The Application Of Controlled Blasting Technology In The Composite Stratum Shield Engineering

With the rapid development of urban tunnels,urban tunnels are facing more and more adverse geological conditions,and their challenges are increasing.Especially in shield tunneling projects commonly used in the construction of urban tunnels,the local existence of bedrock protrusions and orphans in the excavation section is the most important.In the major coastal cities in southeastern China,such as Xiamen,Shenzhen,Hong Kong,Guangzhou and other places,there are some spherical weathered rock bodies and basement outbursts intruded locally in their granite strata.In this bad stratum,because the strength of the spherical weathered rock mass is far greater than that of the soil,it can not be effectively broken by cutter head.Traditional ground treatment methods or cabin opening often have great limitations,and urban tunnels are deeply buried,and the safety of manual removal is low.Therefore,this bad formation needs a high efficiency,low cost and high security processing method.Depending on the project of shield tunnel along the west of Shenzhen Metro Line 9,and aiming at the risk of the project,this paper uses deep hole controlled blasting technology to pre-treat the bedrock protrusion and solitary stones in the shield contour line.The key technologies include the selection of construction site,the determination of the location and thickness of solitary stones,the protection of surrounding underground pipelines,the unit consumption of controlled blasting and the blasting network and so on.The determination of blasting parameters,the treatment of pressure-retaining grouting in blasting area and the setting of shield cutter changing point are used to determine the actual rock breaking effect by core pulling test.Through monitoring data of blasting vibration,the blasting vibration is analyzed,the attenuation parameters in the direction of coastal zone are calculated by Sadovsky formula,and the maximum safe charge quantity in different distances is calculated by the attenuation parameters.It provides some reference for the later blasting construction.The vibration reduction methods of shield deep-hole controlled blasting,such as interference method,increasing free surface method and controlling maximum detonation charge,are analyzed.The numerical simulation of deep hole blasting is carried out by ANSYS software,and the blasting parameters are corrected by feedback.Firstly,the simulation of single-hole blasting in shield blasting is carried out,and the rationality of numerical simulation parameters is verified by the variation of stress peak value.Then,the simulation of double-hole blasting in shield blasting is carried out to analyze the cracks,stresses and blasting chambers of group-hole blasting with different spacing of blasting holes.The feedback blasting parameters are 0.8m,and the blasting effect is better.Figure[51]Table[15]Parameter[49].