高速滑坡中的热效应分析

从理论和数值分析两方面讨论滑坡滑带内热致孔隙压力及其对高速滑坡的影响。首先给出土体动力平衡方程、热和孔压的产生与耗散方程构成的热–水压–力学模型,然后在该模型基础上讨论滑带(局部化剪切带)产生的条件,对滑带宽度的演化及影响因素进行分析,最后探讨土体变形产生热而导致高孔隙压力及低摩擦系数的问题。结果表明,当热软化效应超过应变硬化效应后,失稳就将发生。失稳后,土体发生剪切局部化变形,在滑坡的滑面内产生剧烈变形。一般情况下,滑带宽度是变化的,其变化对滑带内应变、应变率有很大的影响,从而导致滑带内孔隙压力、温度等的明显变化。滑坡的加速运动是由于剪切带中材料的变形,热被集中于剪切带内,而导致其中孔隙压力的快速上升和土体强度的快速下降引起的。

THERMO-EFFECT ON HIGH-SPEED LANDSLIDE

The effects of the thermal and the pore pressure generated by high-speed landslide are discussed. First, the controlling equations that govern the thermo-pore-mechanical phenomenon in high-speed landslide are given. Second,the initiation conditions of slide-band(shear band) and the evolution of the band are discussed. At last,the generation and diffusion of the thermal and pore pressure which may cause the obvious decrease of friction coefficient in slide-band are analyzed by numerical simulation. The results show that the instabilization,which is the precursor of the forming of slide-band , initiates once the thermo-softening effect overcomes the strain-hardening effect. After instabilization the localized shear strain becomes severe. Generally,the bandwidth develops with time,which can cause severe changes of the strain and the strain ratio in the band. The drastic changes of strain and strain ratio can cause distinct increase of pore pressure and temperature in the band. The accelerated motion is caused by material strain softening,which further promotes the material strain-rate softening inside the shear band. Owing to the speed of initiating process,heat is trapped inside the shear band,which leads rapidly to the increase of pore pressure,total loss of strength,and uninhibited sliding motion on a small-friction or frictionless base.