Precast Solutions - March/April 2008 - (Page 22)

match design parameters and geotechnical information complements proper pipe material selection and clearly defines the installation requirements of a pipe product. A good starting point to develop proper pipe specifications is a review and in-depth understanding of current and accepted national standards. ASTM and AASHTO standards are based upon research, field experience, test projects, and debate and input from all stakeholders. Proper installation details for any pipe product should be clear, constructible, technically correct and without contradiction to written project specifications that are also technically correct. To develop installation details, the designer must completely understand what the field conditions will be when the product is being installed, or make proper judgments based upon experience that will be conservative enough in approach and design as to safely overcome any field condition or installation shortcomings. Concrete pipe can compensate for some inadequacies in bedding and backfill, and even trench wall conditions. Recent publications by Professor Pat Galloway, P.E., provide sobering information on the engineer’s liability in specifying materials for pipe installations. In general, the engineer’s liability is greater when selecting HDPE conduit, because ASTM D2321 indicates that the engineer is responsible for ensuring proper backfill and pipe installation. Unless the installing contractor has an established reputation for following recommended installation procedures for plastic pipe, the engineer, if not present during construction, may face liability. Because reinforced concrete pipe is installed as a structural element, contractor installation and soil conditions are not as critical as they are for HDPE conduit installations. Safety and security are paramount to a professional engineer. Engineers must ensure, through specifications and other design guidelines, that projects are designed and constructed in a way that protects the safety and security of contractors and the public. Design engineers consider the following when specifying pipeline products and materials for safety and security: • flammability of the plastic pipes that could lead to failures and road closures (RCP does not burn) • oxidation of flexible pipeline products that could lead to failures and road closures • damage to pipelines by construction equipment and installation methods • premature and unexpected catastrophic structural failures of pipelines • use of products with lowest risk of failure in critical high-volume roadways and/or evacuation routes • vandalism of flexible pipelines that affects performance and/or could cause roadway closures When evaluating the bidding practices to be used on a project, the engineer must consider economics. An economic analysis is much more than comparing historical unit bid costs. Specifiers often select drainage systems based solely on initial or capital costs. Lower initial costs, however, do not always result in the most economical storm sewer. A life-cycle cost analysis of the pipeline for each of the materials being considered can be included in the bid to compare overall lifetime cost of a project in today’s dollars. Many local and state governments are increasingly including some type of economic analysis in their material selection processes. The importance of considering the future of a facility during the design phase has been made clear by the multitude of problems many authorities are facing as our infrastructure deteriorates. The additional maintenance costs, replacement cost and cost for detours, traffic delays, and social and economic costs for one replacement of an inferior product will far exceed any first-cost savings over a product that does not require replacement during the intended service life. What is the cost if there is a structural failure of an installed pipeline? If a pipeline fails, there may be upstream flooding, property damage and possibly personal injury. It is obvious that unanticipated failures can have significant economic impacts, but these situations can also have various serious social impacts as well. Lowered expectations and less respect for the civil engineering profession are included in the social costs that should be of great concern to all engineers and designers. Reinforced concrete pipe is the only pipe product that utilizes local raw materials. It is manufactured and transported by people who most likely live and pay taxes in the community served by the concrete pipe facility. Incomes generated by a concrete pipe facility tend to support other community services and 22 PRECAST SOLUTIONS | MARCH/APRIL 2008

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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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