Experimental Study On Structural Strength And Shear Strength Of The Unsaturated Loess

Loess is a Quaternary deposit in the arid and half arid area,is one kind of typical structural soil,its special structure and special sensitivity to water affect on the characteristics of engineering mechanics of loess. Alonged with our country's west exploitation strategy has been implementing, the quantity and scale of foundation engineering construction was increased suddenly in northwest loess area,enabled the research on Strength characteristics of unsaturated loess have great practical significance .In this paper, based on the observation and analysis of a large number of literature references, through series of static test on unsaturated loess(such as intact loess, disturbed loess and saturated intact loess), the variation characteristics of soil structure and strength of loess are earnestly researched. Above all,based on analyzing the structure characteristics and its developing mechanism, the intact loess'Structural Strength have been studied by Triaxial Shear Tests. As the result of the test shows:The strength of loess is formed by Structural Strength and compaction strength, and the Structural Strength can be expressed by the difference of Principal Stress between intact loess and disturbed loess,the curve of structural strength exerting process reflects that structural strength changes from strain;there is an obvious power function relationship between the structural strength and initial water content,and the structural strength increases with the increasing of the Confining Pressure under the same initial water content;the loess'structural strength is linearly related to its cohesion.And then, this paper analyzed the history of the study on structure of soil,and also analyzed the Micromechanism of loess'structure. By the Triaxial Shear Tests of intact loess,disturbed loess and saturated intact loess,This paper adopts a conception labelled structure parameter which is expressed on the base of stress,also named strain comprehensive structure potential parameters. through this structure parameter , we have studied structure characteristics of intact loess,the results show that this structure parameter can roundly affects the connection and arrangement of the loess'structure,and the shape of stress-strain curves has became congruously after applied this parameter.On the base of study on loess'Structural Strength,the shear strength indexes of disturbed loess is studied,analyzed the variation law of index changed with water content and dry density,the variation law of soil sample's volume also studied. The research results shows:the cohesion of disturbed loess is decreases with increase of water content,the change law of Internal Friction Angle of loess is same to cohesion,it also decreases with increase of water content. cohesion is increases as the dry density increases,but as to Internal Friction Angle,at low water content,Friction Angle increase at the previous period and decrease at the later period with the increase of the dry density,at high water content,Friction Angle stayed increase with the increase of the dry density. At low water content or low confining pressure,the volume of soil sample was bulged in the course of shearing,at high water content,the volume was decreased under different confining pressure. Under the same axial strain and same confining pressure,the volume strain of intact loess is less than that of disturbed loess.