VALUATION OF EARTH PRESSURES ACTING ON FOUNDATIONS DURING STRONG

研制了一套三轴扭剪试验系统，该系统可以测量处于主动和被动状态之间的土压力。试验结果表明，正常固结砂土在主动和被动状态下的土压力可以用砂土的内摩擦角和主、小轴应变之间的应变率来表示。根据这一发现，通过扩展朗肯和库仑提出的理论，确定了主动和被动状态之间的静土压力。同样地，在地震中，在主动和被动状态之间的土压力的公式和估计动土压力的方法作用于埋地结构和挡土墙。通过与前人研究结果的对比，验证了所提方法的有效性。为了研究在液化和横向扩展的地基中作用于嵌入式地基和桩的土压力，对桩基的充分记录的案例历史进行了拟静力分析，并反向计算了桩的水平路基反力和最大反力的比例因子。分析结果表明：(1)横向扩展土的桩的水平路基反力系数和最大反力均为非液化土的0.05 ~ 0.2倍；(2)桩的刚度和桩与周围地面的相对位移使作用于嵌入基础上的土压力由主动状态变为被动状态。

A torsion triaxial shear test system is developed with which earth pressures in between the active and passive states can be measured. The test results show that earth pressures of normally consolidated sand in between the active and passive states can be expressed in terms of the angle of internal friction of the sand and the strain rate between minor and major axial strains. Based on this finding static earth pressures in between the active and passive states are formulated by extending the theories presented by Rankine and Coulomb. Similarly, earth pressures in between the active and passive states during earthquakes are formulated and the methods to estimate dynamic earth pressures acting on buried structures and retaining walls are presented. The effectiveness of the proposed methods is confirmed based on the comparison with the results of previous studies.To examine the earth pressures acting on embedded foundations and piles in liquefied and laterally spreading ground, pseudo-static analyses are conducted for well-documented case histories of pile foundations and the scaling factors for the horizontal subgrade reaction of piles and for the maximum reaction force are back-calculated. The analytical results show that : (1) both the coefficient of the horizontal subgrade reaction of piles and the maximum reaction force of laterally-spreading soils are 0.05-0.2 times those of non-liquefied soils, and (2) the earth pressure acting on the embedded foundation varies from the active to passive state depending on the pile rigidity and relative displacement between the embedded foundation and the surrounding ground.