**1. Introduction**

In China, coal is the major energy source and it accounts for about 68% of the total primary energy consumption. As the coal resources within shallow grounds are depleting, mining operation have been moving to increasing deep grounds in recent years [1]. In China, the average depth of coal mining operations has reached up to 556 m and it is increasing at a rate of 8 to 12 m per year. For metal mines, the depths of mining operations are even higher. For example, the Mponeng gold mine in South Africa extends 4250 m below the surface [2]. As the depth of mining works increased significantly, potential risks such as the collapse of roadways surrounding rocks, high coalbed methane emissions and outbursts, as well as groundwater inrushing increased dramatically [3–6]. Consequently, an increasing amount of coal mines have started excavating permanent or semi-permanent roadways

within rock layers rather than coal seams to obtain increased safety during mining and roadway excavation operations [6]. Compared with coal, rocks have higher strength and it is beneficial to increase the stability of roadways and reduce risks. On the other hand, the higher strength of rocks also increases the difficulties of roadway excavation and slows down the excavation speed. At present, excavation speeds in rock layers are significantly slower than these in coal seams (40 to 100 m/mth in rock layers vs. 120 to 300 m/mth in coal seams) [7]. Typically in mining operations, roadways in rock layers include main roadways and other auxiliary roadways for transportation, ventilation, coalbed methane drainage, and groundwater drainage roadways purposes. They should be finished before the coal seam roadways start being used for excavation. Obviously, a whole mining operation would be delayed by a low penetration rate in rock layers.

Increasing the safety and speed of coal mine roadway excavation is the key factor for safe and effective mining operations. For over one hundred years, roadways or tunnels were excavated by using drilling and blasting technology. While intensive application of explosives increases potential risks in roadway excavation, and toxic smoke also results in health hazards for miners. Since the 1960s, mechanical excavation equipment (roadheader, continue miner, etc.) were introduced in roadway excavation. The use of these machines dramatically increased safety and excavation speeds. Nevertheless, these machines are not able to break hard rocks [8]. TBMs (Tunnel Boring Machines) have a higher rock breakage capacity. Moreover, rock breakage, rock chips loading, and roadway support can be conducted simultaneously by using TBMs [9]. TBMs have been widely applied in tunneling, though application cases of TBMs in coal mines have barely been reported [10].

After excavation, roadway rock deformation or damage is encountered. Therefore, these roadways need reinforcement and support to ensure the safety of excavation works. Much research has proposed the optimization of coal mine roadway support design based on the results of numerical simulation or in-situ monitoring [11]. Based on the simulation results of FLAC3D, Wang proposed full cross-section anchor-grouting reinforcement technology and applied it in underground coal mine roadways with loose and fractured surrounding rocks based on simulation results of FLAC3D, while Cao resolved the problems of lateral wall collapse and severe floor heaving in roadway support involving fractured rock layers [12,13]. Huang proposed a concrete-filled steel tubular support structure to eliminate the problems of large-scale deformation of deep roadways [14]. Stone presented a designing methodology of roadway support based on statistical evaluation of in-situ monitoring results [15]. Yang evaluated the rock mass properties of roadways surrounding rocks by using the geological strength index (GSI) and established the numerical model for roadways using UDEC (Universal Distinct Element Code). Deformation and stress behavior of roadways under different support conditions was obtained and a "bolt-cable-mesh-shotcrete + shell" combined support mode was subsequently proposed [16]. When compared with traditional roadways or tunnels, TBM-excavated roadways have some different characteristics on surrounding rock properties (TBMs are typically used in hard rock strata), for cross section geometry (rectangular or straight wall arch cross section of traditional method vs. circular cross section of TBM method), as well as for excavation-induced stress paths (dynamic blasting loading vs. static loading of machine cutting). These differences mean te support pattern and parameters of TBM-excavated coal mine roadways still need to be settled.

This paper proposed a support design methodology for TBM-excavated roadways in deep coal mines. First of all, the very specific in-situ stress parameters were obtained by in-situ measurement. Secondly, an innovative rock constitutive model which takes anisotropic damage and failure into consideration was established, and a non-linear failure criterion obtained from previous laboratory rock tests rather than conventional universal linear failure criteria was also used to further enhance calculation precision. Thirdly, a proposed constitutive model and failure criterion were introduced into computer simulation software by using new DLL (dynamic link library) files of simulation software and roadway support design was made based on simulation results. Finally, the in-situ monitoring of TBM-excavated roadway was implemented in Zhanji coal mine, Huainan, China and the proposed support design was verified by monitoring data [17–19]. The study results indicated that the roadway

surrounding rocks remained stable after excavation and roadway supporting, and the supporting design is able to fulfill requirements of ensuring roadway stability and enhancing the efficiency of supporting roadways.
