ABSTRACT:

Numerous hydropower projects build the underground powerhouses in Southwest China subject to the topography conditions and structure layout. The underground powerhouse is one of the most significant structures that will be permanent in use. Large scale excavation usually poses a threat to the stability of the underground powerhouse and the surrounding rock mass damage is required to be qualified for excavation schedule and support design. Various methods such as displacement measurement, acoustic wave test and numerical calculation have been used to quantify the rock mass damage. As a new monitoring method in hydropower underground powerhouse, the microseismic (MS) monitoring technique has been rarely used for quantifying surrounding rock mass damage. In the present study, an MS monitoring system was established to capture the microcracks induced by excavation of the underground powerhouse at the Houziyan hydropower station and a damage-driven numerical model based on MS data is adopted to quantify the surrounding rock mass damage. The rock mass is degraded and simulated by a micromechanics-based constitutive model described by the fracture density, which is determined by the amount and size of the microcracks. The material property input for this model are Young’s modulus, Poisson’s ratio of the intact rock and the MS information such as the location and the source size calculated from seismic source parameters. A typical profile (#2 unit profile) of the underground powerhouse is selected for damage analysis. Combined with field excavation process, the related MS data are imported to the numerical model for damage calculation. The results show that the surface displacement of each bench excavation of the underground powerhouse using the damage-driven numerical model is approximately 30-40 mm larger than that using the original elastic model. Furthermore, the displacements of rock mass considering the effect of MS damage are in good agreement with the field measurement.

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