Generalized Model Of Fissures Distribution & Slope Stability Analysis For Unsaturated Expansive Soils

"Two Chain" model for deformation and stability prediction of expansive soil slope is the framework for this research, in which it is considered that the reduction of strength of expansive soils during infiltration is mainly resulted on two aspects: 1) soils characteristics variation and 2) suction reduction while water content increasing. Focused on the former in this paper, the fissures of expansive soils regarded as most important characteristics are analyzed through laboratory test, field observation and numerical simulation. Scheduled experimental researches are carried out on quantificational description of fissures, healing of fissures during infiltration, seepage characteristics of fissures network and strength characteristics of fissured soil. Based on tests results, numerical models for fissures network seepage and unsaturated fissured expansive soil consolidation are developed and applied to a finite element method analysis of an expansive soil slope during infiltration under different fissures states.Firstly, the expansive soils fissures at test field in Zaoyang, Hubei province, are observed and counted by sketch and photograph, and expansive samples are by continuous photographic measurement using long-distance-microscope-system in laboratory. Generalized model of fissures distribution for unsaturated expansive soils is put forward. The conception of fissures degree is clarified and used to describe the fissures growth extent in unsaturated expansive soils. Numerical simulation and auto-generation of random fissures network are conducted by Monte Carlo method.Secondly, one-side immersion swelling tests are carried out, and time-travel expansive process regulations are obtained. A method is proposed to calculate expansive deformation of soils round fissures by time-travel expansive curve, and then to determine fissures' healing progress. Cycled shear tests for different part expansive soils and triaxial shear tests for different fissures growth extent expansive soils are carried out. The strength variation of expansive soils along with the variation of fissures degree and saturation degree is summed up, and fitting formulas are summarized.Finally, based on the test results, effective stress principle for unsaturated soils is developed. Numerical models for fissures network seepage and unsaturated fissured expansive soil consolidation are developed and finite element programs named USFEM and UCFEM are designed respectively. In the numerical models, fissures characteristics of seepage, deformation and strength are overall considered, and then fissures healing process can be simulated. The numerical models are applied to the analysis of water-air transmission, deformation and strength variation in an expansive soils slope during infiltration. The results of numerical simulation quantificational describe the influence of fissures position, fissures growth extent on expansive soils slope infiltration process, fissures healing process during infiltration as well as the variation process of soils strength and slope stability. The analyses on numerical simulation results reveal the characteristics of water-air-transmission and deformation in the unsaturated expansive soils slope during infiltration. According to numerical simulations, some suggestions are proposed for design and construction of expansive soils slope.