Fluid-Solid Interaction Based Study On Evolution Of Surrounding Rocks Around The Underground Powerhouse Of A Hydropower Station

As one of the most critical pivots of hydropower construction,the safe construction and stable operation of underground powerhouse system is the top priority of hydropower projects.The underground powerhouses of hydropower projects are not only large in scale,but also exist in complex in-situ stress field and seepage field.The interaction between the two fields under the condition of engineering excavation is the key factor for the stability of surrounding rock.To this end,relying on a hydropower project,taking the underground powerhouse system as the research object,based on the principle of fluid-solid interaction,using on-site investigation,internal and external experiments,and numerical calculation methods,the research on the dynamic evolution law of the surrounding rock of large underground caverns under the action of fluidsolid interaction is carried out.The main research results are as follows:（1）The permeability of rock mass in the study area is mainly weakly permeable,and the rock mass permeability has significant anisotropy.The anisotropic seepage model using permeability tensor as the seepage characteristic parameter can more accurately reflect the actual state of rock mass seepage.（2）The formation of rock mass stress field in the study area is complex,which is affected by multiple factors such as valley stress,tectonic stress and rock mass self weight.In the near-surface area,the principal stress direction is obviously deflected.As the burial of the rock mass increases,the stress distribution gradually tends to the state of the self-weight stress of the rock mass.The stress level of the powerhouse location is low,and the overall stress field is medium and low.（3）After the excavation of the cavern,a low water pressure area appears centered on the powerhouse area,forming a water pressure drop funnel.The distribution of seepage vectors is the most densely on the left wall of the main powerhouse and the right wall of the surge shaft,and the distribution of pore pressure due to the excavation of the cavern shows a certain spatial difference.The position of the middle section of the workshop is the area where the pore pressure changes the most.（4）Under the fluid structure interaction,compared with the condition without seepage,the rock mass stress increases as a whole before excavation,and the increase of the minimum principal stress is the most obvious.After excavation,the interaction action intensifies the stress release and concentration of the surrounding rock.At the same time,the existence of anisotropic seepage field makes the stress redistribution of the surrounding rock more complicated,and the deformation of the surrounding rock of the cavern also increases significantly.The disturbed depth of rock mass caused by excavation and the extent of surrounding rock plastic zone increased significantly at local locations.（5）The fluid-structure interaction has more significant spatial differences in large underground powerhouses.Changes along the height and axial direction of the cavern.Compared with the no seepage condition,the interaction effect on the stress and deformation distribution of surrounding rock at different positions of the cavern has obvious differences.The effect of fluid-solid interaction varies with the depth of the rock mass and the height of the water head.increases,the more significant the performance.