Underwater Demolition Means Something Very Different Now
By Ray Whitfield, ADCI-certified commercial dive supervisor. Reviewed by Amanda McCallister, editor.
Marine Construction | Boat Lift Installation October 2003, Lake McCall, Idaho. The water was 44 degrees and murky as a pint of stout. The client, a county engineer, wanted a concrete intake structure gone. "Just blow it," he said. I shook my head. That's not how it works anymore. I'm Ray, an ADCI-certified dive supervisor with 28 years on dams, bridges, and water tanks. In that time, I've watched underwater demolition flip from messy, dramatic, dangerous blasts to precise, quiet, controlled cut-and-break work. The change isn't nostalgia — it's physics, regulation, and common sense. This is how we do it now. No dynamite. No shaped charges. Just sharp steel, hydraulic pressure, and expert divers who know that the toughest part is seeing your hand in front of your face.
The Blow-and-Hope Era
When I started, explosives were common. We'd drill holes, pack them with dynamite, and detonate. It was fast, but it sent shockwaves through the water, killed fish, rattled nearby structures, and left jagged rebar that was a nightmare to remove. Permitting? Forget it. You needed clearance from every agency from the Corps to the local water board. One mistake could crack a dam's face or take out a bridge pier. Today, responsible contractors avoid explosives unless there's no alternative — usually for large rock beds in isolated areas. For concrete structures standing in water, there's a better way.
Start with a Survey
The first step is knowing what you're cutting into. We send down a diver or an ROV with sonar and cameras. We map the structure, measure the concrete thickness, and locate the rebar with a membrane scanner. If there's silt, we use airlifts to uncover the base. Last year on a bridge pier job, we found that the concrete was far worse than the drawings claimed — spalled and honeycombed. A blasting plan would have been suicide. With the survey, we adjusted our cutting points and saved a week. Lesson: never trust the paper prints. The water lies, but the structure tells the truth.
Cutting with Diamond Wire
For demolition, we cut concrete like marble. A diamond wire saw is a loop of steel cable embedded with diamond segments. We drill a start hole through the concrete, thread the wire through, and close the loop. Then a hydraulic power pack spins it while we pull it back and forth, cutting through the structure from the inside. It's slow — maybe a foot an hour — but it's clean, quiet, and doesn't disturb the water. For pads or piles in shallower water, a diver-operated concrete chainsaw works. It's exactly what it sounds like: a chainsaw with diamond-tipped teeth. You cut lines, then hydraulically crack off sections. The trick is keeping the cut aligned so the debris breaks off as a manageable slab.
Breaking Without the Boom
Once we've cut the large pieces free, we still have to reduce them to liftable sizes. That's where hydraulic bursters come in. We drill a hole, insert the burster, and pump oil in to expand a steel sleeve. It pushes against the concrete and splits it along the line of the cut. You hear a sound like a heavy blink — not a bang. On one tank job, the fish in the nearby canal didn't even swim away. For slabs, we use expanding grout. You mix powder with water and pour it into holes; it cures, expands, and slowly cracks the concrete from the inside. No pressure, no shock, just time. We wait overnight, and the piece is ready for the rigging.
Get the Debris Out
Cutting and breaking is only half the battle. The last step is removing the pieces without lifting the whole river. We use crane barges with clamshell grabs for the big chunks, but for narrow spaces, divers attach airbags. Fill an airbag with air bottom-side up, and it lifts a ten-ton block to the surface. Chain hoists, rock grapples, and submersible pumps do the rest. The final sweep is critical. We send a diver down in a grid pattern to feel for rebar spikes and sharp edges. That's what we did in Lake McCall — and the piece we'd cut was still sitting there, wedged against the intake. I'd misjudged the cut angle. The client watched me swear into the comms headset. We re-cut, and it came free. That's the job. Always check your cuts before you pick.
Frequently Asked Questions
Is underwater demolition still dangerous work? Yes, but the danger has moved from explosion to the dive itself. Modern non-explosive methods mean fewer shockwave injuries and less uncontrolled debris, but you're still working in zero visibility with heavy rigging. That's why ADCI-certified supervisors and adherence to dive safety practices are non-negotiable. Do you ever use explosives underwater anymore? Rarely. For large isolated rock jobs, we might use shaped charges to fracture the base, but for concrete structures — dams, piers, shields, tanks — a hydraulic burster or diamond wire saw is cleaner, legal, and safer. Getting a blast permit in a working waterway is nearly impossible these days. What's the most important thing a diver on a demolition crew needs? Situational awareness. You can't see the whole structure, so you have to feel it and know how the tools react. That plus patience. If you rush, you'll cut the wrong line or rig the lift improperly. Experience counts more than brawn.