Experimental Research On Residual Strength And Modified With Cement Of Expansive Soil

Expansive soil is a kind of clay with cracks,rich hydrophilic minerals and obvious swelling and shrinkage characteristics formed under special geological conditions.Expansive soils are widely distributed all over the world.From lake sediments to shale,they may be expansive soils.Many countries,such as South Africa,China,Myanmar,the United States,Canada,the United Kingdom,India and so on,raised their problems in expansive soil treatment at the international conference.Expansive soils have been found in many provinces in China,among which Anhui is one of the most widely distributed provinces.Expansive soils have been found in Hefei,Fuyang and Luan.The special properties of expansive soil determine the instability and failure of expansive soil foundation or slope.The main reason for this instability is the residual strength of the expansive soil.The residual strength of the expansive soil is obtained from the gradual attenuation of the shear peak strength of the soil.Therefore,in the analysis of expansive soil foundation and slope stability,we should focus on the peak residual strength,so it is necessary to improve the safety of the project by controlling expansive soil.In some foundation treatment,chemical solidifying agent is added to reinforce the slope and foundation.The commonly used chemical solidifying agents at home and abroad include lime,fly ash,cement and so on.Cement can not only effectively improve the performance of expansive soil,but also lightly pollute the environment.Compared with other chemical treatment agents,it is more suitable for improving expansive soil.In this paper,the expansive soil in Hefei area was studied by strain type direct shear apparatus,residual strength tester,electron microscope and related data processing software.Through indoor physical properties index,the basic parameters of soil are obtained,and the influence of water content and vertical normal stress on shear strength and residual strength of soil is obtained.The main contents of this paper are as follows: 1.The indoor physical properties of expansive soil mixed with different proportions of cement,the results of improving expansive soil by cement,and the shear strength of expansive soil mixed with ash.(1)Firstly,the research situation of expansive soil at home and abroad isreviewed,and the distribution,burial depth,macroscopic and microscopic characteristics of expansive soil in Hefei area are analyzed.The swelling-shrinkage characteristics,influencing factors and distribution of expansive soil are studied scientifically and systematically,and the relationship between expansive characteristics and burial depth is clarified.(2)The residual strength characteristics of saturated expansive soils were studied by four times of cyclic shear at slow shear rate under different vertical stresses.The relationship between initial water content,vertical normal stress and residual strength is analyzed.The unsaturated weak expansive soil is tested by four times of repeated shear tests under different vertical stresses.The residual strength characteristics of weak expansive soil with different initial water content under different vertical stresses are analyzed,and the relationship and difference between them.(3)Through the air-drying of expansive soil,the influence of mixing ash on dry density,liquid-plastic limit and free expansion rate of expansive soil is studied.The change of shear strength of remolded expansive soil after mixing ash is analyzed systematically,and the influence of mixing ash rate on C and ? is revealed.