Influence of Small, Clear Distance Cross-Tunnel Blasting Excavation on Existing Tunnel below

Abstract

The vibration effect generated during tunnel excavation can influence or damage adjacent tunnels. Studying and controlling the blasting vibration effect has important theoretical and practical significance, especially for new tunnels. This paper takes the tunnel project of Gao Jiu Lu-Jia Hua Cross Tunnel in Chongqing as the research background and assesses the blasting vibration influence in the up-down cross-tunnel. Onsite monitoring and numerical simulation were used to analyze peak particle velocity (PPV) changes, stress distribution, and crown settlement during the excavation process of Gao Jiu Lu I Tunnel at Jia Hua Tunnel Left Line in the cross-section. Influence laws of blasting excavation in a small, clear distance cross-tunnel on an existing tunnel below were obtained. Results show that new tunnel blasting vibrations exerted the largest influence on the crown of the existing tunnel below in the cross-section. The maximum tensile stress of the secondary lining of the existing tunnel below was mainly concentrated in the crown area. The maximum compressive stress during excavation was concentrated in the crown foot, and the stress value was less than the tensile and compressive strength of the concrete. The loosening of the surrounding rock from blasting excavation of the new tunnel caused secondary settlement of the existing tunnel crown below. The cumulative settlement value at the cross-section of the two tunnels was the largest. With an increase in axial distance from the cross-section of the existing tunnel crown, the settlement value gradually declined and became stable. These research results have reference value for the construction of a small, clear distance cross-tunnel and provide theoretical guidance for similar tunnel excavation projects in the future.

Longitudinal Deformation of Deep Shield Tunnels Caused by Upper Load Reduction

“…The preceding paragraphs show that if the shield tunnel is shallow, the upper strata do not provide foundation reaction forces. Then, the subgrade modulus coefficient k 1 is zero, and Equation ( 6) is consistent with the deflection differential equation of the singlesided elastic foundation beam model [10][11][12]. For the deep shield tunnel, two cases must be considered: (1) the excavated soil is above the ground arch.…”

“…Numerical analysis methods can consider the interaction between underground structures and surrounding soils and simulate the entire construction process. Therefore, it is mainly used to optimize the construction schemes for adjacent excavation [6][7][8][9][10][11]. However, to obtain the ideal calculation results, much modelling, calculation work and professional simulation software is required, which limits the application of the numerical analysis.…”

“…In the figures, are the foundation reaction forces before the existing tunnel deformation;11 F and 22 F are the foundation reaction forces after the existing tunnel deformation; 1 k and 2 k are the subgrade modulus coefficients of strata above and below the tunnel; σ is the vertical unloading stress on the existing shield tunnel;w is the vertical deformation of the existing shield tunnel; M is the bending moment;…”

Researches on the Influence of Blasting of Newly Built Tunnel on the Existing Tunnel Structure with Small Cross Angle

“…e importance of the blasting methods R 1 , surrounding rock conditions R 2 , cross angle R 3 , and clear distance R 4 to the optimal indicator I is compared on the basis of the published literatures [20,[31][32][33][34][35][36][37][38][39]. Combined with Saaty's scale table, the judgement matrixes are constructed as follows:…”

Controlling Vibration Speed in Tunnel Excavation Using Fine Blasting Method under Complex Environmental Conditions

“…Chai et al studied the effect of the arrangement of cut holes on the control blasting effect and they found that the layout of four empty holes could improve the utilization rate of explosive better than the two, indicating that reasonable reserved compensation space could improve the blasting effect and tunneling efficiency [9]. Duan et al investigated the influence of blasting excavation on existing tunnels under small spacing [10]. Wang et al studied the rule of buffer layer on vibration velocity and propagation energy attenuation by constructing a specific shape of loose body, and they found that a reasonable arrangement of buffer layer in oriented blasting could greatly reduce touchdown vibration [11].…”