Study on Lipuefation Behavior of Sandy Ground Using Online Test with Drainage Control

采用基于Dynth定律的排水控制的在线试验方法，研究了桑迪地基的液化特性，该方法考虑了循环荷载引起的地基软化和排水引起的体积变化的影响。我们开发了一个系统，包括一个线性定位工作台和一个活塞缸精确排水控制。该系统采用单位时间体积应变等于排水系数与超静孔隙水压力乘积的控制规则，能够直接控制体积应变，减少了数据分散，提高了控制精度。排水系数值越大，对应的地基渗透性越强，排水距离越短。一系列不同排水系数的在线试验表明，从真正的不排水条件下的剪切行为的逐渐变化与修正的膜顺应排水条件。在 关于我们 在较高的排水系数下经受相对低的加速度的渗透物的情况下不液化。同时，当试件产生相当于有效围压65 ~ 70%的超静孔隙水压力时，由于排水不足，试件立即发生破坏。抗液化强度在细粉含量为5%时最高，然后随细粉含量的增加而降低。而在静三轴压缩试验中，纯砂的强度最大，抗剪强度随细粉含量的增加而降低。通过对砾石的三轴试验，研究了最大粒径和膜柔度对砾石力学性能的影响。少

The liquefaction behavior of sandy ground was investigated by means of the online test with drainage control based on Drecy's law, which incorporated both effects of the softening of ground due to cyclic loading and the volumetric change due to drainage. We developed a system consisting of a linear positioning table and a piston-cylinder for precise drainage control. The system was capable of direct control of volumetric strain, which reduced data scattering and improved precision in control.The tests employed a control rule in which the volumetric strain per unit time was equal to the product of a drainage coefficient and excess pore water pressure. The larger values of the drainage coefficients corresponded to the higher permeability of ground and the shorter drainage distance. A series of online tests with different drainage coefficients showed the gradual changes in shear behavior from truly undrained condition with correction for the membrance compliance to drained conditions. In … More the case of speciments subjected to relatively low accelerations under higher drainage coefficients did not liquefied. Meanwhile specimens that developed excess pore water pressure equivalent to 65 to 70 % of the effective confining stress did liquefy immediately after because insufficient drainage.The online tests were also carried out on sand specimens added with 5,10, and 15 % fines (kaolin). The resistance against liquefaction became highest in the specimens with 5 % fines, then decreased with increasing fine content. While in the case of static triaxial compression tests pure sand speciments showed the greatest strength and the shear strength decreased with increasing fine content. The static tests on the speciments with 5 % fines, however, showed the highest dilatancy ratio in the medium strain region, which might be reflected in the cyclic behavior mentioned above.A series of triaxial tests was also carried out on a gravel in order to study the effects of the maximum size and membrane compliance. Less