基于耗散能量的饱和黄土动孔压模型

Dynamic pore pressure model for saturated loess based on dissipative energy

通过一系列不排水动三轴试验探究了饱和黄土振动液化过程中孔隙水压力和累积耗散能量的演化模式,并讨论了围压、动应力幅值和固结应力比对其演化过程的影响。结果表明:饱和黄土的孔隙水压力和耗散能量随着循环荷载作用逐渐累积。固结围压抑制孔隙水压力增长而消耗更多能量;更大的动应力幅值使得孔隙水压力增长更快而消耗能量更少;等压固结下,孔隙水压力增长至围压从而触发初始液化,而偏压固结下,通常先达到振动液化应变标准而孔隙水压力并没有增长至围压水平,并且固结应力比越大,液化时孔隙水压力越小,消耗能量也更少。归一化孔隙水压力u/σ0’与累积耗散能量W/Wf之间关系受围压、循环应力比和固结应力比影响较小,可统一用双曲线模型表示。

A series of undrained dynamic triaxial tests is carried out to investigate the evolution patterns of pore water and accumulative dissipated energy during the vibration-induced liquefaction of saturated loess,and the effects of confining pressure,dynamic stress amplitude and consolidation stress ratio on them are discussed.The results show that the pore water pressure and dissipated energy of saturated loess gradually build-up with the increase of cyclic loading times during vibration-induced liquefaction.The consolidation confining pressure inhibits the increase of pore water pressure and consumes more energy.Larger dynamic stress amplitude leads to faster increase in pore water pressure and less energy consumption.Under the isotropic consolidation,the increase of pore water pressure causes the effective stress to be 0,thus triggering the initial liquefaction.However,under anisotropic consolidation,the specimen usually reaches the strain criterion for liquefaction first,while the pore water pressure does not increase to the confining pressure level,and the larger consolidation stress ratio leads to the lower pore water pressure and less cumulative dissipated energy during liquefaction.The pore water pressure is closely related to the cumulative dissipated energy,and normalized pore water pressure u/σ0’and the cumulative dissipated energy W/Wf are less influenced by the confining pressure,dynamic stress amplitude and consolidation stress ratio and can be expressed uniformly in a hyperbolic model.