UK Coal’s Harworth mine in Nottinghamshire has for the first time supported one of the facelines by eight-metre long tendons that are installed with a resin anchor and pre-tensioned before the roof has a chance to relax. The result has been a drastic improvement, according to a report in UK Coal company newsletter, NewScene.
Harworth is using MegaStrands, a bolt developed by Melbourne-based company Megabolt Australia.
The tendons are installed with a Hydramatic hydraulic bolter, fitted to a Dosco MD1100 machine or using handbolters. Used in a 3.2 pattern every 2.4m, the initial movement before it stabilised is less than 75mm.
“To drive a faceline at a depth of 1010m in a seam renowned for poor conditions without steel is a very significant step forward,” said roofbolting engineer, Gary Rennison. “Utilising the MegaStrands has allowed us to drive quicker, easier and has provided an excellent 6.5m wide faceline that for the first time does not require additional work before the powered supports can be installed.”
The use of the bolts is attributed with reduced product dilution. More than a metre of dinting was occurring as a result of floor lift, putting too much dirt into the coal product. The use of 45mm diameter cable bolts anchored as high as 8m into the roof still required miners to wait up to three days after grouting before they became effective.
Two MegaStrands on the other hand are installed in under 20 minutes and can be working with a pre-load of 25 tonnes after only two hours.
MegaStrands are also being installed in both gate roadways, providing improved face end conditions conditions and reducing the requirement of ‘double stack’ Fibrecrete and link and lock supports. On roadway development the Hydramatic/Dosco combination has been averaging 50m a week in a 4.2m x 3.3m road with a dense pattern of 21 in the roof and five per rib.
“It’s the most fundamental step forward in strata control I’ve been involved with while I’ve been an engineer,” Rennison said.