| The project of diverting water from Yangtse River to Huai River is a major trans-regional water diversion project,which needs to pass through a large amount of expansive soil area.In order to ensure the stability of the project in the expansive soil area,it is necessary to treat the expansive soil.Considering that the sandstone reserves of the Ji-Huai River Diversion Project are abundant,in order to make full use of the site resources,this paper analyzes the feasibility of improving the expansive soil by using sandstone abandoned materials from river excavation based on laboratory tests.After the sandstone is crushed,the improvement effect is studied from four aspects: the influence of sandstone on the basic physical properties of expansive soil,the influence of expansive characteristics,the influence of strength characteristics and the influence of microstructure.The main conclusions are as follows:(1)Influence of rock powder on basic physical properties of expansive soil.The test results show that sandstone can change the hydrophilic and compressive characteristics of soil samples with different rock ratios.(2)Influence of rock powder on dilatability of expansive soil.Through the free expansion rate of soil samples with different rock mixing ratios,it is concluded that the method of improving expansive soil by mixing rock powder is feasible.The addition of rock powder can effectively reduce the expansion rate of soil samples.The results show that the increase of water content and rock mixing will decrease the no-load expansion rate of the soil samples,while the increase of initial dry density will increase the no-load expansion rate of the soil samples.With initial moisture content,initial dry density and rock mixing ratio as control variables,orthogonal tests were conducted to analyze the sensitivity of different variables to the charged expansion rate of expansive soil.After comprehensive consideration,the optimal scheme was determined when the initial moisture content was 20.5%,the initial dry density was 1.54 g·cm-3,and the rock mixing ratio was 20%.(3)Influence of rock powder on strength characteristics of expansive soil.The direct shear tests under different initial water content and rock mixing ratio show that the increase of water content will lead to the decrease of cohesion and internal friction Angle of soil samples when the rock mixing ratio remains unchanged.When the water content is constant,the increase of rock mixing ratio will lead to the decrease of cohesion and increase of internal friction Angle of soil samples.Triaxial tests are carried out on the samples with different rock mixing ratios and confining pressures.The results show that the maximum shear stress of the samples increases first and then decreases with the increase of rock mixing ratio under the condition that the confining pressure remains unchanged.When the rock mixing ratio is 20%,the maximum shear stress reaches the maximum value.When the rock powder content remains unchanged,the increase of confining pressure will lead to the increase of triaxial shear strength of the sample.(4)Influence of rock powder on microstructure of expansive soil.The expansive soil particles without rock powder are mainly flaky,and there are micro-pores and micro-cracks of different shapes and sizes distributed among the aggregates.After the addition of rock powder,the microstructure of expansive soil changes greatly,and a large number of rock powder particles are filled between expansive soil particles,which makes the connections between micro-aggregates closer,and the particles are interbedded to form a whole. |
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