Overdeflection of 48-Inch Steel Water Line

The contractor installing a 48-inch steel water line filed for bankruptcy and vacated the project after installing approximately 90% of the pipe, but prior to any testing. The contractor's surety company hired another contractor to complete the project, which consisted of approximately 4,800 linear feet of tape coated and mortar lined steel pipe along the busy roadways of Almeda and Holcombe near Houston's Texas Medical Center. Upon arriving at the site, the completion contractor notified the City of Houston of potential problems with the pipe already installed, particularly, excessive deflection or "egging" along the vertical axis. Following this discovery, the City contracted with Lockwood, Andrews & Newnam, Inc., (LAN) and invited the pipe manufacturer to perform an internal inspection to assess the situation and recommend a repair solution. The inspection revealed approximately 141 of 235 pipe sections installed (approximately 3,035 LF, or 60% of the total pipe installed) had deflected beyond the 3% allowed by Specifications. The inspection also revealed several segments with dented cylinders, one with a puncture through the cylinder, and seven with severe longitudinal cracks which are indicative of damage to the cylinder. Pipe sections were observed to have deflected up to a vertical diameter of 44-inches, approximately 8.3%. City of Houston Specifications state that the maximum allowable deflection for mortar-lined steel pipe with a flexible coating is 3% of pipe diameter. This is consistent with AWWA M-11 requirements. (In this case: 3% of 48-inch = 1.44-inch maximum allowable deflection). There are two major reasons for limiting the amount of deflection allowed. First, the pipe relies on a circular shape to support the external loads. Second, excessive over deflection can cause cracking of the interior mortar lining which could lead to corrosion. However, because much of the project limits were within the roadway, and had already been repaved, correcting the pipe deficiencies would have a major impact to Texas Medical Center traffic. LAN and the City agreed on a variance in the maximum deflection, and accepted pipe with up to 4% deflection. A total of 58 pipe segments exceed this deflection. It was required that any pipe to be re-rounded would still meet the original specifications of 3% maximum deflection. The observed deficiencies also led to other concerns regarding possible pipe coating damage and the potential for long-term pipe and pavement settlement. This paper presents the results of internal and external pipe inspections, pipe embedment and backfill testing and discusses the likely causes of over deflection in this flexible pipe. The paper also describes the repair methods used, repair cost, and lessons learned in the process.