Effect Of Load-Bearing Arch In Excavation Or Fill Above Existing Weak-Surronding Rock Tunnel

In recent years, adjacenet engineering of excavation or filling above existing tunnel has proliferated. As for the excavation above existing tunnel, the load on the lining structure might be changed, because the excavation would lead to the destruction of Load-Bearing arch. As for the filling above existing tunnel, it caused of load on the tunnel. The loads is born by Load-Bearing arch and lining, but bearing ratio of lining is affected by a number of factors, and, the mechanism of the change between Load-Bearing arch and linner is not clear in the process of filling, loads increased on lining can’t be predicted accurately. So it is necessary to study about the change of the tunnel Load-Bearing arch in process of excavation and filling above the existing tunnel.This article has researched on the damage of the Load-Bearing arch in the excavation process, and the formed of Load-Bearing arch in filling process, Theoretical study, Centrifugal model experiment and Numerical simulation was used in research process. In addition, based on stress criterion and strength criterion, the influence division was finished for the adjacent construction about excavation and filling above the existing tunnel. The main works and results are as follows:(1) Though theoretical study, the concept of the tunnel Load-Bearing arch was explained.and, the failure process of the Load-Bearing arch in excavation was predicted. In intial of excavation, internal force of lining and surrounding rock pressure decreased. Then, when excavation caused damages of Load-Bearing arch, the loads that Load-Bearing arch bears would transfer to lining, and, caused decrease of load-bearing capacity. There would be a slow down or reverse in decrease tendency of surrounding rock pressure and internal force. As for the embankment above the existing tunnel, Study on characteristic-curve of surrounding rock broughts out that stiffness of the Load-Bearing arch would decrease with the extension of plastic zone under the condition of deep buried, and, predicted that force in lining would increase with increase of plastic deformation for filling engineering under the condition of deep buried.(2) Results of centrifugal:1) Changing process of internal force for excavation above tunnel was agreement with the theoretical prediction. It expelled a sigh of relief and reverse in decreasing tendency of surrounding rock pressure and internal force.Meanwhile, the Crustal Stress Bearing Ratio was defined and used as the main criterion of the Load-Bearing arch destruction.Through this method, range of the Load-Bearing arch was judged between 1.0D and 1.5D under rigid supporting condition and between 2.0D and 2.5D under flexible supporting condition.2) Changing process of internal force for filling above tunnel showed an approximately linear increase. Extension of the Load-Bearing arch in the process of filling can be reflected by the change of the crustal stress bearing ratio.Owing to the limit of lining for deformation of surrounding rock, plastic zone of the Load-Bearing arch can not extends, so internal force and surrounding rock pressure shows linear growth in the process of filling. In addition, there was stress concentration besides side wall and wall footing. Through comparative analyses, the crustal stress bearing ratio of side wall was 0.46-0.6 higher than before.(3) Numerical simulation results:1) Numerical simulation with section of centrifugal test, compared the results of centrifugal test and numerical simulation for mutual authentication.2) Numerical simulation with section of high speed railway tunnel gets the change rules of the surrounding rock pressure, the crustal stress bearing ratio, internal force of tunnel in V rock,VI rock and loess. The additional crustal stress bearing ratio was defined to reflect the change rule of the Load-Bearing arch with the process of filling.(4) For excavation and filling engineering, the stress criterion and strength criterion were selected to carry out the approaching division. According to the division result, regression analysis was finished, and it was concluded that mathematical expression of division as the change of initial buried depth.