Study On The Influence Of Deep Foundation Pit Blasting On The Vibration Of Adjacent Subway Tunnel

During the blasting excavation of subway tunnel,the impact of blasting on the vibration of ground buildings is usually considered.After the completion and operation of subway,the impact of foundation pit blasting excavation on the vibration of adjacent subway tunnel becomes an important factor threatening the safety of subway.In this paper,based on the foundation pit project of a blasting excavation within the protection area of Qingdao Metro Line 13,combined with the tunnel vibration monitoring data,through FLAC3 D numerical simulation,the vibration effect of blasting excavation of foundation pit on the adjacent Metro Line 13 is studied from three aspects of stress,displacement and speed.The specific research contents and results are as follows:(1)According to the general situation of the foundation pit project and the general situation of the affected tunnel,the numerical simulation model is established.According to the parameter table of the geological investigation report,the parameters are reasonably selected.Based on the parameters of the foundation pit blasting scheme,the triangular pulse load is used to calculate the blasting load equivalently.With reference to the vibration monitoring scheme of Metro Line 13,the monitoring point is set to simulate the blasting excavation of the foundation pit It is proposed.The accuracy of the numerical simulation results is verified by comparing the numerical simulation results with the actual engineering data.At the same time,the monitoring data is fitted according to Sadovsky formula,and the relationship between the blasting vibration speed and the distance of the foundation pit is obtained.(2)From the aspect of foundation pit blasting,three factors are selected,which are blasting charge,blast hole layout and delay time.The results show that under the same blasting network,the larger the blasting charge is,the greater the tensile stress,displacement and vibration speed of the maximum principal stress on the blasting side of the tunnel will be;under the same blasting charge,the more the number of single blasting holes,the more the blasting charge is dispersed,the greater the distance between the holes and the tunnel will be,and the greater the tensile stress,displacement and vibration speed of the maximum principal stress on the blasting side of the tunnel will be small.Under the condition of a certain amount of blasting charge,the different arrangement of blastholes will have different vibration effects on the adjacent subway tunnels.In the horizontal direction,in the case of a single row of blastholes,when the blastholes are arranged perpendicular to the tunnel,the tensile stress value,displacement and vibration speed of the maximum principal stress of the tunnel are far less than that of the blastholes arranged parallel to the tunnel.In the vertical direction,in the case of two rows of blastholes,when the front and rear rows of blastholes are arranged on the same step,the tensile stress value,displacement and vibration speed of the maximum principal stress of the tunnel are less than that of the front and rear rows of blastholes arranged on two steps.Millisecond delay blasting technology can effectively reduce the damage of blasting vibration.In the case of delay blasting,the tensile stress value,displacement and vibration speed of the maximum principal stress of the tunnel are significantly smaller than that of simultaneous blasting.The longer the blasting delay time is,the more independent the influence of each section of blasting on the tunnel will be,and the fluctuation of each measuring point curve will show obvious periodicity.(3)From the shape and span of tunnel section,the vibration effects of foundation pit blasting on horseshoe,straight wall semicircle arch and circular tunnel are studied.The results show that in the process of foundation pit blasting,the response laws of stress,displacement and vibration velocity of tunnels with different cross-section shapes are basically the same,that is,the maximum principal stress,displacement and vibration velocity of the front side of the tunnel are greater than that of the back side;the larger the cross-section span of the tunnel is,the greater the maximum principal stress,displacement and vibration velocity of the front side are,and the smaller the maximum principal stress,displacement and vibration velocity of the back side are.Under the same section span,the stress,displacement and vibration velocity of the explosion side of the horse shoe tunnel are larger,followed by the circular tunnel,while the stress,displacement and vibration velocity of the straight wall semi-circular arch tunnel are the smallest.