Jetting vs Driving vs Drilling a Pile
By Ed Brannigan, Marine contractor. Reviewed by Amanda McCallister, editor.
Pile Driving & Piling Repair | Boat Lift Installation Back in the mid-'90s, I was running a jetting crew on the Alabama Gulf Coast. We were setting 16-inch spiral weld steel pipe for a sheet pile bulkhead, and the pile driving hammer--an APE D-19 diesel unit--was bouncing off a sand layer like it was hitting asphalt. The owner came out and asked what the holdup was. I said, "We need to wash this soil out that hasn't been wet in 10,000 years." We hooked up a 4-inch jet to each pile, and that sand turned to soup. The piles sank in like they were meant to be there. That job taught me more bout pile construction than a dozen engineering reports. Driving, jetting, drilling--each is a different tool for a different fight. You don't pick the one you like. You pick the one that gets the pile to the depth and capacity the plans call for without breaking something. In this post, I'll lay out the differences, when to use each, and what I've learned from thirty years of sticking steel in the seabed.
The Bottom Line
The smartest contractors don't pick one method--they combine them. Say you have a dense sand layer that the hammer can't penetrate. You jet to wash the sand out, then drive the last few feet. Or you predrill with a small-diameter auger to break up a stiff clay, then drive the pile into the loosened zone. We did that on a bridge replacement in Virginia--we used a 24-inch auger to go down 10 feet through stiff clay, then drove the 12-inch pipe with a diesel hammer. That clay was so tough that jetting didn't touch it, and the hammer just bounced. The predrill changed the soil structure, and the pile seated properly. The key is to think of these methods as tools on a belt. Some contractors own a jetting setup, some own a drill, but the ones who make money have a clear plan for the soil that's on the boring log. If I'm bidding a job, I price the primary method, but I always include an allowance for alternate methods if the soil turns out to be different. That's how you stay out of claims court. I've seen too many jobs where the owner assumes driving is always cheapest, and the contractor takes a bath when the hammer can't make it through a cobble. So my advice: be ready to switch. It's not about ego. It's about getting the pile in the ground.
Frequently Asked Questions
Is pile jetting cheaper than driving? Not necessarily. Jetting can save time in sandy soils, and time is money, but you have to factor in water supply, pumping equipment, and cleanup. On a recent project, jetting cut our pile count from ten days to six, but we spent two extra days handling the muddy runoff. In the end it was about a 10% savings. If you're in soft sand with a good place to discharge water, jetting can be cheaper. In mixed soils or tight sites, driving is often the better deal. Can you jet piles in clay? You can try, but it won't work well. Clay doesn't simply liquefy under water jetting. The water forms channels and goes around the pile, and the pile starts to lean. I've seen it happen. If you have stiff clay, you're better off with a hammer or predrilling. Jetting in clay is a waste of water and time. Do jetted piles have the same load capacity as driven piles? No. Jetting removes soil and reduces the friction along the pile shaft, which lowers load capacity. That's why we always drive the last few feet after jetting. That compacts the soil at the toe and restores some capacity. If the engineer approves a jetted pile without a re-drive, you're usually looking at a lower allowable load. Check the specs before you rely on it. When is drilling the only option? When you have rock, dense cobble, or very stiff layers that a hammer can't penetrate and jetting can't wash out. Also, if you're working near sensitive structures and can't use impact hammers due to vibration, you might need to drill through the top layers and then gently drive the pile. Drilling is the slowest and most expensive, but it's the only way to make a pile in some ground conditions.