Analysis Of Surrounding Rock Stability In Underground Caverns Of Jiangmen Neutrino Experimental Station

With the acceleration of the country's urbanization process,the per capita living space is constantly decreasing,and cities are becoming more and more crowded.Therefore,it is urgent to find solutions to change the living environment of human travel and residence.There are very few humans that can be exploited on the ground space,and underground space has not been fully utilized due to the difficulty of its development.For large-scale underground engineering,if the safety and stability of the construction project can be numerically simulated at various stages of the construction project,combined with the comparative analysis of the measured data of the project,the weak points of the cave structure and the possible damage forms of the cave can be found,and the corresponding measures should be taken in advance accordingly.Support measures will definitely reduce accidents,economic losses and casualties.This article takes the underground experimental hall of Jiangmen Neutrino Experimental Station in Guangdong Province as the engineering background,and builds a finite element model of the underground experimental hall by using large-scale finite element software ANSYS to study the stability difference of the experimental hall before and after the support,and enters the El Centro wave duration This paper analyzes the dynamic response of the experimental hall before and after its support under horizontal earthquakes,and gives the static and dynamic characteristics of the supporting structure of the underground experimental hall.The main research contents and conclusions of the paper are as follows:(1)A finite element model of the underground experimental hall was established,and the stability of the experimental hall under static force was numerically simulated.The structural weakness of the experimental hall was explained,and the stress conditions of the lining and the anchor were analyzed.The strength reduction method was used to solve the safety factor of the experimental hall before and after the support under static force,and the stability of the underground experimental hall was comprehensively evaluated based on the specifications and the displacement and stress data of the cavern.(2)The time-history analysis method is used to compare and analyze the displacements,stresses,and other responses of the experimental hall before and after the support under horizontal earthquakes,revealing the deformation law of the experimental hall under dynamic action,and supporting the lining and anchors.The dynamic response of the structure is analyzed,and the degree of influence of the earthquake on the structure under static force is explained.(3)Under the action of static force,the displacement of the cave is symmetrically distributed under the vertical uniform load,and the change law is obvious.The horizontal displacement and the circumferential displacement before and after the support are distributed in a sinusoidal curve,and the vertical displacement and radial displacement are approximately presented.Normal distribution,the horizontal displacement magnitude is millimeter level,and the vertical,radial,and circumferential displacement magnitude is centimeter level.After the support,the displacement of the nodes in all directions of the cave decreased to varying degrees.The vertical displacement of the nodes was positively related to the distance from the bottom of the model.The larger the displacement,the more obvious the effect was after support.However,the supporting structure did not change the deformation law of the cavern,and the position where the maximum displacement occurred in each direction did not change significantly.The area with large vertical displacement is mainly located near the upper vault,and the area with large horizontal displacement is mainly located near the middle of the high side walls on both sides.(4)The tensile stress concentration area of the cave under static force is mainly at the upper part of the middle of the upper and lower side walls and the lower arch waist,and the compressive stress concentration area is mainly at the upper arch feet and the lower wall foot.After the support,the stress generated by the compression in all directions of the cave decreases to varying degrees,and the stress generated by tensile increases to varying degrees.The compressive stress area of the cave is significantly smaller than that when the support is not taken.The stress area increases,which makes the area with greater stress in the underground cavern smaller,the area with less stress increases,and the stress distribution in the cavern is more uniform.For underground structures dominated by compression,the stress concentration area can be reduced,and the probability of stress-type failure in the cavern can be reduced.(5)The safety factor of the cavern after support under static force is increased compared to when the support is not adopted.The safety factor is essentially a conversion of the material strength of the rock mass into a clear indicator,to a certain extent.It is beneficial to the quantitative analysis of the stability of underground engineering.However,this safety factor only reduces the two factors of cohesion and internal friction angle.Using this safety factor cannot independently evaluate the stability of the cavern.Deformation,stress,and tunnel construction excavation specifications evaluate stability and safety.(6)The deformation and stress of the cavern under earthquake are not significantly changed compared with the static force.The displacement and stress of the cavern before the support gradually stabilize with time fluctuations,and the displacement and stress values after thesupport are more stable than those of the support.The overall front is significantly reduced.Although the value of stress and displacement at a few locations is increased or changed from that before the support,its absolute magnitude is small and does not affect the stability of the cavern.Secondly,according to the time-history curve of displacement stress,it can be known that the support measures can reduce the fluctuation of the displacement and stress of the cavern under the earthquake,so that the nodes of the cavern tend to stabilize more quickly,which is very conducive to improving the stability and stability of the surrounding rock of the cavern.safety.(7)Locations with large bending moments and shear forces of the tunnel lining under static and dynamic forces are mainly located at the upper arch foot,upper wall foot,and lower wall foot.The surrounding rock is prone to crush damage.Therefore,the lining support should be strengthened in the weak position of the structure.Protection thickness,or increase the lining reinforcement to ensure safety.The overall anchor bolts show a trend of tension.The axial force of the anchor bolts in the caverns gradually decreases from the air surface to the inside of the rock mass as the anchor rods penetrate deeper,especially in the support design of city gate tunnels.This law is more obvious in other parts.Of course,the anchor shaft forces such as arch feet and wall feet in special parts will change abruptly,affecting the stability of the structure.(8)According to the "Code for Construction of Underground Excavation Engineering of Hydraulic Structures" and "Code for Design of Hydraulic Tunnels" and the static and dynamic effects of the experimental hall before and after the support,the displacement and stress of the test hall are comprehensively judged when the support measures are not taken.The underground experiment hall of the sub-experiment station is in an unstable state,and it is in a stable state after support,and the safety is good.