Experiment Research On Dynamic Failure Of Locked Segment In Touzhai Rock Avalanche

Rock avalanche as a kind of geological disasters with strong destructiveness,great harm,high monitoring difficulty and a wide range of impact,accompanied by small earthquakes,it has always been the focus of scholars both at home and abroad,and its destabilizing mechanism is the hot and difficult point of studying such disasters.This article takes Tou Zhai rock avalance disaster as an example,Through field investigation and indoor rock sample shear test,acoustic emission monitoring technology,microseismic monitoring technology and high-speed camera monitoring technology as a monitoring tool,Study on the dynamic instability mechanism and the vibration acceleration of the rock burst on Tou Zhai rock avalanche,The critical acceleration of Tou Zhai rock avalanche instability is calculated by the renormalization group theory and its failure mode is analyzed.The results show:(1)Studying the kinematic characteristics of TouZhai rock avalanche,Tou Zhai rock avalanche has the characteristics of high speed(maximum speed of 87m/s),long distance(the farthest distance of 3.5km)and low apparent friction angle(H/L=0.237).At the same time,the occurrence of Tou Zhai rock avalanche is accompanied by an earthquake event of about magnitude 4,resulting in the above characteristics resulting from the dynamic instability of the locking section instability.In order to identify the locking section dynamic instability basis,the equivalent diameter and accumulation position of the massive rock in the Tou Zhai rock avalanche area and the grading features of the fine particles were investigated.Massive rock are mostly concentrated in the lower part of the accumulation body,the equivalent directly more than 1~2m,and a small amount of equivalent size of 6~7m lmassive rock distributed in the desposition fan,while the fine particle sieve test The experiments show that the characteristics of fine grading are basically the same from the shear opening to the desposition fan.The above investigation shows that the failure mechanism of the TouZhai rock avalanche lies in the fact that the basis of the dynamic instability of the locking section is undoubted.(2)In order to find out the instability mechanism of locking section,shear tests on rock samples of 5×5×5cm and 13×13×13cm were carried out respectively,and the acoustic emission monitoring technology and microseismic monitoring technology were used as monitoring measures.AE test results show that the destruction of rock samples are divided into four stages:initial compression phase,elastic stage,plastic stage,and unsteady development stage.At the same time,the damage of rock samples can be divided into two kinds:one is that the rock samples are damaged only once or twice,and the energy generated by the damage is larger;the other is that the rock samples are destroyed many times,The resulting energy is smaller,namely"burst tire instability"and"slow spreading gas instability."Facts have proved that only"flat tire"instability in order to produce a similar rock avalanche catastrophic geological disasters.Microseismic monitoring tests show that the maximum acceleration caused by rock sample damage is up to 40g,which explains the phenomenon of rock avalanche disaster accompanied by earthquakes.The test uses two kinds of fixture with the shear zone of 1cm and 5cm.The test results show that theshear zone of the different width has a great influence on the test result.The rock specimen with the width of 5cm Tou Zhai rock avalanche more in line with the actual situation.The damage process of rock samples monitored by high-speed video cameras found that the failure of rock samples started from the boundary of the rock samples and penetrated to the other side,eventually destroying the rock samples.At the same time,the crack caused by the rock sample destruction is not a uniform shear fracture surface,but a shear fracture zone formed by the echelon tension fissure,match with TouZhai locking section stepladder landform.(3)According to the direct calculation method and the actual situation of TouZhai rock avalanche,the peak accelerations of TouZhai are calculated as 1.4×10~4m/s~2(width of shear slit 5 cm)and 3.4×10~5m/s~2(width of shear slit 1 cm).The renormalization group theory is used to calculate the critical failure probability of rock sample damage,Combined with the actual situation of Tou Zhai rock avalanche,the critical accelerations of the failure of the TouZhai rock avalanche sections are calculated to be 7.02×10~4 m/s~2(width of shear slit 1 cm)and 2.98×10~3 m/s~2(width of shear slit5 cm).And the failure modes of the failure process of the locked section are established.They are the failure modes of bottom instability at the beginning of the end,instability of the central part of the beginning of the end and the instability of both sides.