Experimental Study On Swelling And Shrinkage Deformation Characteristics Of Strong And Weak Expansive Soils

In this paper,some tests of properties of strong expansive soil in Chenggong of Yunnan and weak expansive soil in Meishan of Sichuan were finished by using the improved swelling force testing device,inflation rate testing device,porous scale plate device and ? ruler device respectively.These tests include expansion force test,expansion rate test,shrinkage rate test and the suction and swell-shrink cycling test.The main research results are as follows:1.Through the improved experiment device,the expansion force is measured and the relationship between inflation rate changes and moisture content are probably determined: After the expansion force reaching its maximum,it will not increase with the moisture content in weak expansive soil,while it decreases dramatically with the increase of moisture content in strong expansive soil;The expansion rate presents three stages during the increase of moisture content: fast,slow and stabilization.According to the test curve,the changing rules of expansion coefficient and moisture content are obtained,and the equations of expansion force and the expansion rate,which can provide effective help for engineering practice.2.Through the research and improvement of the porous scale plate test device,the relationship between the shrinkage deformation and moisture content is obtained,and three stages,which can be called fast,slow and stabilization,of shrinkage are determined.The time to achieve the three stages are roughly the same,and the vertical shrinkage value is greater than the radial shrinkage value.The causes of losing water and shrinkage during each stage are analyzed.According to the test curve,the relation between shrinkage coefficient and moisture content is obtained,and the line contraction and body contraction equation.The relationship between matrix suction and moisture content was obtained by filter paper tests,and it can be indicated that the contraction deformation was closely related to the substrate suction.3.Through the improved ? ruler swell-shrink cycle test device,by comparison of two plans(shrink before swell or swell before shrink),the conclusion is drawn as follows: When expansive soil shrink first and then expand,its swell-shrink deformation law is same as the results drawn by using traditional test device,and its relation between swell-shrink deformation and initial moisture content presents the opposite;When expansive soil expand first and then shrink,the expansion deformation is consistent with the experimental results of traditional device tests,while the law of shrinkage deformation is different from that of traditional tests.So that the experiment still needs further optimization and exploration.4.Through the comparison of the properties of expansion and contraction,it is concluded that the essence of swell-shrink deformation is caused by changes of soil moisture.Through the swell-shrink driving force and the mechanism of swell-shrink,the changes of micro deformation of expansive soil swell-shrink process are respectively analyzed,and the rationality and deficiency of the lattice expansion theory are obtained.Compared with the lattice expansion theory,the theory of double layer can explain the swell-shrink mechanism into full play.