Abstract：The suction is closely related to the mechanical characteristics of unsaturated soil，to explore the suction law of unsaturated soil，the total suction and matric suction of Jingmen unsaturated expansive soil are measured under six levels of compactness and thirteen levels of gravitational water content by using the filter paper method. The test cases cover almost the entire range of moisture and dense state of the expansive soil. Test results show that both the moisture and dense state have significant effect on the suction. With one fixed density，the suction of soil can increase greatly with the decreasing degree of saturation. On the other hand，under one fixed degree of saturation，the suction increases with the increasing density. The suction varies within wide range for the samples at the lower degree of density，whereas the suction for the samples at the higher degree of density changes gradually. Based on the test results，the constitutive formula is presented for predicting the suction which is the function of the degree of saturation and the void ratio. The comparison between tested suction and predicted suction indicates that the proposed constitutive formula can describe the suction law of compacted expansive soil in the may range of dense state and water-holding state.
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2013, Vol. 32 
