Precast Solutions - March/April 2008 - (Page 21)

Section 30 of the AASHTO LRFD Bridge Construction Specification for HDPE, and ASTM A 798 and AASHTO Section 26 for CMP). Because flexible (HDPE and corrugated metal) pipe transfers loading to the surrounding support soil, the type of backfill used, the width of the installation trench and the resulting soil strength must be carefully determined, approved and inspected during installation by the specifying engineer. Deflection testing of HDPE and CMP pipelines, usually 30 days after installation, is now required by some state transportation agencies for underground drainage pipe. Mandatory mandrel testing, video inspection and laser deflectometer testing of the interiors of drainage culverts for ovality are becoming standard DOT requirements. In some of the DOT specifications, published research data on hydraulic efficiency and accepted roughness coefficients combined with an understanding that lab values under ideal circumstances will be much lower than design values. The concrete pipe industry recognizes and promotes a 20 percent to 30 percent increase in the lab-tested value of 0.010 and suggested Manning’s roughness coefficient (typically denoted as “n”) with a value of 0.012 for storm sewers. Years of field experience and lab work indicates that Manning’s “n” values for corrugated metal pipe ranging from 0.022 to 0.024 are reasonable. The use of smooth lined plastic pipe lab values of 0.009 to 0.015 for design applications has been questioned in third-party research papers, including “Installed Condition of HDPE in Kentucky and Ohio” and “Health of Installed HDPE in Texas” by the University of Texas at Arlington. Installation of RCP, high-density polyethylene pipe (HDPE) and Corrugated Metal Pipe (CMP) must be performed according to the manufacturer’s specification and comply with relevant standards (ASTM C 1479 and AASHTO Sect. 27 for RCP, ASTM D 2321 and AASHTO deflections exceeding 5 percent to 7.5 percent constitute structural failure of flexible pipe systems and require removal, reduction in payment to the installer, or some type of permanent remediation or ongoing monitoring. The current AASHTO specifications mentioned above contain very specific language about allowable deflections and remedial actions required for the various piping products. Current research by Professor Ali Abolmaali, University of Texas at Arlington, from field laser testing of HDPE pipelines indicates that certain plastic pipe installations may result in failed ovality tests if proper installation is not performed. Reinforced concrete pipe is less dependant on soil support; however, in critical installations some DOTs require video inspection for excessive cracking or possible joint separation to confirm proper installation procedures have been successfully completed. To assure successful completion of proper pipe selection, the design professional must prepare a complete set of contract documents. A combination of specifications, plans and standard installation details to MARCH/APRIL 2008 Only by visiting pipe production facilities can designers and specifiers see how products are manufactured and how vigorously the producer verifies the quality of the finished product. | PRECAST SOLUTIONS 21

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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