Study On Natural Foundation Stability In Dolomite Areas With Strong Degree Of Karst Development In Liuzhou City Of Guangxi

This paper studies the natural foundation stability in dolomite areas with strong karst development in Liuzhou city of Guangxi province, and analysises the main influencing factors of natural foundation stability on the base of karst collapse case occurred in Liuzhou dolomite region in recent years. Then studies the stability of karst cave roof based on the theory of small deflection of circular plate, and then researches the expansion mechanism of soil cavity and the changes in stress-strain around soil cavity by considering the influence of the changes of groundwater table caused by human engineering activities. Last this paper uses Analytic Hierarchy Process(AHP) to evaluate the karst collapse risk of a construction site. This paper has got the following results through above research.(1) This paper considering the development degree of shallow karst, landform, stratum lithology, and groundwater as the main influencing factors of karst collapse besides considering human engineering activities. While human engineering activities are the main inducing factors of karst collapse in recent years.(2) Some different results can be got by considering the influence of ratio of karst cavity roof thickness to its span on stress. The impact of ratio on the maximum tensile stress of roof is unconspicuous when the ratio greater than 0.5, but the ratio have a significant impact on the maximum stress of roof when the ratio is less than 0.5, and the maximum tensile stress is increases sharply with the decrease of the ratio.(3) When a karst cave roof with local concentric symmetrical distributed uniform pressure, the influence of the ratio of karst-cavity-roof span to pile's diameter on the stability of karst cave roof should also be considered besides considering the influence of the ratio of karst-cavity-roof thickness to its span.(4) Groundwater shows a series of actions on the expanding of the soil cavity. The plastic and elastic zone around the soil cavity changes with the fluctuations of undergroundwater table, which leads to the variation of deformation, stress and strain of soil mass around soil cavity.Then leads to form a loose circle in the interface of elastic-plastic zone around soil cavity.(5) The safety factor of karst cavity roof is greater than 1.4 when the karst cavity roof thickness to its span is greater than 1.0 if the basic quality degree of rock mass of karst cavity roof is?and ?.