Abstract: Conventional advance pipe roof grouting reinforcement in open tunnel boring machines (TBMs) often results in excessive pipe roof inclination and insufficient support coverage. To address these issues, a front-mounted advance drilling and grouting reinforcement technique suitable for open TBMs was developed and applied in the Daliangshan No. 1 tunnel on the Lechang-Xichang expressway. To implement this technique, targeted modifications are made to the shield structure, multifunctional cutterhead, and pipe roof drilling rig of China′s first remanufactured open TBM. In situ advance drilling and grouting reinforcement tests are conducted to verify the technique′s feasibility and effectiveness in soft ground conditions. The results demonstrate the following: (1) The digital pipe roof drilling rig effectively identifies various drilling processes and stratigraphic lithologies. (2) Compared to the conventional direct drilling method, the core-based initiation method under small-angle conditions improves drilling efficiency by 50% and yields better borehole quality. (3) The front-mounted pipe roof exhibits a considerably smaller inclination angle (only 4°) and a larger grouting reinforcement range than conventional rear-mounted pipe roofs. The successful application of this technique in the Daliangshan No. 1 tunnel offers valuable references for the design and modification of open TBMs and research on advance drilling and grouting reinforcement techniques in soft, weak, and fractured surrounding rock conditions.

Key words: open tunnel boring machine, advance drilling, grouting reinforcement, remanufacturing, drilling parameter