Microbial (or bio-) desaturation is a new method for mitigation of the liquefaction hazard of sand. In this paper, a series of monotonic and cyclic triaxial tests was performed on bio-desaturated sand under undrained conditions to demonstrate that the bio-desaturation method is effective in enhancing the liquefaction resistance of sand under either monotonic or cyclic loading conditions. The test results showed that, under monotonic loading, the undrained shear strength increased by more than two times and the behaviour of soil changed from strain softening to strain hardening when the degree of saturation (S_r) reduced from 100% to 86·4%. The undrained shear strength ratio (s_u/p′₀) has a unique relationship with the peak excess pore water pressure ratio (Δu_max/σ′_c) regardless of different effective confining stress conditions. Under the applied cyclic load, the liquefaction resistance showed a significant increase when the sample was slightly desaturated. For the same cyclic stress ratio and number of cycles, the accumulated excess pore water pressure (Δu) in the sample with a degree of saturation of 96% was only a quarter of that in the fully saturated sample. The instability behaviour of sand was also studied. The results showed that the slope of the instability line, which is a measurement of the resistance of sand to collapse, also increased with the reduction in degree of saturation under monotonic loading. The failure stresses obtained in cyclic triaxial tests conducted under different cyclic stress ratios coincide with the instability line obtained under monotonic conditions for sand with the same degree of saturation. This provides good support for the use of the instability line to predict the failure stress state of sand for both monotonic and cyclic loading conditions.

中文翻译：

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不排水单调和循环荷载作用下生物饱和砂的应力应变行为

微生物（或生物）去饱和是减轻砂土液化危害的一种新方法。本文在不排水条件下对生物饱和砂进行了一系列的单调和循环三轴试验，证明了生物去饱和方法可以有效地提高单调或循环载荷条件下砂的抗液化性。试验结果表明，当饱和度（S _r）从100％降低到86·4％时，在单调荷载下，不排水的抗剪强度提高了两倍以上，土壤的行为从应变软化变为应变硬化。。不排水剪切强度比（š _û / p ' ₀）具有与所述峰值孔压比（Δ的唯一关系ü_最大值/ σ ' _ç不管不同有效围胁迫条件下）。在施加的循环载荷下，当样品略微降低饱和度时，抗液化性显着提高。为周期的相同循环应力比和数目，累积孔隙水压力（Δ û）样品中饱和度为96％的样品）仅为完全饱和样品中样品的四分之一。还研究了沙子的不稳定性行为。结果表明，在单调加载下，饱和线减小时，失稳线的斜率（用于衡量砂土的抗倒塌性）也会增加。在不同的循环应力比下进行的循环三轴试验中获得的破坏应力与在饱和度相同的情况下在单调条件下获得的失稳线一致。这为使用不稳定性线来预测沙子在单调和循环载荷条件下的破坏应力状态提供了良好的支持。