不同应力历史条件下软黏土强度时效特性

Time-Dependency of Undrained Behavior of Natural Soft Clay with Different Pre-shearing Stress History Based on Laboratory Test

摘要:

采用恒定剪切速率的室内试验,对经历不同应力历史的天然软黏土的不排水强度时效特性进行了研究,探讨了软黏土不排水强度的时效特性、有效应力路径、不同应力历史的影响和软黏土应变速率变化对不排水强度的影响规律和影响程度.为了消除土体各向异性对试验结果的影响,对同一土样采用了变剪切速率的试验方法.土样在剪切前,采用了不同应力路径进行固结.试验结果表明,在三轴压缩条件下,剪切速率每提高10倍,不排水抗剪强度平均提高9.7%;三轴拉伸条件下,剪切速率每提高10倍,不排水抗剪强度平均提高7.2%.

Abstract:

The time-dependency of undrained behavior of the tested natural soft clay as well as the influence of pre-shearing stress history on the studied subject was examined based on experimental data.The tested clay was characterized by high water content and high plasticity with slight organic debris.Triaxial undrained constant strain rate(UCSR)tests were employed to study the strain-rate sensitivity of the undisturbed natural clay by using computerized testing system with stress-path controlled.The specimens were loaded to different stress state after re-consolidation with in-situ stress and pore pressure and before the UCSR tests were performed.The specimens were sheared at step-changing axial strain rates respectively to exclude the influence of instinctive heterogeneities of different specimens.The strain-rate dependent properties of undrained shear strength and effective stress path as well as the effect of pre-shearing stress history on the strain-rate dependent properties of the natural soft clay were examined based on triaxial UCSR experimental results.The results show that the undrained strength increases by 9.7% in compression tests and 7.2% in extension tests caused by the 10-times increased strain rates for the tested clay.