软黏土加载速率效应特性试验研究:进展与趋势

Progress and trend of experimental investigation on rate-dependent behavior of soft clays

大量的室内和现场试验都表明,软黏土的强度与变形速率相关。为了更深入地认识软黏土的加载速率效应特性,首先分析了一维应力条件下先期固结压力和三轴应力条件下不排水抗剪强度的加载速率效应及应力-应变关系的归一化,探讨了一维和三轴条件下的5个速率方程(2个指数形式和3个对数形式)在拟合黏土先期固结压力和不排水强度加载速率效应上的适用性;使用5个速率方程估计了一维和三轴条件下的加载速率参数,以及拟合了加载速率参数与液塑限的关系,并且分析了复杂应力(十字板剪切和旁压条件)下的非理想土单元体的黏土加载速率效应特性等;讨论了黏土加载速率效应特性在一维和三维、压缩与伸长、不同超固结比(OCR)条件下的统一性;最后,从香港黏土压缩与伸长和不同OCR条件下的剪缩、剪胀特性方面更深入地探讨了软黏土加载速率效应特性,并讨论了典型的剪缩、剪胀方程在黏土的力学特性模拟中的有效性。结果表明,为更好地描述黏土的应力剪胀特性,现有典型的剪胀关系需要更一步改进。

Extensive laboratory tests and field observations show that soft clay exhibits significant rate-dependent behavior. Based on published data from the view of the rate dependencies of preconsolidation pressure and undrained shear strength. The ratedependencies of soft clays under both 1D and 3D conditions are first studied. The applicability of five rate-dependency equations（two equations in exponential form and three equations in logarithmic form） in correlating the preconsolidation pressure and the undrained shear strength with strain-rate is then discussed. Rate parameters under both 1D and 3D conditions for various clays are estimated by using five rate-dependency equations and correlated with Atterberg limits. Furthermore, the rate-dependencies of soft clays under complex stress conditions including shear vane tests and pressuremeter tests are also analyzed. Then, the uniqueness of rate-dependency between 1D and 3D, between triaxial compression and extension, between different OCR（over consolidation ration） conditions is discussed. Finally, the influence of applied strain-rate on the stress-dilatancy of Hong Kong marine clay for triaxial compression and tension tests under different OCR conditions is investigated with some typical stress-dilatancy equations. The results show that the existing typical stress-dilatancy relationships need further enhancement（e.g., amount, anisotropy） for better describing the stress-dilatancy of soft clays.