HORIZONTAL DIRECTIONAL DRILLING
Horizontal Directional Drilling was used twice on this line: once to preserve the beauty of the Exedown escarpment on the North Downs, by drilling down under the scarp some 250 vertical feet, and at Borough Green the line was drilled under the Railway line, two main roads, a roundabout, a nursery and a stream. Both drills were some half a kilometre, and pulled 300 tonnes of 48" pipe back through the drilled holes.
The pilot drill can be steered, and once the correct route has been drilled, successively larger reamers are pulled back and forth until the hole is big enough for the pipe.
Click the pic to see the new video of the Big Pull at the Exedown HDD, musical clips by Tom Thomson as a background.
The drill advances in 30ft increments, with extra drill strings added as they go. The drill bit can either be rotated by itself with a hydraulic motor driven by the pressure of the bentonite drilling mud, or the whole string can be rotated.
Click on the pic to see video of the drill bite taking the first bite
The final reamer and drill string are dragged back and connected to the head of the pipe.
The front of the pipe disappears into the hole
Getting close now
The last few feet disappear into the ground
The grout has to set, and (below) the bottom tie-in to the main line before the drill rig is released. You never know, it just might have slid back out again !!
CLICK on the pic below to see the Celcon HDD and Pull
300 tonnes of pipe stretches half a kilometre into the distance, all sitting on rollers, and here arched on earth mounds to keep the famous Pilgrims Way ancient path open.
As the reamer is pulled back to the bore hole, the sidebooms lift the pipe and carry the weight forward. As they near the hole, they lift the pipe so that it curves downward to align with the borehole.
The McGinty calls for another inch of height on the front boom as the pipe is aligned and pulled into the bore
Often forgotten in the excitement of the Big Pull are the fleet of tractor tankers continuously ferrying the Bentonite slurry back to the top of the bore.
Great Excitement as the reamer, and then the pulling head and the pipe emerge at the top of Exedown
LEFT Grouted in and cleaned up , the end of the pipe awaits the tie-in crew. It may be quite quick in the telling, but it takes the pipe 10 hours to travel that half kilometre. Click on the pic to see how fast it actually travels