Abstract
In order to probe into one simplified method to predict the shear strength of Shaoxing unsaturated silty clay, the test method combining unsaturated soil consolidation instrument and conventional direct shear instrument is used to study the shear strength, and the method is compared and verified with the results of equal suction direct shear test. The research results show that the soil water characteristic curve fitted by the measured data points and VG model has obvious stage characteristics in the range of 0~38 kPa, 38~910 kPa, and 910~10000 kPa. The shear strength of unsaturated soil measured by consolidation meter combined with conventional direct shear test is in good agreement with that measured by equal suction direct shear test in the range of 0~500 kPa. The results show that the shear strength, total cohesion, and effective internal friction angle of soil increase slightly with the increase of matric suction in the range of 0~38 kPa. When the matric suction increases from 38 kPa to 500 kPa, the shear strength and total cohesion force of the soil have similar stage characteristics with the SWCC, which first increases and then tends to be stable, while the effective internal friction angle changes slightly. Finally, taking the air-entry value as the demarcation point, an improved model of unsaturated shear strength is proposed by analyzing the error value. Compared with the measured value, the absolute value of relative error is basically kept in the range of 5%~10%, which is close to the measured value.
Highlights
Unsaturated soils widely exist in nature, and their engineering properties are quite different from saturated soils
The infiltration of rainwater during rainfall affects the negative pressure of the pore water which decreases the additional shear strength of the unsaturated soils and leads to slope failure [1, 5,6,7]
Based on the soil-water characteristic curve obtained in the above test (Figure 2), samples are taken according to the volume water content corresponding to the matric suction of 25 kPa, 38 kPa, 50 kPa, 75 kPa, 100 kPa, 150 kPa, 200 kPa, 300 kPa, 400 kPa, and 500 kPa, and the volume water content corresponding to the suction path is 43.3%, 41.8%, 40.4%, 37.4%, 34.8%, 30.8%, 28.8%, 24.4%, 22.3%, and 20.9%, respectively
Summary
Unsaturated soils widely exist in nature, and their engineering properties are quite different from saturated soils. Mohr-Coulomb strength theory has been confirmed by a large number of tests and engineering practice It can accurately determine the shear strength of saturated soil. According to the influence of matric suction on the cohesion and internal friction angle of unsaturated soil, many scholars used the Mohr-Coulomb strength failure criterion of saturated soil and the measured shear strength parameters of saturated soil and soil-water characteristic curve to predict the shear strength of unsaturated soil. The influence of matric suction on the shear strength of soil is analyzed by combining the unsaturated soil consolidation test with the conventional direct shear test and by comparing and checking the partial equal suction direct shear test. At the same time, based on the soil-water characteristic curve fitted by VG model, the shear strength prediction values of three typical models are calculated, and the model is improved through error analysis
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