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

采用基于德雷西定律的排水控制在线试验，综合考虑循环加载对地基的软化作用和排水对地基体积变化的影响，研究了砂土的液化特性。我们开发了一个由线性定位台和活塞缸组成的精确排水控制系统。该系统能够直接控制体应变，减少了数据的散射，提高了控制精度。试验采用单位时间体积应变等于排水系数与超孔隙水压力乘积的控制规则。排水系数值越大，地表渗透率越高，排水距离越短。一系列不同排水系数的在线试验表明，从真正的不排水状态到排水状态，在修正了膜的顺应性后，剪切行为逐渐发生变化。在较低的加速度和较高的排水系数下，试样未发生液化。而当试件产生相当于有效围应力65% ~ 70%的超孔隙水压力时，由于排水不足，试件随即液化。同时对添加5%、10%和15%细粒（高岭土）的砂样进行了在线试验。细粒含量为5%时，其抗液化能力最强，随细粒含量的增加而降低。静三轴压缩试验中，纯砂强度最大，抗剪强度随细粒含量的增加而减小。而在细粒含量为5%的试件静力试验中，中应变区剪胀率最高，这可能反映在上述循环行为中。为了研究最大粒径和膜柔度的影响，还对砾石进行了一系列三轴试验。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