THE FAILURE OF SHIH-KANG DAM by Amokomowo Aderemi Dawoud Adenaiye Oluwaleke

Contents Introduction Geology of the dam Failure of the dam Cause of failure Solutions adopted Rehabilitation Process Conclusion

Introduction Shih-kang dam is located about 100km southwest of Taipei and built in 1977 Dam dimensions – 357m long 25m high and 540m wide at the base Reservoir Capacity: 3.38million m3 Dam failed in 1999 as the first concrete dam to be directly damaged by the active fault in the history of the hydraulic structures

Geology of the dam Geological Map of Shih-Kang map The geology of the Shih-Kang Dam site is composed of about 6-meter thick deposition layer on the surface and the next is the soft bedrock of the Cho-Lan formation. The deposition layer is formed by unconsolidated gravel, sands, silts and clay. The bedrock, soft and easily weathered, is mainly formed by slate-gray sandy-shale and silty-sandstones.

FAILURE OF THE DAM Impact type damage. Effects of the large ground motion. Impact type damage. Strong contact impact of every adjacent weir body during the earthquake. Fault rupture type. Most complicated type.

Cause of failure Remarkable rupture of fault Strong motion of earthquake Remarkable rupture of fault Large displacement of ground surface.

Solutions adopted Construction of a new reservoir in the upstream of the Shih Kang Dam away from the Che-Lung-Pu fault Rehabilitation work was carried out in an economic, efficient, and effective way.

REHABILITATION PROCESS First phase   Repairing of the intake structure and the tunnel. The ruined concrete lining tunnel was coated by steel pipe lining. The wing wall of the left abutment was rebuilt. Second phase Repair the dam-body out of the fault aligning area. The cement grouting was taken in the dam foundation. Epoxy cement was injected into the cracks of the dam-body and stilling basin. The new downstream tail dam was installed. Third phase To reserve the right part of the dam, which was located on the fault aligning area, to be a memorial of Chi-Chi earthquake. To install a cofferdam in front of the right part of the dam.

RECOMMENDATION Adequate Site Investigation Construction Monitoring Periodical Long term Monitoring

CONCLUSION Dam failure caused strong motion of earthquake and remarkable rupture of fault New dam construction away from the fault followed adequate site investigation after the failure

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