砂土液化后再固结体变规律表征与离心模型试验验证

Characterization of reconsolidation volumetric strain of liquefied sand and validation by centrifuge model tests

针对一定相对密度的饱和砂土,首先开展单元体K0固结试验和振动液化试验研究,发现饱和砂土液化后体变规律受再沉积和再固结两种机制制约:其中再沉积部分与所受振动历史密切相关,尤其是液化触发后的应变历史,土骨架累积剪应变比越大、再沉积体变越大;而再固结部分受先期固结历史和循环振动历史影响显著,再固结曲线会沿原有正常固结曲线趋势发展,其稳定段再压缩指数比相同条件下的正常固结曲线的压缩指数稍大。据此提出了考虑先期固结和振动历史的砂土液化后体变模型和简化算法,将再沉积和再固结两者统一表达成再固结体变,并建议了再固结压缩指数和假设起始应力的确定方法。进一步开展了水平场地地震液化离心机模型试验,监测模型固结和振动液化过程的沉降,从模型尺度进一步揭示砂土液化后体变规律,并初步验证了本文模型与简化算法的有效性。

The results of consolidation tests under K0 condition and cyclic triaxial tests on Fujian sand at a given relative density are introduced, and the mechanism of the liquefaction-induced volumetric strain is revealed, which is composed of the re-sedimentation and the re-consolidation processes. The re-sedimentation is closely related to the cyclic shear strain history, especially that after liquefaction, and the more the accumulated shear strain ratio is, the more the re-sedimentation volumetric is. Besides, the re-consolidation behavior is significantly affected by the previous consolidation history and cyclic stress history, and the post-liquefaction reconsolidation will follow the trend of the previous normal consolidation curve, and the compression index is larger than that of the normal consolidation curve under the same conditions. A post-liquefaction volumetric strain model accounting for both the consolidation and cyclic shear strain histories is proposed, which treats the re-sedimentation as part of the re-consolidation by introducing the concept of assumed initial stress, and the estimation methods for re-compression index and the assumed initial stress are recommended accordingly. Then dynamic centrifuge model tests are performed, and the consolidation settlement and liquefaction responses are monitored, whereupon the mechanisms of liquefaction-induced volumetric strain are observed at the model scale, and the proposed model for post-liquefaction settlement estimation is preliminarily validated.