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Rock bolt installation in underground mines

Pumpable Resins as an alternative product in rock bolting

Background

An effective ground support design matches the response of the support to the anticipated rock mass failure. Rock reinforcement elements are a component of the ground support system installed within the rock mass; thus, a successful installation is critical to realising the capacity of the rock reinforcement element. The traditional installation of resin grouted rockbolts, as illustrated in the figure below, requires a support hole to be pre-drilled followed by the installation of the resin capsule (a). The rockbolt is then spun into the grout (c -f).

Challenges faced when installing a resin capsule grouted rockbolt

To ensure a quality installation the hole diameter, rate of rotation, rate of insertion and spin time should be monitored, and discipline is required to achieve an effective installation. Deviation from the manufacturers specifications can result in a reduction of the resin strength and failure of the support system. Additionally, in highly stressed or poor ground the presence of fractures, shear features and altered rock can lead to unravelling of the support hole and result in blockages preventing the installation of the resin capsules. Consequently, the support holes are often redrilled, leading to oversized holes, increased installation times, and poor installation quality. Finally, the volume of the resin within the capsules is fixed therefore variations in hole diameter and resin losses into voids can result in a failure to achieve a full column bond.

Rock bolt installation in underground mines

Tackling the challenges

The development of high strength polyurea silicate resin’s such Potentia Thixo developed by Weber Mining & Tunnelling in partnership with Epiroc , in combination with the high performance Boltec and post grouted rockbolts developed by Epiroc, offers an effective package to overcome the challenges faced with capsule resin.

The installation process illustrated in the image below is more resilient to changes in the rock mass. The rockbolt is inserted into the predrilled bore hole and the pumpable resin is then injected through the rockbolt filling the bore hole from the back to the collar. Post grouting ensures that a full column is achieved as resin is injected through the bolt until resin is observed at the perimeter of the plate. The thixotropic nature of the resin ensures the resin remains in the borehole whilst rapidly curing to strengths in excess of 35 MPa.

Rock bolt installation in underground mines

Additional benefits

The resin and catalyst, which are the two components of Potentia Thixo resin are stored and transported in IBC. The 2-year shelf life is not affected by temperature which simplifies the logistics and supply chain.

The quality of the mixed Potentia Thixo is auditable and assured as the two components are mixed in a 1:1 ratio by a digitally controlled pumping system on the Boltec. Therefore, the quality of the resin mixture is established prior to injection into the rockbolt and remains consistent through varying ground conditions. The setting time of Potentia Thixo can be tailored from 35 seconds for bolting application to 900 seconds for cable bolting applications.

Greig Knox is R&D Manager at Epiroc

 

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