'Expansive shale,' wet weather springs complicate D-B building project

Rick Wagner • Apr 2, 2018 at 2:02 PM

KINGSPORT — Wet weather springs and something called “expansive shale” at Dobyns-Bennett High School are making the Regional Science and Technology Center a little more expensive than first estimated.

Stephen Trimble, an architect with Will+Perkins, and Kingsport City Schools Chief Financial Officer David Frye recently gave the Board of Education a combined geology and finance lesson of sorts.

Trimble explained that expansive shale can be unsteady and cause issues when oxygen reaches it and creates cracks that allow water to enter and fracture the rock. He said the fix is to undercut footers, seal the trench and surfaces with asphalt or bitumen, backfill with gravel and add rebar to the poured floor slab. He said similar, but less serious, issues arose during construction of the football field house.

“When this material is exposed to air, it tends to expand, causing the slab on grade to rise and crack,” Trimble’s presentation said. 

“The potential for expansive behavior is considered high at pyritic sulfur concentrations of greater than 0.5 percent,” the presentation noted. “Samples that have been taken indicated concentrations of 1.17 to 1.32 percent.”

Trimble told the BOE that the problem is partly because of wet weather springs that keep some areas in that part of town damp. He said the issue is that 15 to 20 feet below what was the grade level for the original front completed in 1968, water is present, but it isn’t the result of surface water running down into the soil and rocks from the immediate area, but rather from wet weather springs.

What the geology lesson means in cost for the $20 million project, Frye said, is $123,126.14 in proposed change orders for BurWil Construction. That amount will coming out of roughly $1.2 million in contingency funds.

Four already approved change orders of $87,221.90 would come from a separate soil allowance fund that is down to $412,378.10. However, Frye said that estimated remaining extra costs will probably run $440,000 to $450,000, exceeding the solid allowance fund, meaning the contingency fund will have to be tapped again.

For now, Trimble said, the rock and water troubles mean that construction work on the project, set to be finished in the spring of 2019, will be focused on the north side of the D-B front rather than the south side, where the rock and water issues are. The project bid was $19,812,354.

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