Determination Method for Warning Deformation of Surrounding Rock in Underground Caverns with Complex Geological Conditions

For a deep-buried complex cavern with complex geological conditions, it is difficult to determine the critical warning deformation of surrounding rock. A determination method for warning deformations based on rock strength is proposed to study the warning status of the surrounding rock of the Baihetan left-bank underground powerhouse. Three warning levels—blue, yellow, and red—are numerically established based on crack initiation stress, dilatancy stress, and uniaxial compressive strength of the rock mass. These warning deformations are influenced not only by the critical stresses but also by the cavern shape, rock position, deformation properties and in situ stresses. The in situ stresses were inversely analyzed by a three-dimensional geological model orthogonal to the principal stresses and present a high determination coefficient of 0.834 with the measured results. However, the complex geological conditions could bring great uncertainties to the simulation results and significantly reduce the warning deformations. Thus, the monitored deformations that reflect these uncertainties, instead of the simulated stresses or deformations, were used to predict the warning state of the surrounding rock, which was analyzed by comparing the on-site monitored deformations with the critical warning deformations. The warning results demonstrated that the proposed methodology enables prediction of warning location, timing and grades, and 85.9% of monitoring points obtained correct warning signals.