CTLGroup was retained by a Municipal Water Utility to perform an evaluation of pipeline thrust restraint in a water transmission main. The transmission main is comprised primarily of 66-in. diameter Prestressed Concrete Cylinder Pipe (PCCP) with distress and multiple failures occurring near directional changes in the pipeline (i.e., near bends, wyes or tee fittings), which prompted concerns related to the adequacy of thrust restraint provided at these locations.
CTLGroup’s evaluation included review of documentation related to the transmission main; internal and external condition assessment of accessible in-service pipe sections located adjacent to fittings; dissection of exhumed pipe sections to document pipe fabrication details and distress; testing pipe component materials obtained during dissections; and structural analyses to evaluate thrust demand and restraint at all bend, wye or tee fittings in the transmission main.
The evaluation indicated that failures were due to deficiencies in the original design and/or installation. CTLGroup provided recommendations for removal and replacement of certain pipe sections exhibiting evidence of distress; timely assessment of other regions of the transmission main incorporating bend, wye or tee fittings that were not accessible at the time of our investigation; and further concurrent evaluation of both design and condition assessment data associated with each fitting (bend, wye or tee) in order to determine if any further modifications of the existing thrust restraint systems are necessary or advisable.
