Experimental Research On The Effect Of Blasting On New-cast Ultra-short Age Second Lining Concrete Of Tunnel

With the rapid development of highways,railways and rail transit in China,mountain tunnel construction has become the first choice to overcome elevation and plane obstacles.Because of the instability of the surrounding rock of the tunnel,the construction of the tunnel may cause geotechnical deformation,land subsidence,collapse and other disasters.In order to ensure the safety and integrity of the tunnel,the second lining structure of the surrounding rock blasting excavation of grade IV and V is closely followed by the face of the tunnel.However,the second lining structure closely following the face of the tunnel will cause the blasting construction to have a certain impact on the quality of the second lining structure,so it is of great significance to study the impact of blasting vibration on the newly poured ultra-short age second lining concrete of the tunnel for the construction of the tunnel.Based on the project of Laomuyu No.2 Tunnel in Zhangjiajie,through theoretical analysis and field test,this paper studies the concrete blocks newly poured for the second lining in the ultra-short age of tunnel blasting construction,and obtains the law of damage disturbance and intensity disturbance,which can provide some reference for the future study of blasting vibration on the second lining structure of tunnel.The specific contents of this paper are as follows:(1)The development history of the influence of blasting vibration on the secondary lining structure at home and abroad,the propagation law and the influencing factors of tunnel blasting excavation are expounded.This paper introduces the application of blasting seismic wave propagation characteristics and blasting vibration to the second lining structure in tunnel blasting.(2)Based on Lao Muyu No.2 Tunnel Project,the general situation of the project,geological conditions and blasting construction scheme are introduced.Based on the orthogonal test,the influence factors of blasting vibration on the secondary lining structure are discussed.The three factors and four levels test scheme in the orthogonal test is adopted.Through analysis and calculation,the sensitivity from high to low is: concrete strength,detonation center distance and concrete age.(3)According to the results of orthogonal test,three groups of test combinations with different strength,different age and different spacing of detonation centers were designed,and all the composite concrete blocks were placed in the tunnel to carry out a blasting vibration test.After blasting vibration,the vibration concrete blocks and the concrete blocks without blasting vibration are put into the standard curing room for maintenance.(4)After 28 days of curing all concrete blocks,the time,amplitude and frequency of ultrasonic wave propagating in vibration concrete blocks and ordinary concrete blocks are measured by non-metallic ultrasonic testing instrument.Then the ultimate load of concrete blocks with different strength is measured by pressure testing machine.Finally,the influence law of blasting on secondary lining concrete blocks is analyzed based on the test results.Combining with the engineering practice,the control measures of blasting vibration are put forward.