| With the continuous construction of tunnel and underground engineering and the complexity of geological conditions in the western region of China,the research on high ground stress and rock burst is particularly important.The new and old Erlang mountain tunnels are in the same tectonic setting,and their geological conditions are similar,but the rock burst in the two tunnels in the construction is quite different.The new Erlang Shan Tunnel has a deeper buried depth and a longer length,but the rock outburst is far weaker than the old Erlang mountain tunnel.Therefore,it is necessary to make a comparative study on the characteristics of the development of rock burst in the new Erlang mountain tunnel,and to find out the reasons for the difference of rock burst and provide reference for other tunnel projects through Erlang mountain.On the basis of the present situation of the research on rock burst at home and abroad,combined with the geological conditions and the characteristics of the development of rock burst in the new Erlang mountain tunnel,the development rule of rock burst in the new Erlang mountain tunnel is summarized,and the similarities and differences of the characteristics of the rock burst in the new Erlang mountain tunnel are analyzed.Secondly,the new old Erlang is combined with the new and old Erlang.The geostress test results and numerical simulation methods are used to discuss the variation characteristics of the geostress in the tunnel area before and after the strong earthquake,as well as the influence of the ground stress on the new Erlang mountain rock burst.Third,the influence of the rock mechanics on the rock burst in the new Erlang Mountain Tunnel is analyzed with the uniaxial test of the rock mechanics and the rockburst tendency index.Finally,the influence of geological structure and surrounding rock quality on rockburst is analyzed.Through the study,the main achievements are as follows:(1)In the old Erlang mountain tunnel,there have been more than 200 different intensities of rock burst,including strong rock burst in the surrounding rock section of 19 m.The new Erlang Mountain Tunnel mainly consists of slight rock burst,13 m long medium rock burst section,and no strong rock burst.Generally speaking,the rock burst condition of the new Erlang mountain tunnel is not as strong as that of the old Erlang mountain tunnel.The rock burst in the new Erlang Mountain Tunnel occurred in hard and intact rock mass,and the old eriro mountain rock burst occurred in sand y mudstone,siltstone,sandstone and quartz sandstone,and the rock burst in the new Erlang Mountain Tunnel occurred only in the granite.(2)The maximum principal stress 35.3MPa of the old Erlang mountain tunnel is measured in depth(750m),and the maximum principal stress 29.1MPa of the new Erlang mountain tunnel is measured(burying depth 1252m).From the absolute value point of view,although the old Erlang mountain tunnel has a deeper depth than the new Erlang mountain tunnel,its geostress is higher than that of the new Erlang mountain tunnel.(3)Through the inversion analysis of the change of the stress field in the new Erlang Shan Tunnel before and after the strong earthquake in Longmen mountain,the maximum main stress of the tunnel after the earthquake is reduced to 41 MPa from the 50 MPa before the earthquake,and the stress of the tunnel site is released to a certain extent after the strong earthquake.After the earthquake,the stress field of the fault and its nearby stress field decrease obviously.Therefore,the reduction of ground stress makes the occurrence of rock burst in the new Erlang Mountain Tunnel decrease correspondingly.(4)The rock uniaxial compression test shows that the rocks of quartz sandstone,siltstone,limestone and sandy mudstone in the rock burst area of the old Erlang Shan Tunnel all have type II destruction,while the sandrock,siltstone and quartz sandstone in the new eriran mountain tunnel are all type I failure,and only the granite is type II failure.From the perspective of rock mechanics properties,the rock brittleness of the new Erlang mountain tunnel is similar to that of the old Erlang mountain tunnel,which is not conducive to rock burst.The test of rock burst tendency index Wet also shows that the Wet index of quartz sandstone in the old Erlang Shan Tunnel is more than 2,and a slight rock burst occurs.The Wet index of quartz sandstone in the new Erlang mountain tunnel is less than 2,the rock burst is not occurred,the granite Wet index is 2.28,and a slight rock burst occurs.The test results are basically consistent with the rock burst characteristics of the new and old Erlang Mountain Tunnel in engineering practice.The effect of lithology on the rock burst of the new Erlang mountain is verified from the experimental point of view.It shows that the rock burst tendency index is high under the lithologic condition of hard brittleness,which is beneficial to the occurrence of rock burst.(5)Although many fracture zones are developed in the old Erlang mountain tunnel,the influence zone of the tunnel is narrow,tight and cemented,and the surrounding rock around the fracture zone of this background i s beneficial to the storage of strain energy.The fracture zone of the new Erlang Shan Tunnel has a high degree of fragmentation and affects its bandwidth.Its surrounding rock is not conducive to strain energy storage.The difference in geological structure influences their rock burst characteristics to a certain extent.Because the fault fracture zone of the new Erlang mountain tunnel is not conducive to the storage of rock mass energy,the rock burst characteristics of the new Erlang Shan Tunnel are not as obvious as those of the old Erlang mountain tunnel.(6)According to the construction of surrounding rock grade,the proportion of class II and III surrounding rock in the new Erlang mountain tunnel is 6.26% and 17.15% respectively.The proportion of second class and grade III surrounding rock in old Erlang Shan Tunnel is 29.44% and 52.90% respectively,which shows that the surrounding rock integrity of old Erlang mountain tunnel is good.From the basic conditions of rock burst,rock burst usually occurs in the whole hard rock,that is,the rock stratum with better surrounding rock,and the surrounding rock of the new Erlang mountain tunnel is poor,which is not conducive to the occurrence of rock burst. |
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