Xepian-Xe Namnoy Saddle Dam Collapse Is Not Force Majeure, Says A Report

(KPL) The findings of an investigation conducted by a panel of professional and independent experts have suggested that the root cause of the saddle dam D of the Xepian- Xe Namnoy hydropower project is not force majeure.

The National Investigation Committee revealed on Tuesday the results of the dam collapse investigation which has been conducted by the Independent Expert Panel, IEP.

The IEP’s members are Prof. Anton J. Schleiss of Switzerland, Honorary President of the International Commission on Large Dams (ICOLD), Mr. Ahmed F. Chraibi of Morocco, Former Vice President of ICOLD and Dr. Jean-Pierre Tournier of Canada, a Vice President of ICOLD.

The government also invited foreign parties to take part as observers in the investigation process to determine the underlying cause of the dam collapse.

The Korean company involved in the development of the project is also undertaking an investigation into the cause of the incident.      

The investigation conducted by the IEP was based upon the supporting information available to the IEP, the IEP’s observations made over the course of three site visits conducted since August 2018, and the results of the recommended post-failure geotechnical investigations.

The failure of the Saddle Dam D occurred on July 23, 2018 during the filling of the reservoir. Even if the rainfall was quite heavy during the days before the failure, the reservoir level was still below the maximum operation level and well below the crest level when the failure started. Thus the failure incident cannot be considered as “force majeure”.

The IEP found that the root cause of the failure is related to the high permeability combined with erodible horizons mainly due to the existence of canaliculus interconnected paths. With raising water level during the filling of the reservoir, seepage flow developed in the foundation along these paths and horizons with high permeability. This resulted in internal erosion and softening of the Laterite soil.

When the erosion and softening in the foundation reached a certain extent, the dam stability was no longer ensured and a deep rotational sliding at the highest section of the saddle dam was triggered. This finally led to complete breaching of the saddle dam and its foundation resulting in the catastrophic uncontrolled release of water from the reservoir.

According to the IEP, the foundation is without doubt involved in the failure, which could have been prevented by adequate treatment measures.

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