Deformation Failure Mechanism And Stability Analysis Of Surrounding Rocks Of Shuangjiangkou Hydropower Station

A large number of large-scale complex underground caverns have been built in southwest China recently,to meet the needs of hydropower supply.Most of these underground caverns are located in the geological environment with high geostress and complex geological environment,and are accompanied by various weak structural surfaces(fissures,joints and faults).Unloading damage and activation of weak structural surface during the excavation seriously affect the stability of the caverns,threatening the safety of construction personnel and equipment.Therefore,it is urgent to study the deformation and failure mechanism of surrounding rock of underground caverns.The underground powerhouse of Shuangjiangkou Hydropower Station is located in the high geostress area with large buried depth.During the excavation of underground powerhouse of Shuangjiangkou Hydropower Station,many kinds of rock failures of rock mass,such as cracking,slope,falling block and rock burst occurred seriously affecting the excavation progress.Therefore,it is of great importance to study the deformation,failure characteristics and mechanism,and evaluate the stability of surrounding rock during the construction period.In this paper,the phenomena and characteristics of surrounding rock failure of underground powerhouse of Shuangjiangkou Hydropower Station are investigated on site.The relationship between the apparent damage of surrounding rock and surrounding rock damage is established based on the monitoring results of surrounding rock loosening depthand deformation.Then,the laboratory tests of static state and dynamic state are carried out to measure strength parameters of the sample gathered from the field site.Then CT scanner is utilized to analyze the number of internal fissures in surrounding rocks in different areas.Finally,combined with field exploration and laboratory test results,the numerical simulation considering and not considering the layers is established respectively.The effects of the layers on the deformation and failure of the surrounding rocks are analyzed,and the stability of the surrounding rocks is evaluated.The main research contents are as follows.(1)Combined with the geological characteristics,geological structure and mechanical properties of surrounding rock of underground cavern of Shuangjiangkou Hydropower Station,the typical failures of surrounding rock of main powerhouse and main transformer chamber during the excavation of the middle drift is summarized.(2)According to the measurement results of acoustic wave method and multi-point displacement meter,the internal failure and apparent failure of surrounding rock are analyzed.It is found that the apparent deformation of main transformer chamber is larger than that of the main powerhouse,and the corresponding relaxation zone depth is greater than that of the main powerhouse,which indicates that the deformation of surrounding rock is closely related to damage.(3)Initial damage analysis of surrounding rock of main transformer room and main powerhouse is carried out,and its laboratory static and dynamic mechanical properties are studied.The initiation and propagation of cracks in rocks of main powerhouse and main transformer room under dynamic loading were studied by means of CT scanning of samples after dynamic testing.The mechanism of rock deformation and failure is studied from the microscopic point of view.(4)Based on the result of field monitoring data and laboratory tests,a discrete element numerical model is established to reproduce the distribution of stress state and displacement of surrounding rock after excavation and unloading.The results show that the redistribution of stress after excavation is the triggering factor of rock deformation failure.(5)Comprehensive analysis of field investigation data,field monitoring,laboratory experiments,construction conditions and numerical simulation results reveal the relationship between mechanical behavior of surrounding rock deformation and layers.The results show that the deformation and failure of surrounding rock during excavation of underground caverns are mainly controlled by layers,and the number of cracks is positively correlated with layers.The displacement of surrounding rock is mainly shear displacement in the stratum control area,while the displacement of other areas is mainly unloading rebound deformation.