Stability Analysis Of Shallow Tunnel In Expansive Soil Under Rainfall Infiltration

The shallow expansive soil tunnel reveals significant moistening swelling effect induced by rainfall infiltration. The force and deformation in support system become larger with the increase of surrounding rock stress level and further endanger the project. Therefore, it is of great practical engineering value to study the stability of expansive soil tunnel with rainfall infiltration. In this thesis, based on a shallow expansive soil tunnel, a series of correlational researches were carried out combined of laboratory tests, theoretical analyses and numerical simulations. The main contents and conclusions are as follows:(1) The mechanical properties and swelling potential grade were obtained by laboratory tests. The empirical equations for the variation of strength parameters of expansive soil versus various moisture contents were evaluated on the basis of Direct Shear Test. The variation of matric suction versus moisture contents during the moisture absorbing process was measured by filter paper method. Based on the test result, the curves were fitted and the parameters were determined by the V-G model.(2) According to the ‘humidity stress field theory', a numerical solution was presented by combining the seepage module and thermal module in FLAC3 D packages. Based on the similarity of the thermal and seepage differential equations, the relation of the parameters in the thermal and seepage fields were determined. By FISH programming, the unsaturated seepage and expansion of soil was simulated with rainfall infiltration.(3) Based on the project of shallow expansive soil tunnel, the deformation of surrounding rock mass and stress in the support system with rainfall infiltration were studied by the aforementioned method. And the parametric study of the impacts of permeability coefficient, expansion coefficient and rainfall intensity on the stress in support system was presented. The result shows that: during the rainfall infiltration process, the horizontal stress of surrounding rock mass increases remarkably, whereas the vertical stress changes in a small range. The vertical extrusion deformation of the support system is initially much more evident than the horizontal extrusion deformation, whereas it gradually decreases and becomes less obviously than the latter. The permeability coefficient, expansion coefficient and the rainwater infiltration exert great impact on the stress in the support system. The waterproof and drainage measures should be taken in advance to strictly control the rainwater infiltration capacity when the tunnel is excavated in the area where fracture is well developed or soil exhibits strong expansibility.