Shotcrete Design of Rock Support for closed Mining with Steel Fibers

Different from other civil engineering structures, mine entrances must withstand substantial deformations caused by progressive mining.

Steel fibres give concrete and shotcrete ductility, which absorbs rock motions and redistributes loads to boost bearing capacity.

Instability in the mine’s surrounding rock threatens both employees and equipment.

Failures in the rock surrounding a stope can dilute the ore, reducing the profitability of mining operations.

Mine entrances may have to withstand substantial deformations due to changing stress conditions generated by progressive passage back into the rock mass. Shotcrete provides effective assistance in these situations and should be used more.

Deep rock is stressed by the weight of above strata and tectonic pressures. When a mine opening is excavated in this rock, the stress field is localized and additional stresses are created. Estimating the rock mass’s strength and deformation qualities is a fundamental challenge in subterranean opening design.

Rock Support Design

Rock mass collapse around an underground hole depends on in situ stress and rock mass properties. Failure around apertures in mildly stressed rock masses progresses from brittle spalling and slabbing to ductile failure for strongly jointed rock masses.

Rock mass deformation

The tunnel may not collapse if the surrounding rock is plastic. The failing material still has considerable strength, and if the plastic zone is thin relative to the tunnel radius, only a few fresh cracks and slight raveling and spalling may indicate failure.

When a huge plastic zone forms and the tunnel wall moves inward, the falling rock mass loosens, causing spalling, raveling, and the collapse of an unsupported tunnel.

Supports restrict inward wall displacement and prevent loosening, which can cause tunnel collapse. Overstressing a tunnel cannot be prevented by rock bolts, shotcrete lining, or steel sets.

But shotcreting with Steel fibers along with rock bolts do play a major role in controlling tunnel deformation.

Support deformation

While the failure zone may take time to develop, minor rockfalls can occur close to the tunnel face and threaten work teams. The Fiber reinforced shotcrete support carries the broken rock’s dead weight and prevents rock falls near the workers. 

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