Study On Stability Of Surrounding Rock Based On Field Test Of Menghua Railway Jiuling Mountain Tunnel

In recent years,due to the underground construction chamber instability,the tunnel arch collapse phenomenon surge.This is due to the underground engineering excavation process,the surrounding rock strength is lower than the secondary stress.The surrounding rock enters the shaping deformation stage and forms a plastic zone.Without timely support,the top of the rock easily fall.To this end,the study of underground space engineering excavation caused by the stability of the surrounding rock,rock collapse arch law,not only the theoretical signifi-cance,but also has important practical value.At present,China’s two-lane railway tunnel rock composite lining of the initial support by the anchor,shotcrete,steel mesh and steel frame and other combinations.In order to study the influence of the initial support parts on the stability of the tunnel,the paper analyzes the stability of the tunnel and the stability of the tunnel by combining the FLAC^3d strength reduc-tion method and field experiment.The collapse effect of the collapse arch is studied on the MengHua Railway Jiuling Mountain Tunnel.The main contents include:（1）Using FLAC^3d strength reduction method,the failure mode of tunnel surrounding rock is prejudged.The safety factors of Ⅱ-Ⅴ grade surrounding rock tunnel are 3.05,3.40（Ⅲ-level surrounding rock with systematic anchor）,3.35（Ⅲ-level surrounding rock without systematic anchor）,3.14（IV-level surrounding rock with systematic anchor）,3.45（IV-level surrounding rock without systematic anchor）,2.85（V-level surrounding rock with systematic anchor）and 2.90（V-level surrounding rock without systematic anchor）.In the background engineering research area,the strength of the surrounding rock after tunnel excavation can resist the stress,that is,the tunnel failure is not stress-induced failure.In addition,the failure mode of the tunnel is analyzed,and the damaged part appears in wall and vault.（2）The force of the anchor rock of Ⅱ-Ⅴ is generally small,but the failure state of the rock is not obvious.The analysis shows that the anchor force not comes from collapse arch load but the broken rock（geometric instability）.The anchor only plays a role in anchoring around the tunnel broken rock（geometric instability）.In the test,the initial support force of the experimental support section of the system is obviously larger than that of the non-system bolt support test section,which shows that the bolt has played a certain role.（3）Compared to the material limit compressive strength,shotcrete and grating steel frame force is small,with a large safety reserve.But with the analysis of the stress of the bolt,there is no collapse arch load.The surrounding rock of each test section has a good self-carrying capacity in a certain buried depth.Ideally,the surrounding rock can be self-stabilizing.The initial support force mainly comes from the loose load（deformation pressure）of the broken rock（geometric unstable body）around the tunnel.（4）The crushing conditions of the surrounding rock mass and the development of the joint fissure in the different surrounding rock test section can reflect the deformation pressure of the surrounding rock to a certain extent.The initial support force is related to the timing of the support and the stress release of the surrounding rock.The groundwater condition of the surrounding rock also has a great influence on the initial support force.（5）Ⅳ level of the surrounding rock dome accumulated value of 7.62mm and the level of convergence cumulative value of 11.70mm.The cumulative value of vault subsidence of grade Ⅴ is 2.6mm and the horizontal convergence is 4.56mm.The tunnel is deformed as a whole to the clearance side.Which is consistent with the data that the grid steel frame and the shot concrete are generally under pressure.It shows that the initial support of the surrounding rock tunnel is mainly small eccentric compression.