Excavation-induced damage zoning of the underground powerhouse with high geostress based on multiple monitoring methods

The primary factor restricting the construction of deeply buried underground projects is the imprecise identification of the surrounding rock damage zone. This study examines the Shuangjiangkou underground powerhouse to investigate damage zoning in the surrounding rock mass. The temporal and spatial characteristics of deep rock mass deformation evolution are studied by multipoint extensometers, microseismic (MS) monitoring, acoustic wave testing and borehole TV. Subsequently, a quantitative analysis delineating damage zones is executed by evaluating alterations in displacement, wave velocity volatility, and the distribution of MS events within the surrounding rock mass. The excavation zone of the surrounding rock mass is segmented into distinct sectors: highly damaged zones (HDZs), excavation-damaged zones (EDZs) and excavation-disturbed zones (EdZs). Additionally, the energy ratio of S-waves to P-waves (E_s/E_p) and the moment tensor inversion (MTI) are introduced to reveal the failure mechanism of the surrounding rock mass in each damage zone. The results show that the rock mass fracture around the Shuangjiangkou underground powerhouse presents remarkable zonation characteristics. The spatial depth ranges for the HDZs, EDZs, and EdZs, determined quantitatively based on multivariate monitoring data, are 0–5 m, 5–10 m, and 10–20 m, respectively. The failure mechanisms of surrounding rock mass differ across various damage zones: the HDZ primarily exhibits tensile failure, while the EDZ is mainly characterized by shear failure. The research provides a valuable reference for evaluating the stability of surrounding rock during the excavation of underground caverns of Shuangjiangkou hydropower station.