# Review on Engineering Application Status of Gob-Side Entry Retaining Technology in China
## 2 The Current Status of GSER Technology Development in China
Based on the clarification of the stress transmission mechanism of the wedge-shaped area roof in the retained entry goat, a reinforced support technology system for retained entry surrounding rock control based on high-prestressed anchor bolts and cables was formed [16; 17; 18; 19; 20; 21; 22]. With the gradual application of GSER technology to thick coal seams and even fully mechanized mining faces, the deformation and stress evolution characteristics of the surrounding rock of GSER in fully mechanized mining faces were investigated [23], and the calculation formula for the support resistance of entry-side filling body under different geological conditions was further improved. It was found that the caving of the roadway roof is directly related to the main roof [24; 25]. Particularly in the 21 st century, high-performance concrete [26], steel-reinforced concrete piers and columns [27], new ultra-high-water materials [28; 29; 30], flexible formwork concrete [31], and other construction materials have been continuously developed, as well as the rapid development of technologies related to roof-cutting and pressure relief in the roadway. Consequently, the maintenance effect of the retained entry surrounding rock has been significantly improved, and the study of the stress evolution characteristics of the retained entry surrounding rock has become more in-depth and detailed [32]. Different retained entry construction processes, supporting equipment, and support techniques have been formed according to different engineering geological conditions, and GSER technology has been widely promoted and applied. Engineering practice has also shown that the existing active and passive combined support technology has proven insufficient in effectively achieving stable control of the surrounding rock of retained entry under complex geological conditions. Only by using methods such as presplitting blasting and hydraulic fracturing to break the roof near the goat and optimize the cantilever structure for roof-cutting can a favorable stress environment be created for the stable control of the surrounding rock of the retained entry [33; 34; 35]. Subsequently, roof-cutting and pressure relief in thin and medium coal seams and automatic tunneling without coal pillar technology were proposed, and supporting materials and equipment such as constant resistance anchor cables and seam drilling vehicles were developed [36; 37; 38; 39; 40]. Besides, GSER technology based on working face backfilling has also begun to be applied in engineering sites [41; 42; 43], greatly reducing the strong dynamic pressure impact caused by traditional GSER methods. This method provides new ideas for the development and application of GSER technology in China. Based on the above, the main classification and application conditions of GSER technology systems in China are shown in Table 1. But their applicable conditions in practical engineering still need further study and clarification. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Classification by** & \multirow{2}{*}{**Classification by Entry-Side**} & \multirow{2}{*}{**Technical Characteristics**} & \multirow{2}{*}{**Application Conditions**} & \multirow{2}{*}{**Development Trends**} \\
**Construction** & & & & \\  
Figure 4: GSER with paste filling in filled working face of Daizhuang coal mine in 440 m buried depth. Figure 3: GSER with entry-side filling of high-water material of Liangshuijing coal mine in 130 m buried depth. Figure 2: GSER with concrete filling of Guqiao coal mine in 780 m buried depth.