This paper introduces the development in the design guideline and safety management of reservoir structures in Taiwan. The design guideline introduced includes the basic requirements, design principles and standards, loading conditions and their combination, safety criteria, structural analysis and design methods. As the safety management issues are concerned, the regulation and provisions for safety assessment, the concept and procedure of risk assessment with emphasis on FMECA approach, are described. Some concluding remarks are given in the final part of the paper aiming at the advancement trend in the design practice and safety management of reservoir structures in the future.
A natural river bed is generally covered with a layer of gravel and cobble protection formation. This formation is the remains of hydraulic sorting, which serves to stabilize the river bed and protect the bedrock down below from scouring. After the installation of a weir, flow velocity and energy may increase in the downstream channel, resulting in severe local scouring that could endanger the safety of weir upstream. Ji Ji Weir is an important intake facility in the central region of Taiwan, there is a deep concern among the public on the erosion situation of its downstream channel. This paper addressed issues such as channel geology, bed grain size distribution, flow path characteristics, scour and deposit features, as well as prevention measures for public reference.
The mechanism that led to the loss of protection layer and scouring of the Ji Ji Weir downstream channel is extremely complicated. It is believed that factors such as local scouring in the early stage of weir operation, rejuvenation and head ward erosion induced by 921 Earthquake, and local erosion of the broken bedrock of Chu Shiang fault are the main culprits. In recent years, riprap and concrete infill had been used to slow down the scouring rate, and early success of these prevention measures were observed.
In recent years, owing to the prosperous industrial and business activities in southern Taiwan, the water demand has been becoming increasingly acute. To meet the mid-term and long-term water demand in this region, the Water Resources Agency, Ministry of Economic Affair, with the approval of Executive Yuan, decided to carry out the Tseng-Wen reservoir transbasin water diversion project in 2003. This project commenced in 2005 and was originally expected to complete before April of 2012. The progress of overall project reached 31.07% as of July of 2009.
East and west water diversion tunnels are critical-path engineering of this project. To make sure this engineering could be fulfilled on schedule and to achieve the goal of this project, a thorough geological investigation was implemented in the design stage as a basis for designing. In 2004, the tender work of water diversion tunnels was completed and the excavation started from January 1, 2005. However, on the 8th of August in 2009, Typhoon Morakot brought an unexpected downpour and seriously damaged the completed structures of this project. Since the main channel of Laonong creek may shift in the coming decade, no appropriate locations could be chosen as the sites for water diversion engineering. Therefore, the survey and monitoring on landslide, debris flow and channel change should be executed in the first priority followed by reviewing the feasibility of resuming the construction of tunnels.
Xin-Shan earth dam was reconstructed to raise the maximum reservoir water level to EL.86 m. But several abnormal leaks appeared on the downstream face and remain mysterious. The objective of this study is to investigate the mechanism of the abnormal leakage though review of historical data, results of monitoring, and newly-conducted non-destructive testings, including water quality analysis, temperature profile, tracer test, and electrical resistivity tomography. Two distinct seepage problems has been revealed, including the abnormal phreatic line over the drainage layer and leaks on the downstream face. The phreatic line higher than designed is attributed to lower drainage capacity of the drainage layer, likely due to overestimation of Kh/Kv ratio. The special ㄑ-shaped drainage layer is also not favorable for the overall performance of the drainage layer. The elevations of the abnormal leaks on downstream face are still much higher than the phreatic line, indicating possible horizontal flow along relatively impervious stratified layers.
The original Shimen irrigation canal water intake is located in the lower part of Shihmen Dam (EL.195m), so during the typhoon season, the turbidity of raw water is often too high to be purified by all water purification plants. To solve this problem thoroughly, Northern Region Water Resources Office decided to add an intake shaft on the left side of the dam to obtain water, and deliver the raw water to the downstream end. However, because of the following factors, the joint became the passageway of the gush and shear zone cause the high-hydraulic-pressure ground water. :1. the dam is still in use during the construction; 2. the bedrock of the work site, which is near the valley, has been decompressed, 3. Shihmen dam is near the Hsindian fault.
In this case, the geological conditions is re-estimated by the Geological Survey, and concluded that the hydraulic-geology model are different between intake shaft and the tunnel. Consequently, different solutions are adopted.
The construction of the dams of Hushan Reservoir project were started in June 2007, and are scheduled to be completed in September 2014. Hushan Reservoir will operate in conjunction with the Chi-chi Weir and provide about 694,000 tons(max.) of surface water per day, after the completion of the project. During the planning and design stages, the subjects of the demand for environmental protection, the acquired knowledge from 921 Chi-Chi earthquake, the difficulty of grouting in soft rock foundation were discussed and solved, for providing a dam in accordance with the principles of security, environmental protection and economy.
This paper describes the case learned from the designing and contruction of the wan-sung hydraulic power generation project. It includes the high intake structure which is seated at 40m below mean water level in wu sui reservoir, grounting treatment and excavation for the cross-river section of the sung-lin headrace tunnel, and cover and cut method for forebay contruction. The paper is expected to throw some design and construction on the similar geological condition or engineering projects.
Large diameter Catchment wells were widely used in the fields of landslide remediation and groundwater exploitation. It consists of concrete segments and radial drilled holes to maintain the shaft and drain groundwater. Steel liner plate and reinforced concrete segments are two main types of well structures commonly seen. The precast RC segment design, construction and issues in its application are discussed.
Wushanto Reservoir diversion tunnel is located in poor geological stratum. A deep Catchment well is used to relieve excess ground water pressure around the tunnel. Due to poor geological condition, precast RC segments with better stiffness were adopted. The gravity of the segments were used as counterforce to advance downwards. The radial drains were installed after the well structure is completed in order to lower groundwater table nearby.
There are 13 high capacity sedimentary pools in the Shihmen Reservoir system. The total volume of these sedimentary pools is 3.8 million m3 with a coverage area of 70 hectares. The fact that settling of fine sediment in these sedimentary pools follows gravity settling principles, the consolidation time was exceedingly long and hence the fine sediment was very high in water content, rendering it difficult to remove or utilize the deposited fine sediment. Physical and chemical tests showed that the fine sediment is fine-grained and rich in clay content, and is quite suitable for use as basic material. The present project attempts to explore the possibility for high efficiency multiple utilization of the material as treatment plan. In-situ tests and appraisal performed showed that high-efficiency technique for dehydrating the fine sediment is feasible. Consequently the site of the 13 sedimentary pools of the Shihmen Reservoir can be designated as a special fine sediment treatment area.