Study on Drilling and Blasting Construction of a Small-Spacing Tunnel and Vibration Characteristics of Intermediate Rock Strata

Abstract

The dynamic response of rock stratum in a small-spacing tunnel under a blasting load is studied based on field vibration monitoring of the drilling and blasting excavation of a small-spacing tunnel in the WenLing city railway S1 section. The vibration velocity spectrum, amplitude distribution of surrounding rock particles, and vibration blasting of the left and right face under a blasting seismic wave are analyzed. This paper focuses on the vibration characteristics and propagation law of rock stratum and the blasting face in a small-spacing tunnel. The results show that, in the same cross section, the blasting side of the middle-intercalated strata is the area with the maximum particle vibration velocity and its horizontal radial vibration velocity is largest. Additionally, the vibration velocity of cut-hole blasting is dominant and is about 1.5–2 times that of the auxiliary hole. The influence of the blast center distance on the blasting action can be reduced by reducing the charge amount of the cut hole and increasing the number of free surfaces. The main frequency of the vibration velocity is distributed at ∼15–110 Hz and the attenuation of a high frequency seismic wave is fast. The tunnel cyclic blasting damages the surrounding rock in the middle rock layer such that the peak velocity of particles in front of the tunnel are generally larger than those in the rear. With a reasonable arrangement of the amount of dosage, the blasting vibration in the far rock of the tunnel face is greater than that in the near rock, which weakens the influence of the blasting center distance on blasting vibration.