Treatment and Erosion Protection, Upper Slope of Tunnel Portal , Taichung, Taiwan

This project took place at the portal area of tunnel No.9 of an abandoned railway (currently remodeled as a scenic bike path) in Taichung. The surface of the upper slope at the portal area has been covered by a layer of completely weathered and fractured sandstone with a thickness of 1 to 2 meters. According to the environmental geological studies given by the Central Geological Survey, the site has been classified as debris sliding zone. It appeared to be very unstable and risky upon any disturbance.

In July 2006, a torrential rainfall attacked the site and totally saturated the decomposed slope surface. A typical shallow plane failure was then triggered and caused the surface to slide off the bedrock. The movement further loosened the cementation of the weathered sandstone and thus seriously jeopardized the traffic safety of the portal area. The managing authority called for an immediate rehabilitation not only to stabilize the upper slope but to resurface the portal area for scenic improvement as well.

3D diamond-shaped high-tensile steel wire mesh was first secured onto the bare slope using grouted rock nails. A base layer consisted of mixed seeds, fertilizer, and water-bearing material was hydro-sprayed on top of the wire mesh networks. ACEMat™ R turf reinforcement mat, a 3D cellular and high tensile strength confinement material, was then fixed together with the steel wire mesh using rock nails.

The composite slope protection system not only secures the weathered sandstone, it gives a fresh green looking at the portal area as well. ACEMat™ R offers spaces for vegetation to grow. It is also attractive for a variety of local species to stay. Although the site has experienced several challenges of strong typhoons and torrential rainfalls, it remains stable with richly grows vegetation. The design scheme has proved such composite slope protection system with ACEMat™ R totally meets the demands of an eco-friendly environment with sound stability.