The Construction Method Study Of Shallow Buried Karst Caves Tunnel

To meet the needs of economic development and traffic construction, construction of tunnel engineering in karst region is becoming more common. Although existing construction technique can satisfy the construction of karst tunnel, the existing specifications have no detailed provisions of how to make choice of karst tunnel construction scheme. The designers choose the scheme mainly through their experience which is easy to underestimate the probability of karst tunnel geological disasters caused by landslides, mud water, surface subsidence and other engineering disasters, even threatened the life safety of site construction personnel.This thesis takes Zhangjiawan tunnel which is in the expansion of railway station project from Loudi to Shaoyang, as the background. Design parameters and typical sections of Zhangjiawan tunnel are referenced for research. Elastic-plastic theory and ABAQUS numerical simulation are used for study on single concealed karst cave in different position around the tunnel of influence on the stability of surrounding rock. And this thesis also combines the construction process of three steps method, both side heading method and CD method (middle bulkhead method) to compare and select the construction methods of the shallow buried karst tunnel, in order to provide the basis for future design and construction. The research content mainly includes the following aspects:(1) Measurement data of Zhangjiawan tunnel is organized. A regression equation for fitting the convergence curve of the settlement of surrounding rock and surrounding rock is established. The stability of surrounding rock of tunnel which is under excavation is evaluated in the thesis.(2) Based on elastic-plastic theory, the range of plastic zone under the secondary stress state and three times stress state after tunnel excavation and the plastic area of the cave range is studied. On the basis of the plastic zone of both side is not connect, the formula of the safe distance between tunnel and karst cave is deduced in the thesis.(3) The numerical simulation model based on DK19+405 section of actual engineering of Zhangjiawan tunnel is established by the ABAQUS software. The model simulates single concealed karst under different position, the tunnel excavation process in three steps method, both side heading method, CD method. And the data of crown settlement, ground settlement, surrounding rock convergence, plastic stress field in the whole process of construction is finished, the best construction method is selected finally.(4) The construction methods of three steps method under the condition of 90°,45° and-90°are respectively optimized by the ABAQUS software.