Effect of Anchor Plate on Prestressed Anchor Cable Performance in Soft Rock Tunnels

In deep-buried soft rock excavation, the stability of prestressed anchor cable system is impacted by uneven contact with rough rock surfaces, which affects prestress effectiveness and loss. However, the influence of anchor plate deformation under varying contact conditions has not been systematically studied. To address this research gap, this study introduces a new classification of plate-rock contact into five types: full-face, partial-face, concave, irregular and angular. The influence of the five conditions on anchorage system performance was investigated through numerical simulation and field tests. Results reveal non-uniform anchor plate-rock contact leads to significant stress concentration, anchor plate deformation, and increased prestress loss in anchor cables, which has not been quantified in previous studies. In addition, increasing anchor plate thickness can help mitigate prestress loss, and an optimised thickness selection approach based on contact conditions is proposed. Using a 15.5 mm anchor plate is effective for full-face, partial-face, and concave contact conditions, whereas a 31 mm plate significantly reduces deformation and prestress loss for irregular and angular contacts. The findings of this paper offer practical guidelines for improving the long-term stability and performance of prestressed anchor cable systems in soft rock tunnels.