Large-Span Rock-Anchored Beam Safety Pre-warning Method and Its Application in Underground Powerhouse

A statistical analysis of the displacement monitoring data, the rock bolt stress and the joint meter opening degree during construction has been performed based on the monitoring data of five large-span rock-anchored beams of underground powerhouses, such as Pubugou Hydropower Station. It is proposed to classify the displacements of rock-anchored beams into large, medium and small types based on the average displacements of greater than 20 mm, 10-20 mm, and less than 10 mm, respectively. When the average displacement of the rock-anchor beam is within the large displacement range, pre-warning shall be given. The rock bolt-joint meter correlation pre-warning method is put forward here, which says that the maximum allowable deformation of the rock bolt is derived from the design tensile strength of the rock bolt and the unanchored length of the rock bolt and compared with the joint meter opening degree monitoring data in actual projects. The results show that the allowable deformation range coincides with the rock bolt deformations in different projects. The calculated allowable deformation can be regarded as a very important reference value in pre-warning of the joint meter opening degree. The rock bolt-joint meter correlation pre-warning method may be used in similar projects.