Water management in Vietnam is a complex balance between large natural water basins on one hand and the needs of the population in terms of water for agricultural irrigation, seasonal drought and hydro-power on the other.

As part of the regional water management program, the Hanoi Provincial Department of Agriculture and Rural Development (DARD) recently constructed an earthen dam at Trung Mầu on the Duong River to control seasonal flooding.

The design included a reengineered 3m high slope at a very steep grade of 22 degrees (10-12m length of slope) on the Western bank to withstand flooding during the monsoon season. This required the best available slope protection solution to prevent soil erosion into the dam.

The required solution was to mechanically confine soil to control erosion, but had three additional requirements:

• Reinforcement – increase the slope strength to improve local stability and prevent deformation.
• Fast Solution – Time was critical, as the slope required a solution immediately after its construction before the beginning of the rainy season began (including re-vegetation).
• Natural Landscape – The solution had to be a natural green landscape based on native grasses, which are best suited to binding the soil and tolerate flooding.

Conventional Solution

Native vegetative cover and moderate grades protect natural slopes from rain and erosion. However, re-engineered slopes are typically reconstructed at unnaturally steep grades. These are subject to erosive forces after construction until the vegetation has a chance to re-establish itself for effective soil-root interlock. Re-engineered slopes require mechanically stabilized soil protection solutions, particularly in Vietnam where torrential rains can create havoc on exposed slopes.

Neoloy Tough-Cell Solution

The Neoloy Tough-Cell was selected by DARD as the fastest, most reliable and cost-effective solution for slope erosion control protection. Neoloy Tough-Cells have a higher long-term strength and environmental durability than any other geocell or geosynthetic.

Neoloy Tough-Cells 660-100 (height) were used for the project. Pre-fastened sections where anchored with steel anchors at the crest on the top of the slope and then the sections were opened downslope.

Wooden stakes were installed on the slope at a density of 4×4 cells to anchor the system to the slope. Locally available topsoil was used for infill. The 2 cm overfill was compacted with the back of the excavator shovel. Native grass seedlings were planted and established a sufficient ground cover within 2 months in time for the monsoons.

The slope protection system has experienced two rainy seasons without any noticeable erosion, to the full satisfaction and certified approval of the DARD authorities.

Client Benefits

• Simple logistics and construction method
• 50% faster installation than concrete based solution
• Utilized locally trained work crews
• 25% cost savings
• Sustainable solution – designed to last, utilized local materials, fully integrated with natural landscape