Study On The Permeability Law Of Deformation And Failure Of Guilin Sand

The sand layer in Guilin karst area is mainly located in the first grade terrace of Li River.The infiltration of surface water and seepage of groundwater will be happen,and those foundations will be easy to occur seepage deformation and failure during the extreme weather.Study on the permeability law of deformation and failure of the first order terraces of Guilin under the groundwater has important significance for selecting some suitable treatment schemes in different projects.According to the characteristics of gravels in the Li River of Guilin.Using a self-made seepage deformation instrument,through the control of grains gradation,compaction,clay content and the analysis of mineral composition,the deformation law of the regional sand is discussed.The main conclusions are as follows:(1)Under the condition of the same grain composition,the influence of different dry density on the stability of sand was studied by controlling the compaction degree of sands.The test results show that the permeability coefficient of sand decreased with the growth of dry density,which have high correlation.The larger the density,the larger the critical hydraulic gradient,the permeation damage slope has been increasing rapidly with the decrease of void ratio,and the variation range is larger than that of the critical value,which shows that the seepage velocity increases sharply after the failure of sands,the permeability of the seepage channel is enhanced.(2)Through studying on the control experiment of the permeation damage slope of different grain composition,it points out that there is relativity between the scope of permeation damage and its grain composition.The permeability coefficient is related to the non-uniformity coefficient and the curvature,which are increased with the growth of the permeability coefficient.The critical hydraulic gradient is negatively correlated with the non-uniformity coefficient and curvature.However,the failure hydraulic gradient had no obvious regularity.(3)According to the regional sand mixed with clay seepage deformation experiment,this paper explores the influence of fine particle effect on permeability damage.The results show that,this velocity of seepage failure is faster than that of sands without clay,the more the clay content is,the lower the permeability coefficient is.When the clay content is less than 10%,the permeability coefficient decreased greatly,when this content exceeds 10%,the permeability coefficient decreases slowly.However,the critical hydraulic gradient and damage slope increased while the clay content increased,mixed sands grow out of nothing,the clay makes its void ratio changed.(4)In the X-ray diffraction experiment.This test results show that,the clay sand,with different crystal structure,makes the activity of cohesive force changed,the clay shows"molasses” function which is distributed in the pore between sand grains,thus decreasing the permeability coefficient of sand.