Abstract: To address the challenge of low drilling efficiency when using a single-unit anchor drilling rig for long anchor holes in small-aperture prestressed anchor cables, a case study is conducted on a vehicle passage of the Muzhailing highway tunnel. The spatial boundary conditions and primary lithological characteristics of the surrounding rocks are analyzed, and an anchor cable drilling vehicle is developed using cutting drilling as the primary method, with impact rock breaking as an auxiliary method. This drilling vehicle is suitable for small space sections in soft-rock tunnel construction. Key technical parameters, including cutting and impact forces, are determined during the design phase, and the strength of the drill rod is verified. Subsequently, comparative on-site drilling tests are performed using multiple types of equipment. The main conclusions are as follows: (1) The developed small-section anchor cable drilling vehicle has overall dimensions of 2 950 mm (length) × 1 230 mm (width) × 2 650 mm (height), meeting construction requirements for small-section spaces. It employs a rotary drilling vehicle equipped with an impactor to achieve combined "rotary-impact" drilling. By combining high-speed rotary cutting drilling with low-frequency, low-impact energy, the system enables effective drilling primarily in soft rock while accommodating soft-hard interbedded surrounding strata. (2) Compared to conventional rotary drilling rigs and impact-rotary drilling rigs, the combination of the small-section anchor cable drilling vehicle, a B25 drill rod, and a 32 drilling tool is more suitable for efficiently constructing deep anchor holes for smallsection prestressed anchor cables in soft-rock strata. The maximum drilling depth exceeds 15 m, with drilling times of approximately 16 and 36 min for 5 and 10 m, respectively.

Key words: soft rock tunnel, anchor cable drilling vehicle, small-aperture anchor cable, drilling efficiency, single-unit drilling rig