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.
Highlights
Topographic and geological constraints often cause two parallel tunnels to be excavated in parallel; alternatively, a new tunnel can be built near the existing tunnel. e blasting excavation of the construction tunnel may cause nearby damage to the surrounding tunnel rock, thereby affecting surrounding rock stability in the existing tunnel, jeopardizing tunnel safety, and hindering safe construction of the new tunnel. e safety influence of a newly built tunnel on the structure of the adjacent existing tunnel mainly manifests through two aspects: blasting vibration and stress redistribution caused by tunnel excavation
In the study by Zhao et al [7], based on the blasting vibration velocity and vibration frequency, the axial and radial blasting vibration velocity distribution of the existing tunnel under the influence of the explosion vibration of adjacent subway tunnels is studied. e results showed that the numerical simulation can optimize the blasting vibration response of adjacent tunnel blasting excavation to existing
E main stress cloud map of the secondary lining of Jia Hua Tunnel Left Line in Figure 15 shows that the maximum tensile stress of the secondary lining was mainly concentrated in the crown area. e maximum tensile stress was only 0.005 MPa, far less than the tensile strength of the concrete. e maximum compressive stress was concentrated in the arch foot area. e maximum compressive stress was only 0.15 MPa, far below the compressive strength of concrete. us, the upper part of the tunnel was mainly supported by surrounding rock and initial support, and the secondary lining was safe
Summary
Topographic and geological constraints often cause two parallel tunnels to be excavated in parallel; alternatively, a new tunnel can be built near the existing tunnel. e blasting excavation of the construction tunnel may cause nearby damage to the surrounding tunnel rock, thereby affecting surrounding rock stability in the existing tunnel, jeopardizing tunnel safety, and hindering safe construction of the new tunnel. e safety influence of a newly built tunnel on the structure of the adjacent existing tunnel mainly manifests through two aspects: blasting vibration and stress redistribution caused by tunnel excavation.To evaluate the blasting vibration effect of tunneling, scholars have conducted extensive research on the propagation law of blasting vibration waves and the influence on underground opening through blasting vibration in onsite and indoor tests [1,2,3,4,5]. E safety influence of a newly built tunnel on the structure of the adjacent existing tunnel mainly manifests through two aspects: blasting vibration and stress redistribution caused by tunnel excavation. Chen et al [8] studied the effect of blasting excavation disturbance on the surrounding rock damage zone in deepburied tunnels by means of in-situ rock mass acoustic velocity detection and numerical simulation. In order to study the effects of tunnel blast construction on the surrounding rock and the lining systems of adjacent existing tunnels, Li et al [11] monitored the vibration of the existing tunnel real time, and the monitoring results showed that the main frequency distributions of the radial, tangential, and vertical vibration of the subway tunnel were significantly different. Liang et al [15] studied the interaction mechanism between existing tunnels and proposed a simplified analysis and evaluation method to better understand and evaluate the impact of cross-tunneling on existing tunnels
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