The Ha Long - Van Don Expressway is one of the most important transportation construction items for connecting the whole transportation routes between the capital city to the northern cities in Vietnam. Because of the mountainous terrain in this area and the importance of this expressway, many kinds of slope surface protections are used for the excavated slopes along this expressway. From June to August 2018, there was a 2-month-prolonged rain and then caused a tremendous scale of landslide on the top slope in the section of Km 51+280 - Km 51+500 of this expressway due to the poor geological conditions (the soil in jobsite mostly is clay mixed with broken rocks)!
What was the challenge?
According to the results of the survey, the sliding length of this landslide is about 200m and the total sliding height is more than 40m, and there are some barrier lakes on the top platform which is caused by the erosion of this landslide area. Surface runoff and water seepages (causing by the rain fall) are considered as the main factors leading to landslides as described above. Because the catch drain system on the top is not completed yet, the soil strength is reduced when the runoff flowing and seeping into the soil layer, and the runoff also flows into the tension cracks (which is caused by the excavation and soil decompression) and greatly increases the possibility of slope sliding, therefore there’s a great scale of landslide in this project! As this is the most important expressway connecting the main economic axis: Hanoi capital and Van Don Airport, so it's important to repair this landslide by using a safety, sustainable and eco-friendly construction methods.
A Geogrid-reinforced structure (GRS) wrap-around with ACEGrid® were chosen to repair this sliding slope, and placed above the base of slope which is with existed surface protection (covered with concrete brick/slab). This GRS was constructed in 4 to 9 sequential tiers and up to a final height of 45m with the embedded ACEGrid® length is 8 to 12m long. Along with that is the top drainage system combined with the drainage system inside the structure, which are installed to collect effectively the surface water on the top slope and the groundwater inside structure and could quickly to drain the collected water into the horizontal and vertical ditches.
The impact of the solution deployment?
Simple construction machines and equipment, short construction time, low construction cost, the eroded soil in place reuse which could reduce costs for the purchase and transportation of soil from other places, green slope surface with natural vegetation, extremely low carbon emission, and etc. These are the benefits for adopting GRS (by applying ACEGrid®) to a landslide repair. As a relatively new solution in Vietnam, the Geogrid-reinforced Structure (GRS) for landslide repair has already shown the remarkable efficiency when comparing to other traditional alternatives.