Controlled Blasting Technology For Tunnel Enlargement By Drilling And Blasting Method In Urban Environment

With the rapid development of national economy and the increase of traffic volume,the existied tunels can not meet the demand of transportation and safety in our country.In particular,the city traffic environment to further complete and improve the situation,this demand is particularly prominent in traffic construction and reconstruction of mountainous city or city in the mountain tunnel.Therefore,control blasting technology for tunnel enlargement by drilling and blasting method deep researches in urban environment,which is a kind of scientific value and practical significance of the urgent assignment.In this paper bases on the Jinji-mountain tunnel enlargement in-situ project of Fuzhou city ring,through blasting vibration tests and numerical simulation,which studies on controlled blasting technology for tunnel enlargement by drilling and blasting method deep researches in urban environment.The main research work and main conclusions as follows:1.Based on the field test and data analysis,the blasting vibration speed of the surrounding buildings was mainly focused on.The adjacent tunnel lining on each measuring point of the maximum velocity not emerges in Caving Blasting with the largest single segment,but appeared in the cutting blasting.Further,attenuation and sadove fitting empirical formula of blasting vibration speed,Ⅳ grade rock K value is about 100～110.The K value range was smaller than the related rules proposed,to explain both the surface absorption and release of blasting vibration energy,so it may be appropriate to reduce the charge of the cut and increasing the expansion holes and auxiliary holes.At the same time to overlay the vibration effect,there must be some delay intervals between various holes.2.Through numerical simulation of single hole under different dynamite installation,the emphasis is focused on the development of the crack under the action of blasting load and the time history curve of pressure on the boundary of the crushed zone.The formation time of the smash district is very short,but the formation time of the cracking zone is relatively long.Furthermore,the relationship between the dimensionless radius and the axial non coupling coefficient is fitted.By analyzing the peak pressure,the peak pressure is exponential decay with the increase of the coupling coefficient,and the attenuation coefficient is-0.62 approximately.The expression of peak pressure on the boundary of the IV grade granite smash district was obtained by the modification of the semi empirical and semi theoretical formula.3.The curve of single hole fine simulated pressure was effected on the hole grinding hole wall area boundary,focusing on the face of blasting vibration on surrounding buildings.From two aspects of effective stress and blasting vibration speed,both the existing tunnel and the expanded tunnel’s detonation surface were larger than the back surface,and the maximum effective stress and the maximum blasting vibration velocity peak were met safety requirements.The period of blasting vibration wave obtained by numerical calculation was the same as that measured by the vibration waveform,however,the value of the blasting vibration velocity was slightly larger than the measured value.