Research On Microseismic Monitoring Of Rock Mass Collapse During Tunneling Through Karst Cave District

In recent years a large number of highway tunnels have been built in the southwestern region of China,and radical changes in burial depth(from shallow,such as a dozen meters,deep buried Jinping 2.5km)and tunnel length have occurred.It is worth mentioning that the detection and warning of landslide disasters in karst tunnels has become a major problem in engineering.At present,the conventional monitoring methods can not play an early warning role in time due to the phenomenon of tunnel overexcavation,resulting in frequent tunnel collapse disasters.Microseismic monitoring technology has been widely used because of its three-dimensional,integrated and real-time characteristics,which can make up for the shortcomings of conventional monitoring methods.In order to explore the spatio-temporal evolution law of microseismic events of construction collapse disaster during tunneling through karst cave district,based on the WenQuan tunnel of the extension section of Zunyi to Suiyang Expressway in Guizhou Province,the following work has been carried out by using microseismic monitoring technology combined with field geological data:The geological overview of the WenQuan tunnel is briefly introduced,indicating the main karst collapse disaster of the WenQuan tunnel.Combined with the theory of seismology wave,the theoretical basis,basic principle,system composition and function of the microseismic monitoring system are introduced.Combined with on-site geological data,design conditions and construction methods,a microseismic monitoring system scheme for the joint deployment of inside and outside the karst tunnels is proposed.The monitoring scheme is implemented on site and microseismic data are collected.The quality evaluation of the microseismic monitoring data of the WenQuan tunnel was carried out,and the three aspects of microseismic signal filtering,noise reduction,microseismic signal identification and microseismic signal localization were described.Statistical analysis of microseismic data location error distribution shows that the data quality can meet the needs of surrounding rock stability evaluation.Through the analysis of microseismic data processing,the change of prediction index of microseismic monitoring in the process of collapse is studied,the results show that before the collapse,the number of microseismic events and microseismic energy show the rule of initial stable-rapid growth-decline-rapid growth-decline damage.With the passage of time,the microseismic events gradually gather in space,and the gathering location is near the collapse area.The spatial evolution of microseismic events can reflect the damage of surrounding rock.The cumulative apparent volume shows the rule of initial steady growth-fast growth-steady growth-fast growth-destruction.The b-value shows the rule of rising-falling-rising-falling-destruction.The energy fractal dimension gradually increases with time,and there are 2 extreme points.The stress drop shows the rule of initial stable-sharp decline-sharp rise-sharp decline-sharp rise-sharp decline-sharp rise-decline damage.Therefore,in the actual construction process,the relationship between the surrounding rock collapse and the site construction should be established.The spatio-temporal evolution law of microseismic events of construction collapse disaster during tunneling through karst cave district is explored,and the feasibility of microseismic monitoring applied in the early warning of karst tunnel collapse is determined.