Award of Excellence
The object of this renovation project is the Zhongsha Bridge located on the Zhuoshui River in west-central Taiwan. The 2,345m-long bridge spans the Zhuoshui on the border between Changhua and Yunlin counties.
The bridge was built in 1978 with prestressed hollow core piles and prestressed beams. It is part of Sun Yat-sen Freeway (Freeway No. 1), the north-south arterial roadway that connects major cities on the west coast of Taiwan. Therefore, this renovation construction had to be in conformity with high standards and under strict controls.
The project included renovation of riverbank protections below the Zhongsha Bridge as well as repair and reinforcement of submerged-weir groundsel works and aprons downstream. The primary objectives of this project were to secure the adjacent farmland against erosion and to ensure the safety of vehicles on the bridge.
In this project, geotextile tubes and geotextile mattresses were used to effectively address construction and erosion issues.
For decades, the river reach near the Zhongsha Bridge has endured continuous impact of fluvial processes, including erosion and deposition. Furthermore, the jobsite was situated on the outer concave bank of the river where erosion problems were more serious and, thus, the foundations of the piers were undermined by the flowing water.
With the soil erosion, the foundations were exposed. The situation was much more threatening during typhoon seasons when large-scale floods with sediments struck the exposed foundations and jeopardized bridge traffic. The muddy floods also submerged the farmland adjacent to the river and put the residents and their property in danger. It was urgent to fortify the pier foundations and enhance the protection of the embankments on the riverbanks.
Tubes and mattresses
The many highway curves near the jobsite made the project more challenging from a geotechnical engineering perspective.
The protection was designed to be 5.6m high with four layers of geotextile tubes. After each layer was filled with in-situ sand, in-situ soil was then placed and leveled on top to make an even surface for the installation of the next layer. This procedure was repeated until the four layers were completed.
At the conclusion of construction, the four-layer structure was covered with geotextile mattresses filled with concrete mortar that not only increased the impact resistance of the structure and kept tubes from external damages caused by river current debris coming down the river but, in the meantime, also enhanced the stability of pier foundations and embankments.
Furthermore, the mattresses used here had permeable filter points, which allowed the excess water in the structure to discharge into the river and maintain the stability of the structure. The geotextile tubes and mattresses also proved to be a fine solution because of their flexibility that allowed them to adjust to various land forms in the process of construction.
The combination of these two materials provided reliable protection for the pier foundations and the embankments and, as a result, effectively improved the structural safety of the bridge.
The foundation improvement part of the project started in 2012. The budgets called for riverbank protection and maintenance every year, with the purpose of ensuring the safety of neighboring residents and drivers.
Both geotextile tubes and mattresses were used from the beginning of this project because of their eco-friendliness and cost-effectiveness. Structures made of these innovative flexible geotextile materials make better use of in-situ sand and soils than those made of concrete. They also reduce greenhouse gas emissions as well as producing environmental sustainability and allowing construction to proceed.
The flexibility of these materials makes them adaptable to other kinds of landforms and site conditions. It not only makes construction easier, but also helps the structures coexist with the environment. Even typhoons that bring disastrous floods were not able to cause any damage to them and the completed structures provide good erosion prevention. Lush vegetation now grows on the adjacent fertile land, making the site blend in with the surroundings.
Ace Geosynthetics and IFAI’s 2015 International Achievement Awards; edited by Geosynthetics magazine