Influence Of Bound Water On Physical And Mechanical Properties Of Loess

Loess has the characteristics of low density,low humidity,loose structure,porosity development,vertical fracture structure,and a certain collapsibility.The engineering characteristics of loess are closely related to its internal structure and water content.The increase of the bound water content will destroy the original structure and reduce the strength of loess.Based on the laboratory test,the thesis studies the bound water in the loess from a mesoscopic point of view and analyzes the effect of the bound water on its physical and mechanical properties.The following is the main contents:(1)Based on field sampling,the mineral composition,gradation and physical indicators of the undisturbed loess in different depths of Shichuan River in Fuping County,Shanxi Province were tested.The results show that clay mineral content is positively correlated with clay content,natural moisture content,liquid limit,and plasticity index.(2)Compression tests and direct shear tests for undisturbed loess in different depths are carried out.The results indicate that the more clay content there was at the natural moisture content,the greater the deformation and the smaller the shear strength of the loess under the same pressure.(3)Isothermal adsorption and thermogravimetric analysis were used to test the bound water of undisturbed loess in different depths,and the type of bound water was defined and quantified.Water-vapor equilibrium pressure of 0.9 is the critical point of strong and weakly bound water.The thermal weightlessness interval corresponding to strong bound water is 120?~230?,while is 75?~120? with weakly bound water.(4)The compression tests and direct shear tests of undisturbed and reconstituted loess samples with different moisture contents were carried out to analyze the influence of different states of bound water on the mechanical properties of loess.The test results show that strong bound water has little effect on the strength and deformation of loess.However,the weakly bound water has a significant effect on its deformation and strength.