Research And Application Of Efficient Analysis System For Shear Strength Of Regional Unsaturated Soil

With the acceleration of urbanization, a large number of projects, such as, high buildings, subway and underground space, are under construction. With these large-scale civil engineering works, the stability of foundation of structures has attracted much attention. During the stability evaluation of deep dip and the high slopes, the shear strength plays an important role, which is the most important parameters of the soil mechanics. According to the current design applications, the determinations of parameters for shear strength are often based upon the tests from theory of saturated soil. However, in our country, especially in northern areas, most of the land is in arid or semi-arid state, where unsaturated soils are always encountered in practical engineering. Thus, in applications, the fact that by use of the theory of saturated soil engineering problems in unsaturated states is very unreasonable and not economical. Especially in the northern areas of deep excavation, how can reasonably accurately determine the slope stability by use of the shear strength from unsaturated theory have a great economic and scientific values.The soil samples used in this paper are from respective areas of Hebei region, which are Shijiazhuang, Zhangjiakou and Handan. Through the unsaturated triaxial test and the conventional tests, soil mechanics characteristics of unsaturated soils including of different types of unsaturated silt, silty clay from northern China. Meanwhile, the researches about strength characteristics and the permeability of unsaturated soil have made considerable progress. The relationship between the two parts, however, has no been fully considered. The soil water characteristic curve is a bridge connecting the two parts. By using of the soil water characteristic curve database in Hebei, simplified strength equation based on unsaturated theory is proposed in this paper. The following items are carried out in this paper.(1) The soil mechanics tests and unsaturated soil test from Shijiazhuang, Handan and Zhangjiakou are carried out firstly. For every sample parallel tests are need.(2) Lab conventional tests including triaxial compression test are carried out to understand each of the physical and mechanical properties of samples.(3) The suction effects for unsaturated soil under different confining pressures are tested.(4) Through around 40 years development unsaturated soil, many types of equations to describe the shear strength of unsaturated soil have been proposed by researchers. Among them, however, suction is regarded as an individual factor. Due to that suction is hard to be measured, the application of these equations is limited. Based on experimental results and the database of SWCC, a new type of formula to describe the strength behavior of unsaturated soil is proposed, among which no suction item is included. (5) Finally, the program for prediction of unsaturated soil based on the equations proposed is made. The difference between the predicted results and experimental results are analyzed. Well agreements can be observed.