Numerical Analysis Of Stability Of Caverns In Construction Process

In the projects of hydropower development and mining,underground caverns with different scales will form.The stability of caverns is a difficult and hot topic in underground engineering research.The topic selection has great theoretical significance and important engineering value.Taking the recovery stability of a copper mine of Tongling Nonferrous Metals Group as the engineering background,relying on the Hunan Provincial Natural Fund Key Project?13JJ2033?and the Zhuzhou United Fund?2018JJ4007?,based on the principle of elastic-plastic mechanics,the stability evaluation method of the cavern group was studied.Comprehensive use of damage proximity parameters,strength reduction method and loading and unloading response ratio theory,FLAC3D numerical simulation of the stability of the cavern group during construction.The main research content is as follows:?1?The FLAC^3D software was used to simulate the distribution of the stress field during the excavation of the cavern group,and the stress field was described according to the distribution characteristics of the rock masses,,and Lode.The damage closeness index was introduced to analyze the safe state of the rock mass during the excavation of the cavern group.The study shows that the damage proximity not only gives the extent of the plastic zone,but also gives the damage degree of the rock mass beyond the plastic zone.The danger of caverns.?2?Based on the analysis of the construction excavation method and the excavation sequence between the chambers in the cavern group,the effects of various excavation methods on the stress field,displacement field and damaged area of the surrounding rock were compared.The following conclusions were drawn:First,compared with full-section excavation,the maximum principal stress,displacement,and volume of the plastic zone are reduced.Second,comparing the two excavation sequences,the study shows that the two excavation sequences have little effect on the stability of the cavern group.?3?Based on the principle of strength reduction method,a method to induce the overall safety factor and induce the local safety margin is proposed for the cavern group.The strength reduction method is combined with the Hoek-Brown criterion and the Mohr-Coulomb criterion to analyze the stability of the cavern group.The conclusions are as follows:Using the Mohr-Coulomb criterion strength reduction method,the equivalent plastic strains of the rock masses between the various caverns are interpenetrated as the instability criterion of the cavern group,and the safety factor is obtained as 1.53.By introducing a condition artificially,that is,applying load induction to the cavern group,the local safety margin of the cavern group is analyzed.The study shows that the sensitivity of the safety margin changes near the top centerline of the cavern group is the highest.Using Hoek-Brown criterion strength reduction method,the stress,displacement and plasticity distribution of surrounding rock in different excavation stages of cavern group were analyzed,and the safety factor of the cavern group was 1.65.The difference in the overall safety factor between the two is 8%.?4?The monitoring points are arranged inside the cavern group.Through the dynamic load action,the general law of deformation of the cavern group is sought.The LURR theory is introduced.The loading and unloading response ratio model of the cavern group is established and the cavern is obtained.The loading and unloading response characteristics of the group.By using the displacement,velocity,and acceleration as the response parameters,the loading and unloading response ratio model proposed in this paper is used for calculation.It is found that the load-unload response ratio time-series curve characterizes the nonlinear characteristics of cavern group instability,indicating the adoption of displacement,velocity,and acceleration.The loading and unloading response ratio of the response parameter is a feasible method for the stability prediction of the cavern group.In summary,this paper studied the stability of the cavern group by using different numerical calculation methods.The evaluation of the stability of the cavern group should be selected in combination with the actual conditions of the project.In the absence of a cavern,first select the general analysis method for the stability of the cavern group,taking the stope of the Dongguashan mining area as an example,and pass the stress field,displacement field,Parameters such as plastic zone and failure proximity qualitative analysis of the stability of the cavern group,followed by the implementation of strength reduction method,quantitative evaluation of cavern group stability.In the case of existing caverns,the theoretical analysis of loading and unloading response ratios was selected,and the monitoring of the surrounding rock mass of existing caverns was used to predict the stability of the cavern group.