As Lao Dong reported, since the end of March 2025, in Kim Lu commune, Na Ri district, Bac Kan (old), now Na Ri commune, subsidence holes have appeared continuously.
Notably, on May 26, at the death hole on National Highway 3B, a motorbike driver fell into a deep hole. The complex geological background, the sinkhole is about 24 meters deep, leaving the missing victim unused.
On August 2, information from the Thai Nguyen Department of Construction, the province assigned the unit to be the investor of the project "Emergency to overcome the consequences of natural disasters, ensuring traffic on National Highway 3B at Km 80+050" to handle the subsidence point in Na Ri commune.
The project has a total investment of more than 4.3 billion VND from the state budget, aiming to urgently ensure traffic safety and stabilize the lives of people in affected areas.
The repair plan is applied according to a special technical process, suitable for the mountainous terrain and complex limestone foundation.
The sinkhole will be dug and expanded to create a construction site, then the steel baskets stuffed with boulders will be treated into 3 - 4 layers to stabilize the bottom of the hole. After that, the construction unit will pour boulders to the elevation about 3m from the old road, then place handmade stone baskets to create a solid foundation for the cage mouth.
The structure of the road will be returned according to technical standards, including the technical technical technical fabric layer below, the type 2 crushed stone layer 30cm thick, the type 1 crushed stone layer 18cm thick and finally the three-layer plastic layer with a quota of 4.5kg/m2. The construction area extends from Km79+900 to Km80+100 on National Highway 3B.
As of the afternoon of August 2, the construction unit has completed releasing 156 steel baskets stuffed with clay and gravel to the bottom of the hole to create a stable linkage of the geological foundation. At the same time, more than 100m3 of boulders have been filled to create a solid foundation layer.
The project is expected to be completed before August 31 if construction conditions are favorable.
Previously, according to the Institute of Geological Sciences and Mineral Resources, the death holes in this area formed on a geological background consisting mainly of strongly phonglized limestone, combined with the activity of the underground water mach underground below.
The prolonged silent erosion process created underground holes, at one point causing a sudden subsidence. With such a complex geological structure, the treatment requires careful survey, avoiding the application of simple hole filling measures that will not be able to solve the problem at the root.
