## 1 Introduction  
As the main energy source in China, coal accounts for over 60% of China's energy consumption [1]. However, mining and excavation are the most dangerous production links during coal exploitation, and the fully mechanized working faces turn into accident-prone areas in coal mines [2]. Furthermore, gas, water, dust and other factors pose threats to worker safety. The environment is extremely tough [3, 4]. The continuously increasing depth of coal exploitation leads to greater difficulty in coal mining. In addition, deep mining, especially the mining of deep coal seams with large dip angles, has encountered increasingly severe problems [5, 6]. In such seams, poor stability of the roadway-head surrounding rock, harsh environment, small working space and difficult support result in slow excavation, which seriously imbalances the time distribution during excavation, support and anchoring, critically affecting the speed of roadway excavation [7, 8, 9, 10, 11, 12]. Thereby, it is of great urgency to expand advance-support equipment for deep, fully mechanized roadways [13, 14, 15, 16, 17] so as to ensure parallel operations of excavation, support and anchoring and to improve excavation efficiency while guaranteeing the roadway construction safety. In recent years, many scholars have conducted considerable research on the advance support for fully mechanized roadways. [PERSON] et al. [18] established the vibration-mechanics model of advance support in the full-support state and performed vibration tests. [PERSON] et al. [19] divided the deformation and failure evolution of the trend of abandoned roadway roofs into four stages: initial deformation, bending-separation deformation, fracture failure and collapse failure. The technology for filling and controlling the trend of abandoned roadways, with high-water material over the fully mechanized mining face, was proposed, and the effect of the filling body on the roofs of the abandoned roadways was revealed. [PERSON] et al. [20] studied the stability and strength of the column cylinder of the self-moving advance support by means of simulation. Based on the simulation results, they analyzed the stress and deformation of the roof beam and the main beam of the support. [PERSON] et al. [21] adopted a grouting anchor cable (bolt) + U-type steel + a single-prop-combined support technology to support the roof, and on this basis, proposed grouting the anchor cable to reinforce the weak surface of the roof and plug the cracks. In order to enhance the stability and safety of the advance support for roadways during stepping advancement, [PERSON] et al. [22] formulated a control method for stable stepping advancement, in accordance with the principle of the average hydraulic-oil volume release. Meanwhile, they constructed a prototype of a similar test model with a compression ratio of 1:8 and developed a test platform and a measurement datum frame for simulating the roadway roof. In this way, the mechanical tests were carried out on the coupling system of the roof and the advance support. Given the problems of untimely support, low support strength and labor-consuming and time-consuming processes that exist in the current mode of advance support for mechanized roadways, [PERSON] et al. [23] developed a new set of stepping self-moving advance supports. Considering that the advance support for mechanized roadways faces the problems of long support time, poor quality and low strength, [PERSON] et al. [24] designed a set of self-moving advance-support equipment and performed mechanical analysis, numerical simulations and field tests. To sum up, the existing studies demonstrated that current advance-support equipment of fully mechanized roadways confront many problems, such as complex processes, slow movement, low work efficiency, high labor intensity, difficult roof management and poor adaptability, failing to ensure safety.