Geotextile Reinforced Soil Retaining Wall for Hetaoyu Mine Coal Processing Plant

TenCate Geosynthetics

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 percent stake in Huaneng Power International, 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 hydro power plants. The client is also actively investing in coal sources to secure supply at stable prices. The company is developing a coal processing plant at Hetaoyu (which literally means Walnut Valley in Chinese) Coal Mine Complex in Zhengning County, Qingyang City of Gansu Province in China. A platform of approximately 1 kilometer long and 140 meters wide is created to site a new coal-processing plant.

A retaining wall was constructed to create the platform from rugged slope terrain to site the new coal-processing plant. The reinforced soil retaining wall is about one kilometer long and averages 30 meters in height but is 35 meters at its highest section. To optimize the creation of usable land the retaining wall had to be constructed right beside the Jinghe River which flows by the southern boundary of the development site. The platform for the new coal-processing plant is reclaimed by cutting into the hill slope adjacent to the river and recompacted with Mirafi® polyester (PET) reinforcement inclusions to construct a strong and lasting reinforced soil retaining wall structure. The reinforced soil retaining wall is divided into a few bermed segments. The reinforced soil wall was built in vertically faced segments until site elevation 896 meters. The portion of wall above site elevation 896 meters until final platform elevation 914 meters was constructed with vertical to horizontal inclination ratio of 4V:1H. Soil bags with Mirafi® PET geotextile wraparound technique of construction at the wall facing prevented surface erosion from occurring during the construction period. For aesthetics and permanent protection a combination of concrete and shotcrete facings were provided. For the portion of wall constructed to vertical facing, a 0.5 meter thick reinforced concrete facial structure was provided. For the portion of wall constructed to inclined facing, a 150 millimeter thick steel wire mesh reinforced shotcrete cover was provided. A cast-in-place reinforced concrete edge capping unit of 0.3 meters deep and 1 meter wide was provided for at the final platform elevation. The retaining wall system was economical, required comparatively shorter construction time than other alternative systems, allowed local borrowed fill to be used, is able to withstand earthquake forces and can provide resistance against surface erosion during and after the construction period.

Hetaoyu Coal Mine Complex is located within the Loess Plateau of China. The Loess Plateau, where the sedimentary loess deposits may be hundreds of meters thick in places, stretches over seven provinces in China, including Gansu Province. Situated in northwest China, the Loess Plateau covers an area of 640,000 square kilometers. It is located in the middle reaches of the Huanghe River (Yellow River) and bordered by the Taihang Mountains on the east, extending westward to the Wuqiaoling and Riyue Mountains, and by the Qinling Mountains in the south, stretching northward to the Great Wall. The Loess Plateau, with an altitude of 1,200 meters to 2,000 meters, reduces in height 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 that have been deposited by wind. Although reasonably high in shear and compressive strengths, the loess deposits are susceptible to rapid erosion that can severely affect geotechnical stability. Loess soil backfill need special consideration in construction due to its susceptibility to rapid erosion. The area is also affected by earthquakes. Occasionally landslides occur in the Loess Plateau and are predominantly triggered by earthquakes or precipitation. A Mirafi® PET geotextile reinforced soil retaining wall withstands earthquakes through a well proven and documented system. The use of soil bags with Mirafi® PET geotextile wraparound technique of construction eliminated the problem of rapid soil erosion that typically happens during occasional intense rainfall in an otherwise semi-arid area. This resulted in significant project cost savings as there was no need for imported selected backfill, which would have been extremely costly. The wall system blends in with the earthworks and therefore is time-efficient for the overall construction. Because of the extreme wall heights and thepotential influence of earthquakes, the wall foundation would have to be founded on solid sandstone bedrock. The sandstone bedrock stratum surface is highly uneven. The Mirafi® PET geotextile reinforced soil retaining wall system adapted to this uneven sandstone bedrock stratum surface. The alternative option of providing a piled foundation was cost prohibitive.

Mirafi® PET reinforcement geotextiles were used to successfully reinforce locally available loess soil fill to construct an extensive retaining wall supporting a new coal processing plant at Hetaoyu Coal Mine Complex. The wall construction was completed within the allotted schedule. The Mirafi® PET geotextile reinforced soil retaining wall system resulted in significant cost savings over other alternative systems that were evaluated.

Project details

Location: Gansu Province, China
Size: 60,000 sq.m PET100/50; 200,000 sq.m PET200/50; 250,000 sq.m PET300/50
Fabrics: Mirafi PET Geotextiles by TenCate Geosynthetics from TenCate Geosynthetics
Engineer: Wuhan Design & Research Institute of Sinocoal International Engineering Group
Project Manager: China Gezhouba Group Company Ltd.