Analysis of the galleries cracking causes in the backfill area of pumped storage power station based on monitoring and numerical simulation: a case study of Hohhot upper reservoir

Pumped storage power stations usually arrange galleries in the backfill area at the bottom of the reservoir basin. Under the influence of uneven deformation, the galleries may be difficult to adapt to deformation and generate cracking, which can affect dam safety. In this study, the upper reservoir of Hohhot pumped storage power station was taken as a case study. Through a combination of monitoring data and numerical simulation, the deformation characteristics of the galleries on the backfill foundation were analyzed, and the causes and mechanisms of galleries cracking and structural joints damage were revealed. The in situ monitoring records cover the internal settlement of the dam, the deformation and seepage flow of the galleries, and the ambient temperature. Based on actual engineering data, a numerical model considering the structure and filling method of dam, backfill area, and gallery was established, and the calculation parameters of rockfill material constitutive model were inverted by the direct back analysis method. The monitoring data analysis and numerical calculations showed that the long length of the gallery and the sudden drop of the ambient temperature were the main reasons for the longitudinal microcracks in the top arch of the galleries in the backfill area; the strong constraint of bedrock and the uneven settlement of backfill foundation were the root causes for the penetrating cracks in the galleries at the junction of backfill area and bedrock. In addition, the depth of the gallery embedded in the bedrock determines the deformation form (torsional deformation or bending deformation) of the galleries at the junction of the backfill area and bedrock. Based on the monitoring and numerical simulation, the long-term deformation of the galleries and the development of structural joints were also predicted.