VALUATION OF EARTH PRESSURES ACTING ON FOUNDATIONS DURING STRONG

研制了一套扭转三轴剪切试验系统，可以测量主动和被动之间的土压力。试验结果表明，处于主动和被动状态之间的正常固结砂土的土压力可以用砂土的内摩擦角和小应变与大应变之间的应变率来表示。在此基础上，推广了Rankine和Coulomb的理论，得到了处于主动和被动状态之间的静力土压力公式。给出了地震作用下处于主动和被动状态之间的土压力的计算公式，并给出了计算作用在地下结构和挡土墙上的动土压力的方法。为了检验液化和侧向扩展地基中埋入地基和桩上的土压力，对已有文献记载的桩基实例进行了拟静力分析，并反算了桩的水平地基反力和最大反力的比例系数。分析结果表明：(1)桩的水平路基反力系数和横向扩展土的最大反力都是非液化土的0.05~0.2倍；(2)作用在埋入地基上的土压力随桩的刚度和埋入地基与周围地基的相对位移而由主动变为被动。

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.