Analysis Of Mechanics In Excavation Process Of Hongtudi Large-span LRT Station And Optimization Of Core Pillar

In recent years, more and more cities have emerged the upsurge of building subway and rail transit in order to alleviate the traffic pressure, thus large span tunnels and underground projects gradually increase. In view of the limitations of geological conditions and mechanism of rock mechanics, the design and construction of large span tunnel are still in the stage of exploration and attempt, although the construction technology of such tunnel has currently developed well. The existing specifications can only direct the design and construction of tunnels within the span of 15m . Therefore, it is necessary to study the mechanical state of surrounding rock in the construction of such tunnels.Based on Hongtudi station of Chongqing Rail Transit Line VI, the paper, by means of FE numerical simulation and insitu-monitoring, analyzes the following three questions:①Analyzing relationships of hance & vault settlement between the step sequences during the excavation above the big arch foot, and that the relationships between support structure stress and excavation step sequences at the parts of arch foot, hance & vault. Results of numerical analysis and situ-monitoring data are compared, and reasons of such differences are also analyzed;②Analyzing the influences to upper primary support from excavation sequences of the both TBM holes.③As for the optimization problem of core pillar width in excavation of large span tunnel with double side heading method, the paper analyzes relationships between surrounding rock stress , plastic strain,support internal force, vault settlement and excavation steps based on the 2-D FE simulation in different core pillar widths;In 3-D FE simulation, relationships between the 1st stress of surrounding rock, plastic strain,support internal force and excavation steps in different core pillar widths are also analyzed. From the results of numerical analysis, the optimization core pillar width in excavation of Hongtudi station is 6m, and it is suggested that the reserved width of core pillar is 0.3 times as large as the tunnel span,which is of great practical significance for other similar tunnels.