Abstract: To explore the stress characteristics of the anchor bolt support in small-section TBM tunnels and assess the rationality of the support parameters, a case study is conducted on the Tongcheng pumped storage power station′s self-flow drainage tunnel project in Anhui province, China. The rock mass mechanics method and numerical simulation method are used to calculate the anchor internal force and surrounding rock displacement under the Grade Ⅲ surrounding rock conditions. Three monitoring sections are selected immediately following the TBM in the TBM excavation section of the tunnel, and the anchor stress meter and multi-point displacement meter are used to monitor the anchor internal force and surrounding rock displacement under actual working conditions. After comparative analysis of the results obtained by the three methods, conclusions are drawn as follows: (1) The changing trends of the axial force calculated by the numerical simulation method and the geotechnical method are similar. The maximum axial force value appears in the middle of the anchor bolt, which is consistent with the neutral point theory. The maximum axial force is 4.78 kN. (2) The changing trends of the surrounding rock displacement obtained by the three methods are similar, with the maximum displacement appearing on the surface of the tunnel surrounding rock, and the smallest displacement of the surrounding rock inside the rock layer, with the maximum displacement being 2.03 mm. Furthermore, compared with the existing research results on the structural stress of larger cross-section tunnels, it is shown that compared with larger cross-section tunnels, the anchor bolt axial force and surrounding rock deformation of small-section TBM tunnels are smaller, and the anchor support function has not been fully utilized. Based on this, optimization suggestions are put forward to delay, reduce or cancel the anchor support of small-section TBM tunnels.

Key words: tunnel boring machine, anchor bolt support, structural analysis, numerical simulation, parameter optimization