Water conservancy and hydropower projects have the characteristics of long construction period, complex structure, and being greatly affected by natural factors. An accidental factor in operation may sometimes lead to systematic safety accidents of the whole hydropower station. The author summarizes some typical cases of domestic hydropower station accidents in recent years, and analyzes some risk factors needing attention in the construction and operation management of hydropower stations, to provide reference for design, construction and operation management.

To compile the Guide for safety assessment of hydropower dams in operation, the author collected the cause reasons for the typical cases of dam failures and accidents at hydropower stations domestic and abroad. This paper presents 8 cases, for reference.

Based on the excavation and disclosure of the downstream slope of the right dam abutment of lower reservoir of Zhouning pumped storage power station in Fujian province, combined with analysis of structure characteristics of slope rock mass as well as the relationship between the structure planes and the excavation surface, traditional stereographic projection software is used to evaluate the stability of excavated slope. Moreover, two-dimensional modeling and analysis is carried out by use of discrete element program UDEC, and together with engineering geological conditions, the stability of excavated slope is comprehensively analyzed and evaluated. Without support, the safety factor of the potential rock composite of the slope under transient working conditions cannot meet the requirements from specifications. After completion of shallow support (including shotcrete, system anchor and anchor piles), the safety factor of the potential rock composite of the slope under transient working conditions can basically meet the requirements from specifications, but the safety margin is not high. The application of system anchor cable support has better control effect on the stability of the rock composite.

During investigation, design, construction and operation of tunnels, due to constraints and mistakes, failures happen. There are 10 cases at home and abroad presented in this paper, as well as the cause reasons and the lessons learned, for reference.

According to SL 274—2020 Design Code for Rolled Earth-rock Fill Dams, Sherard inverted layer design criteria are recommended. Based on the characteristic particle size of protected soil, the characteristic particle size of filter material and the envelope are calculated, and constraint condition for the closure and recovery of the crack in impervious body is presented, which make the inverted layer more reliable and reasonable.

By comparison the definitions in regulations of the former Soviet Union and China, the term precision, accuracy and trueness are redefined. Different from accuracy and trueness, it can be quantified.

Data abstraction and structure design are the foundation of application system construction, which are related to the practicability, scalability and stability of the system. Before the application system is put into service, the necessary work flow is to initialize the system, create an instance of the management objects for the system, and then applications are implemented. This paper, taking dam safety monitoring and management information system - iDam as an example, elaborates its basic data structure design and implementation of initialization, for reference.

Leakage is common for reservoir dams which not only affects the project benefits, but also causes serious hidden risks, can even lead to a dam break. Locating the leakage and its passage is the basis for further treatment which is key to ensure the safe operation of reservoir dams. At present, there are many leakage detection methods with their own applicability and limitations, and are restricted by site condition, environmental condition and geological conditions. Suitable methods should be selected based on method characteristics and site conditions, to achieve better detection effect.

HK-968 elastic epoxy coating is modified by chemical toughening. It combines the elasticity of polyurethane materials with the strength and adhesion of epoxy materials. It cures at room temperature and has better durability on the concrete surface which exerts good effect on the treatment of difficult problems such as cavitation and abrasion damage of hydraulic structures. This paper introduces the development process of HK-968 elastic epoxy coating from the aspects including main agent selection,
performance tests and adjustments, durability tests and so on, and two application cases are presented, for reference.

Collimation method is most commonly used in monitoring of horizontal displacement of a dam. With the popularization and application of total station instead of theodolite, the total station is widely used for horizontal displacement monitoring with the collimation line small angle method. To ensure the accuracy, one or more intermediate stations should be added as the maximum length of the collimation line of concrete dam is more than 300 m, while the maximum length of the collimation line of earth dam is more than 500 m. The analysis and practice of segment monitoring shows that it is of high precision provided that the displacement monitoring precision of the intermediate station is well controlled.

From the perspective of the role played by reservoir dams, the importance of reservoir dam safety to the realization of national water security strategy and dual carbon goals is emphasized. The safety operation of reservoir dams is always faced with severe situation and risks. By reviewing and summing up the safety supervision of hydropower dams, some suggestions are put forward.

Baihetan hydropower station has a huge installed capacity as well as large unit capacity, therefore, the transportation of major parts is one of the important tasks. Combined with the feasibility study of Baihetan hydropower station, the implementation of transportation of the major parts is introduced in this paper, for reference.

GB/T 51416—2020 Technical Standard for Concrete Dam Safety Monitoring specifically points out that concrete dam safety monitoring should run through the whole life cycle of concrete dam design, construction and operation. In each stage of the period, the objectives in stages should be accomplished, equal importance should be attached to the operation, maintenance and construction of the monitoring system, and equal attention should be paid to patrol inspection and instrument observation, data
analysis and acquisition as well as risk early warning and feedback analysis. To accurately understand this new concept, combined with the current status of concrete dam safety monitoring, the relevant contents are briefly introduced and explained, for reference.

The measured tail water level and flow rate of Ertan hydropower station as well as the data of sedimentation and water level upstream of Tongzilin hydropower station are analyzed, and the influence from main cascade hydropower stations upstream and downstream to the flow of Ertan hydropower station during normal and dry periods is studied, which provides the basis for further restoration works of the downstream river revetment.

The deformable body of Guobu slope is on the right bank of Laxiwa hydropower station, 0.9~1.7 km upstream the dam. It is an ultra-large granitic rock slope with a volume of 102 million m 3 , affected by various deformation mechanism, mainly toppling deformation, and is classified as Class B Grade I. After the reservoir impoundment in March 2009, obvious deformation of Guobu slope is observed. Hence, scientific research, safety monitoring and risk control measures are carried out, including geological exploration, deformation monitoring, numerical calculations using various methods, and stability analysis. Due to the high deformation rate of Guobu slope in the early stage of reservoir impoundment, the deformable body of Guobu slope was assessed as a major hazard of Grade Ⅱ. In 2018, based on study results, Guobu slope was reclassified as a safety risk of Grade Ⅱ (acceptable risk of Grade Ⅱ). In October 2015, the reservoir water level reached the normal impoundment level of 2 452 m. Long-term monitoring data since then show that the deformation of Guobu slope has slowed down after the reservoir water level stabilized between 2 450 m and 2 452 m. The daily deformation rate by the monitoring point at the maximum deformation decreased to less than 2 mm/d. Currently, the deformable body of Guobu slope is generally stable, and the risk is controllable. This paper introduces the specific measures and achievements in the treatment of the deformable body of Guobu slope of Laxiwa hydropower station, for reference.

The calculation and analysis of dam break flood is an important basic work for dam risk assessment and emergency management. The size of dam break has a great impact on the calculation of dam break flood. At present, most research on the development of dam break is about earth rock dams, while the research on concrete dam break is less. So in the calculation of dam break flood, the geometric size of concrete dam break is usually assumed based on experience. According to the database of historical concrete dam break cases at home and abroad, combined with structural characteristics of concrete dams, the causes and failure modes of concrete dam break are counted and analyzed, and the general principle for estimating the size of concrete dam break is introduced, which provides a reference for determining the parameters of concrete dam break in flood calculation.

Consolidation grouting is very important for foundation treatment of hydraulic structures. The author mainly introduces the construction technology and related construction parameters of consolida-tion grouting through guiding pipe for dam foundation of hydropower station. It is proved by practice that the technology is feasible, economical and reasonable, and the grouting quality meets the requirements of design and specifications.