A major design change to work at the 19 Mile slide will add up to $2 million to the cost of the Haines Highway reconstruction project and may delay a final layer of paving until next year, according to officials with the state Department of Transportation.
The modifications include adding reinforced concrete, steel reinforcing bar, and crushed rock to massive abutments intended to channel mountainside debris into five garage-size culverts to be placed beneath the roadway.
The project also will raise the roadbed there about 40 feet.
Frequent debris flows and flooding at the site have made the stretch of highway one of the state’s most expensive to maintain. State transportation officials are hoping the improvements will reduce the cost and frequency of road-clearing efforts.
Changes to plans include adding “tie-backs,” or buried cement anchors attached by steel cables to concrete headwalls and to change the type of fill material behind the walls to crushed rock from uncrushed rock.
“The designer recognized that the original plans were structurally deficient and came up with workable solutions with the least impact on construction. These solutions relied on materials available to the project and incorporated the original design so that completed work could remain in place,” said John Kajdan, DOT’s construction project manager.
Work at 19 Mile is expect to cost up to $5 million. The construction contract for widening and rebuilding Haines Highway between 12.2 Mile and 20 Mile is $38.5 million. The total cost of rebuilding the road between town and the Canada border is estimated at $102 million.
Kajdan said a stop-work order was issued when the state recognized a change was needed, resulting in concrete workers being sidelined for a few days. Modified headwalls and wing walls are now under construction, he said.
The engineering firm DOWL designed the walls. “Recognizing the issue, they modified the design,” Kajdan said.
DOT said the project contractor is planning to pave the portion of the project between mileposts 16 and 20 this year. The pavement will be placed in two layers. “The top layer of pavement for this segment of the project may be pushed to next year, but the project will have at least the bottom layer of pavement down before winter,” Kadjan said.
Kajdan said costs of the modifications will be shared between DOWL and the state. “Design of the tie-backs will not be charged to (the state). Some of the added construction costs may be shared by the designer. Administering the change and additional construction costs will be paid by (the state).”
Kajdan said crushed rock “will exert significantly less pressure against the wall than the uncrushed fill previously allowed. When under pressure, the angular faces on each particle of the crushed rock lock together where soil or rounded aggregates would begin to spread apart.”
Officials at the DOWL office in Juneau referred the CVN to Alaska DOT.