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I-89 Emergency Reline

Georgia, Vermont

Reline

Owner:

Vermont Agency of Transportation (VTrans)

Engineer:

Vermont Agency of Transportation (VTrans)

Contractor:

S.D. Ireland Brothers Corporation

Installation:

March 2020

Technical Description:

  • Product: HEL-COR® Polymer-Coated CSP, 10 GA
  • Diameter: 108-inch
  • Length: 620 LF

Culvert rehabilitation remains a growing industry in an aging infrastructure. Vermont Agency of Transportation (VTrans) has, for a couple of decades, taken the lead on identifying, inspecting and addressing culverts for potential rehabilitation that are near the end of their useful life. VTrans has used various methods including open cut and replacement, reinforced concrete inverts, and segmental sliplining. A majority of the rehabilitated culverts under Vermont’s interstate and state road system are relined with a new smaller pipe with the same roughness coefficient as many culverts built in the 1950’s and 1960’s were, fortunately, oversized based upon older hydraulic analysis tools. Open-cut and replacement is expensive, especially under deep fills, and VTrans has only completed those where the hydraulic capacity cannot be accommodated. In many cases that approach can be 3-5 times more costly when factoring in staged construction and maintenance of traffic.

During a site visit in November 2019, VTrans, Contech and SD Ireland inspected a culvert just downstream that was an 11’ diameter vertical ellipse (139” x 126”) and was 580 LF long crossing under both the south and north bound main lines of I-89 and a local road on the downstream end. This fairly long culvert, with an average of 17’ of earth cover, typical in Vermont, was at a 45-degree skew to the highway. It was determined that this would be a prime candidate for a segmental liner pipe. The hot dipped galvanized steel plate culvert was installed in 1967 so had met the initial design life expectations for a highway bridge structure of around 50 years.

A large rain event that occurred earlier in October caused damage to this existing corrugated metal plate structure. The high water washed material away and settlement caused by the piping material was observed in the median. During monitoring a second area of settlement was observed closer to the shoulder. The northbound lane was subsequently closed.

In early February 2020, VTrans personnel reached out to Contech and SD Ireland as the VT State Police reported a sinkhole appearing under the right shoulder of the northbound lanes of I-89 near the downstream end of the 580’ long culvert. The shoulder and northbound right lane were immediately closed by VTrans and SD Ireland personnel. By mid-February, they determined that this would be lined with 620 LF of 108” diameter round 10 gage polymer-coated HEL-COR® pipe and SD Ireland immediately began working. VTrans ordered the pipe from the Contech State culvert contract and 12” – 6” sloping fish baffles were fabricated in the liner pipe at 8’ centers to facilitate Aquatic Organism Passage (AOP). Several rock weirs were also proposed in the downstream outfall channel to create back water up into the outlet end for AOP. An improved inlet cast-in-place concrete headwall was proposed for the upstream end to lower the entrance loss coefficient by a 33% reduction in flow area and a toe/cradle wall for the downstream end.

Three 30” diameter solid wall polyethylene directional bores at 550 LF were required to run under I-89 to handle the stream relocation base flow thru a 24” diesel pump. Once the directional drills were complete and the base flow by-passed, SD Ireland installed a shallow concrete mud mat in the bottom to fill some of the obvious voids under the culvert of the vertical ellipse and to create a flat working platform. This was not a typical approach, but due to cold weather and groundwater infiltration was required and once complete made installing the liner much easier. The first liner pipe sections were delivered on March 16, just as the COVID-19 shutdowns were commencing. March is not an ideal time in Vermont for work with the snowpack melting and the spring rains present, but there was no other choice for this critical interstate repair. Given the critical nature of this project, it was imperative to the infrastructure that the installation proceed. All involved were deemed essential workers and able to continue with the installation to avoid further degradation to the roadway above.

The estimated cost to open cut and replace this structure with a 20’ span RC Box at 600 feet long, using the same size box structure as installed under the upstream ramp was $11 M. VTrans also investigated replacement with 3 new integral abutment bridges. These options would have required similar water diversion strategies but would have been more complicated by the staged construction and maintenance of traffic and would have cost significantly more time and money. Total installed cost for the 108” diameter CSP segmental slip-liner was $4.66 M. In the past 12 years, VTrans has installed about 25 large-diameter, segmental CSP slip-liners under their interstate system with excellent results.

Technical Description:

  • Product: HEL-COR® Polymer-Coated CSP, 10 GA
  • Diameter: 108-inch
  • Length: 620 LF

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