Taiwan | 2005-2009

A Complex Reinforced Structure Applied at Hilly Road Repair Case, Pingtung, Taiwan

Products:ACEGrid® GG, ACETex® NW, ACEDrain™ S

Application: Slope Stabilization

Background

This project is located in Route 35 in Pingtung County, Taiwan. From July 7 to August 9, 2006, torrential rainfalls continuously attacked Pingtung; a county contains the oldest and the largest national park at the southernmost part of Taiwan. The accumulated 1,380mm precipitation completely soaked the ground and therefore caused a section of downslope collapsed in Route 35.

Problem / Task

The subgrade of Route 35 was damaged badly and the highway had to be closed for safety. Forensic investigation indicated that the sliding was mainly due to the enormous surface overflow out of the drainage gutters along the highway. The collapsing area was very deep with a height up to 18m, and the place available for building foundation was limited by the terrain.

Solution/ Design & Construction

Considering cost, efficiency, sustainability, and site conditions, the designer introduced a composite protection system for the rehabilitation. Firstly, a reinforced concrete mat foundation with drilled root piles were installed as base support. Then, the designer contracted representatives of ACE Geosynthetics and adopted ACEGrid® geogrid as the reinforcing material to build a 3-tier reinforced earth slope (RES) to support the highway. Additional soil nails, tied up securely with geogrid, were installed to dowel the deep-seated failure plane to ensure stability and reduce the requiring area of the foundation. RES was constructed with geogrid wrap-around facing set back with an averaged inclined ratio of 1:2 (H:V). It was built in layers using the collapsed residues on site. Fill materials were placed and geogrid installed at a vertical spacing of 50 cm and they were piled up until reaching the final height of 16-18 m. Soil-filled and hydro-seeded soil bags were stacked for slope face protection. They also functioned as the medium of planting as a vegetated slope not only provides an aesthetic appearance, but is also an eco-friendly environment. Interior intercept trenches and horizontal drains were also arranged to prompt the dissipation of groundwater. Finally, longitudinal and horizontal trench systems were installed to facilitate the drainage of surface run-off.

Result

By using the innovative design, the difficulty of construction was overcome and a safe, economic, and eco-friendly structure has been built. The flourish green vegetation on the RES not only has given the site a natural appearance but also has become a favorable place for many local species. It appropriately maintains the traffic safety for the residents and warrants the site to be an eco-friendly environment as well. Since the completion of the project in 2007, the site has remained in good condition through several attacks of strong typhoons, including the deadly Typhoon Morakot in 2009. The success of the case has proved the value and possibility of the complex reinforced structures with geogrids.

Slope Stabilization

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