3D Geomechanical Model Test And Numerical Simulation Research On Coral Reef Limestone Underground Chamber

The coral reefs are the rock-soil mass formed by the remains of the hermatypic coral community during a long period of geological action.In petrology,the coral reefs are collectively called the reef limestone,which are carbonate rocks of marine biological origin.The coral reefs of China are mainly distributed and the only land type of China in the South China Sea.The development and utilization of underground space in reef limestone formations becomes an important support for the construction of marine engineering in the South China Sea.Due to the particular composition and development environment of the reef limestone,its surrounding rock stability in underground engineering construction is significantly different from that of other terrestrial rocks.In the construction of engineering facilities,it is inevitable to encounter a large number of mechanical problems in the deep coral reef limestone formations.Therefore,the use of physical model experiments and numerical calculation methods to research on coral reef underground chamber excavation is a major requirement of the national marine strategy,and it is one of the key technologies for the development and utilization of underground space resources in the reef limestone area.This paper focuses on the stability of surrounding rock in underground chamber excavation of coral reef limestone by physical model experiments and numerical calculation.The main research contents and results of this paper are as follows:(1)The quartz sand,barite powder,high-strength gypsum,calcareous sand,cement and water are selected as the raw materials.Based on the similarity theory,the similar materials of reef limestone are configured by orthogonal proportioning tests and physical mechanical tests.The ratio scheme of quartz 12%:barite powder 30%:calcareous sand 10%:high-strength gypsum 6.6%:cement 13.4%:water 28%was selected to simulate the reef limestone with a uniaxial compressive strength of about 10MPa.(2)A three-dimensional geomechanical model excavation experiment of a coral reef limestone underground chamber was carried out.The displacement and stress of the surrounding rock during the chamber excavation were analysed under 7 working conditions.(3)According to the displacement change law of each monitoring point during the chamber excavation,the displacement and deformation of the rock mass are divided into three stages:?)Advance displacement and deformation of the front rock mass;?)The sudden increase in displacement and deformation of the revealed surrounding rock;?)Stable displacement and deformation of the surrounding rock.According to the stress change law,the stress changes of the chamber vault,spandrel,haunch and bottom surrounding rock showed a zigzag trend during the excavation of the chamber.The stress is in a stable state at the beginning.As the excavation gradually approached the monitoring section,the stress at each monitoring point shows a downward trend,and the stress release rate gradually increases,After the excavation revealed the location of the monitored section,the stress drops sharply,the stress release rate increases rapidly,and then becomes stable.(4)Numerical calculations were carried out for the influence of the buried depth of the underground chamber and the strength of the reef limestone on the stability of the surrounding rock during the chamber excavation.By analyzing the displacement and stress changes of the surrounding rock at the monitoring point,the.The influences of the buried depth and the strength of reef limestone on the stability of surrounding rock during excavation were obtained.(5)The method of numerical calculation is used to simulate the change laws of displacement and stress during the chamber excavation under working conditions 1 and 5.The displacement and stress change laws of the surrounding rock in the model experiment are similar to the numerical calculation results.The average error of displacement between the physical model experiment results and the numerical simulation results is about 21%,and the average error of stress release rate is about 6%.The results of the physical model experiment have certain accuracy,so the displacement and stress change laws in this model experiment have a useful engineering reference value.The results of this study have certain reference significance and engineering application value for the excavation of underground chambers in reef limestone formations.