## 3 Synergistic Support System of \"LDAGF\"  
### Principle of the Synergistic Support System  
Synergy refers to the process or ability of multiple different resources or individuals to achieve a goal in a coordinated manner [23]. With respect to the safety of roadway SR in coal mines, a synergistic support aims to achieve the best control effect of SR stability at the minimum support cost. Therefore, based on the engineering response and support mechanism of roadway SR, and guided by the basic principle and methods of synergetics, the synergistic support of roadway SR in coal mines can explore the synergistic effect and evolution mechanism of a support-SR system in the stability control of roadway SR. In this process, the deformation control of roadway SR is the key. With the aid of a reasonable design and optimization of the support system, the interaction between roadway support and SR can be realized; the mechanical properties of the support and SR are fully utilized so that the overall support effect of the support system is superior to the sum of different support modes at the macro level, that is, the synergistic support effect of \"\(1+1>2\)\" is achieved, thereby avoiding the instability of roadway SR and the failure of the supporting structure. The basic function of a roadway support system is to maintain long-term stability of the roadway SR. In this system, roadway SR, as the main body of support, exists objectively. In terms of its function, the essence of roadway synergistic support is \"mobilizing the bearing capacity of SR\" and \"assisting SR in playing the bearing role\". Apparently, SR is both the source and the major bearer of load, and its mechanical behaviors inevitably affect the stability of the whole system [24,25]. Therefore, maximizing the self-bearing capacity of SR is the basic principle of roadway support in coal mines. For an ESFMCFR, \"mobilizing the bearing capacity of SR\" can be realized by improving the performance of shallow SR, hence giving full play to the bearing capacity of SR. \"Assisting SR in playing the bearing role\" requires assistance from the supporting structure; that is, a reliable control of SR stability can be realized through the joint action of the supporting structure and the SR.  
On this basis, a synergistic support system of \"LDAGF\" was proposed considering the reasons for the roadway instability (Figure 5). This system can fundamentally solve the problems of serious deformation and failure, difficult support, long support time and slow excavation of the ESFMCFR in thick seams. The technical measures adopted include floor breaking and side lowering of roadway, bolt advance support, anchor cable support, advance water injection and grouting and flat-root U-shaped steel shed support. These measures improve the SR environment, fully utilize the deformation characteristics of SR and its own bearing capacity, and maintain the stability of the roadway. More specifically, these measures involve the following:  
1. \"L\"--floor breaking and side lowering: According to the dip angle of the coal seam, reasonable floor breaking and side lowering is carried out to ensure that the shed legs at the two sides take root firmly and improve the lithologic strength at the roadway sides. 2. \"D\"--bolt advance support: Advance roof protection by self-drilling bolts for grouting is conducted along the roof of the shed beam. Then, the roof is grouted for solidification and the prevention of air leakage and roof caving. 3. \"A\"--anchor cable support: To improve the strength of the roadway support and enhance the stability of the flat-roof U-shaped steel shed support, anchor cables are used instead of bolts. The roof and sides are strengthened with long anchor cables and short cables, respectively. 4. \"G\"--advance water injection and grouting: To enhance the plasticity of the coal body, the coal body at the head undergoes advance water injection while the roof is solidified by advance grouting before shed establishment with the aid of advance self-drilling bolts for grouting. 5.