VIENTIANE, May 29 (Xinhua) -- The collapse of saddle dam D at the Xe-Pian Xe-Namnoy hydropower project in Laos' southern Attapeu province last year was not considered as "force majeure", local daily Vientiane Times on Wednesday, quoted a senior government official as saying.
Singphet Bounsavatthiphanh, Vice President of the National Investigation Committee (NIC) which was formed by the Lao government to investigate the cause of the disaster, which killed dozens of villagers and left thousands homeless, revealed the findings of the investigation at a press conference on Tuesday.
Singphet said that even if rainfall was quite heavy on the days before the July 23, 2018 tragedy, the reservoir level was still below the maximum operation level and well below the crest level when the failure started.
"Thus, the failure incident can not be considered as 'force majeure,'" he told local media.
The Lao government set up the NIC to thoroughly investigate, verify and report to the Lao government, the general public, the international community and other stakeholders with regard to the underlying causes of the collapse of the saddle dam.
To ensure the transparency of the investigation of the causes of the collapse, the committee engaged and gave full authority to a panel of professional and independent experts (the Independent Expert Panel, or IEP) with globally recognized reputations to conduct an independent investigation and to report the results of that investigation. In addition, the Lao government invited foreign parties to take part as observers in the investigation process, said the report.
The Lao government understands that the Korean company involved in the development of the project is also carrying out an investigation into the underlying causes of the collapse.
The IEP outlined its findings on the failure of saddle dam D in a final report, and submitted the report to the NIC on March 20, 2019.
It also found that the root cause of the failure was related to high permeability combined with erodible horizons mainly due to the existence of canaliculus interconnected paths.
As the water level rose 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, which reached a certain point, 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 foundations. The foundation is without doubt involved in the failure, which could have been prevented by adequate treatment measures, according to the Independent Expert Panel.
The dam collapse resulted in devastating floods, leaving 42 killed and 23 missing, the Lao government reported in last December. The Xe-Pian Xe-Namnoy hydropower plant is invested by South Korean, Thai and Lao companies.
