主应力方向变化路径下等压固结粉土强度特性差异和能量评价方法研究

主应力轴方向旋转变化是地基在波浪、车辆等荷载作用下经受的一种复杂而典型动力路径特征，为研究粉土在不同主应力轴方向变换条件下的强度特性差异，以初始密实度为70％的长江入海口饱和粉土空心试样为对象开展主应力轴旋转、拉压交变动三轴和双幅扭剪三轴试验。试验发现，等压固结条件下3种路径均使试样出现小应变崩塌液化破坏，且崩塌应力状态，可在p’-q空间中用近似平行的一组准不稳定相态线归一。而在液化和崩塌振次上，以同剪应力峰值的动扭剪下最高，动三轴次之，主应力轴旋转最低。在此基础上，提出采用崩塌损耗能对不同路径下土体动强度进行评价，结果表明，崩塌损耗能与剪应力幅值无显著关系，而在上述3种动力路径中，试样崩塌损耗能依次降低，这与3种路径下得到崩塌时刻递增的有效围压特征相匹配。崩塌能强度标准的采用，克服了复杂动力路径下由于剪应力恒定或循环变化造成应力水平无法统一而干扰强度评价的不足

Strength characteristics of isotropically consolidated silt under change of principal stress orientation and correlative evaluation method with collapse energy

Principal stress rotation is a kind of typcial stress path supplied to the ground,when it is subjected to wave or vehicle loads.In order to study the strength characteristics of silt under different combinations of principal stress orientation, a series of hollow cylinder sample tests were performed with saturated silt of Dr = 70% from the sea entrance of the Yangtze river. The tests include cyclic principal stress rotation (CPSR), cyclic triaxial (CT) and cyclic torsional shear (CS) tests. It is found that isotropic consolidated samples under the above tests would collapse at minor strain and liquefaction, which is featured by the excess pore water pressure reached initial effective confining pressure. And the effective stress states at collapse points could be normalized by the parallel quasi-instable lines in the p’-q space. As to the liquefied and collapse cycles, CS had the maxium and CPSR had the minimum under the same peak values of shear stress. Furthermore the collapse energy is put forward to evaluate the dynamic strength under different paths. It is shown that the energy is related to the kinds of stress paths but not shear stress level. And the collapse energy decreased in CS, CT and CPSR in turns, which matched the characteristics of increased effective confining pressure at the collapse points under these three paths. The adoption of collapse energy overcame the interference of nonunified shear stress level on the failure criteria under complicated stress path, in which the shear stress might be constant or change cyclically.