| Expansive soil as one type of special soil shows significant swelling and contraction with the change of water content. The bearing capacity of expansive soil will take more substantial attenuation after flooding. Correspondingly, expansive soil slope has particular engineering stability which is distinct from property of other soils. This thesis takes the expansive soil slope on Shitian Highway as the research object, which is near the Wuhou service station on the highway in Mianxian County, Hanzhong City, Shanxi Province. By using several research methods included laboratory test, theoretical analysis, development of computer program and numerical simulation, the author conducted study for more insight into the basic characteristic of expansive soil firstly. Then the author carried out research on the rainfall-induced landslide’s mechanism and rainfall warning threshold for expansive soil slope considering the influence of soil crack. Some results and awareness are achieved in this thesis as follows:(1) TWRI tests were conducted on several soil samples which the author collected near Wuhou service station of Hanzhong area. Soil-Water Characteristic Curve (SWCC) and Hydraulic Conductive Function Furve (HCF) that corresponded different hydraulic path conditions were obtained through TWRI tests. The results indicate that expansive soil has a characteristic of obvious "hysteresis effect". As for the same soil sample but under different hydraulic path conditions, it exhibits a significant difference from each other about the related hydraulic properties. Through the observation of microscopic structure, the occurrence and seepage form of pore water has been studied and it revealed the mechanism of hysteresis effect for unsaturated expansive soil.(2) The results of shear strength test which is conducted under different hydraulic path conditions and water contents show that, the matric stress of soil will enhance soil strength as saturated soil convert into unsaturated state. However, this strength contribution was mainly from the transformation of soil cohesion. But it cannot be considered that the larger matric stress or lower water content will bring more shear strength for unsaturated expansive soil. During the normal range of water content variation, the peak value of soil shear strength will reach due to matric stress contribution.After implementing study on the consolidation characteristic of saturated expansive soil located in Hanzhong area through consolidation tests which are under different loading conditions, the related drainage consolidation was demonstrated by using a self-developed computer program. According to the local stress environment where soil samples was collected, stress path was set within loading of deviatoric stress. And a series of triaxial creep tests were conducted under six levels loading condition. Based on the test results, one creep model equation has been proposed. Consolidation deformation and creep deformation model equations were combined with each other so that it could be used to describe the rheological properties of expansive soils.(3) As XRD spectrum of expansive soil collected in Hanzhong area were obtained in this thesis, the content and component of soil’s main hydrophilic mineral have been confirmed. By using micro-structure scanning, the author determined the regularities of mineral chemical reaction and distribution of soil particles contact or arrangement (three forms of face to face, face to point and point to point). Furthermore, the author conducted research on the law of crack development for unsaturated expansive soil, and wrote a crack identification program by using the theory of Otsu image segmentation algorithm. An empirical equation which can describe the relationship between crack rate and water content also was proposed in this thesis.(4) Through the cracks uniforms distribution theory and the obtained empirical equation, the author performed the research on the deformation development and potential landslide form of expansive soil cutting slope with different crack rates under several rainfall conditions. Due to these researches, the author got in-depth understand about the mechanism of rainfall-induce landslide for expansive soil cutting slope. On this basis, some major factors such as evaporation process, rainfall duration and rainfall intensity have been considered to put forward an empirical formula of rainfall warning threshold which is applied to the rainfall-induced landslide in Hanzhong area.(5) According to the special engineering properties of expansive soil cutting slope with different crack rates which is commonly influenced by rainfall, the anchor and frame beam system has been suggested to use as a suitable structure on the control of landslide. Additionally, the corresponding optimized design analysis also performed in this thesis. |
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