Evaluation And Experimental Study Of Earth Pressure For Anisotropic Sand Under Any Lateral Deformation

Evaluation of earth pressures is of practical significance for the design of retaining structures such as retaining walls, sheet pile bulkheads, bridge abutments, and basement walls of buildings. It is one of the key research subjects in soil mechanics and geotechnical engineering. In this dissertation previous researches on earth pressures against rigid retaining structures are reviewed critically and systematically. Experimental and theoretical investigations are made on the mechanism of generation and methodologies of evaluation for the earth pressures induced due to anisotropic sandy backfill against rigid retaining walls that fall at an intermediate state from active to passive states. Several new main achievements obtained in such studies are as follows:1) A new strain-path controlled test system is developed based on a triaxial test apparatus. The devise can be well applied to the studies on the stress-strain behaviors of anisotropic sand under the condition where axial and lateral stresses are exerted along different constant strain increment ratio paths. A new centrifugal model test facility is developed to investiagte the variations in the earth pressure with the wall displacement from the at rest state to active state for the rigid retaining wall system. Experimental facts confirmed the good precision and effectiveness of the above two devises.2) Quantitative influence of the anisotropy of sandy backfill on the relationship of the earth pressure coefficient with the strain increment ratio is found from a series of soil element tests. Moreover, significant effects of the anisotropy on the variation of the earth pressure against a movable rigid retaining wall with the increasing lateral soil deformation are confirmed from the centrifugal model tests. Test results show that, in comparison with the backfill of isotropic sand, anisotropy can result in an obvious increase of the coefficient of earth pressure at rest from 15 to 50%, but it has a little effect on the coefficient of active earth pressure. It is postulated from experimental analysis that anisotropy leads to the decrease of the earth pressure at passive side.3) Compression-dilatancy coupling effect is found to be responsibe for the dependency of the change of the earth pressure on the strain increment ratio and also the lateral strain constraint of the backfill. The key issue in the study of earth pressure under any lateral deformation is to establish the quantitative relationship between stress ratio corresponding to the asymptotic state and strain increment ratio. New asymptotic state criterion is proposed to describe the effect of anisotropy on the above relationship. In addition, an asymptotic state criterion is suggested to determine the above relationship for isotropic sand under three-dimensional stress states.4) Methodologies and formulas proposed by Zhang et al (1998) to evaluate the earth pressure under any lateral deformation are extended to be more suitable and effective in the evaluation of earth pressures for three conditions including i) the wall rotation about some point above the top, ii) all the stress states at the passive side and iii) the backfill of over-consolidated sand. New methodologies and formulas are proposed to evaluate the earth pressure for anisotropic backfill from the state at rest to the active state, and their essential effectiveness are confirmed experimentally.