Keep to the schedule of building and opening by 2020

Tue, 09/04/2018 - 4:00pm

Lynda Clancy

CAMDEN — In a joint meeting Aug. 29, the Camden-Rockport School Board, Middle School Building Committee, architects, contractors and a geo-engineer arrived at the same conclusion: To approve a project change order amounting approximately to $369,000, with possible price reductions, in order to secure a scheduling timeline for the new Knowlton Street middle school, and ensure the building will be constructed on a firm foundation.

Site work for the $32 million school began in mid-July. The timeline for the project had been disrupted earlier in the spring when the school board grappled with a financial setback after opening construction bids and learning that the project was $5 million over budget.

Meetings to decrease project costs got underway and although the funding and financial package was eventually resolved (Camden, Rockport voters approve middle school financing package), subcontractors, as subcontracted by Ledgewood Construction, were delayed in getting to the site by several weeks.

The project budget has a $1.3 million construction contingency line, and the $369,000 change order may be adjusted downward to $353,000, but on Aug. 29, the board and subcommittee agreed that the only way forward was to approve the change order to keep the project on track for a September 2020 new school opening.

That $369,000 includes $60,000 for potential temporary heat and tenting for cold weather construction.

Keeping the schedule intact means getting the foundation squared away for the 84,000-square-foot building in the warmer months and avoiding additional contractor costs that could be associated with bringing heaters on site to help dry the concrete, fuel for those heaters, and temporary shelters over it all.

Preloading versus light-weight concrete

In July, contractors began demolishing some of the existing middle school, piling the rubble aside to be used for preloading the new school foundation. That preloading was to help push down the silty clay that defines the building site. But concern grew about the schedule, financial and construction timeline risks.

During the design process, engineers had determined that the clay soil on the Knowlton Street site, which abuts the Megunticook River, presented potential construction issues, in particular its settlement where the new school building expanded from one floor to three floors.

“The design of the internal retaining wall that separates the lower level with the main level was particularly challenging due to the type of soils found in the area,” wrote architects at Oak Point Associates, in an Aug. 28 memo to the school board. (See attached PDF)

The design included a phased six-week period to allow the clay to settle after the site was preloaded with demolition debris. But, the delay back in May over resolving the budget and financing introduced scheduling risks.

“This meant multiple starts and stops for numerous subs and some unpredictability in the schedule,” according to Building Committee Chairman Will Gartley.

“Because the use of crushed stone would result in increased pressure on the clay deposits, and clays settle slowly, a six-week minimum settlement period after the wall is built and backfilled was required to pre-compress the clay before additional building construction along and near the wall could proceed,” wrote Oak Point Associates architects in a memo to the school board. “The actual time to pre-compress the clay could be longer depending on how the clay behaves along the length of the retaining wall. A longer than anticipated preload period could delay other parts of construction and extend foundation work further into winter conditions.”

When the school board paused in May to deliberate how to resolve the project price increase, contractors and engineers considered changing the site work methods. That value management process was done quickly to a) get the contract signed with subcontractors, and b) maintain the schedule and avoid extra winter costs.

“The proposed value management item that included an alternate way to consolidate the clay was to preload using on site material prior to foundation placement, and included consolidating two phases of demolition into one, and increasing the scope of foundation work that could happen this summer,” said Gartley. “This initially seemed viable and was accepted as the new plan. As the engineers got into the details of this design, the timing, the area that the preload encompass and the impact to the schedule became much less attractive.”

That’s when engineers considered reverting to one of the original design ideas, which included light weight fill instead of demolition debris, because it would eliminate the need for the clay to settle.

That plan had been scrapped because it was considered too expensive.

But, the conversations shifted again when a supplier of the light-weight material surfaced, and was willing to provide the material at a reasonable cost and meet the desired schedule, said Gartley.

Maintaining the timetable again convinced those overseeing the new middle school construction project that the lightweight material was the solution, after all.

This lightweight cellular concrete backfill, which is mixed with air, is being used more in the North East, according to Oak Point’s Aug. 28 memo.

According to the American Concrete Institute: “Cellular concrete is a mixture of cement, water, and preformed foam. The purpose of the foam is to supply a mechanism by which a relatively high proportion of stable air voids can be induced into the mixture and produce a cellular or porous solid upon curing of the mixture. When cellular concrete hardens, it has an oven-dry density of 50 lb/ft3 (.8 t/m3)or less.”

While the school board and building committee committed to the change order, they did not approve making project cuts, such as eliminating stage lighting and rigging from the new auditorium, or wardrobe cabinets in the classroom.

Instead, the board and building committee agreed to see how the site work ultimately is completed, and with what associated costs.

Watch the meeting here.

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