Study On Analysis Methods And Application About Stability Of Deep Excavation With Pile-Anchor Structure

The pile-anchor reinforcement structure is a new type of slip resisting structure, which is widely used in the reinforcement of deep excavation and slope. The pile-anchor reinforcement structure has been used more width because of its many advantages. But in recently the studies on its numerical realization method and application study on foundation pit stability are still not enough.Stability analysis is an important issue in the design and construction for deep excavation. The differenecs between limit equilibrium method, shear strength reduetion method and slip surface stress FEM analysis method are compared, in which the mechanism and limitation of the limit equilibrium method are analyzed, the characters and implementation procedures of the shear strength reduction method and slip surface stress FEM analysis method are studied, which validates the strength reduetion method and slip surface stress FEM analysis method.The PLAXIS3D TUNNEL numerical simulation method based on the strength reduetion method is used to study the distribution of slip plane and stablity safety factor Fs of deep excavation with pile-anchor structure. The results show that the safety factors of three methods are some different. The main causes about this differenecs ars that numerical simulation method can consider the interaction effects between pile and cable and soils, and soil nails at the upper part and the pile-anchor reinforcement structure at the down part of the deep excavation can were modeled meantime. But limit equilibrium method could not consider well the interaction effects between structures and soils.The FEM calculated results show that the internal force in upper nails is related to the locations of nail and down part excavation and construction. The forces in nails at the top layer are small. Axis stress in each layer of nails changes during the excavation of soil layer under the nail location and the axis stress increases with the increase of the depth of excavation.The application of shear strength reduetion method and slip surface stress FEM analysis method can provide some guidance for the design and construction o f a deep excavation with pile-anchor structure.