Numerical Study on the Mechanism and Application of Artificial Free Surfaces in Bedrock Blasting of Shield Tunnels

Abstract

During the pretreatment construction of blasting in shield tunnel bedrock, in order to reduce the impact of blasting vibration on the surrounding environment and improve the effect of rock blasting, the method of creating an artificial free surface is proposed. From the point of creating an artificial free surface, this paper numerically studies the function mechanism and parameter optimization of artificial free faces in shield tunnel bedrock blasting construction. The propagation characteristics of explosion stress waves at the interface between the rock and the artificial free face and the effect of the artificial free face on the shield tunnel bedrock blasting were analyzed. The results indicate that, as the explosion stress wave transmits to the artificial free face, a part of the stress wave is reflected back to the bedrock, increasing the energy in the bedrock that needs blasting and improving the blasting effect and utilization rate of the blasting energy. The reduction degree of the peak velocity of the surface particle is more than 50%, and the reduction degree of the peak velocity of the particle near the artificial free face is more than 77%. The existence of the artificial free face reflects the stress wave and superimposes with the original stress waves, increasing the effective stress in the blasting area, and the effective stress can be increased by 5 MPa or more. The peak vibration velocity of the surface particle decreases with an increasing diameter of the empty holes and the distance between the empty holes and the blasting holes. The parameter design value of the artificial free face is put forward: the diameter of the hole is 200 mm, the distance between the empty holes and the center of the blasting holes is 60 cm, and the depth of the empty hole is the same as the blasting hole.

Preconditioning High-Strength Boulders for TBM Tunnelling by Ground Drilling and Blasting

“…The calculated specific charge values from Equation ( 11) are much higher than the ones from the Swedish formula given in Equation (1), as indicated in Table 3. By using Equation (11), the explosive charge weight corresponding to each practical boulder can also be determined.…”

“…Sun [10] analyzed the effects of the charge, borehole spacing, interval charging, and continuous charging on the fragmentation in boulder blasting, and obtained the maximum fragmentation corresponding to different row spacing and charging structures. In order to improve the blasting effect, the empty hole was applied in boulder blasting [11]. Although many results have been obtained and some new technologies have been applied in boulder blasting, in order to study the ground movement patterns in case an undetected large boulder is accidentally encountered by tunnelling, a hybrid extension method encompassing both convexity control and overlap detection was developed, and several influence factors including the boulder size, orientation, position, and morphology were included [12].…”

Propagation characteristics of vibrations due to rock blasting in silt-rock strata

“…In 2020, 33 cities had 177 subway lines in China [1]. In the construction of metro-tunnels using the shield method, mixed strata are often encountered within the tunnel's cross-section, such as in the Guangzhou Metro Line 7 [2], the 2.3-km-long C line and the 4-km-long S line of the Oporto Metro [3], the Tabriz metro line 1 [4], the Kranji tunnel in Singapore [5], the Shenzhen Metro Line 11 [6], the Xiamen Metro Line 2 [7], the power tunnel in Shenzhen [8], and the Fuzhou Metro Line 6 [9]. When the shield machine bores through silt-rock strata, the rock stratum in the lower part of the cross-section is too hard to bore, while the silt stratum in the upper part of the cross-section easily enters the soil chamber, especially for silt stratum that is rich in groundwater.…”