Study On The Optimal Design And The Construction Safety Forewarning System Of Tailrace Surge Chamber

With the development of hydropower in the western region of China, the geological environment of underground house of hydropower station has become more complex, and lots of factors affect the stable operation of generators. Practice shows that theoretical study on axises arrangement of caverns, structural shape optimization, and engineering safety evaluation system of underground structures still lags behind engineering practice. Therefore, the underground powerhouse of Xiao wan, Huangdeng and other large hydropower projects are taken as the typical engineering examples in the dissertation, to carry out the research on the tailrace surge chamber arrangement, the structural shape optimization and the safety forewarning in construction period, etc. The main research results are as follows:(1) On the basis of analyzing the underground structure arrangement plan in the domestic two typical built hydropower underground powerhouses (Dachaoshan project and Ertan project), the main problems existing in the distribution of underground cavern groups were proposed. From perspective of the hydraulic transition of generators and the stability of surrounding rock, the axial layout and spacing of cavern groups were deeply studied, then a new arrangement mode which is that the axis of tailrace surge chamber and the axis of main powerhouse and main transformer chamber is space-line has been put forward. This mode was successfully applied in Xiao wan hydropower project, and the practice indicated that the arrangement mode was propitious to the improvement of the surrounding rock stability and the hydraulic conditions.(2) According to the requirement of underground powerhouse arrangement and operation, the necessity of setting underground powerhouse tailrace surge chamber was probed. The hydraulic conditions for three main shapes of simple gallery type, cylindrical double chamber and cylinder impedance type were analyzed comparatively and the main problems were proposed. Based on considering the hydraulic conditions, geological conditions, surrounding rock stability, supporting measures economy etc, the selection principles and requirements of tailrace surge chamber structure form were studied, the determination method of tailrace surge chamber structure shape was established. The above method was adopted in Xiaowan hydropower station underground powerhouse, and the results showed that a very good actual effect was obtained in aspects of the hydraulic conditions and the rock stability.(3) Base on the consideration of the actual construction process and technology and the characteristics of large complex underground caverns in construction period, the important factors of the construction traffic, surrounding rock stability were studied thoroughly, and the selection principle of construction procedures and supporting schemes for the complex underground caverns was presented. Then, the construction scheme of complex cross cavern groups in the tailrace surge chamber of Xiaowan hydropower station was designed, and the implementation effect of construction program and the surrounding rock stability were analyzed and evaluated. The construction scheme proposed in this dissertation can be a reference for similar engineering.(4) Having been investigated the difficulty and applicability of optimal cable-implemented opportunity based on the theory of New Austrian Tunneling Method, some key problems in Xiaowan hydropower station underground powerhouse were pointed out; Accordingly, the selection idea and method of optimal cable-carried time and supporting force were presented, as well as the related parameter values of cable surpporting was recommended.(5) The concept of the life cycle of underground powerhouse was introduced; the key technology to realize hydropower project lifecycle system was analyzed. Taking Huangdeng underground hydropower plant as an engineering background, the system analysis and system design of life cycle information system were finished. BIM (Building Information Modeling) was built, and the safety monitoring information module,3D visualization and analysis module, monitoring and numerical analysis results comparison module, simulation feedback analysis module, safety evaluation and prediction module, rock safety early warning and decision making module were developed and assembled; the safety forewarning system was applied in Huangdeng underground powerhouse during its construction period and played a positive action in the process of construction safety warning, quality control, schedule optimization etc..In summary, the achievements in this dissertation did not only guide the tailrace surge chamber arrangement, design optimization and the decision making of construction scheme in Xiaowan and Huangdeng underground powerhouses, but also provided theory support and accumulated valuable practical information for the similar engineering.