Study On Deformation Response Mechanism Of Surrounding Rock And Supporting Measures For Layered Excavation Of Extra Large Underground Caverns

The layered excavation of the cavern leads to continuous adjustment of the surrounding rock stress,and the deformation and failure of the surrounding rock is significant.Its specific performance is:Damage of surrounding rock slope of crown arch is serious;Affected by C2 interlayer dislocation zone,surrounding rock deformation obviously leads to block instability and failure;When the cavern is excavated to the seventh floor,the deformation of surrounding rock in the upper part of the cavern keeps increasing rapidly,which leads to the overloading failure of some roof arches against the anchor cables and the upper and middle prestressing anchor cables in the side walls.The essence of surrounding rock failure is that the deformation of surrounding rock is too large.Based on the monitoring data of multi-point displacement meter,combined with rock mechanics test,full-hole imaging technology,acoustic monitoring and other means,the deformation response mechanism of surrounding rock in layered excavation of caverns is analyzed.The finite element numerical simulation software is used to predict the subsequent deformation of the surrounding rock in the excavation of the cavern.The prestressed anchor cable parameters are optimized according to the prediction results.The numerical simulation calculation and evaluation are carried out.The main main points are as follows:1)The difference of rock mass quality results in that the deformation of surrounding rock at S side of powerhouse is larger than that at N side of powerhouse;Influenced by geological structure,the deformation of surrounding rock is large in the left 0+228 and the left 0-10 of the power-house.With the development of layered excavation,the areas with better integrity of roof arch surrounding rock show the elastic deformation characteristics of first upward rebound and then small settlement,while the macro-deformation of surrounding rock is small.The plastic deformation characteristics of continuous large subsidence in the area of fractured rock mass.The difference of deformation between upper and lower side walls is small,and the deformation of upper side walls with higher elevation is larger than that of lower side walls with lower elevation.2)In the area where the deformation of the surrounding rock is large,the stress increases rapidly with excavation,and there is a large overload or even failure.When the surrounding rock of the side wall is in a relaxed state,the stress loss rate of the anchor of the upstream side wall is higher than that of the downstream side wall.In tension,the opposite is true.With excavation,the upper side wall anchor cable has a large overload phenomenon,while the lower anchor cable stress growth rate is small,even a small amount of relaxation.3)Based on the parameters obtained from rock mechanics test,the mechanical parameters of surrounding rock excavated in the fourth floor are selected by repeated iteration calculation with displacement back analysis method.The deformation response of surrounding rock under stratified excavation is obtained by finite element numerical simulation.Although the position with the largest deformation is in the side wall,the higher the elevation,the smaller the displacement release rate of the side wall,and the subsequent deformation is larger The sooner the side wall is excavated and exposed,the greater the deformation in the later stage,the ratio of deformation of surrounding rock before and after excavation is about 35?68%.The deformation of surrounding rock decreases slowly with the increase of surrounding rock depth,and the convergence speed is slower.4)The stress response of surrounding rock in stratified excavation is accompanied by different types of damage in surrounding rock.In the first four layers of excavation,the compressive stress at the top of the arch and excavation continues to rise,and the local surrounding rock is damaged by the piece.The third layer of excavation generates tensile stress only on the upstream side wall and localized damage to the surrounding rock.The fourth layer excavation,the area of increased tensile stress is more significant,combined with the structural surface to produce block instability and other damage.5)Prestressed locking value should be increased for roof-arch stable surrounding rock support.The roof arch unsteady surrounding rock support scheme is similar to the reinforcement scheme of the side wall anchor cable.The most important thing is to control the plastic deformation of the shallow surrounding rock and increase the integrity of the rock mass.It should increase the anchoring depth and increase the anchor cable.Cross-sectional area and reduction of pre-stress lock value.For areas with good surrounding rock stability,the anchoring time can be appropriately delayed.6)After the support measures are optimized,the displacement release rate is calculated by numerical simulation.The displacement release rate of surrounding rock in the upper part of the cavern and the upper part of the side wall is improved compared with that before optimization.It is proved that the subsequent deformation of the surrounding rock is small,so that the prestressed anchor cable is not stretched too much,so that it does not suffer from overload tensile failure.The displacement release rate of the surrounding rock in the middle and lower part of the side wall is reduced,and the subsequent deformation is improved,which is beneficial to the full tension of the prestressed anchor cable and exert its proper supporting effect.