Evaluating Buckling in Fusible PVC for Trenchless Installation

Every year, the trenchless industry design and construction teams push the limits of what is conceived to be possible for plastic pipe installations to accommodate challenging sites, owner, and regulatory requirements. Most of these longer installations are accomplished by Horizontal Directional Drilling (HDD), which involves pulling the pipe into a prepared hole under tension. Increasing HDD installation lengths point to the desirability of pipe-side compression force assistance to reduce the pull force and stress on the pipe. Additionally, Direct Pipe applications may be possible using plastic as the jacking pipe. Due to its relatively high strength, Fusible PVC (FPVC) in particular holds the potential for compression installation. If proven workable, this methodology would eliminate the current requirement of thrusting steel jacking pipe and either leaving it in as casing for plastic pipe or attempting to retract the steel pipe in situations such as electrical utility, where the steel jacking pipe cannot be left in place. As part of the proof-of-concept effort to further understand the capabilities and potential applications of FPVC in compression, full-scale testing has been completed with thrust equipment that shows FPVC can be clamped and subjected to compressive thrust forces of up to 800,000 lbs. Subsequently, a series of compression tests on smaller diameter FPVC pipes have been undertaken to develop a detailed engineering approach to compression in trenchless methods. FPVC pipes of varying diameters, lengths, and wall thicknesses have been tested in unconfined compression using a variety of end fixity conditions to evaluate stress-strain loading behavior. To further evaluate pipe behavior in compression within a soil overcut, additional testing is being performed using constrained loading scenarios (test pipe placed within another larger pipe) to evaluate buckling stress and the ultimate yielding stress and strain behavior. This paper summarizes the current industry needs for compression loading of FPVC and describes the methodology and results of the constrained compression testing.