| Unsaturated soil is widely distributed on the surface of the earth.The engineering properties of unsaturated soil are very different from that of saturated soil.Due to the unsaturated soil research is more complex,the current research results are far from the point of engineering construction needing.The theory of saturated soil is used to approximate the strength parameters of unsaturated soil,which is unfavorable to the actual engineering cost and safety,etc.Especially in the excavation and slope engineering,the use of saturated soil parameters for design is conservative,when rains it will affect the stability of the slope.Therefore,how to make full use of the shear strength characteristics of unsaturated soil is one of the key problems in the foundation pit and slope stability analysis.Ground water level is low in Shijiazhuang region of Hebei province,the vast majority of the soil is in the unsaturated state.As urban subway project and the construction of the high-rise buildings,unsaturated soil research is put forward higher requirements in foundation pit supporting,and the slope stability problem in this region.Therefore,this paper,the intensity of regional unsaturated soil in Shijiazhuang area are studied.the main research is as follows:(1)The soil-water characteristic curves of regional unsaturated silty clay in Shijiazhuang area are measured.The experimental results of two kinds of soil samples are compared with the experimental results of saturated and non saturated gas.Research shows that the test of undisturbed soil and remolded soil after extraction of saturated and without saturated extraction process conditions,soil water characteristic curve there are no obvious difference.The unsaturated soil intake value of undisturbed soil is between 50kPa-80 kPa,and the air inlet of unsaturated soil is between 130 kPa and 80 kPa.This suggests that undisturbed soil and remolded soil under the same experimental conditions soil water characteristic curve is different.(2)By fitting analysis of the soil water characteristic curve of the experimental results using Garden equation and Fredlund & Xing equation,the fitting results of the regional soil using Garden equation are better than the Fredlund & Xing equation,but the overall fitting results are not satisfactory.In this paper,the three parameter equation of the unsaturated soil in the region is proposed,which is better than the Garden equation.(3)In this experiment,the shear strength index of unsaturated soil was found to carry out the three-axis UU test,and the shear strength index of unsaturated soil was larger than that of three-axis CD test.The strength index of direct shear strength of unsaturated undisturbed soil is less than the strength of the three axis UU test.The friction angle of the soil samples obtained from the saturated undisturbed soil and the undisturbed unsaturated soil UU is close to the soil sample,But sticky cohesion cohesion is smaller than the undisturbed unsaturated soil saturated soil samples.(4)The non saturated soil three axis CD test shows that the effect of the matrix suction onthe effective internal friction angle of unsaturated soil in the area is small,and the effect of the soil sample is more effective.With the increase of the matrix suction,the effective cohesion of the matrix suction is increased from 68.3% to 91.75%.(5)on the basis of these results of soil water characteristic curve and shear strength test,numerical analysis software ABAQUS was used to analyze the stability of unsaturated soil slope under rainfall condition.The study found when soil strength index is high,at the same time the rainfall reaches 72 h,the slope soil vertical when settlement than the low intensity index decreased 14.6 %,slope stability is improved. |
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