Link-Belt LS-308H II and LS-218H II are good dam cranes

UXBRIDGE, Mass. — Paris, France-based Soletanche-McManus JV recently marshaled two Link-Belt lattice boom crawler cranes, the LS-308H II and LS-218H II at the West End Dam on the West River in Uxbridge, Mass. The project’s objective was to perform some much needed embankment remediation, according to Senior Project Manager Michel Gavillet. Excess seepage through the foundation of the 2,400-foot long earth embankment structure had been detected as early as 1979. Several previous attempts had been made to stem the flow at the Corps of Engineers' dam, all without noticeable success.

"At times our progress is measured inch by inch or minute by minute. The boulders we encounter are often harder to remove than the solid rock. Soletanche is using one of the most technologically advanced earth drills in the world. But we must fall back on an old-fashioned gravity-powered drop chisel mounted on a new Link-Belt crane to crush the rock before it can be removed by the drill," said Gavillet.

The joint venture would, for the first time at the West End Dam, construct a subsurface concrete cutoff wall imbedded at least two feet deep into bedrock to assure complete water seepage cutoff. The equipment spread includes the piece of equipment developed and constructed by Soletanche specially designed for deep and difficult slurry trench excavation — the hydrofraise. The hydrofraise contains a dredge type pump located just above two cutting wheels, to pump the excavated materials, which are in suspension in the bentonite slurry.

A Link-Belt LS-308H II lattice boom crane would break boulders and the bedrock with the drop chisel when the specialized drill reached refusal. A second Link-Belt crane, a LS-218H II, would act as a combination concrete placement tool and service crane. About 75% of its time was involved with concrete placement. The LS-308H II would also be a tool carrier equipped with a special Soletanche-designed clamshell bucket when excavating the upper 15-ft. of the cutoff wall trench. The hydrofraise could not self-start the panel excavation.

This specialized bucket was also used to remove many of the large boulders encountered when drilling. Often these boulders were clumped together into what the senior project manager referred to as boulder "nests".

"You need three cranes to build a project like the one we have here at the West End Dam in Uxbridge, MA. We brought in our own machine for the hydrofraise. The other two Link-Belt cranes were rented from Wood's CRW Equipment Corp. for the length of the job," added Gavillet.

Over 15,000 cubic yards of poured-in-place concrete would be required for the cutoff wall construction. The 4,000-psi panel concrete was trucked to the site in ready-mix trucks. There was a significant concrete quantity (more than 20%) overage. The original plans failed to include the amount of extra concrete that would be required to fill the voids left by the boulder removal.

"Some of the panels required twice the estimated amount of concrete because of the voids left by the removal of the boulders. They have been a very significant problem in the construction of the cutoff wall," continued Gavillet.

This dam was implemented when it became painfully obvious in 1955 that a series of new flood control dams were needed to protect Southern New England. Hurricane Diane had deposited up to twenty inches of rain over the area and caused $540 million in downstream flooding damage. That became the impetus for the 1959-61 construction of the West Hill Dam at a cost of $2.3 million.

As constructed, the 48-ft. high earth fill dam would impound a 12,440-acre-foot reservoir. This is the equivalent of storing four billion gallons of water from an upstream 27.9 square mile drainage area. Normally West Hill is a dry bed reservoir. However, during flood events, its pool can cover 1,025 acres and extend upstream for about 4.5 miles.

It was during flood events in 1979, 1987 and 1998 that excess seepage through the structure had occurred, prompting the need for embankment remediation.

Gavillet said that their first operation was to remove the top ten feet of the dam and to stockpile it for later replacement. This provided a larger work area for the equipment spread and was done employing typical earthwork methods. The next procedure was to build twin guide walls. Only then could the construction of the paneled cutoff wall begin. Work actually began in August 2001. A hiatus was declared during January and February 2002 because, due to subfreezing onsite temperatures, the exposed bentonite lines to and from the Soletanche hydrofraise to the pump would have frozen.

The cutoff wall was cast in place by building a series of alternating and interlocking primary and secondary panels. Only after the primary panels were allowed time to cure could the secondary panels be built.

"The total length of the cutoff wall was about 1800 linear feet. In between each two primary panels was a secondary panel. The primary panels were each 23-ft. long. The secondary panels were 9-ft. long. Both panels were 31.5-in. wide. This is the width of both the hydrofraise and the special clamshell bucket. The deepest cutoff panel was drilled down 123-ft.," explained Gavillet.

The granite Gneiss bedrock at the West Hill Dam is up to 30,000 psi in hardness. The four chisels used on the project were 31.5-in. diameter, 15 to 20-ft. high and weighed from 12 to 17 tons. Each chisel would last approximately three to four days under heavy duty rock crushing.

A welder was then required to spend at least a full workweek rehabilitating the manganese-cutting bar on the bottom of the chisel.

All in all the rehabilitation of the West End Dam was a very challenging project. It required the extensive technical knowledge of Soletanche. It also required the reliability and duty cycle capability of two of Link-Belt's newest conventional HYLAB lattice boom cranes.