Research On The Effect Of Blasting Vibration On The Initial Support Concrete Spray Layer Of Tunnel

At present,the excavation of mountain tunnel in China mostly adopts the method of drilling and blasting.This method has the advantages of economical and efficient tunnel excavation;however,the accompanying blasting vibration effect during the excavation process will affect the stability of the tunnel support structure and surrounding rock.Especially for tunnels with poor surrounding rock properties.As the supporting structure adjacent to the tunnel drilling and blasting face,the initial support concrete spray layer of the tunnel is most affected by the blasting vibration.Based on this,it is urgent and necessary to study and analyze the influence of the blasting vibration on the initial support concrete spray layer.Based on the Shenjiaba No.1 Tunnel of the Emei-Miyi Section Expansion Project of the Chengdu-Kunming Railway,through theoretical analysis,field test and numerical simulation,the vibration response of the initial support concrete spray layer of the tunnel under the action of blasting vibration is studied,and the vibration velocity and stress distribution law of the sprayed layer of initial support concrete;and on the basis of the study on the decay law of blasting vibration of shotcrete layer of initial support,the short-age(6h,12 h,24h,48 h,72h)initial support concrete under the action of blasting vibration is further studied.According to the law of damage,the safe step distance between the short-age shotcrete layer and the tunnel face and the safe vibration velocity threshold of the short-age shotcrete layer are analyzed.The main contents of the research are as follows:(1)The survey on the project overview,geological and hydrological conditions and drilling and blasting construction plan of Shenjiaba No.1 Tunnel was conducted.Design a blasting vibration monitoring program based on the research content,the vibration response of the initial support concrete spray layer during drilling and blasting construction is monitored and measured.The wavelet transform method is used to analyze the time-frequency of the blasting vibration signal,and the time-frequency characteristics of the blasting vibration signal are obtained.Based on the Sadov’s empirical formula,linear regression analysis was performed on the experimental vibration velocity data,and the blasting vibration decay law of Shenjiaba Tunnel No.1 was obtained,and the vibration velocity of the initial support concrete spray layer and the charge amount and the blasting center distance under the dynamic load of the blasting were fitted.The relationship curve is used to guide the drilling and blasting construction of the tunnel.(2)The finite element numerical model of Shenjiaba No.1 Tunnel is established to simulate and analyze the vibration response of the initial support concrete spray layer during the drilling and blasting construction of the tunnel.By comparing and analyzing the vibration velocity and stress distribution of the arch foot,arch waist and arch crown of the initial support concrete spray layer of the tunnel,the vibration velocity and stress distribution law of the initial support concrete spray layer under the blasting action are obtained;and the initial support concrete spray layer is combined the simulated vibration velocity and the empirical formula fitting vibration velocity were compared and analyzed,which verified the correctness and effectiveness of the numerical simulation.(3)Design a test plan for the influence of blasting vibration on the short-age initial concrete.During the test,the on-site blasting excavation was used as the test vibration source,and the short-age initial concrete test blocks produced in the test were placed at different distances from the blasting center to receive the blasting dynamic load.The study analyzes the relationship between the change of longitudinal wave velocity,compressive strength reduction and blasting center distance,concrete age and vibration velocity of the initial concrete test block,so as to obtain the damage law of the initial support concrete under the blasting action and the safety threshold of the blasting vibration velocity.(4)By modifying the parameters of the material model of the initial support concrete,five kinds of shotcrete layer models with different short age of 6h,12 h,24h,48 h and 72 h are obtained.The damage range of shotcrete layer with different short age under blasting dynamic load is simulated and analyzed,and then the safe step distance between shotcrete layer with short age and tunnel face and the safe vibration velocity threshold of shotcrete layer with different short age are obtained.By comparing and analyzing the safety vibration velocity of the initial support concrete spray layer obtained by numerical simulation with that obtained by experiment,the recommended safety vibration velocity of the initial support concrete spray layer with short age is optimized.