Study On Seismic Safety Evaluation And Countermeasure Of Large Underground Caverns

The large underground cavern group in hydropower projects is often distributed in the mountain canyon area with complex geological conditions and located in high seismic intensity area.It has important theoretical and practical significance to study the seismic safety evaluation and countermeasure of large underground cavern group in order to prevent and mitigate earthquake disasters and protect people's lives and property safety.Currently,the study of seismic safety evaluation in the underground cavern is based on single indictors,such as displacement or stress,which cannot comprehensively evaluate the safety and stability of underground cavern in seismic load.In addition,the research of earthquake countermeasures is engrossed in urban road transportation and other fields at present,lacking of the analysis of the earthquake countermeasures in the underground caverns.In view of the existing problems in the seismic safety evaluation and countermeasure research of underground cavern group,a seismic safety evaluation method and system for underground cavern was put forward in this paper.This paper,combining with many advanced theories and methods,such as hydropower engineering 3D fine geologic modeling method,numerical simulation analysis method,safety evaluation theory and earthquake emergency management,carried out the earthquake safety evaluation and the earthquake disaster countermeasure research.The earthquake disaster analysis model provides the basic information for seismic safety evaluation and countermeasures research in underground cavern group.The finite analysis of seismic safety factors of underground cavern group and the sensitivity analysis of surrounding rock parameters provides the mechanical analysis data for the seismic safety evaluation and countermeasures of underground cavern group.The main research results are as follows:(1)Based on the comprehensive analysis of the project information,3D model and seismic information,the basic information analysis model of earthquake disaster evaluation for underground cavern group has been established.Large underground cavern group seismic evaluation and countermeasures require much information,so how to effectively deal with information and analysis is the first problem to consider in the earthquake safety evaluation of underground cavern group.Based on the engineering basis information,the 3D geological model of underground cavern group with complex geological structure was set up.Combining the selection principle and process of seismic wave,the basic information analysis model of earthquake disaster evaluation in underground cavern group was established.Based on the engineering information,3D modeling,information processing and seismic information from the basic information analysis model,this paper comprehensively and systematically carried out scientific and effective analysis of model and information required in the earthquake safety evaluation for underground cavern group.Thus,it provides data guarantee and research foundation for the research of seismic safety evaluation and emergency countermeasure system for underground cavern group.(2)Considering the earthquake safety and stability influencing factors for large underground cavern group with complex geological tectonic characteristics,the underground cavern surrounding block contact dynamic anti-sliding model has been established to study the mechanism of underground caverns seismic safety influencing factors.The complex strata,fault,soft interlayer and a large of number of joints and cracks distributed around the underground cavern group may bring about the curved blocks with different shapes,direction and size by the cross cutting action between the structure plane and the free face of the cavern.These are the reasons that cause instability under the action of earthquake underground cavern structure.To a large extent,these determine the damage characteristic and safety of underground cavern.Considering the influence factors of the seismic safety of the underground caverns,such as the friction and the bonding characteristic of the block with the surrounding rock,the fault characteristics of the surrounding zone and the location of the cavern section,the numerical simulation analysis of dynamic response characteristics of underground cavern and curved surface block structure under the influence of these safety factors was carried out firstly in this paper.Then,because of the existing bonding effect between the surface block and the surrounding rock mass,the underground cavern surrounding block contact surface dynamic anti-sliding was established.This paper analyzed the bond characteristic factors on the stability safety of single block,classes I adjacent block and II adjacent block in modified anti-sliding model,and studied the response of friction and bond parameters to the block structure in modified anti-sliding model.(3)Based on Garson algorithm and PaD2 method,the local and global sensitivity analysis of stability parameters of surrounding rock for underground cavern group under earthquake action was carried out,and the key parameters and the sensitivity of each parameter were determined.Currently,most of the sensitivity analysis studies in the field of hydropower engineering are concentrated on sensitivity analysis of the slope and foundation.In the rare cases of underground cavities,the frequently-used sensitivity analysis method is local sensitivity analysis based on mathematical statistics,lacking of global sensitivity analysis of earthquake safety and stability for underground cavern.Aiming at the shortage of above research,this paper carried out the local sensitive analysis on surrounding rock parameters according to the BP neural network with Garson algorithm,studied the elasticity modulus,Poisson ratio,cohesion,internal friction angle of the surrounding rocks base on the safety and stability analysis indices of the underground caverns and feature points of blocks.Fully considering the sensitive analysis of single factor,PaD2 method was chosen to conduct global sensitive analysis under the interaction between two factors,from which the ranks of sensitive coefficients of every parameter and the critical as well as the secondary critical parameters in the surrounding rock property information can be obtained.(4)With the comprehensive consideration of multi-criteria grade estimation of earthquake security evaluation,the safety evaluation model and method system of large underground cavern group has been proposed.Usually,the safety evaluation of underground cavern under earthquake is influenced by multi indices including displacement,acceleration,stress and so on.However,most of the researches evaluate the single index such as the displacement and acceleration,which leading to the obvious limitations of evaluating results.This paper combined the theoretical analysis,numerical simulation and optimization algorithm,and integrates strength reduction method,particle swarm optimization(PSO),projection pursuit method and set pair analysis model based on Vague set,to conduct the research on safety evaluation of large-scale underground cavern under earthquake.Also the safety evaluation methods and system of large-scale underground cavern under earthquake were built,proposing the comprehensive analysis method under earthquake considering the multi-index influence of displacement,acceleration,pressure stress and some other indices.Moreover,the safety evaluation method of underground cavern under earthquake was presented.Then,the effectiveness of this system and the reasonability of the results were verified through the Dowding C H and Sharma S evaluation methods respectively.(5)From the perspective of the management and decision-making research for earthquake disaster emergency,analysis countermeasure study on Large-scale Underground Cavern Group under seismic catastrophe has been conducted in this paper to effectively reduce the earthquake disaster loss.From the perspective of the management and decision-making research for earthquake disaster emergency,the seismic catastrophe countermeasure research,considering the characteristics of both earthquake disaster and the spatial distribution of underground cavern group,has been launched from the following aspects: the earthquake resistant effect,the emergency evacuation path,the earthquake disaster emergency management and the seismic prevention and disaster mitigation.At first,the anti-seismic effects lining support measures had on underground cavern group and the cavity structure dynamic response regular under different thickness of the lining were implemented.Secondly,on the basis of the security stability analysis results of underground cavern evacuation path,the Dijkstra method,the shortest path method and the yield of the evacuation path length were adopted to study the emergency evacuation path for maintenance staff when they are at the most unfavorable position.Then,aiming at the three phases: before,during and after the earthquake,the emergency management process of underground cavern was studied.The interactional cycle process among the three phases was discussed in the meantime.At last,the non-engineering measures,including geological analysis and site selection,measures to absorb shock,the control and repair of construction quality of underground cavern was researched.What's more,the non-engineering measures,the disaster prevention propaganda and drill,the guarantee for emergency resources,the earthquake emergency response administration and the earthquake emergency preplan were further studied.