Port kills two runway issues with one drill

It’s no simple matter to lay thousands of square feet of pavement, especially when that pavement is going to be expected to bear up to 175,000 pounds at one time.

Therefore, the Port of Bremerton — at the behest of the FAA — is taking its upcoming Bremerton National Airport runway realignment very seriously.

Last week, a drilling crew from Puyallup was out at the airport taking core samples — eight of them — to determine what kind of dirt the current runway and the proposed expansion site is sitting on. The concerns over soil composition, explained airport operations director Fred Salisbury, are real ones — unstable dirt inevitably makes for an unstable runway.

In fact, the port is already dealing with an instability problem with its current runway — the center of the runway has inexplicably grown weaker over time and the port believes what lies underneath may be to blame.

“Because this thing is built on a bog, we want to see what we’ve got under here,” Salisbury said.

Technically, the bog no longer exists and drainage swales dug 10 years ago are supposed keep the runway free of standing water.

However, if the drains aren’t working properly, water can still collect and destabilize the ground under the pavement.

And there’s not much real soil under the runway anyway — the drilling crews hit old bog peat only 7.5 feet down and kept pulling out huge clumps of the stuff as they bored deeper.

Peat, a by-product of decades of decaying marsh plants, does not make for the most stable runway surface. Nevertheless, Salisbury said it typically hasn’t caused any problems so long as what’s above it stays solid and dry.

But has it stayed that way? The port believes it hasn’t.

Salisbury had the crews take samples of the existing runway in order to confirm a long-held suspicion — somehow, despite the swales, water is collecting under the pavement.

In 1996, the port had pavement engineers stress-test the runway for load-bearing capacity. The results weren’t great — even though the runway is supposed to support up to 175,000 pounds, the test showed the runway could only handle approximately 70,000 pounds on a regular basis.

To put it in perspective, Gulfstream planes, typically used as private corporate jets, put about 65,000 pounds of pressure on the runway. Right now, those are the largest planes allowed to regularly use Bremerton National — larger planes have to call ahead for specific permission to land.

The soil samples taken last week will all be lab-tested to determine exact composition. The results of the samples taken from the project area will be used to aid the engineering for the expansion — the port is hoping for nice, dense soil that will easily support a commercial-grade runway.

The samples taken from under the runway will also be examined for composition, but will also be tested for water content to see if it is water pockets that are causing the load reductions.

If Salisbury’s suspicions are concerned, he said it’s a relatively simple matter of re-digging the swales and improving drainage along the main runway in order to bring the facility up to full load capacity.

Happily, the boggy problem does not extend into the realignment area. The drilling crews found mostly medium-density materials at the south end of the runway, where the expansion is scheduled to go — “good materials” for a runway base, said project manager King Sampaco of Bellevue-based H2MH.

The entire re-alignment project, which is being almost entirely funded at the federal level, was mandated by the FAA because of a conflict between the airport and State Route 16 to the north.

At its north end, the runway comes within a few hundred feet of State Route 3. The FAA requires, at a minimum, a 500-foot by 1,000-foot area of clearance at both ends of the runway.

To comply with the requirements, the port plans to dig up approximately 147,000 square feet of the runway and 49,000 square feet of the adjacent taxiway. A similar area south of the runway will then be paved, effectively moving the runway several hundred feet to the south and leaving the north end clear of the highway encroachment.

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