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This project, submitted by TenCate Geosynthetics, won an Award of Excellence in the 2011 International Achievement Awards(IAA) / Geosynthetics presented by the Industrial Fabrics Association International. Each project in its own special way, exhibits outstanding innovation, technical skill and design excellence.
Submissions of geosynthetics projects for the 2011 International Achievement Awards are being accepted now. Submit your projects by July 15, 2012.
Project description
China Huaneng Group, a Fortune Global 500 company, is China’s largest power producer. The company oversees the national government’s interests in 10 subsidiaries, including a 51% stake in Huaneng Power Intl., a company simultaneously listed on the stock exchanges of Hong Kong, Shanghai, and New York.
Through subsidiaries, it develops and operates more than 85 thermal and hydropower plants. The client is also actively investing in coal sources to secure supplies at stable prices. The company is developing a coal processing plant at Hetaoyu (which means “Walnut Valley” in Chinese) in the Qingyang Prefecture of Gansu Province in north-central China.
Retaining wall
A retaining wall was constructed to create the platform—approximately 1km long and 140m wide—from rugged slope terrain to site the new coal processing plant.
The reinforced soil retaining wall is about 1km long, about 30m high, with the highest section 35m. To optimize the creation of usable land, the retaining wall was constructed adjacent to the Jinghe River, which flows by the southern boundary of the development site.
The platform for the new coal processing plant was reclaimed by cutting into the hillside slope next to the river and recompacting with PET geotextile reinforcement to construct a strong and lasting reinforced soil retaining wall structure. The reinforced soil retaining wall is divided into bermed segments.
The reinforced soil wall was built in vertically faced segments up to 896m. The portion of the wall above elevation 896m to 914m was constructed with V:H 4:1. Geotextile-wrapped soil bags at the wall facing prevented surface erosion during the construction. For aesthetics and permanent protection, a combination of concrete and shotcrete facings were installed.
A 0.5m-thick reinforced concrete facial structure was built for the vertical facing portion of wall. For the inclined facing part of the wall, a 150m-thick steel wire mesh-reinforced shotcrete cover was provided. A cast-in-place reinforced concrete edge capping unit 0.3m deep and 1m wide was provided at the final platform elevation.
The retaining wall system was economical, required comparatively shorter construction time than other alternative systems, allowed use of local borrowed fill, is able to withstand earthquake forces, and can provide resistance against surface erosion during and after construction.
Loess Plateau
The Hetaoyu Coal Mine complex is located in a north-central region of China called the Loess Plateau. The Loess Plateau, where the sedimentary loess deposits may be hundreds of meters thick in places, stretches across several Chinese provinces, including Gansu Province.
Situated in northwest China, the Loess Plateau covers an area of nearly half a million km2. It is located in the middle reaches of the Huanghe (Yellow) River, bordered by Taihang Mountains on the east, extending westward to the Wuqiaoling and Riyue mountain ranges, and by the Qinling Mountains on the south. The Great Wall of China marks the north border of the plateau. The Loess Plateau, with an altitude of 1,200–2,000m, slopes downward from north to south and from west to east.
In simple terms, loess is a light-colored, fine-grained accumulation of clay, silt, and fine sand particles. Although reasonably high in shear and compressive strengths, the wind-blown loess deposits are susceptible to rapid erosion that can severely affect geotechnical stability.
Loess soil backfill requires special consideration in construction due to its susceptibility to erosion. The area is also affected by earthquakes. Occasional landslides in the Loess Plateau are predominantly triggered by earthquakes or precipitation.
The geotextile reinforcement for the retaining wall is well-proven for withstanding earthquakes. The use of soil bags using a geotextile wraparound technique of construction eliminated the problem of rapid soil erosion that can occur during intense rainfall in an otherwise semi-arid area. The retaining wall and geotextile bags accounted for project cost savings because there was no need for imported backfill.
Because of the wall heights and the influence of earthquakes, the wall foundation was established on solid sandstone bedrock, a stratum surface that was uneven, but the geotextile reinforced soil retaining wall system adapted to this uneven bedrock surface. An alternative option of providing a piled foundation was cost prohibitive.
Conclusion
Reinforcement geotextiles were used to reinforce locally available loess soil fill in the construction of an extensive retaining wall supporting a new coal processing plant at the Hetaoyu Coal Mine Complex in China. The wall construction was completed within the allotted schedule, and the geotextile-reinforced soil retaining wall system resulted in significant cost savings compared to other options that were evaluated.