Source: Highway & Heavy Construction Magazine
Two large hydraulic dredges, teamed with smaller floating units and shore-based draglines, averaged about 60,000 cu.yd. of dredging per day while quickly clearing four miles of the ash-laden Cowlitz River following the eruption of Mt. St. Helens. But dismantling the big dredges, transporting them and reassembling and launching them took five weeks.
Canonie-Bultema Pacific Corp., a subsidiary of The Canonie Companies, Inc., South Haven, Michigan, used a marine-based approach while clearing about 4.4 million cu.yd. of sandy sediment from the Cowlitz River under two back-to-back contracts for the Corps of Engineers. The contracts were valued at almost $20 million.
Jim Collins, project manager for Canonie-Bultema, led a team of 75 to 85 prime and subcontractor personnel working two 12-hour shifts, seven days a week.
"The first big effort was getting the equipment here," said Collins. "The Bobby J, a 1700-hp, 18-in dredge weighing 375 tons, was disassembled in Michigan, loaded on transport trucks, moved 2200 miles, reassembled and in production in 30 days."
It took five weeks to move the 500 ton "Marialyce Canonie", 2250-hp, 24-inch dredge 2800 miles from Baltimore. The "Marialyce Canonie" is an Ellicott® Series 3000 "SUPER-DRAGON®" dredge. The two dredges and other supporting equipment required a fleet of more than 60 trucks to make the move.
The two big dredges were assembled and launched near the mid-point of the four-mile project, with the 18-in. dredge making its initial pass upstream and the 24-inch unit working downstream. Three smaller dredges were launched separately and worked as a team on the south end of the job, while yet another 14-in dredge worked the extreme north end.
When the initial pass was completed, the Bobby J was turned downstream and the Marialyce was turned upstream widening the cut to almost full channel width. The two big units then ran a final cleaning sweep.
The large dredges each swing over about a 200 ft. width while pivoting about the working spud. The five and six blade cutterheads were mounted on wedged-over ladders to excavate the 19 ft. bank. Each unit would advance about 8 ft. per set, with additional 80 ft. lengths of floating pipe being added to the discharge line as needed.
Four large draglines, a Lima 2400 with an 8 cu.yd. bucket, a Bucyrus-Erie 88B with a 5 cu.yd. bucket, an American 7260 and a P&H 966, both fitted with 4 cu.yd. buckets, did the edge cuts along the channel banks and finished the sloping sides of the 350 to 450 ft. wide channel.
Initially, spoil from the dredges was deposited in dike-like mounds along one shore. Three Fiat-Allis 21B dozers and two smaller Caterpillar machines were used to push the top of the spoil pile back to form a second landside dike, and to cut drainage ditches from the rear of the spoil containment basins back to the river. The basins formed were partially filled during the later sweeps of the two big dredges and still had available capacity if needed.
In most cases land within the flood plain is simply being raised in elevation, but some owners had specific uses in mind. A local motorcycle club owning one large tract expects to construct stands along the riverbank levee facing a drag strip and a motorcross circuit shaped out of the spoil piles.
Average daily production rates were about 30,000 cu.yd. with the Ellicott® "SUPER-DRAGON™" Marialyce, 15,000 cu.yd. for the Bobby J, and 15,000 cu.yd. with the others.
Three key problems cited by Collins were unstable soils in the disposal areas, abrasion on cutting edges, and finding experienced personnel.
"Normally dry and stable silt deposits in the disposal areas turned thick when saturated with the working water from the dredges," Collins said. "Reshaping of spoil piles to construct the landside dikes was sloppy work for the dozers and was made much tougher by soft, unreliable footing.
"The sand-like ash is sharp and abrasive. It caused severe wear on the cutting edges and moving parts of the land-based machines and in the cutterheads, impellers, pump cases and liner plates on the dredges. Suppliers weren't able to keep up with the sudden demand for replacement parts. We had to fabricate many of our own replacement parts and do more repairing and hard facing of used parts than normal.
"Historically, the Northwest has not had a great deal of river dredging work, and the Corps of Engineers has handled most of it with their own maintenance equipment and people," Collins added.
"But this job was so big that a large amount of equipment and experienced personnel had to be imported from the mid-west and south to meet the special needs after the eruption."
Reprinted from Highway & Heavy Construction Magazine