交通荷载应力路径下K_0固结软黏土变形特性试验研究

Deformation behavior of K_0-consolidated soft clay under traffic load-induced stress paths

交通荷载作用下,软黏土路基土单元体上所受主应力的大小和方向是同时变化的,即在剪应力幅值改变的同时主应力轴连续旋转。针对该问题,利用GDS空心圆柱系统对K_0固结天然温州软黏土进行不排水大数目(10000次)循环扭剪试验,分析了K_0固结软黏土在考虑主应力轴旋转时不同动应力水平下的应变特性。试验结果表明:主应力轴旋转的存在将使土体内产生更高的孔压,并在轴向上产生额外变形,且随着扭剪应力的等幅增加,竖向应变和孔压的增加量将越来越大。考虑主应力轴旋转时不同动应力水平下K_0固结软黏土的变形发展模式有所不同,可由安定理论进行解释。确定了考虑主应力轴旋转下K_0固结温州软黏土的临界动应力水平——即门槛循环应力比、容许循环应力比和临界循环应力比的范围。提出可将容许循环应力比作为道路工程沉降控制的准则。与三轴试验结果相比,考虑主应力轴旋转时,道路设计中对动应力的控制应更为严格。

Under waffle loads, the magnitudes and directions of the principal stresses applied in the soil elements of soft subgrade change simultaneously. Namely, as the shear stress changes in amplitudes, the principal stress axes continuously rotate. For this problem, a series of undrained long-term （10000 cycles） cyclic torsional tests on the natural Wenzhou soR clay after K0 consolidation are conducted using the GDS hollow cylinder apparatus. The deformation behavior of the K0-consolidated natural Wenzhou soft clay under different dynamic stress levels considering the rotation of the principal stress axes thereby is analyzed. The test results show that the rotation of the principal stress axes causes a higher pore pressure in the soil and an extra strain in the vertical. Besides, with the equidifferent increase of the torsional shear stress, the increments in both vertical sWain and pore pressure grow up gradually. Considering the diversity of deformation development pattern of K0-consolidated soft clay under different dynamic stress levels considering the rotation of the principal stress axes, the shakedown theory is utilized. Thus, the scopes of the critical dynamic stress levels, namely the threshold cyclic stress ratio, the allowable cyclic stress ratio and the critical cyclic stress ratio of K0-consolidated soft clay considering the rotation of the principal stress axes are determined. It is proposed that the allowable cyclic stress ratio should be the criterion of settlement control for road engineering. Compared with the results of triaxial tests, when considering the rotation of principal stress axes, the control of dynamic stress in road engineering should be stricter.