Conclusion on the cause of the incident
The Dak N'Ting Reservoir Project's Cause Assessment Team (abbreviated as Assessment Team 1552, established by the Dak Nong Department of Agriculture and Rural Development (now the Department of Agriculture and Environment), under the direction of the Provincial People's Committee) has concluded the cause of the landslide.
Accordingly, the cause of the formation of the slide originates from a combination of adverse factors such as terrain, geology, hydrology and human impact.
The hillside area on the right side of the project has steep terrain, the ground is made of strongly mobilelized basalt layers, low load-bearing, and easy to saturize.
The geological structure is tilted towards the reservoir bed, causing instability when the groundwater rises. Before the construction of the project, the right hillside had a stable coefficient of 1.05, showing that the right shoulder of the project was at risk of instability.
In 2023, there will be a record amount of heavy rainfall. This is one of the main causes of large fluctuations in the groundwater level on the slope, changing the mechanical indicators of geological layers causing landslides on hillsides.
In addition, spontaneous farming activities on the hill have created many erosion ditches. Surface water is concentrated and absorbed deeply, increasing the pressure of groundwater. The steady coefficient of the slope has decreased sharply. The slide moved strongly towards the project, causing heavy damage to items: dam body, flood overflow, dam surface.
The 1552 appraisal team concluded that continuous heavy rain combined with complex terrain and geological conditions caused a slide on the hillside of the project. The movement of the slide directly affects the project, causing damage at the flood discharge and land dam.
This is the force majeure cause of the Dak N'ting reservoir landslide.
The main project is comprehensively reinforced
According to the 1552 Appraisal Team, the dam's soil currently appears in many cracked, broken, and broken areas. The dam body has a phenomenon of rising, moving nearly 0.5m higher than the design, causing the fill soil in this section to be damaged, layered and strongly seeping. The Dak N'ting reservoir's dam is currently unsafe for water storage.
The flood discharge system of the project has cracked and broken in many locations and is not safe. Upstream and downstream wing walls and connecting joints have been deformed. The joints between the foundation and the concrete foundation have been deformed and destroyed.
The spillway of the project was quite seriously affected. Some bridge spans have long and wide cracks. Some level girders have cracks and peels coming off the girder owner. Some abutments, piers, and bridge bearings are skewed, damaged, and unsafe.
The 1552 assessment team believes that the hillside slide near Dak N'ting reservoir is at high risk of landslides because this area has enough unfavorable factors.
Faced with the above risk, the Department of Agriculture and Environment of Dak Nong proposed immediate and long-term solutions for the Dak N'ting reservoir project. For now, the entire lake is kept at the lowest water level and the water storage is completely stopped.
The drainage is done through sewers or the installation of a forced silencing system. The cracks on the slope are covered with clay and waterproof nylon.
The project is closely monitored, fenced off dangerous areas, put up warning signs, and organized the evacuation of people in directly affected areas.
In the long term, the main project is comprehensively reinforced. The total cost of repairing the landslide at Dak N'ting reservoir is expected to be more than 23.1 billion VND.
Previously, Lao Dong Newspaper reported that the Dak N'Ting Reservoir Project was approved by the Dak Nong Provincial People's Committee in 2018. The total investment is nearly 137 billion VND, invested by the Dak Nong Provincial Construction Investment Project Management Board.
The Dak N'Ting reservoir project has a capacity of more than 2.1 million m3. The project's goal is to provide irrigation water for 680 hectares of crops and the daily life of about 1,000 surrounding households.
At the end of July and the beginning of August 2023, due to the impact of prolonged heavy rain, a large slide appeared on the dam surface of Dak N'Ting reservoir.
Due to the complicated situation of landslides, the Dak Nong Provincial People's Committee has declared a natural disaster emergency at the Dak N'Ting reservoir project.
