Study on low-vibration and dust-reduction excavation techniques for shallow-buried hard rock metro tunnels

The excavation of shallow-buried hard rock tunnels in urban subway projects faces significant challenges due to excessive vibration and difficult dust control, which not only hinder construction progress but also increase project costs. Relying on the Qingdao subway engineering project, the vibration speed and dust concentration change law of the double-arm drilling and splitting trolley and the blasting excavation are analyzed by means of on-site monitoring the oretical analysis and numerical simulation, and the vibration and dust reduction technology of hard rock excavation in subway tunnels is studied. The research results show that: 1) The blasting method of excavating the hard rock of the subway tunnel generates tremendous vibrations, with peak velocities of 0.95 cm/s directly above the tunnel face and1.03cm/s near the excavation face, whereas the vibration tester was not triggered during the operation of the double-armed drilling and splitting trolley. 2)The construction of the double arm drilling and splitting cart produced significantly less dust, and the maximum average concentration of dust produced by a single cycle was 64.37 mg/m3 . In contrast, blasting and excavation produced a dust concentration of 500 mg/m3 , which is nearly eight times that of the double-armed drilling and splitting trolley. 3) Under the action of stable pressing air flow, the dust generated by the double-arm drilling and splitting cart in the boring operation is less and stable, and the dust concentration near the working face is less than60mg/m3 , which is 88.1% lower than that of the blasting method, and reduces the dust discharge pressure of the windpipe. 4) The total cycle time of the whole process was shortened from about 24 hours for blasting construction to 12.75hoursafter using the double-arm drilling and splitting trolley, which increased the construction efficiency by 29.7%. The results demonstrate that the double-arm drilling-splitting trolley effectively addresses vibration and dust pollution while enhancing construction efficiency and safety in hard rock tunnel excavation.