Engineering Geological Evaluation Of Air Cushion Surge Chamber Diversion-Type Hydropower Station

The air cushion surge chamber is a kind of closed air chamber in rock mass, which was surrounded by the rock and the water body. It is a good facility of controlling water hammer and surge wave, using air to chamber high-pressure air to form a "cushion" to curb indoor water level and water level fluctuation amplitude. To a hydropower station of long water-diversion and high-head type, air cushion surge chamber as an ideal building program, for that the conventional surge chamber has more adits and the corresponding mountain roads. They have more negative impacts to environmental protection, construction costs, and construction schedule and construction difficulty. The location selecting of the surge chamber is critical in the construction of a project. The safety of the construction is determined by the geological condition and rock stability, so the geological evaluation of air cushion surge chamber area is significant.Mu Zuo hydropower station located on Huo xi river, one of the primary tributaries of Fu Jiang. It is the third one of "four stations in one reservoir" on the river. To minimize damage to the natural environment and beneficial to the protection of the ecological conditions, the engineers have proposed "slope to the end" water diversion lines and air cushion surge chamber programs in the beginning of the construction of power station.Firstly, this paper makes full use of the datas obtained by flat hole, drilling and rock mass in situ testing, hydraulic fracturing stress measuring method and high pressure water test based on a careful investigation of Mu Zuo hydropower station’s basic geological conditions. Then, based on the analysis of rock mass, rock mass structure, stress state, rock permeability about conventional surge chamber and air cushion surge chamber, compares and selectes the prioritization scheme, evaluates the appropriateness of air cushion surge chamber and proposes development scheme. Finally, the article evaluates the rock stability of proposed surge chamber, including the condition of burrow in the rock mass, anti-mountain lift, rock fracturing and permeability resistance etc.The main results and conclusions can be expressed as follows.(1) After the comparison of geological conditions between conventional air cushion surge chamber and air cushion surge chamber, Mu zuo hydropower station will admit the building program of air cushion surge chamber.(2) The suitability of construction has been done, according to the engineering practice and engineering geological evaluation criteria in Norway and China gaining from some built air cushion surge chambers such as in Zi yili hydropower station.(3) With the location, hole axis and the seepage-proofing type selecting of air cushion surge chamber in Mu zuo hydropower station, the general requirements of location, route selection and lectotype of air cushion surge chamber are proposed(4) The systematic assessment of engineering geological conditions of air cushion surge chamber includes the condition of burrow in the rock mass, anti-mountain lift, rock fracturing and permeability resistance etc.. And wall rock supporting and seepage-proofing treatment are proposed.