A Drainage Services construction supervisor’s simple-but-brilliant invention – conceived on a table napkin and built with scrap metal in the ‘back shop’ – has saved city taxpayers millions of dollars since 2009.
But money wasn’t Dwight Schiewe’s initial motivation in dreaming up the reaming tool that speeds up and simplifies the boring of wide-diameter shafts plunging as deep as 40 meters underground.
“I really wanted to save our people all those hours of incredibly backbreaking labour; I always knew there was a better way to drill wide shafts,” says Dwight.
“The breakthrough came in 2008 when the then-head of Drainage, Siri Fernando, asked me if the City could make our own drilling rig pay for itself instead of using private contractors. I leaped at the opportunity!”
Before the City bought the $1 million mobile drilling rig and Dwight reached for his table napkin, contractors would use augers to drill an initial, relatively shallow hole a few feet wide. City crews would then use jackhammers, shovels and a 1-yard bucket to widen the hole up to 17 feet in diameter.
“It took six crew an entire 8-hour shift to dig the hole just two feet deeper,” says Dwight.
“Now with the new method we can drill four feet in just three hours. The tool has really cut the cost of drilling shafts, so over the years, we’ve paid for the mobile drilling rig many times over.”
Then, as now, workers would hammer in strong wooden planks to completely line the hole. Every four feet they’d reinforce it all with vertical and horizontal steel ribs.
Dwight’s idea was to build extendable bars on top of a hollow 7-foot guide cylinder, and to attach carbide-tipped teeth to the ends of the bars.
Here’s how the process goes now:
- A 7-foot auger drills a pilot hole 30 feet deeper than the level where the shaft widening work will happen. The auger brings all that dirt to the top, leaving an empty pilot hole.
- The auger is exchanged for Dwight’s guide cylinder/reamer bar tool, and the cylinder is lowered into the pilot hole.
- The reamer bars are extended; as its teeth bite further into the soil, the dirt falls into the hollow pilot hole.
- When that 4-foot-deep section of shaft is the correct diameter (varies between 12 feet and 17 feet), the now-full pilot hole is covered, and crews install the next layer of wood siding and steel reinforcing.
- The auger then cleans out the pilot hole, and drills it a little deeper, ready for the next four-foot section of reaming.
As elegant as Dwight’s invention is, it was also cheap and highly cost-effective.
“The materials cost maybe $2,000. We built it ourselves, and the prototype was so good, we’re still using the original,” says Dwight.
“It’s saved a lot of wear and tear on the crews, because now no one’s even down there when the shaft is being widened.
Drainage Services uses wide vertical shafts to lower mechanical tunneling ‘moles’ to where they bore horizontal tunnels. Shafts also service hand-tunneling crews working on narrower-diameter horizontal tunnels.
Dwight says the City is the only organization in this region capable of drilling wide diameter shafts as deeply, quickly and cost-effectively as it now can.
He’s pretty humble about his contribution. Newly retired, Dwight says he’s just happy to leave behind a legacy that can be used by others for a long time to come.