With aggravation of disastrous climate in the world, geological disasters related to unsaturated soil mechanics in engineering construction activities have become more serious. These are mainly manifested in the following four aspects, expansibility, stability, flowability and effect on retaining structures. Based on mechanics theory of unsaturated soil and related studies, the mechanism of geological disasters is analyzed. The result shows that it is rainfall that causes moisture content of expansive soil increase, matric suction decrease, acting force of soil particle decline and expanding stress exceed matric suction. Expanding-shrinking deformation results in geological disasters. Rainfall infiltration causes matric suction of slope soil decrease and strength and stability of rock-soil mass decline, which triggers collapse and landslide. The developing course of debris-flow disaster is a process that materials change from unsaturated state to saturated state during rainfall. Matric suction plays a role of catalyst in this process. The changes of matric suction may cause strain and displacement of unsaturated soil mass, which generates interaction with retaining structures. The changes of its mechanical behavior and range of the changes are closely related with attenuation velocity of matric suction.%随着全球灾害性气候加剧,工程建设活动中与非饱和土力学有关的地质灾害问题也日益突出,主要表现为如下4个方面:胀缩性、稳定性、流动性和对围护结构影响.基于非饱和土力学理论和已有研究,分析总结和探讨了地质灾害的灾变机制,认为降雨致使膨胀土含水量增大,基质吸力减小,土粒间作用力下降,膨胀应力超过基质吸力的束缚作用,胀缩变形引发地质灾害;降雨人渗引起斜坡土体基质吸力降低,导致岩土体强度以及稳定性下降引发崩滑灾害;泥石流灾变过程即降雨时物料从非饱和状态转变为超饱和状态的过程,基质吸力在此过程中起到了"催化剂"作用;基质吸力变化会引起非饱和土体应变和位移,由此与围护结构产生相互作用,且其力学性态的变化及大小与基质吸力衰减速度密切相关.
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