Research On Macro And Micro Mechanism Of Rock Mass Instability In Water Sealed Gas Reservoie Cavern

Based on a water sealed gas reservoir project,a similar model test is designed in this paper.Combined with DIC optical measurement technology and acoustic emission system,the instability and failure process of cavern rock mass is explored from multiple angles;At the same time,the particle flow simulation technology is used to study the instability and failure characteristics of various forms of cavern rock mass at the meso scale,and the main conclusions are as follows:(1)In the model test of the instability process of the cavern rock mass,tension cracks first appear on both sides of the circular cavern;The front and rear sides of the inner wall appear spalling phenomenon,and then the two sides of the hole appear airfoil tension shear composite cracks;The cracks in the straight wall arched cavern first develop from the arch angle and gradually extend to the arch spandrel,and the slab crack layer appears at the arch bottom;The ring count and energy count of acoustic emission results become extremely active after 21.5mpa;And reach the maximum at the peak load and then drop rapidly;In the DIC results,the vertical strain concentration area is easy to form above and below the slope of the portal.Under the peak load,the distribution of the tensile strain concentration area and the shear strain concentration area almost coincide.(2)In the PFC test of circular caverns,the micro cracks in the rock mass are mainly tension cracks,and slender and penetrating crack zones are finally developed on both sides of the portal;In the PFC test of arch cavern with straight walls,the main reason for the failure of the cavern is that the straight walls on both sides form a through fracture zone and cut the rock mass into blocks.(3)The tunnel shape has a great influence on the bearing capacity of the surrounding rock of the construction roadway.The peak load of the oval,egg,horseshoe and straight wall arch sections are 96.41%,95.22%,94.06% and 87.33% of the circular sections respectively.The horseshoe section has the earliest response to the stress;The stress level of egg shaped and straight wall arched sections is low when particles pop up.(4)Excessive height span ratio will significantly weaken the ultimate bearing capacity of the rock mass of the main cavern.The failure of the 0.8 and 1.0 height span ratio models is due to the vertical expansion of the fracture zone to the deep of the rock mass;The failure of 1.5 and 1.8 height span ratio models is the formation of a wide range of arc-shaped fracture zones at the vertical walls on both sides.(5)The spacing of caverns has a significant effect on the failure mode of the surrounding rock of the main cavern group.With the increase of the spacing,the distribution of the force chain in the rock mass between the two caverns becomes sparse;When the load reaches the peak value,the number of shear cracks in the 1.0,1.5 and 2.0 times of tunnel span spacing model accounts for 10.47%,12.32% and14.26% respectively.The increase of tunnel spacing enhances the internal shear effect.