Research On The Stability And Countermeasures Of The Expansive Surrounding Rock In The Guiyang Metro S1 Line Are

In recent years,in order to alleviate the contradiction between people and land in urban areas,the construction of public transportation has continued to increase,among which the subway project can be described as a’sudden rise’.The subway project site is densely populated and the underground environment is complex.If special geology such as expansive surrounding rock is encountered,the construction difficulty will be multiplied.There are numerous accidents caused by the uniqueness of expansive rock and soil in the engineering field,especially in the field of tunnel engineering.In order to explore the stability of expansive surrounding rock in the field area of Guiyang Metro Line S1,this paper relies on the expansive surrounding rock（mudstone）between Huanghebeilu Station and Wangchengpo Station of Guiyang Metro Line S1 as the research object.Through field sampling,laboratory test research,theoretical calculation analysis,numerical simulation and combined with tunnel field monitoring and measurement,the main work and results are as follows:（1）The basic physical and mechanical properties of expansive surrounding rock（mudstone）were tested.The basic physical and mechanical parameters of surrounding rock in the study area and its water softening deformation characteristics were measured.It was found that the average water content was 6.84%.The density of natural water-containing and dried samples was 2.57g·cm^-3and 2.50g·cm^-3,respectively.The average particle density was 2.69g·cm^-3,and the average porosity was 7.07%.The uniaxial compressive strength of the natural water content state is7.21MPa,and the uniaxial compressive strength after drying is reduced by 55.9%.When the water content increases to 8.20%,it decreases to 0.51MPa.After losing water,it encounters water again,cracks develop rapidly,the disintegration speed of rock mass is faster than that of natural mudstone,the rock mass after disintegration is finer and the disintegration is more thorough.（2）The expansion characteristics test and microstructure test of expansive surrounding rock（mudstone）in the study area were carried out,and the expansion mechanism of expansive surrounding rock（mudstone）was revealed.It is found that the lateral constrained expansion rate is significantly higher than the axial and radial free expansion rate,and the expansion pressure of the rock sample fluctuates greatly,ranging from 66.21k Pa to 106.95k Pa.The content of clay minerals in rock samples is47.2%,mainly illite（30.8%）.The microscopic surface is rough,the fracture is developed,the cementation between particles is weak,and the pores are interconnected,which is conducive to water entry;because its clay mineral content is mainly illite,its expansion characteristics are not prominent,but tunnel excavation causes the development of secondary fissures in rock mass and the expansion characteristics of rock mass are enhanced.（3）Based on the tunnel pressure arch theory and rock mass mechanics method,the calculation model of expansive surrounding rock pressure is constructed.The influence of the additional pressure coefficientηon the surrounding rock pressure is calculated.The theoretical formula of the stability analysis of expansive surrounding rock is derived.Based on the safety factor k of surrounding rock,the stability criterion of expansive surrounding rock is preliminarily given.（4）The numerical simulation of tunnel excavation under different working conditions is carried out.It is found that under the action of expansion pressure,the deformation of surrounding rock is obviously accelerated compared with that without expansion pressure,and the deformation of the left and right tunnels is higher than that without expansion pressure.The principal stress values in the X direction are higher than those without expansion pressure,and the maximum value is located in the inverted arch area,which is 1.7 times that without expansion pressure,and the principal stress of the vault is significantly larger than that without expansion pressure.The maximum principal stress in the Y and Z directions is located at the arch waist,which is 33.87%and 18.04%higher than that without expansion pressure,respectively.It shows that the expansion of surrounding rock will lead to the increase of stress and strain of surrounding rock and the prolongation of convergence period,which will greatly reduce the stability of surrounding rock,especially the influence of tunnel invert.（5）Considering the expansion characteristics of the surrounding rock of the tunnel in the study area,the on-site monitoring and measurement are carried out.It is found that the deformation of the expansive surrounding rock lasts for a long time and the surrounding rock pressure fluctuates greatly.The law is basically consistent with the theoretical analysis of the stability of the expansive surrounding rock,and countermeasures and suggestions are put forward for the treatment of such engineering sites.