Since 1995, MTO has made use of innovative slip lining technology to rehabilitate drainage pipes. Sliplining culverts (SLC) reduce the need for open trench construction and costly road closures by relining the deteriorated portion of a culvert with inserted liners/pipes that meet or exceed MTO material standards. In the past, reinforcing existing culverts has saved the ministry between 30 to 50 percent in direct and indirect costs, yielded a greater degree of accuracy for total project cost estimates and provides an environmentally sensitive alternative to open cut construction.
A culvert is traditionally defined as a pipe that conveys surface water or air through an embankment. It can be used as an equalizer in a wetland environment, thereby preventing adverse drainage impact and allowing highway infrastructure to be built across water passages. Lining of the existing pipe is usually done if the pipe is in good shape/condition and the reduced flow capacity is acceptable. Previously, MTO utilized open cut construction to remove and replace existing drainage pipes. Rehabilitation of culverts with open cut technology involved detouring traffic off-highway or costly construction staging to permit the on-site flow of traffic. The existing water passages were dammed and excavation occurred at the project site as well as the surrounding highway. The original culvert was removed and a replacement installed with new granular compacted around the sides. Once re-covered, the pavement would be replaced to match existing highway conditions.
While open cut construction effectively replaced deteriorated culverts, local road detours required the cooperation of affected municipalities and MTO to investigate suitable detours and construction time. The staging and traffic management involved with open cut construction on a high traffic volume roadway is not generally preferable.
SLC enables the construction to be simplified with far less adverse effects on the surrounding environment. The existing culvert remains intact for suction cleaning, then a new pipe inserted and secured into the old. The cavity between the old and new form is blocked with grout and the water flow restored. A temporary trench may be dug into the back slope of the ditch to allow a level entry of the new culvert (Figure 1). In contrast to the necessary granular and new pavement for the highway, SLC requires no backfill or pavement replacement after project completion, thereby preventing the risk of insufficient compaction or the risk of settlement. Construction occurs within 4-5 workdays with little impact on highway traffic flow, sensitive streams and fish habitats, and lowered use of aggregates or pavement. While the cross section of the pipe is reduced from inserting a replacement into the old steel pipe, the smooth lining material will usually maintain the flow capacity of the culvert (Figure 2).
There are different lining materials available, including steel liner, stainless steel liner, and fiberglass and plastic. For the past decade, one of the products the ministry has used with success has been Weholite, a lightweight, high-density polyethylene (HDPE) closed profile wall pipe for sliplining roadway culverts. The HDPE pipes meet MTO material requirements for non-pressure polyethylene plastic pipe products, bringing corrugated steel pipe culverts to current safety standards on freeways and exceeding current standards on secondary highways. Weholite pipes are joined with the Thread-Loc" joint, wherein corresponding male and female Thread-Loc" ends are rotated into each other, eliminating the need for special equipment. HDPE pipes are chemically inert, corrosion and abrasion resistant and lightweight. The ministry has experienced lower installation costs, and lower transport costs. Full culvert replacement is considered only once the option of SLC is ruled out.
In 2006, Operational Services - London Area Office in Southwestern Region tendered a project for SLC of 8 culverts crossing Highway 403, west of Brantford. Alexman Contracting was awarded the contract using Terrafix Geosynthetics as a subcontractor to supply Weholite from KWH Pipe as the lining material. Approximately 202 metres of 36-inch diameter pipe was utilized on site. The September 2006 project was completed in one week, with cost savings on liner type, construction and restoration time. The ministry also experienced minimal traffic disruptions, repair costs, and the service life reduction normally associated with open cut construction. MTOs commitment to environmentally friendly innovation that meets or exceeds current standards has made sliplining the leading culvert maintenance technique.
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