Study On Influence Of Sand Content On Frost Heave And Permeability Of Soil Material For Dam Construction In Plain Reservoir

With China's rapid economic development and population growth,the demand for water resources is increasing and the contradiction between supply and demand of water resources is becoming increasingly prominent.In order to alleviate the shortage of water resources in northern China,the South-to-North Water Diversion Project has been implemented.With the completion of the East Route of South-to-North Water Diversion Project,more plain reservoirs have been built in seasonal frozen areas in our country.The slope protection of plain reservoirs is mostly of underlying typical soil,and the damming strata are mostly Quaternary new diluvium,and the soil is mostly of soft soil such as silt soil and soft clay,belonging to strong frost heaving soil.Therefore,it is of great significance to study the frost heaving characteristics of soil materials on the dam slope of plain reservoirs for frost resistance design of plain reservoirs.Based on the“Twelfth Five-Year”Science and Technology Support Program?2015BAB07B05?Research and Demonstration of Health Diagnosis and Protection Technology for the Plain Reservoir of South-to-North Water Diversion Project during Operation",this paper takes the dam slope soil material of Da Tun Reservoir in seasonal frozen soil area as the research object,and determines the basic physical properties of the dam slope soil material through particle analysis test,compaction test and limit moisture content test.The test device of freezing temperature was improved,and a soil frost heaving rate tester was developed,which is suitable for testing different soils and freezing temperatures.The influence of sand content on freezing temperature,frost heaving rate and permeability coefficient of dam soil was studied by using research and development equipment,and engineering measures to improve dam slope soil were put forward,which provided reference for the construction of plain reservoir.The main conclusions of this paper are as follows:?1?The basic physical properties of the dam slope soil material were tested,including particle analysis test,compaction test and boundary water test.The maximum dry density was1.71g/cm³,and the optimum moisture content was 18%.?_L=32.2,plastic limit?_P=19.3,plasticity index I_P=12.9.It is determined by the above test that the dam slope soil is a low liquid limit clay,which belongs to strong frost heaving soil.?2?Using the improved freezing temperature test device,the freezing temperature of dam slope soil with different sand content was studied,and the freezing process of soil sample and the influence of sand content on dam slope soil were analyzed.The cooling and freezing of soil sample experienced three stages:super cooling occurs,latent heat of crystallization precipitated rapidly increased,and the temperature reached the temperature.The freezing temperature gradually increased with the increase of sand content.When the sand content exceeded 15%,the freezing temperature of soil sample increased slowly.?3?After freezing,the soil sample shows obvious water migration phenomenon.The water content at each position is obviously higher than the initial water content.The higher the sand content at the same position,the lower the water content of the soil sample after freezing is completed.The development process of frost heaving rate of soil samples can be divided into three stages:The first stage is freezing and shrinking stage.The second stage is the stage of rapid frost heaving growth.The third stage is frost heaving stabilization stage.The influence of sand content on the frost heaving rate of soil samples is analyzed,and it is found that the frost heaving rate of soil samples decreases with the increase of sand content,and when the sand content exceeds 25%,it turns into weak frost heaving.?4?The influence of sand content on the permeability coefficient of dam slope soil is studied through variable head permeability test,and it is concluded that when the sand content is less than 9%,the permeability coefficient gradually decreases with the increase of sand content,and when the sand content exceeds 9%,the permeability coefficient gradually increases with the increase of sand content.At 9%sand content,the permeability coefficient appears to be at least6)=2.65×10^-5 cm/sThe research results have certain reference value and guiding significance in frost resistance and seepage prevention design of plain reservoir dam slope.