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I-89 Relines, Quimby Mountain Rd & Exit 2

Sharon, Vermont

DOT Culvert Relines


Vermont Agency of Transportation (VAOT)




Morrill Construction Corporation


Winter 2010

Technical Description:

  • Products Used:
  • CORLIX® 96”-dia. 10-gage aluminum pipe
  • 128”-dia., 10-gage corrugated steel pipe

Between 2009 and 2012, the Vermont Agency of Transportation (VAOT) sliplined approximately 10,000-LF of large-diameter, 40-year-old culverts under Interstates 89 and 91. Diameters of the new corrugated metal culvert liners ranged from 60-in. to 128-in., with fill heights from 40-ft. to more than 100-ft. Most of these culverts were installed in the 1960s, and are on very steep grades.

Culverts on steep grades generally are in Inlet Control, so only the area of the opening and the entrance type affects the headwater depth and flow capacity. The inlet ends received new headwalls which were added for the installation of a beveled inlet (improved entrance coefficient) to improve flow capacity.

In particular, two CMP liner pipe projects in Sharon, VT, provided unique challenges. Three High Density Polyethylene (HDPE) pipe, 12-in. for Exit 2 and 10-in. at Quimby Mountain Road, were placed at the invert of the existing host pipe to convey the stream base flow and a serve as a slip line construction platform. These new HDPE pipes, kept in place between the host and liner pipes, allow for a future bypass system if a liner repair is required. I-89 and Quimby Mountain Road Crossing The first structure was an existing 114-in. rise by 103-in. span vertical ellipse steel plate that crossed under I-89 at the Quimby Mountain Road underpass (mile marker 12.38). This culvert is on a steep 8.2% grade with significant bed load from mountain runoff. Further, there is an existing six-degree elbow located onethird of the way from the outlet. The existing structure was in excellent shape except for some minor wear at the invert. The engineers decided to line this structure with 500-LF of 96-in. diameter CORLIX® 10-gage aluminum pipe with 3-in. by 1-in. corrugations. This was selected for its superior abrasion resistance of aluminum, and deep corrugations to help reduce velocities through the structure.

I-89 and Exit 2 Crossing

The second crossing was located where the two mainlines of I-89 crossed the northbound exit ramp and southbound entrance ramp for Exit 2 at mile marker 13.3. The existing structure was a 152-in. rise by 138-in. span vertical ellipse steel plate on a 3.9% grade. This 578-LF structure also had only minor wear at the invert. The liner selected was a 128- in. diameter Aluminized Steel Type 2 corrugated steel pipe in 10-gage thickness with five-by-one-inch corrugations. This was the largest round pipe that could be pushed through the extreme fill areas, the worst-case clearance areas, of the highway due to deflection of the existing plate pipes. Internal bands with fiberglass insulation are used to connect existing pipe lengths and minimize grout infiltration while grouting. Typically three 16-foot pipe lengths are pushed through and intermediate bulkheads are constructed every 48 feet to isolate each compartment to ensure a successful staged grouting operation.

On every crossing, grout ports are placed strategically detailed by Contech engineers in coordination with the contractor and fabricated at the Contech manufacturing plant. Floor jacks provided during the grouting operation assure the invert of the new liner pipe closely matches the invert of the existing culvert. The grout is placed in stages determined by the contractor and Contech. New headwalls were provided at the inlet of each structure to improve the entrance coefficient, minimize undermining by the raging mountain brooks and retain the highway embankment.

Through 2012 in Vermont, Contech manufactured and provided technical support on nearly 10,000- LF of large-diameter corrugated metal liners for interstate culverts since the 2009 national “shovel ready” infrastructure stimulus program began. This method of sliplining has been an excellent solution for the VTRANS, other state DOT’s and the Federal Highway Administration, since it provides the most cost-effective manner to gain an additional 75 to 100 years of service life from these large culverts under deep fills with almost no maintenance of traffic issues providing effective use of federal and state taxes.

Technical Description:

  • Products Used:
  • CORLIX® 96”-dia. 10-gage aluminum pipe
  • 128”-dia., 10-gage corrugated steel pipe

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