DWR_2801674 - Laserfiche WebLink

6 Photo 1: Severely deteriorated CMP.1 Rehabilitation Alternatives Of the two rehabilitation alternatives noted above, the more common option is sliplining (see Photo 2). High density polyethylene (HDPE) and properly coated steel pipe are the two most common pipes selected for sliplining rehabilitation and have similar design parameters. With little maintenance the service life of HDPE pipe can typically range between 50 and 100 years. Steel pipe requires provisions for adequate coating to provide similar levels of design life. Fiberglass reinforced pipe (FRP) and polyvinyl chloride (PVC) have also been used, but have drawbacks with regards to jointing (i.e., bell and spigot) and brittleness. Design considerations along with a comparison of HDPE pipe and coated steel pipe are summarized below. Photo 2: Installing HDPE Liner pipe.2 1 Photo courtesy of www.cleanculverts.com Existing Conduit Inspections: It is important to complete a thorough cleaning and inspection of the existing conduit before moving forward with the design. For large diameter pipes the inspection can be completed visually by entering the pipe from either the downstream or upstream end, although confined space entry procedures should be followed. For small diameter pipes the inspection should be completed using a remote operated vehicle (ROV). The alignment (straightness) of the pipe, severity of deterioration, and location and dimensions of protrusions should be noted during the inspection. Size Selection: When selecting the size and wall thickness of the carrier pipe, the designer needs to consider the hydraulic capacity, clearance from the existing pipe (annular space) including consideration of irregularities and protrusions, and the internal and external loadings. For large internal and external loadings, steel sliplining pipe may be required. The reduced diameter of the carrier pipe may not result in a reduced hydraulic capacity due to better hydraulic efficiency (lower friction losses) of the new carrier pipe. However, hydraulic capacity of the new carrier pipes needs to be checked against requirements. Seepage Paths: After sliplining is complete the existing (host) pipe is essentially sealed. Depending on the severity of deterioration, the existing pipe may have been acting as a large drain for the embankment due to excessive seepage through the pipe/joints. Once the pipe is sealed, it is possible that phreatic levels in the embankment may increase, possibly increasing the potential for internal erosion (piping) along the conduit. To address this concern, the rehabilitation design should always consider adding a filter diaphragm near the downstream end of the pipe. Thermal Expansion: In general, the sliplining pipe will be buried deep in the embankment and will experience limited temperature changes during the service life; however, the designer needs to understand the expansion and contraction limits of the selected pipe. Thermal expansion is not typically a large concern for steel pipe. However, if installed in very hot or very cold ambient air conditions, is it necessary to let the pipe reach equilibrium temperature before annular grouting. 2 Photo courtesy of www.hydroworld.com