Precast Solutions - March/April 2008 - (Page 14)

RESEARCH ON FIELD LASER TESTING OF HDPE PIPE BY DR. ALI ABOLMAALI, P.E. At the University of Texas at Arlington, we have been conducting structural failure analysis on the HDPE pipes on several diverse locations throughout the United States. Field data collected identifies several failure modes including excessive deformation; buckling; joint separation; cracking; snapthrough (inverse curvature); and corrugation growth. A field study of more than 90 installed pipes indicates that the HDPE pipes exhibited multiple failure modes as described. Particularly, the maximum deformations in excess of 5 percent limit were observed in the majority of the pipes with maximum values as high as 22 percent in some cases. The circumferential and longitudinal buckling failure modes, along with the corrugation growth, were also observed in the pipes throughout the study. Dr. Ali Abolmaali, P.E., is an associate professor in structural engineering and applied mechanics at the University of Texas at Arlington and the director of the new UTA Center for Structural Engineering Research (CSER). For more information about the CSER, see “Concrete Testing on a Grand Scale” on page 24. greater when selecting HDPE pipe, because ASTM D 2321 indicates that the engineer is responsible for ensuring proper backfill of plastic pipe installation. It is important that the installing contractor has an established reputation for following recommended installation procedures for plastic pipe and that the engineer be present or have inspectors on site during construction. Because RCP goes into the ground as a structural element with known bearing strength, the vagaries of contractor installation and soil conditions are not as critical as they can be for HDPE pipe installation. HDPE pipe than other state agencies and specifies the most restrictive protocol of those agencies surveyed for predicting service life for plastic pipe. It is important to remember that HDPE is a relatively new product, while concrete pipe has been in use for centuries. Old concrete pipe systems are often incorrectly criticized for having poor-quality joints, and a brief history of these early installations explains why. Connections for these older concrete pipe systems were not designed to prevent soil/water infiltrations or to stop leakage from the pipe to surrounding soils, but simply to keep the pipe in line. Service life and joint integrity. Concrete has an established historical record for long service life as a construction material. As a much more recently developed material, HDPE obviously does not have as long a history of performance, yet the plastic pipe industry has made claims that extrapolates a service life of nearly 3,000 years for some applications. Service life specifications for both HDPE and RCP vary throughout the United States. Some DOTs specify a 50-year service life for both products, while other agencies look for a 100-year service life for stormwater drainage pipe. Florida’s DOT has probably done more research on In fact, engineers often desired subsurface water infiltration into and through concrete stormwater pipes, because this process lowered local water tables and allowed for increased surface development. Thousands of miles of concrete pipe, built and installed with these original design considerations, are still used today performing exactly as specified. In the 1950s and 1960s, soil tightness and watertightness started to become important design considerations for water mains with high internal pressures. With the onset of new design requirements, the concrete pipe industry developed new joint designs 14 PRECAST SOLUTIONS | MARCH/APRIL 2008

Table of Contents Feed for the Digital Edition of Precast Solutions - March/April 2008

Precast Solutions - March/April 2008 Contents Smooth Move Riding the Waves Comparing RCP With Plastic Pipe Cost-Value Analysis of Storm Sewer Pipe Concrete Testing On a Grand Scale Building Confidence

Precast Solutions - March/April 2008

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