Experimental Study On Unsaturated Creep Characteristics Of The Sliding Zone Soils Of Weijiagou Landslide

Sliding zone is one of the most important structural elements of the landslide. Forming with the development of a landside, slip soil is a kind of special rock and soil mass, of which the creep behaviors directly reflect a landslide’s evolvement process. Based on numerous studies, most of landslides were caused by water which played a decisive role. Rainfall is the main cause of Weijiapo landslide instability, slip soil changes between saturation and unsaturation on the effect of ground water level responsible to rainfall. As a result, soil shear strength and landside stability decreased greatly, and slip soil exhibits as unsaturated soil considering strength and deformation. Furthermore, landslide’s evolvement process has time responses, namely rheological behaviors. Classical saturated soil theory based on saturated soil research failed to describe the mechanical properties of unsaturated soil, and it’s meaningful to study on the creep characteristics of unsaturated slip soil.Series of unsaturated triaxial creep tests on slip soil were taken using Chen’s loading method. With the change of confined pressure, matric suction and stress level, different unsaturated soil creep levels were obtained. The main results were concluded as follows:(1) Geological characteristics and inducement mechanism of Weijiapo landslide were analyzed, and basic physical mechanics property indexes including shear strength were obtained by series of laboratory tests.(2) Unsaturated soil triaxial creep apparatus was used to test on unsaturated slip soil of Weijiapo landslide in different confined stress, matric suction and stress level with Chen’s loading method. And a series of step loading creep levels were obtained and analyzed in detail.(3) Based on laboratory tests, matric suction can be shown as a new kind of stress level was defined, and then new Singh-Mitchell model and new Mesri model were built considering matric suction. When compared the test curves with model curves, we found that the two kinds of curves fitted well. Considering Singh-Mitchell model adapted to the situation of stress level changing from 0.2 to 0.8, Mesri model was adopted to analyze the creep characteristics of unsaturated slip soil, and the unsaturated slip soil properties had a good reflection.(4) Burgers model was adopted to describe unsaturated slip soil of Weijiapo landslide, and factors of component model were obtained by fitting. With the help of FLAC 3D software, elastoplastic analysis without time considering and viscoplastic analysis with time considering were done respectively. At last, stress distribution, displacement change and plastic zone expansion were analyzed.