Field Performance of 120-Inch PressureCast Steel Pipe Sections

Large diameter conventional steel pipe with a typical 1/2-inch, spun-cast mortar lining is very flexible and must be strutted for handling, stabbing of the joint, and to prevent against over-deflection during backfill consolidation. Therefore, the standard trench requirements normally call for self-consolidating materials that can support the pipe and be placed with minimal compactive effort, which helps minimize pipe deflection. PressureCast Steel Pipe (PCSP) with pre-compressed high strength structural concrete or mortar lining is much stiffer, regardless of diameter-to-steel cylinder thickness ratio. The stiffness of this pipe eliminates the need for struts during transportation and installation. The increased stiffness, compared to conventional welded steel pipe, also permits the use of many native materials for backfill due to PCSP's semi-rigid behavior. In order to document the field performance of large diameter PCSP, two 120-inch pipe sections were installed in the Pima Feeder Canal Reach of the Pima-Maricopa Irrigation Project in Coolidge, Arizona for the Gila River Indian Community. The pipe sections are in an inverted siphon under the Florence-Casa Grande Canal and subjected to 15 feet of earth cover with a design pressure of 30 psi. A wide trench design was used due to the twin parallel pipes installed at 17 feet on center. Use of large diameter welded steel pipe for the other sections of the siphon utilized controlled low-strength material (CLSM) for pipe embedment to provide support in order to limit deflection. The inherent strength of the PCSP sections permitted the use of granular materials for the upper two-thirds of the pipe zone. To review the installed pipe's performance, deflection readings were taken and a complete visual examination of the pipe was performed two years after the pipe was installed. This paper presents the pipe installation details and procedures, the pipe design criteria, and the results of the inspection.