Study On Blasting Vibration Effect And Stability Of The Neighburhood Tunnel With Layered Surrouding Rock

In engineering geology,rock mass with a set of approximate parallel dominated structural plane is called the layered rock mass.The layered rock mass exists very extensively in the nature.For the excavation of a small-distance tunnel in layered rock mass,the excavation blasting of the follow-up tunnel will inevitably have an influence on the supporting structure safety and surrounding rock stability of the existing tunnel.It has important theoretical and practical significance to research both the tunneling blasting vibration effect and the influence mechanism of blasting construction to surrounding rock stability and find a suitable excavation method for small-distance layered tunnel with layered surrounding rock.With the reality of Ya-jiang tunnel project being taken into account,the method of combining field vibration monitoring and numerical simulation was applied in the study of the vibration effect caused by the tunnel excavation blasting in the Neighburhood tunnel with layered surrounding rock.The follow-up of the tunnel was done with conventional wedge cut blasting,whose vibration strength is the largest,about 2?3 times of the other kinds of blasting holes.Thus,controlling the vibration strength of the cuthole is the key of vibration-reducing blasting.When wedge cut is used,the larger the Angle between the cut hole and tunnel face is,the closer the position of the maximum vibration strength to the blasting tunnel face will be and the bigger the vibration strength is to be;The peak monitoring results of the horizontal radial vibration velocity of each measuring point is about 2?3 times of the vertical direction,and the field vibration monitoring should be based on the horizontal radial vibration velocity.The combination of AUTODYN dynamic finite element method and UDEC discrete element method was used to explore the influence of various kinds of blasting holes on the stability of surrounding rock in the process of tunnel excavation blasting.First,AUTODYN was used to calculate the blasting dynamic loads of cut holes,excavating holes and surrounding holes.Then,the blasting dynamic loads were loaded into the discrete element model of the tunnel according to the excavation sequence,to study the influence mechanism of all kinds of blasting holes on the stability of tunnel surrounding rock.Tunnel excavation blasting may cause instability of tunnel with layered surrounding rock,and the influence mechanism of various kinds of blasting holes on the stability of tunnel surrounding rock is different in the whole process of excavation and blasting.The surrounding holes blasting generated the maximum load amplitude with the shortest action time;Cuthole blasting generated the minimum load amplitude with the longest action time;The surrounding hole blasting has the greatest influence on the stability of surrounding rock,and controlling the blasting effect of the surrounding holes in the process of tunneling blasting is the key to stablizing tunnel surrounding rock.The structural characteristics of layered surrounding rock and the blasting effect of the surrounding holes were comprehensively considered,the instability forms of layered surrounding rock under blasting dynamic action were classified,and the stability analysis methods were presented for all kinds of instability forms;The appropriate support and reinforcement measures for each type of instability were selected,and the calculation methods of supporting structure parameters were given respectively.The first kind is the rock mass sliding along the joint surface,the reflection Blasting seismic wave in the interface of the joint will increase the slide block,which can lead to instability;The second is similar to the beam bending fracture occurring in rock tunnel excavation free face.When the crack range of the surrounding hole blasting is smaller than the thickness of the rock stratum,the reflection load generated in the joint interface increases the bending stress of the beam whereas the cracks caused by the blasting weaken the bearing capacity of the beam.The interaction of these two aspects resulted in the instability of the beam body.When the crack range of the surrounding hole blasting is bigger than the thickness of the rock stratum,the soft filler in the joint surface is directly induced by the gas of explosion through the cracks,the rock mass between the surrounding holes was cut off to form smaller split volumes,the final performance of the unstable form was acres of rock strata failure,accompanied by the exposure of a complete rock structure face;Rock blocks under the unstable condition should be supported by rock bolts,which functions mainly as the suspension.When the rock layer thickness was larger than the surrounding holes blasting crack range,the chosen support method should be to consolidate the rock bolt,the main role of which is to decrease span;When the rock thickness was smaller than the range of blasting cracks in the surrounding holes,its more appropriate to adopt the advanced grouting small pipe grouting for reinforcement.SPH algorithm was applied in the research on the feasibility of the implementation of cuthole millisecond blasting in holes.The charging structure of the surrounding holes and the influence of the joint on the blasting forming of the tunnel were studied.Using the millisecond blasting in holes in the tunnel blasting cuthole can achieve the purpose of breaking rock mass and of providing free surface conditions for subsequent blasting.The vibration strength produced by the millisecond blasting was smaller than that of the conventional wedge cutting,thus,for layered surrounding rock tunnel,the application of the technique of millisecond blasting in holes is feasible;When using the non-coupling charging structure in the surrounding holes,the range of cracks produced by blasting can be effectively reduced,a relatively flat excavation face can be got,and the phenomenon of overbreak and underbreak of tunnel can be reduced;The surrounding holes should not be set in the vicinity of the joint surface,and between the surrounding holes should not exist two or more joints at the same time.If the joint is comparatively well developed,the amount of single surrounding hole charge weight should be reduced and the distance between the blasting holes should be shortened to obtain better smooth blasting effect.According to the results of the research on the vibration effect of the Neighbourhood tunnel with Layered surrounding rock and the stability of the surrounding rock,the design method of Millisecond blasting in holes suitable for ??? level tunnel with layered rock was put forward.When this method was applied to Chongqing Nan-fu high-speed Ya-jiang tunnel entrance and watershed tunnel exit section,the maximum vibration strength of the Ya-jiang tunnel was reduced from 11.85cm/s to 7.47cm/s.and the maximum vibration strength of the watershed tunnel was reduced from 17.63 cm/s to 7.31cm/s.The successful application of Millisecond blasting in holes scheme in the above-mentioned two tunnels projects provides similar tunnels a vibration-reducing blasting method as a reference.