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Trenchless Excavation

Boring Sideways

Trenchless Excavation

Boring Sideways

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    Horizontal boring to install drainage pipe proved a more cost-effective alternative to digging a trench, which would have entailed much greater damage to the landscaping.

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    The existing grade channeled runoff between the small evergreen at the center of this photo (taken facing the road) and the corner of the dwelling at right. Digging a swale to divert runoff to the street — as specified by the original plan — would have required tearing up existing landscaping and, most likely, removing the mature tree at the rear of the photo.

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    The controls on the horizontal boring rig allow the operator to "steer" the bit left, right, up, or down.

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    On this job, the angled bit emerged from the soil almost exactly on target about 100 feet away from the drilling rig; note the toppled marker stake leaning against the boring shaft.

My company, Access Builders, often works with banks on foreclosed properties. These bank-owned properties typically just need to be cleaned up and put back on the market, but sometimes we have to deal with an unfinished home that a builder forfeited before receiving a certificate of occupancy.

On one such project in an outer suburb of Minneapolis, we had to address a serious grading problem. The bank owned two duplexes built next to one another on a considerable slope, and the original site plan called for a swale to be dug between the two buildings to divert runoff from the higher unit out to the street.

Unfortunately, the builder never followed through with the grading. By the time we got involved, the driveways were in, the sod was laid, and the landscaping was 90 percent complete. In addition, there were several large trees designated for preservation that would be destroyed if the swale were dug in accordance with the plan.

Finding the Right Sub

I met at the site with the city engineer and our excavator. The engineer insisted that the runoff had to be diverted. It was our excavator who first brought up the possibility of having a directional-boring company pull a drain tile through. Although this seemed like an unlikely solution to me at the time — I assumed that only municipalities, utilities, and other deep-pocketed entities could afford directional boring (also known as trenchless excavation) — the engineer agreed that it was an option, as long as he approved the specifications.

Weighing our options. Our excavator determined that digging the swale to the original spec would require about 100 feet of digging and the removal of up to 400 yards of soil. His estimate was $5,500, not including replacing sod or building the required retaining walls. In all, we figured, it would cost about $8,500 to finish the swale as originally intended — plus any fines for removing protected trees and the costs for replacing them.

Before seeking other estimates, we checked with the engineer who drew the original drainage plan. He also felt that horizontal boring could work and told us that generating the numbers and redrawing the survey would cost less than $1,000. So far, so good.

But after a dozen phone calls to various companies and two on-site consultations, my doubts began growing. I was getting bids anywhere from $4,000 to $6,000, not including material or engineering costs. It was looking as though directional boring would not save us much money after all.

Irrigation, but in reverse. As luck would have it, our longtime irrigation contractor gave us the lead we needed. I hadn’t realized it, but irrigation companies often sub out directional-boring jobs when their supply lines need to traverse driveways and other obstacles. When I mentioned the holdup on this project, he gave me the phone number of Goldade Ditching, a company accustomed to working on small projects like ours. The person I spoke with there readily gave me a rough estimate over the phone, which came in well below the numbers we’d been hearing. Excluding materials, Goldade priced the job at $14 per linear foot to pull a 4-inch pipe, $16 per foot to pull a 6-inch pipe, and $20 per foot to pull an 8-inch pipe. I said I didn’t think a pipe as large as 8 inches would be necessary, but it turned out I was wrong.