A DIRECTIONAL drilling system that uses two bits to bore through difficult ground has solved a damaging mine water leak in Shropshire.
Water from an abandoned mine near Hope Bowdler in Shropshire was leaking from an adit and damaging the A488 road.
Tunnelling contractor Barhale Construction, working for client Shropshire County Council, used horizontal drilling to build a new steel pressure drain from the adit, running under the road and allowing water to flow into a river on the other side.
Work was complicated by the tight confines of the site, the proximity of the road to the adit and the ground conditions. These comprised fissured mudstone, siltstone and sandstone that were too strong for conventional tunnelling or auger systems.
Barhale brought in microtunnelling firm Euro Iseki (EIL), which proposed using the EIL-Numa horizontal drilling system.This is designed to install casing through hard rock and difficult ground conditions and is capable of operating under high groundwater pressures.
The system, the result of a joint venture between EIL and US down hole hammer and drill bit manufacturer Numa, consists of an EIL drilling rig fitted with Numa's Impact Ring Bit system.
The Impact Ring Bit system comprises a twopiece design that has a centre and ring bit combination. The centre bit is attached to the hammer, while the ring bit is welded to the casing being installed. The hammer and centre bit are inserted through the casing and the two bits work together to install the casing when drilling. In horizontal drilling operations, the ring bit is recoverable when the casing emerges at the other end of the run.
At Hope Bowdler, a Numa Challenger 125 down the hole hammer fitted with the system was used to drill and install the 53m long, 613mm diameter horizontal pipe made up of 6m lengths of casing.
The EIL rig was set up on the river bank and used 6m long augers to bore through the rock at an angle of 1:26.
The bit drilled at 2.4m per hour before exiting at the adit. Compressed air was fed to the hammer through the hollow stem augers which also helped clean the hole during drilling.
Work was planned to take three weeks, but took only one.
With the pipe in place, the vast amount of water in the mine became apparent, gushing out of the pipe for almost five hours.