考虑主应力方向变化的原状软黏土应力应变性状试验研究

Experimental study of stress-strain properties of intact soft clay considering the change of principal stress direction

为反映真实工程条件下主应力轴旋转应力路径引起土体性状的变化,对杭州地区正常固结原状软黏土在固结不排水的主应力轴定向剪切和主应力轴单调旋转条件下的应力-应变关系进行试验研究。研究发现,不同主应力方向的定向剪切路径下,随主应力方向变化,试样中各应变发挥程度显著不同,但破坏时的临界八面体应变变化较为稳定,且当八面体应变达到5%时,强度发挥程度已接近甚至超过90%。若剪切过程中增加了主应力幅值不变的不排水主应力轴单调旋转应力路径,只要破坏时主应力方向一致,经历与未经历主应力轴旋转试样的临界应变分量接近,但主应力轴旋转会影响加载阶段试样主应力、主应变增量方向所表现出的不共轴性,并且此影响随旋转时剪应力水平的提高而趋于显著,即使在临界破坏状态下依然明显。试验结果表明,由于土体原生各向异性、黏塑性等性质的存在,并不适宜用相关联流动法则来分析主应力轴旋转条件下土体的应力-应变关系特征。

Experimental study of stress-strain relationship of normally consolidated intact soft clay in Hangzhou under undrained fixed shear of principal stress direction and monotonic rotation of principal stress axis had been done, which was used to reflect the soil properties response to the monotonic rotation of principal stress axis under real engineering conditions. It was found that under the fixed principal stress direction shear, strain components at different principal stress direction had quite different development levels, but the values of most samples＇ critical octahedral strain were comparatively close. Meanwhile, when the octahedral strain reached 5%, the development level of most samples＇ shear strengths had been closed to, even exceeded 90%. When additional stress path of monotonic rotation of principal stress axis was added to fixed shear of principal stress direction, samples critical strain components would not change obviously as long as the final failure principal stress directions were similar. But the direction of principal stress increment and the principal strain increment showed non-coaxiality during the rotation of principal stress axis; and with the development of shear stress level till critical state, such non-coaxiality became more obvious. The experimental results showed that due to the existence of initial anisotropy and viscoplasticity, it was not proper to describe the stress-strain relationship during and after rotation of principal stress with associated flow rule.