Study on deformation and failure of high-strength gypsum surrounding rock specimens (thick-walled cylinder) simulating roadway excavation

In order to grasp the deformation law and failure mechanism of surrounding rock of roadway under the con- dition of excavation and unloading,realize the simulation of actual loading and unloading process during un-loading of roadway excavation,a roadway surrounding rock excavation unloading model test system with inde-pendent intellectual property rights was used to simulate transient excavation,slow unloading and failure of tunnel excavation with the small wall rock specimen (thick cylinder:height 290 mm,outer diameter 200 mm,inner diameter 100 mm) made of high- strength gypsum materials. During the test,the strain of the surrounding rock specimen in both axial and tangential di- rections was collected and the strain-time curve of the whole process of excavation unloading was obtained. The test re- sults show that:① the axial direction of the surrounding rock specimen basically shows the state of compression,and some of the measuring points show the change of tension and compression. The axial strain can fully demonstrate the elastic-plastic deformation when it is unloaded slowly. Most of the deformation is slowly released after unloading,and at the end of unloading the specimen has a slight creep phenomenon;② in the surrounding rock specimens,the meas- ured tangential strain is greater than the outside,that is,the farther away from the wall. The smaller the strain is,the specimen expands inwards during the unloading process;③ at the same measuring point,the tangential strain during unloading is greater than the axial strain,and the tangential strain is more sensitive to the unloading process and has instantaneous response. Rock deformation plays a leading role;④ when unloading failure,the tangential strain changes prior to surrounding rock failure,that is,the failure direction of the surrounding rock specimen faces the hole,and the failure of the specimen is mainly the circumferential shear failure accompanied by the vertical cleavage crack.