Research On Construction Disturbance And Control Of Subway Tunnel Crossing Urban Karst Area

The karst geology of the urban environment has typical characteristics,which are mainly reflected in shallow karst burial and sensitivity to deformation and settlement of the overlying soil.The construction of subway tunnels in urban karst areas has a great impact on the surrounding environment,and buildings(structures)in prosperous areas are sensitive to stratum disturbances.Therefore,understanding the disturbance laws and characteristics of subway tunnel construction under karst occurrence conditions will affect the safe construction of tunnels,control of surface subsidence and It is of great significance to protect the stability of the overlying soil layer.Relying on Guiyang Metro Line 3,this paper uses a similar model test to study the disturbance influence law of subway tunnel construction on karst strata and surface environment under different karst development forms under the full investigation and investigation of the characteristics and laws of karst development in Guiyang urban environment.In this paper,the numerical simulation method is used to analyze and evaluate the karst pretreatment scheme commonly used in engineering.The specific work done in this paper and the main conclusions are as follows:(1)The urban environment subway tunnel construction space is dominated by small and medium-sized karst cavities,and the development height of the cavities below 4 meters accounts for 70-80%.The soluble rock layers near the rock-soil interface are karst geological In the high-incidence area of the phenomenon,karst development in some areas has the characteristics of small volume and high density,the overlying soil layer is undulating,and karst cavities are generally distributed from the bedrock surface to about 5 to 10 meters below,and the density of cavities in different regions varies greatly.Large,and the horizontal distribution range has no obvious characteristics.(2)An experimental study on the occurrence of concentrated karst cavities in different positions of the surrounding rock of the tunnel was carried out by using the method of preburied inflatable airbags.The post-convergence deformation and the reduction of the release of earth pressure,the smaller the distance between the cavity and the tunnel,the greater the influence.When the cavity is located on the side of the arch waist of the excavated tunnel,the bending moment at the arch waist is 1.76 times that of the case without the cavity.The hidden karst cave in the tunnel arch will increase the magnitude and range of the surface settlement above the tunnel cavity after excavation,and the larger the distance between the karst cave and the tunnel arch,and the closer to the surface,the greater the impact on the surface settlement.(3)By pre-embedding dry ice to form cavities with random characteristics in the stratum,the distributed karst geological phenomenon in the superficial rock strata of the urban environment is simulated,and the effects of different karst development intensities and arch karst spacing on the construction of subway tunnels are discussed.Disturbance characteristics and laws,the study shows that under the presence of distributed karst in the tunnel arch,the post-construction convergence deformation,the release of earth pressure and the stress of the primary support structure of the surrounding rock adjacent to the tunnel arch are significantly reduced,and the higher the karst development strength,The closer you are to the tunnel,the greater the reduction.The distributed karst in the tunnel arch increases the magnitude and range of the surface subsidence above the tunnel cavity after excavation.(4)A distributed karst numerical model was established by using random functions,and the common construction measures for karst geology were compared and analyzed in combination with FLAC3 D,and the disturbance control effect was evaluated according to the stress of the surrounding rock and the surface subsidence.The research shows that the overlying soil The effect of layer grouting in controlling the surface settlement is obviously better than that of cavity filling grouting,and the surface settlement of the cavity filling and overlying soil grouting is further reduced,but the decrease is not large.Combined with actual engineering,it is recommended to use overlying soil grouting to control surface subsidence for small and medium karst cavities and distributed karsts with low karst development strength.