Experimental Study On Engineering Properties Of Sliding Zone Soils In Landslides

The landslide is one of the worst natural calamities, and it always causes tremendous losses in the live and properties of people. Compared with the deformation of other slopes, the instability of the landslide lies in one or more slip zones. Whether the landslide would lose stability depends on the stress state of the slip zone and the strength of the sliding zone soils, so the mechanism of the landslide is the deformation and failure of the sliding zone soils actually and a lot of work has been done on it as the important task of prevention and treatment for landslide.Based on the collected the related sliding zone soils physical and mechanical properties of research literature material, we find out the research situation and method of the sliding zone soils and point out existence insufficiency of research on engineering properties of it. That is to say, there are a few of researches on regional sliding zone soils consisting of special rock-mass and soil-body to meet the need of prevention and treatment for geological hazards. Therefore we focus on the sliding zone soils consisting of the soft and easily slipping hyllite, shale and slate in Longnan and Gannan, Gansu Province. The properties of slip soil such as physical properties, shear characteristics, microstructure characteristics and dynamic characteristics, are researched through investigation in the field and laboratory tests. The research achievement mainly has:(1) Physical properties researchThe properties of the sliding zone soils of Xieliupo and Suoertou landslide such as particle dimension, consistency and composition of rock and mineral specimens, are tested in the laboratory, the experiment results show that there is a bigger content of particle in Suoertou landslide and a bigger content of clay fraction in Xieliupo landslide. The slip soils of the two landslides have the same composition of rock and mineral which are mortar and shale but the slip soil of the Xieliupo landslide produces higher performance of water stability.(2) Shear characteristics researchAccording to direct shear test and repeatedly shear test of soils in sliding zone, the effects of the water on the shear are discussed. A series of large scale direct shear tests are conducted on the sliding zone soil of Suoertou landslide in order to study the influence of coarse-grained material on the shear characteristics, these studies indicate that the relationship between stress and strain is controlled by water content of slip soil, it shows a strain-softening phenomenon when water content is less than plastic limit and demonstrates the properties of strain-hardening as water content is greater than plastic limit. The stress-strain relationship of the large scale direct shear tests which can be simulated by using the hyperbola model better is different from direct shear.(3) Microstructure characteristics researchThe microstructure characteristics of sliding zone soil of Xieliupo landslide is studied to compare the differences of equiv diam, area fraction and orientation of pore between sliding zone soil and slip body soil, besides, the relationship between the microstructure fractal parameters of soil pores and shear strength is established based on the fractal geometry. The results show that the equiv diam and area fraction of the sliding zone soil is less than slip body soil, and there are more irregularly shaped pores which tend horizontally in the sliding zone soil. Finally the relationship among fractal dimension, void ratio and shear strength of soil is expounded, indicating that the shear strength increases and the void ratio decreases with the increase of the fractal dimension. It supplies a reference basis for forecasting the mechanical behavior of soil.(4) Dynamic characteristics researchIn order to discuss the motion behavior of sliding zone soil of Xieliupo landslide under dynamic load, the remolded soil samples are tested on triaxial compressor under consolidated and undrained conditions. The experiment results show that the dynamic cohesion decreases with the increase of the moisture content, but the dynamic friction angle has nothing to do with the moisture content. The dynamic elasticity modulus decreases in power exponent form with the increase of dynamic strain, and the relationship between dynamic stress and strain of sliding zone soil of Xieliupo landslide under the variation of water content can be described well with exponential function model.In summery, the physical and mechanical characteristics of the sliding zone soils consisting of the soft and easily slipping hyllite, shale and slate in Longnan and Gannan, Gansu Province, are studied, and the research theory and practical level of the special slip soil is enriched and consummated. References and consults offered in the paper will be useful in prevention and treatment of homogeneous landslides, and these are very instructive in reality.