The dewatering and excavation of sandy soil for below-grade concrete vaults during construction of two public bath houses near the Atlantic Ocean presented a few surprises for the contractor.
C.F. Hastings Company Inc. discovered that working in sand is not as easy as it would seem when the excavating company began driving sheeting at Horseneck Beach State Reservation in Westport, Mass., to allow construction of the 20-foot-deep vaults. The vaults will house Clivus Composting Systems being installed beneath the 4,000-square-foot bath houses by general contractor, Auburn, Mass.-based Builders Systems Inc.
Hastings, a Plainville, Mass., WBE/DBE-certified contractor headed by President Suzanne Hastings, is responsible for digging two, 107-foot by 27-foot by 20-foot-deep holes for the cast-in-place vaults. The contractor rented heavy duty Ground Force Shorco sheeting and bracing systems for the holes from United Rentals' Shrewsbury, Mass., location. Breaking ground during the first week of July, the company quickly realized that driving sheeting in this type of sand would be slower than expected.
"The sand here is very fine," said Keith Hastings, son of the president and foreman/equipment operator. "We used an 8,500-pound vibratory driver mounted on an 80-ton hydraulic crane to drive the sheeting about 25 feet. The sand is so fine that it was actually being compacted under the bottom edge of the sheeting as it went down, slowing the driving." He said it took the crew six days to enclose the first hole. The second took less time, about four days, but this was due to the nature of the sand, a relatively coarser aggregate that didn't offer as much resistance to driving.
With the Atlantic Ocean just a few hundred yards away, the crew knew there'd be plenty of water to deal with. "The water table was just a few feet below grade," Hastings pointed out. They rented dewatering equipment from Thompson Pump's New England office in Providence. This included four, 12-inch Thompson vacuum wellpoint pumps plus enough components to provide 140, 1-1/2-inch well points for each hole, manifolds and discharge lines. Crews placed two pumps, one enclosed sound-attenuated unit and one unenclosed standby pump, at each hole.
Because of the small size of the native sand, Hastings had to form "coarse sand wraps" around each well point to prevent them from being clogged. This was done by first installing temporary 6-inch steel casing in the ground, inserting a 1-1/2-inch well point inside the casing, filling the annulus between the casing and well point with coarser sand, then withdrawing the steel casing.
"You wouldn't think you'd have to bring in more sand to a beach job," mused Hastings.
Together the two dewatering systems are yielding about 2 million gallons of water per day on average, he said. Initially expecting this to be saltwater from the infiltration of the tides, he discovered it was fresh water.
"It's not brackish, even though the ocean is so close," said Hastings. "You could drink it." He suggested that this phenomenon might be caused by a layer of fresh water above seawater.
Hastings employed a Komatsu PC270LC excavator as the main digger, and a YanMar mini-excavator equipped with a dozer blade for fine-grading and for precision digging inside the excavation. By late August, the contractor had completed the excavation for both holes. Lampasona Concrete Corp. of Franklin, Mass., performed the forming and placing of concrete for the vaults. And by late September, Hastings backfilled the completed vaults, extracted the sheeting, and excavated for the footings of decks and boardwalks for the bath houses.
Builders Systems Inc. is constructing the wood-frame bathhouse superstructures and installing the sanitary waste composting systems in the vaults, with Mike Snow serving as project manager. The two bathhouse buildings (one each in the East and West parking lots) will replace a single existing bathhouse, increase the number of toilets, provide new sand rinse stations, and incorporate the composting systems. The latter two features are expected to reduce water use at the facility by at least 50 percent.
Planned for completion by the end of 2007, the bath houses are part of an $8.5-million capital improvement project for popular Horseneck Beach Reservation designed by Stephen Kelleher Architects and Weston & Sampson Engineers. Groundbreaking ceremonies for the program were held July 13, with Massachusetts Department of Conservation and Recreation (DCR) Commissioner Richard K. Sullivan Jr., Representative Michael J. Rodrigues and Senator Joan M. Menard participating in the event.
Comprised of some 600 acres of barrier beach and salt marsh at the western end of Buzzards Bay on the state's south coast, Horseneck Beach is one of the busiest facilities in the 440,000 acres of state parks, forests and reservations managed by the Massachusetts Department of Conservation and Recreation. The breezy 2-mile-long beach offers such recreation opportunities as windsurfing, camping, swimming, fishing and boating, and attracts as many as 15,000 visitors in a single day.
Future phases of the project, the first major renovation in the reservation's 50-year history, entail the construction of a new beach services building and the installation of new utilities. A park administration headquarters, lifeguard facilities, first aid station, and additional public restrooms will be housed in the new beach services building.
Additionally, DCR plans to replace a significant amount of pavement area with pedestrian amenities such as pathways, shade structures and plantings in the vicinity of the new bathhouses.
The overall project is expected to be finished by June 2009.