Determining The Surrounding Rock Displacement Release Coefficient Considering Spatial Effect

Tunnel is one of underground structures located in rock-soil mass.The differencebetweenit and the ground structures is that the rock-soil mass is the main research object.The tunnel engineers are extremely concerned about stability and deformation regularityof rock-soil mass. Due toreceiving the strong influence of the geological environment,so the physics, mechanics, structure and timeproperty of rock-soil mass are verycomplex.It is a difficult problem that understand rock-soil properties scientifically andthe interaction between it and supporting structure. However the domestic and overseasresearchers and tunnel engineers have made great achievementsthrough a large amountof theoretical analysis and engineering practice. They established relatively completetunnel engineering design theory.The tunnel excavation face will produce a radial constraint for the nearbysurrounding rock,equivalent to apply a virtual supporting force to it.The stress anddisplacement of surrounding rock will change with the excavation face advancing,whichis called as the spatial effects of the excavation face.This article will carry onfurther in-depth study to following several questions based on the research result hadachieved about tunnel spatial effect theory. The main works and achievement of thesiscan be drawn as follows:①The thesis will carry on the analysis of the mechanism of spatial effect andconfinement loss factor which reflects the spatial effect; carrying on the analysis tosurrounding rock displacement release on the basis of considering the spatial effect;establishing a relationship between displacement releasecoefficient and confinementloss factor.Finally, the thesis will carry on the analysis to mechanism of rock-supportconsidering spatial effect.②The thesis will simulate the shallow straight wall with arched tunnelexcavation process using finite element analysis software; carry on the analysis oftunnel spatial effect bylongitudinal deformation curve and displacement releasecoefficient curve.Within the range the spatial effect of excavation face, surroundingrock mainly produceelastic-plastic deformation,in this thesis, we will analyze theinfluence regarding physico-mechanical parameters of rock and the tunnel depthsurrounding rock to displacement release coefficient based on Mohr-Coulomb strengththeory by using the numerical simulation method. ③We will determine the influencing parameters regarding surrounding rockdisplacement release coefficient according to the results which alreadyobtained,establish sample setthrough finite element simulation,training BP neuralnetworkusing the sample set(the values of parameters as input, the values ofdisplacement release coefficient as output),validate the BP neural network ensuring theaccuracy of network training.④Taking a tunnel section in Chongqing River Bridge connecting tunnel as anexample, make the prediction of surrounding rock displacement release coefficientcurve using BP neural network,and analyze the application of displacement releasecoefficient in the choice of supporting occasion.In order to ensure the construction of the tunnel safe and reasonable,it isimportant to predict surrounding rock displacement release coefficient accurately.Thetraditional methods determine the surrounding rock displacement release coefficientmainly through theoretical calculation and numerical simulation, these methods arecomplicated and need to spend a lot of time.This thesis presents a new method thatusing artificial neural network to predict the displacement release coefficient ofsurrounding rock. Compared with the traditional method, it is simple and has a higherprecision accuracy, so it has high engineering application value and practicalsignificance.