Discriminant Analysis of Excavation Damage Zone at Underground Powerhouse with High In-situ Ground Stresses during Construction

It is inevitable that excavation at deep underground powerhouse with high in-situ ground stresses induces damages to the surrounding rocks. As a result, reasonable determination of the excavation damage zone (EDZ) is critical to the design, construction and safe operation of the underground powerhouse. This study divides EDZ into excavation highly damaged zone (EHDZ), excavation slightly damaged zone (ESDZ) and undamaged zone (UDZ) so as to better capture the evolving characteristics of the surrounding rocks at deep underground powerhouse with high in-situ ground stresses. With the utilization of acoustic detection, this study introduces the damage factor D to quantitatively distinguish the EDZ. Borehole camera is also employed to observe the characteristics of fissure development within the surrounding rocks. The observed damage characteristics of the surrounding rocks are then compared against the acoustic detection results, showing favorable agreement. Moreover, FLAC3D software is employed to characterize EDZ with the introduction of relative displacement contribution factor and stress restoration level. Based on the actual engineering practice, this study puts forward the discriminating standard for the EDZ at deep underground powerhouse with high in-situ ground stresses during construction. Hopefully, this study could provide some basis for the evaluation of degree of damage of the surrounding rocks as well as the informational design and construction at underground powerhouse with similar conditions.