Experimental Research Of Creep Characteristics Of Silty Mudstone And Its Influence On Stability Of Tunnel Surrounding Rock

As one of the important mechanical properties of rock,creep has an important influence on the stability of geotechnical engineering.It is of great significance to correctly predict and characterize the creep properties of rock.This paper is based on the project of"Yunnan water diversion project of soft rock and soil engineering geological characteristics and influence research".This paper combines theoretical analysis with experimental research and studies the silty mudstone of the J₂z stratum in the Laoqingshan tunnel in the Yunnan water diversion project.According to the creep characteristics of silty mudstone under different water-bearing conditions,a creep damage model suitable for silty mudstone of J₂z stratum is established.Then the improved Burgers model is realized based on the interface provided by FLAC^3D.The secondary development of the creep damage Burgers model was carried out and simulated.The rock water-bearing creep damage Burgers model was developed for actual engineering simulation.The main conclusions of this paper are as follows:?1?The physical and mechanical properties and hydraulic properties of the silty mudstone in the Laoqingshan tunnel were tested.The silty mudstone consists of a large number of felsic granules composed mainly of illite and illite-montmorillonite.The uniaxial compressive peak strength and the elastic modulus decreases with the increase of water content;the shear strength index of rock decreases with the increase of water content;the softening coefficient is lower,indicating that the softening is stronger.The disintegration resistance of mudstone tends to be stable with the increase of the number of cycles;the clay particles contained in the silty mudstone reacted rapidly with water,and the clay particles peeled off in the surface layer after water contact.The expansion force increased rapidly within 1 hour after the test.Afterwards,it gradually slows down and the expansion force is larger.The average saturation coefficient of the silty mudstone is large,indicating poor rock stability.?2?The triaxial compression creep test of silty mudstone in the Laoqingshan tunnel under different water conditions was carried out,and the creep characteristics under different conditions were analyzed.The creep law of the silty mudstone under different water conditions was summarized.An improved Burgers creep damage model based on Burgers model is constructed.The damage variable in the form of negative exponential is used to describe the creep damage process,and the creep equation of the model is derived.The model consists of two parts,the first part is the classic Burgers model,which is used to describe the linear phase creep of rock,and the second part is the nonlinear component considering the water damage.It can be seen from the parameter inversion fitting that the model can not only describe the deformation of the initial and steady creep stages under different water conditions,but also can identify the accelerated creep stage.The model is a six-element model with few parameters and convenient application.?3?The finite difference form of the improved Burgers creep damage equation is derived.Based on the built-in Cvisc creep model source code provided by FLAC^3D,the Fish language classified into the C++programming language is used to implement the second development of improved Burgers creep damage model in the FLAC³DD platform.According to the simulation test based on the creep damage model of secondary development,the simulation results are consistent with the test results.The results show the success of the secondary development of the creep model.?4?Based on the engineering geological conditions of the Laoqingshan tunnel,a three-dimensional numerical model was established,and the deformation support of the tunnel under different water conditions was simulated to verify the correctness of the developed rock water damage model.It is found that the creep deformation of tunnel surrounding rock increases with the increase of water content,and the larger the water content,the more obvious the displacement.Moreover,the creep deformation increases with the increase of time,and the displacement increment gradually decreases with the increase of time,which also indicates that the rock has obvious creep characteristics.?5?This provides a theoretical reference for the construction of water-bearing silty mudstone tunnel,and also explains the rock creep.The variable model considers the necessity of different water cuts.In the construction and support of such tunnels,different support measures should be taken to control the deformation of the tunnel for different water cuts.It is economic and reasonable to adopt such measures.