1 Maintenance Status of Main Roadway

The main coal seam of Xingdong Coal Mine is 2# coal, the mining depth is from 600 m to nearly 1300 m. With the extension of the mine into − 980 m level mining, the roadway maintenance problem is increasingly prominent, the support body is seriously damaged, and the phenomenon of partial or even broken bolt is serious. The surrounding rock of the roadway expands, loosens, breaks, and has a large amount of deformation, as shown in Fig. 1. It has a very adverse impact on mine production and safety (He et al. 2011; Yuan et al. 2011; Wang et al. 2015; Kang et al. 2015).

Fig. 1
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Roadway damage map

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Three observation stations are set in − 980 m roadway, and Table 1 is the statistical table of three observation points. It can be seen from the table that the deformation rate of the roof and floor of − 980 m roadway is higher than that of the two ribs, and the maximum deformation rate is 2.48 mm/d.

Table 1 Statistical table of surface displacement of each measuring station
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According to the characteristics of surrounding rock deformation and engineering technology in Xingdong Mine, the following three different support technologies are adopted: the combined reinforcement technology of roadway bolting and shotcreting, the support technology of floor anchor cable and the support technology of fully enclosed U-shaped steel ring support, which are described as follows.

2 Combined Reinforcement Technology of Bolting, Shotcreting and Grouting

In order to improve the strength of surrounding rock, we should adopt the active, dynamic and active control support concept, and implement the new technology of bolt and grouting support system to repair. And the three support schemes implemented at the same time and in the same roadway (He et al. 2005; Ma et al. 2015; Zhou et al. 2011, 2013; Li et al. 2010; Zhang et al. 2013).

2.1 Reinforcement Technology

Construction process: expanding section → initial spraying 80 mm → drilling the first level anchor bolt and hanging net → re spraying 60 mm → drilling the second level anchor bolt and hanging net → re spraying 60 mm.

Installation of anchor bolt: the anchor bolt is divided into two levels, the first level after the initial spraying and the second level after the re spraying. The specifications of two layers of anchor bolts are GM22/2400 mm high-strength anchor bolts with row spacing of 700 × 700 mm (see Fig. 2).

Fig. 2
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Bolt layout section

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Grouting bolt: the grouting bolt is designed to be a Φ 22 × 2000 mm grouting bolt made of 6 “black steel pipe, and the row spacing between the bolts is 1500 × 1500 mm. The anchor heads of bottom angle grouting anchor and floot grouting anchor are all 100 mm lower than the bottom plate (see Fig. 3).

Fig. 3
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Layout section of grouting anchor

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2.2 Effect Analysis

The technology is applied to − 980 m main roadway, and the surrounding rock deformation before and after support is shown in Fig. 4.

Fig. 4
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Comparison of roof deformation before and after − 980 m roadway support

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According to the above observation results, the roadway deformation can be effectively controlled by the combined reinforcement technology of bolting, shotcreting and grouting, and the deformation speed of surrounding rock changes from 2.6 mm/day before support to 0.7 mm/day after support. During the observation period, the deformation of the roadway did not reach a stable trend (Fig. 5).

Fig. 5
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Comparison of roof deformation before and after − 980 m roadway support

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3 Anchor Cable Support of Floor

By using anchor cable support to change the stress state of the rock near the floor and improve the compressive strength of the surrounding rock, it can effectively prevent the displacement of the floor rock to the roadway, and play a role in supporting and preventing the floor heave.

3.1 Prestressed Anchor Cable Parameters

Specification of anchor cable: φ 21.8 × 8500 mm. Arrangement of anchor cables: row arrangement is adopted. Each row of anchor cables is arranged between two rows of grouting holes with a row spacing of 3.2 m. Seven anchor cables are arranged in each row, including three on the roof, the two corners are placed outside 15°, two on each rib, and the arrangement of anchor cables is shown in Fig. 6.

Fig. 6
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Anchor cable layout

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Floor combined anchor cable: the combined anchor cable is composed of three φ 17.8 × 10,500 mm roof anchor cables, which are arranged in rows with a row spacing of 2.0 m, three cables in each row, and the distance between the two sides of the anchor cables is 0.5 m from the ribs, 15° from the outside, and the central anchor cable is vertical to the floor. Use a φ 80 mm drill bit to drill holes with a depth of 10 m. See Fig. 7 for the arrangement of anchor cables on the floor.

Fig. 7
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Anchor cable layout

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3.2 Effect Analysis

According to the observation data in Fig. 8, the average floor heave of the roadway changes from 3 to 0.8 mm/day after support. The two ribs are consolidated by high prestressed anchor cable grouting, but the effect is not obvious.

Fig. 8
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Comparison of floor heave before and after grouting

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4 Ring Support Technology

4.1 Support Technology

In order to solve the problem that the effect of roadway support is not ideal after the initial support of bolt support in high stress roadway, 36 U-shaped steel ring retractable fully closed metal support is used as the secondary support. The support is shown in Fig. 9.

Fig. 9
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Ring bracket

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4.2 Effect Analysis

According to the observation results in Fig. 10, the fully enclosed U-shaped steel ring support can effectively control the deformation of the roadway, especially the floor heave of the roadway, and the average deformation speed of the surrounding rock is greatly reduced. The supporting effect is shown in Fig. 11.

Fig. 10
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Comparison of front and rear roof of ring support in − 980 m main roadway

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Fig. 11
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Support effect

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5 Conclusions

In Xingdong Mine, due to the deep and high stress of the roadway, the roof subsidence, the convergence of the two ribs, the floor heave, the instability of the support and so on are very serious. According to the characteristics of surrounding rock deformation and engineering technology in Xingdong Mine, three different supporting technologies are adopted. It is proved by practice that the fully closed U-shaped steel ring support technology can better maintain the roadway, and the effect is better. Although the supporting effect of Ring support is good, but the cost is high. It should be used in high pressure areas.