ductility characteristic of soil improvement are rather better when the bamboo chips are mixed.

A Simple Multiscale Model for Granular Soils with Geosynthetic Inclusion

Due to the heterogeneity and anisotropy caused by geosynthetic inclusions, the design of geosynthetic-reinforced geostructures has been largely empirically-based. The presence of geosynthetic reinforcement complicates the stress history and fabric characteristics of the reinforced soil, posing an obstacle to the development of constitutive models for geosynthetic-reinforced soils. To circumvent this difficulty, we employ a simple multiscale model based on a coupled FEM/DEM approach. The displacement in granular soil domain is solved in the hierarchical multiscale framework, while the geosynthetic inclusion that prescribes the boundary conditions are modeled concurrently by discrete bar elements. The responses of both multiscale domains are communicated and updated in an explicit time integration scheme. The main objective in this work is to extend the existing multiscale framework for modeling soil-geosynthetic interactions. The predicative capacity of this model is examined in two numerical examples, i.e., shape-forming and pull-out tests. The multiscale characters of the response of geosynthetic-reinforced soil facilitate a better understanding of the reinforcement mechanisms.

Finite Element Analysis with Joint Element for Model Pile under Vertical Loading

This paper presents the finite element analysis of the model pile loading test considering large deformation theory. The area around pile tip is concentrated with significant compressive and shear stresses. A constitutive model with particle crushing is adopted to describe the mechanical behavior of model ground. The jointed element is introduced in numerical analysis to simulate the interaction between pile and its surrounding soil. The predictions of the relationship between the normalized bearing stress and displacement are good agreeable with the test results. The influences of the joint element on the accuracy of the predicted values are obtained. The figures of distribution for displacement vectors with different penetration depth are shown and discussed.

Study on Foundation Behavior due to Seepage Force of Groundwater

Along with the vigorous developing construction in the world, the number of various underground engineerings is greatly increasing, such as the foundations of subways, tunnels, dams and high-rise buildings etc., where the attention is always paid to the seepage behavior in the soil around the structures. Seepage flow can lead to both horizontal and vertical displacement, but ground behaviors due to seepage force in traditional methods were rarely considered. In this paper, a 3D analysis is made on the foundation behavior due to seepage force of groundwater. The model uses the finite element method to study the problem and the model implemented by FORTRAN code is applied to predict the flow velocity distribution and deformation results of the simulated domain. The analysis shows that horizontal deformation caused by seepage flow plays a very important role in deformation field, which may lead to toppling behavior to the foundation of high-rise buildings.

Ground Behaviors due to Seepage Force of Groundwater

Well pumping leads to both horizontal and vertical displacement, and fluctuation of groundwater level can cause serious damage to structures in a lagre affected area. Ground behaviors due to seepage force in traditional methods were rarely considered. This paper presents a numerical solution of ground displacement behaviors due to unsteady groundwater flow in unconfined aquifer by considering the effect of capillary zone based on the saturated-unsaturated seepage theory, and the numerical simulation code implemented by FORTRAN is applied to predict the flow velocity distribution and the results of ground displacement. The model uses the finite element method and finite difference method to study the problem. The analysis shows that the seepage force and the effect of capillary zone play a very important role in both seepage flow and displacement field.

MECHANICAL CHARACTERISTICS OF REINFORCEMENT SOIL BY BAGS

The soil-bag has the large bearing capacity to the external force, because the materials inside soil-bags are wrapped and confined completely by the bag. In this study, the compression tests and cyclic shear tests were performed to evaluate the mechanical characteristics of the soil-bags for the design of the reinforcement soil by bags. As the results, the experimental compression baring loads almost agree with the theoretical values and the characteristics of the high performance hysteresis damping of the piled up soil-bags were found out.

Consolidation Settlement Analyses on a Composite Foundation System Combined with Walled and Columniform Soil Improvement

To satisfy the geotechnical strength requirements and the serviceability requirements, types of foundation systems (such as shallow foundation, pile foundation and composite foundation) have been developed. Of course, the type of foundation system is determined by many factors such as ground condition, economy and environmental influence of construction. To cope with weak or compressible soils, the authors present a raft foundation system with walled and columniform soil improvement for multistory buildings, which is economical and environment-friendly. In this raft foundation system, different columniform soil improvements in size and depth are used, and the subgrade under the edge of the foundation is walled by soil improvement. It can effectively control differential settlement and prevent relative rising of the structure by adjusting the size and depth of columniform soil improvements according to the soil layer difference of geological situation under the building. We have performed series numerical analyses under two-dimensional plane strain condition to study the settlement behaviors of the composite foundation system, and its effects on controlling differential settlement and improving bearing capacity were verified for immediate condition. As a continuous research, consolidation settlement analyses are performed, the process of excess hydraulic pressure dispersion with time and the consolidation settlement development are studied in this paper.

An Elastoplastic Model Considering Sand Crushing

The behavior of sand crushing will appear when the confining pressure is up to a certain value, which results in disappearing of the positive dilatancy of sand. Adopting a new hardening parameter with the crushing stress, an elastoplastic constitutive model considering sand crushing is proposed. Comparing the conventional triaxial compression test results with the model prediction, it shows that the proposed model can reasonably describe the dilatancy of sand from positive to negative.