Guidelines for Use in Prediction of Subsidence and Associated Parameters in Coal Mines Having Nearly Horizontal Single Seam Workings
2002 Edition

For challenging rock conditions, the recommended bolting approaches include inclined spiling bolts installed prior to blasting to improve standup time, followed by roof shotcrete to stabilize the surface. Final roof bolts, fully grouted for maximum anchorage, are installed after shotcrete application to reinforce the rock arch. In severely poor rock or complex zones like shear zones or rock bursts, specialized treatment beyond standard bolting is necessary to ensure stability.

Effective grouting involves filling voids between the rock and tunnel lining, strengthening the rock mass by filling fractures, and controlling water ingress. Contact grouting is typically limited to the top arch area (±90° from the crown) for tunnels, while consolidation grouting extends uniformly around the borehole to depths between 0.75 to 1 times the tunnel diameter. The grouting strategy must ensure uniform radial coverage, staged pressure application, and adherence to maximum allowable pressures to maintain rock stability and lining contact.

Designing reinforced rock arches involves treating the rock mass as a structural element, minimizing excavation disturbance, and supplementing with shotcrete or steel supports as required. The load-carrying capacity depends on the rock mass's minimum uniaxial compressive strength and the effective arch thickness. A semi-empirical method employing trial and error is used to equate ultimate support pressure with design capacity. Steel ribs are incorporated when pressures exceed 5 kg/cm², with spacing designed accordingly. Bolt capacity and effective support length, along with grouting in water-charged rock, are critical parameters in the design.

Seismic influences near faults or thrust zones require increasing the ultimate support pressure by approximately 25% to address accumulated strains in the rock mass. This seismic effect is considered significant within a zone extending one tunnel width (±B) from the fault line; beyond twice the tunnel width (≥2B), seismic effects are negligible. Design pressures in the seismic zone are adjusted accordingly, ensuring supports are capable of accommodating dynamic loads and plastic deformations caused by seismic events.

Lagging materials include steel elements (such as channels, beams, and liner plates), precast concrete, and timber, though timber use is minimized due to durability concerns. Packing types serve to fill gaps, transfer loads, block crushed rock, maintain contact in squeezing ground, and provide drainage. Dry packing with hard tunnel spoil is applied for moderate rock loads, installed concurrently with lagging from the base upwards. For higher load conditions, concrete packing using M10 grade concrete is employed to embed steel supports effectively.