State-of-the-art of standing supports for gob-side entry retaining technology in China

Gob-side entry retaining technology (GERT) is a popular layout of the roadway in many modern coal mines due to its outstanding advantages in high production yield ratio and enabling the 'Y' shape ventilation configuration. During the past two decades, various standing supports, as the critical component of GERT, have been proposed and implemented. However, few systematic investigations have been conducted. This paper starts with a concise introduction of the movement of the strata overlying the standing support when the whole service period of retained gob-side entry is considered. A recently proposed new classification of standing supports based on the cross-section is then described. To obtain an in-depth comparison of each standing support, the advantages and drawbacks are investigated based on the installment procedure, economic benefits, and mechanical behaviour. Furthermore, recommendations for further research topics have been identified, such as the development of novel hybrid composite structures either in terms of the backfilling materials or the confining material. These backfill materials include coal rejects concrete, geopolymer concrete, high water-content slurry, and other environmentally friendly materials made of industry by-products. Emerging materials, including fibre-reinforced polymer (FRP) composites, high-strength steel, geosynthetic material, and combinations of these materials, should be considered. The key purpose of this review is to offer solutions for the development of easy to-construct, cost-effective, and environmental friendly standing support for CERT.