HYDROELECTRIC DAM RESTORATION AFTER STRONG EARTHQUAKE
Emergency leak-stop and reinforcement of concrete dam structure after earthquake
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1. Project Background
After a severe earthquake in 1999, a power plant dam experienced multiple shear cracks and uplift joints in its concrete structure, leading to water seepage. To prevent the dam from collapsing and causing risks to the lives and properties of downstream residents, the dam management not only urgently lowered the reservoir water level but also assembled a professional team to inspect the dam and develop a repair plan for prompt implementation.
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2. Solution
Due to landslides from the surrounding mountains during the earthquake, debris accumulated around the dam, and numerous roads and bridges in the mountainous areas were destroyed, adding further complexity to the work. To address the on-site conditions and the urgent need for repairs, the following operational plan was devised:
1. Utilize various feasible methods to transport machinery and materials to the site.
2. Clean up the site area.
3. Set up construction scaffolding in the work area.
4. Assess the extent of damage and record the quantity of repairs needed.
5. Carry out repairs in batches.
6. Drill inspection holes to examine the distribution of grout.
7. Gradually increase the reservoir water level, inspect the repair results, and make additional repairs as necessary.
8. Implement long-term monitoring.
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3. Works Design
This dam is of the high dam type, and prior to works, it was necessary to clear the work surface of debris and set up scaffolding. After a preliminary assessment of the damaged areas on-site, the repair process was carried out according to the following steps:
1. Utilize non-destructive testing percussion sounding, on visually prominent or lengthy cracks to determine crack depth.
2. Employ vertical and horizontal drilling for continuous sampling and hydraulic pressure testing to assess the development of internal cracks within the dam’s concrete structure.
3. Conduct compressive strength tests on concrete samples obtained from continuous sampling to examine concrete deterioration.
4. Cut V-shaped grooves at the cracked and leaking uplift joints, clean them thoroughly, apply epoxy resin adhesive evenly, fill with epoxy resin mortar, affix fiber isolation bands, and then seal the surface with weather-resistant silicone elastic filler.
5. Install crack monitoring gauges at appropriate locations along the cracks. Then, use dual-component polyurethane resin, both flexible and rigid, to inject into the cracks in two separate locations based on the elevation of the reservoir water surface at that time. Injection carried out from bottom to top, and the termination of the grouting process determined based on the overflow condition, changes in crack monitoring, and grouting pressure.
6. Drill inspection holes at designated locations specified by the dam management to confirm the distribution of grout.
7. Embed steel bars in the probe holes and inspection holes, and completely fill all grouting holes with epoxy resin mortar.
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4. Works Process & Results
Due to the reservoir’s location in mountainous terrain, road and bridge closures following the earthquake temporarily prevented access. As a result, the transportation of construction machinery and personnel in and out of the area often had to rely on methods such as helicopters, lifting cages, mobile cranes, and hiking on foot, which posed significant risks.
However, due to the urgent need to repair the power plant dam for the safety of the public and to ensure continuous electricity supply, the owner and contractors persevered despite the difficulties. Facing the constant risk of falling rocks along the roads and within the work area they swiftly carried out the necessary repairs.
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5. RESULTS
With the concerted efforts of all units, the reinforcement of existing leakage cracks and uplift joints was successfully completed. However, cracks above the reservoir water level, which are not visibly apparent, coupled with ongoing aftershocks, prevented the inspection of water seepage conditions as the water level could not be raised.
To ensure the safety of the dam structure after the reservoir was restored, it was decided by all units to conduct testing and reinforcement of leakage at locations where water seepage traces were previously identified. When the aftershocks subsided and newly discovered minor cracks were repaired, the repairs were reported for acceptance, and the reservoir water level was gradually increased.
Through monitoring the deformation of the dam structure and observing water seepage conditions, which met the safety operation requirements, the repair work of the power plant dam after the earthquake was confirmed successfully completed.
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