Study On Vibration Reduction Technology Of Bedrock Blasting Of Shield Tunnel Near Ancient Buildings

In some southeast coastal cities,metro shield construction often passes through the upper soft and lower hard strata,so the blasting pretreatment technology of "ground drilling and underground pre-blasting" can be adopted.In the tunnel range between Wushan Square Station and Jiangcheng Road Station of Hangzhou Metro Line 7,boulder and bedrock intrude into the tunnel,and the shield tunnel runs through Hu Qingyu Tang,a national cultural relic protection unit.This brings a challenge to the development of bedrock blasting engineering.In this case,it is necessary to adopt damping technology to carry out bedrock blasting.In order to control the vibration velocity caused by blasting within the limit specified in the current code,this paper studied the vibration damping technology of bedrock blasting for the protection of ancient buildings.Firstly,the mechanism of vibration damping technology was studied.Secondly,different shock absorption technologies are studied from three perspectives:detonation source factor,seismic wave propagation path,hole arrangement and detonation principle.Finally,the actual effect of the comprehensive damping technology is verified through the blasting test of the test section,and the peak value of the surface vibration velocity near the ancient building is controlled within the standard limit.The main work completed in this paper and the main conclusions are as follows:(1)Combining with the actual engineering background,a partition and batch blasting scheme was proposed,and the single hole charging parameters and reasonable hole spacing were determined.The mechanism of vibration reduction and rock breaking of millisecond delay blasting was obtained by theoretical analysis.The optimal interval time of millisecond delay blasting with reasonable hole spacing was obtained from two aspects of vibration reduction effect and rock mass stress level through numerical simulation test.(2)The stress concentration effect and free surface effect of the damping holes were analyzed theoretically,and the positive effects of the deep damping holes on vibration reduction and rock breaking are obtained through numerical simulation tests.The isolation effect of damping ditch on the propagation of body wave and surface wave was analyzed theoretically,and the specific parameters of the damping ditch are studied by orthogonal test.The results showed that the damping ditch should be laid close to the protected building,and the depth of 3 m can achieve the balance between economy and damping effect.(3)The concept of "near weak surface" was defined,and the law of reflection and refraction of stress wave at the near weak surface was studied theoretically.The numerical simulation test showed that the near weak surface has a positive effect on rock fragmentation,and the charging hole at the near weak surface should be detonated first in practical engineering.Different orientations of holes in the blasting area also have a certain influence on the distribution of surface vibration velocity.In actual construction,holes should be arranged parallel to the direction of protected buildings.(4)The field blasting test showed that the comprehensive vibration reduction technology can effectively reduce the surface vibration velocity.The blasting and vibration reduction schemes were developed for the protected buildings through damping holes and millisecond delay blasting techniques.The results showed that the comprehensive vibration reduction technology can achieve the goal of protecting ancient buildings;In addition,the rock fracture level also meeted the requirements of the shield machine through drilling.There are 88 figures,26 tables and 103 references in this paper.