Abstract: To accurately identify potentially unstable blocks during the construction of jointed rock tunnels and develop targeted support schemes, this study proposes a method integrating point cloud technology and structural plane reconstruction for block instability identification and support design. First, point cloud data of the tunnel face are acquired through three-dimensional (3D) laser scanning. The density-based spatial clustering of applications with noise (DBSCAN) algorithm is enhanced using density peaking clustering (DPC), yielding the DPC-DBSCAN algorithm. This approach enables adaptive clustering and information extraction of structural planes, overcoming the limitations of traditional methods that rely on manual parameter tuning and providing increased efficiency and accuracy. Subsequently, a discrete fracture network is reconstructed based on the extracted structural plane parameters. Combined with insitu stress and surrounding rock mechanical parameters, a synthetic rock mass model is established. The tunnel excavation process is simulated using 3DEC discrete element software to achieve 3D dynamic identification and stability assessment of potentially unstable blocks. Finally, the Xiwuling tunnel in Anhui, China, is used as an engineering case in which six support schemes are proposed and compared to determine the primary parameters and implementation strategies for targeted support. The main conclusions are as follows: (1) the proposed DPC-DBSCAN algorithm improves efficiency and accuracy in structural plane clustering, reducing runtime by approximately 38% compared to traditional algorithms and enhancing the automation and reliability of structural plane information extraction; (2) the structural plane parameters extracted from point cloud data agree with field manual measurements, validating the accuracy and engineering applicability of the intelligent identification method; and (3) the targeted support scheme for unstable blocks, which includes locally extending anchor bolts to 5 m, reducing bolt spacing to 0.6 m, and optimizing bolt angles, reduces the maximum displacement of unstable blocks to 1.7 mm. This markedly improves support effectiveness compared to conventional schemes while reducing material usage and maintaining safety.

Key words: tunnel, point cloud data, rock mass structural plane, block instability, targeted support