DAMAGE REPAIR OF HYDROELECTRIC POWER PLANT SURGE TANK AFTER STRONG EARTHQUAKE
Reinforcement of special concrete structures after earthquake
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1. Project Background
A surge tank at a hydroelectric power plant suffered multiple cracks and damage to its concrete structure due to the 1999 earthquake. To ensure the power plant resumed operation as quickly as possible, the management entrusted a specialized company to conduct an on-site investigation. This included a comprehensive assessment of the types and extent of damage to the surge tank and surrounding facilities. After reviewing and approving the proposed repair plan, execution was handed over to the contractor.
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2. Solution
The on-site investigation revealed that the damage was primarily concentrated in the surge tank shaft and the upper, middle, and lower water chambers of the concrete structure, with the external rock mass also exhibiting signs of fracturing and loosening. To ensure normal operation after repairs, the following operational plan was devised:
- Urgently procure well-established repair materials from abroad to ensure post-construction safety.
- Use various resin grouts for crack filling and bonding.
- Apply cement-based grouts for external rock mass consolidation and curtain grouting.
- Utilize rotary drilling machines to investigate the rock bed conditions and lined pilot holes, and employ impact drills for grouting holes to enhance work efficiency.
- All slots and drill holes must be properly filled with high-strength resin mortar.
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3. WORKS DESIGN
The repair work is categorized into two types:
- Concrete Crack Repair
– A. For leaking cracks, first use polyurethane resin for water stopping.
– B. Remove surface attachments along the cracks to clearly define the repair area.
– C. Cut a V-shaped groove along the cracks and apply epoxy resin interface coating after cleaning.
– D. Fill the V-shaped groove with resin mortar.
– E. Drill cross holes along the cracks, ensuring the intersection of the drill holes and cracks is at half the thickness of the lining.
– F. Install injection heads and sequentially inject hydrophilic epoxy resin from bottom to top.
– G. Cut off exposed injection heads and fill the holes with resin mortar, restoring the site.
- Curtain Grouting for External Rock Mass
– A. Use NX drilling for sampling to inspect the rock layer conditions behind the lining and conduct rock mass permeability tests.
– B. After marking the grouting hole positions, use EX casing to penetrate the concrete lining.
– C. Use 50mm and 38mm drill rods to drill grouting holes to the predetermined depth.
– D. Perform rock mass consolidation grouting with cement-based grouts.
– E. Apply fly ash cement mortar for curtain grouting behind the lining.
– F. After cleaning the grouting holes, coat them with epoxy resin and fill them with resin mortar.
– G. Remove the construction scaffolding and restore the site.
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4. Works Process
Due to the severe earthquake, the transportation conditions and site access were extremely poor, necessitating the use of lifting equipment and other aids for moving and installing machinery. Additionally, because the surge tank shaft and water chambers had fallen concrete blocks and rock fragments, cleaning and scaffolding installation were required before starting the repairs.
Furthermore, the limited space at the construction site meant that various equipment had to be installed separately at the top of the surge tank slope, the middle water chamber, and the lower water chamber, increasing the difficulty and complexity of the work.
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5. RESULTS
To quickly restore the power plant’s operation and ensure stable electricity supply for the public, full efforts were made to expedite the work as soon as the imported materials arrived at the site. The construction process went relatively smoothly, and after identifying and repairing the known cracks and newly discovered defects during the construction, an inspection was immediately requested from the supervisory unit.
With the concerted efforts of various professional teams, the damaged components of the power plant were gradually repaired. After confirming that the functionality was normal through phased restarts, the repair work on the surge tank damage at the hydroelectric power plant following the severe earthquake was successfully completed.
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