Study On Stability Of Long Highway Tunnel Passing Through Gypsum Rock Formation

In recent years,with the "The Belt and Road" strategy,the construction of traffic infrastructure,such as expressways,has developed rapidly in Chongqing and other Western regions of China.Due to the terrain in the western region of China is mainly dominated by mountains and hills,it is necessary to build the tunnel in the process of building the expressway.With more and more construction of expressway tunnel,geological and engineering characteristics are more and more complicated.In the process of the construction of the long tunnel,the engineering problems such as high ground stress,Yan Rong,gas,large deformation of soft rock and swelling rock are more and more prominent.Taking the controlling engineering of expressway in Liangping Zhongxian—Li Rang tunnel as the research object.Based on the field investigation,laboratory test,elastic plastic theory,numerical analysis and field measurement,the deformation characteristics and stability of surrounding rock during tunnel construction are studied.This article main research content is as follows:(1)The physical and mechanical parameters such as natural water content,tensile strength,elastic modulus,cohesion and internal friction angle are obtained from natural water content test,tensile strength test,uniaxial compression test and triaxial compression test of gypsum rock,which is collected freshly from the Li Rang tunnel site;(2)The stress-strain curves of gypsum rock under unloading condition are obtained by the three axial compression test which was carried out by the adaptive automatic triaxial testing machine made by TOP INDUSTRIE company.Furthermore,the mechanical parameters,deformation characteristics and energy change of gypsum rock under unloading condition are analyzed;(3)According to the results of triaxial unloading test and the Mohr-Coulomb constitutive model,a new constitutive model is developed to characterize the mechanical behavior of gypsum rock in the unloading process.FLAC3 D software and the new constitutive model are applied to the numerical simulation of gypsum rock samples.The results show that the new constitutive model has better adaptability in describing the strength and deformation characteristics of gypsum rock under unloading condition;(4)Based on a detailed analysis of the gypsum rock mechanical parameters and the geological and hydrogeological conditions of yield region,combined with the generalized Hoek-Brown criterion,the mechanical parameters of gypsum rock mass are obtained;(5)Based on numerical simulation,obtain the variation of deformation of surrounding rock of tunnel during construction through the gypsum rock strata,and the results were compared and analyzed,and monitoring results show that the numerical simulation can reflect the variation of tunnel surrounding rock well;(6)Using FALC3 D software,the influence factors of stability of tunnel surrounding rock through the gypsum rock strata are analyzed.Mainly from the geological strength index GSI,tunnel depth,the lateral pressure coefficient and tunnel flat rate four aspects to discuss the changes of the stability of tunnel surrounding rock.(7)Using MIDAS/GTS software,the internal force of tunnel lining through the gypsum rock strata are analyzed.Based on comprehensive safety factor method,the comprehensive safety factor of tunnel lining is obtained.