Numerical Simulation Study On Expansive Force Of Lining For Tunnel In Expansive Soil

Expansive soil is a kind of expensive geologic body that is crannied. It will repeatedly expand when exposed to water and shrink when lost water, which will do great harm to tunnel construction. So it's very necessary to study the mechanism of action that the expansive soil towards the tunnels and the laws of stress redistribution when expanding. So as to get countermeasures to instruct the design and construction of tunnels in expansive soil.This thesis aims at the numerical simulation of how the expansive soil acts on the tunnel lining after it absorbing water and expanding. Firstly, the reasons and mechanism of expanding and shrinking of the soil are introduced. So are the computation methods of tunnels in expansive soil, the characteristics of expansive soil and the common disease problems and their countermeasures. Then with finite element numerical simulation, the actions of the expanded soil towards the tunnel lining and bolts after excavation are analyzed. And the distribution rules of lining internal forces and the movement around the tunnel in different conditions are concluded. And the conclusions are as follows:(1) The lining internal forces relate to embedded depth, expansion coefficient and the thickness of expansion ring. The effect of expansion coefficient and thickness of expansion ring is great, while that of embedded depth is less.(2) As to a single bolt, the maximum axial thrust locates at the junction of bolts and lining. And the axial thrust of bolt decrease along the bolt from inner to outer. The maximum axial thrust locates at the nance, while the minimum one locates at the arch crown.(3) The tension of bolts has linear relation with expansion coefficient. With certain expansion coefficient, the influence of the thickness of expansion ring towards the bolts is a little.(4) The influence of expansion coefficient and the thickness of expansion ring is much greater then that of the embedded depth.(5) With the expansion of the soil, the land surface is upheaved. And the influence of the embedded depth to the upthrow of land surface grows with the growth of it.(6) The expansion coefficient influences the tunnel structures most, while the thickness of expansion ring less, and the embedded depth least.