Experimental Research On Strength Of Unsaturated Expansive Soils

Unsaturated soils are widely distributed in the earth’s surface.Hydraulic engineering, civil engineering and so on are related to it. Because of the three-phase composition of solid, liquid and gas, the interaction between them make its properties very complex. The theory is not yet mature now.The insufficient knowledge of the strength characteristics of unsaturated soils often leads to increased project investment or major accidents.Piloting studies on strength characteristics of unsaturated soils which revealing its inherent laws is very necessary to further study on theory of unsaturated soil and engineering practice.In this paper take expansive soils at the entrance of Hefei NO.1 subway line for study.Direct shear instrument of unsaturated soils is used for the suction control shear tests of undisturbed soil,remolded soil and the pre-loading-unloading remolded soil samples.Explore the variation of shear strength parameters with matrix suction of the soils under different structure, stress history and other conditions.The results show that: the matrix suction have a significant impact on soil cohesion, its friction angle is less affected.Different soils’ friction angle is not the same as its suction, The suction friction angle of pre-loading-unloading remolded soil is the largest, undisturbed samples is middle, remodeling soil suction friction angle is the smallest.The unsaturated soil consolidation apparatus is used for remolded soil samples of its net pressure control shrinkage tests and the suction control consolidation tests.Obtained the general soil-water characteristic curve with different load conditions and the consolidation e-lgp curve with different suction of unsaturated expansive soil. Respectively discuss the relationship between the soil-water characteristic curve of unsaturated soils and the vertical loads,the relevant laws of unsaturated soils’ consolidation characteristics with different suction condition.The results showed that: different vertical loads corresponding to different soil-water characteristic curve.With the same saturation, vertical pressure of the sample corresponds to a small suction.The smaller the sample matrix suction, the greater the compression.Porosity smaller, more easily yield of the soil.Under the same suction conditions, both instantaneous settlement and primary consolidation settlement of Soil compression exist peaks.Finally, the suction characteristics of unsaturated expansive soils, shear strength formula of unsaturated soils, and the relationship between the soils’pre-stress and the shear behavior are analyzed.