Research On Reasonable Interval Between Separated And Existing Tunnel In Parallel Extension

With the rapid development of the national economy,people’s travel needs continue to increase,and cars and other means of transportation are rapidly popularized.Many original single-hole tunnels have been increasingly unable to meet People’s Daily needs.In order to solve traffic congestion and relieve travel pressure,projects close to new tunnels on the basis of existing tunnels are becoming more frequent.However,due to the influence of complicated geology and traffic conditions,the parallel extension of the existing tunnel often cannot leave enough space,and the smaller space also faces higher design and construction technical requirements.In the tunnel blasting construction engineering,tunnel interval is affected the safety of existing tunnel,one of the most important factors affecting the reasonable interval is close by tunnel design and construction of the important guarantee of success,so one sided parallel to the expansion of the reasonable interval of the tunnel still need scholars further careful study,and the related technology research to mature.Relying on the Dalingshan Tunnel Project,this paper studies the reasonable interval of parallel extension tunnels in blasting construction from three aspects of load,interval and existing tunnels with cracks by means of theoretical analysis and numerical simulation.The main research work and results are as follows:(1)The stress wave diffusion and its influence under the single hole blasting load of 0.3kg-0.9kg charge were simulated.The results show that the extension of the equivalent plastic strain range increases in all directions with the increase of the explosive amount;With the increase of depth,the plastic range in horizontal direction decreases.Equivalent plastic strain the single-hole quantity showed a strong sensitivity,then can be in control of small scale explosive quantity down to reduce a greater proportion of the equivalent plastic strain,combined with the engineering,smooth around the eye take 0.3 kg of short-delay blasting,a reasonable caving eye is set to 0.6 kg,in order to reduce vibration due to the safety of tunnel interval requirements.(2)Establish different interval,advanced tunnel excavation model to new tunnel blasting vibration on both the analysis and study the influence of the tunnel lining and surrounding rock,the results show that tunnel interval increased to 3.0D from 0.5D,the sensitivity of the different parts to blasting also gradually decreases,and when the tunnel span is greater than 1.5D,the sensitivity of the different parts to blasting significantly less than the tunnel interval is less than 1.5D,when the tunnel span is greater than 1.5D to weaken the influence of blasting vibration velocity through the tunnel,to ensure the safety of the existing tunnel structure,so the existing tunnel based on the new parallel blasting engineering in the design of the tunnel,the tunnel interval greater than 1.5D when the hole diameter to weaken the influence of blasting vibration velocity through the tunnel,to ensure the safety of the existing tunnel structure.(3)Based on extended finite element method,the process of crack propagation,the extension of cracks at different positions of the comparison and surface extension crack width are analyzed from the different angles,the results show that the different parts of the crack on the expansion of the tunnel under the action of blasting were extended to arch loin,crack width with the increases of blasting stress,crack width expansion rate after the first increases with the increase of stress of constant.In order to optimize the reasonable interval,the existing tunnel should be repaired by grouting and reinforced by adding anchors to reduce the width and rate of crack expansion.The above research results show the dynamic response and law of blasting load and tunnel interval to the existing tunnel in parallel close tunnel blasting construction,as well as the expansion law of existing lining cracks in the dynamic response.In view of the above research results,the concrete suggestions and measures for optimizing the reasonable interval of tunnel blasting and ensuring the safety of tunnel proximity are given.