砂土地基的黏性特性及其有限元模拟

Viscous properties of sandy foundation and its finite element simulation

采用非线性弹塑黏性有限元法模拟了砂土地基变速率加载室内试验,再现了砂土地基荷载-沉降曲线对加载速率突变、砂土蠕变以及应力松弛等加载情况下的响应和瞬时黏性中砂土黏性随加载进行的衰减现象。在有限元分析中,以非线性三要素模型为理论框架构建了可以综合考虑砂土黏性特性的弹塑黏性本构模型,用动态松弛法进行有限元求解,最后通过有限元与室内试验的对比分析研究了砂土地基所具有的黏性特性,同时验证了非线性三要素弹塑黏性模型用于模拟砂土黏性特征的合理性和正确性。

It is shown that sand has significant viscous properties related to loading rate. The stress-strain curve will jump abruptly upon a sudden change in strain rate. This strain rate effect will gradually fade as loading progresses. The TESRA(Temporary Effects of Strain Rate and its Acceleration) model which highlights the strain rate as the core variable rather than the conventional time variable is used to consider the viscous properties of sand. The dynamic relaxation-finite element method(DR-FEM), which has a high reputation in solving highly nonlinear geotechnical boundary value problems, is chosen as the numerical method. Return mapping method is used for stress update during the calculation. The laboratory tests on sandy foundation under variable loading rates were then simulated numerically by the nonlinear finite element method. The simulated results reproduced reasonably the load-settlement relations under loading conditions such as the changes of loading rate,creep and stress relaxation; and it also performed the decaying of viscosity as the loading progressed. Comparisons are made between test and simulated results to present the viscous properties of sandy foundation. The results also validated the rationality of the proposed nonlinear three-component visco-elastoplastic model for sand.