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Description:
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Traditionally , the Texas Department of Transportation (TxDOT ) has used concrete or corrugated metal pipes in highway subsurface drainage applications . In recent times large -diameter HDPE thermoplastic pipes have emerged in the marketplace as a viable option . However , these pipes require a more care and control during installation . Because of this reason , and due to the lack of statewide experience with this type of pipe . TxDOT has taken a conservative approach and specified flowable backfill as the only acceptable type of backfill material for thermoplastic pipe . Flowable backfill , which is a mixture of sand , cement , fly ash and water , is considerably more expensive than conventional pipe backfill materials such as sand and gravel . As a result when flowable backfill is used , HDPE pipe is no longer an economically attractive option . TxDOT therefore initiated a research project to investigate the possibilities of using alternative backfill materials , chiefly granular materials . The research described in this thesis is part of the work accomplished in the above project . The primary objective of this research was to develop specifications to allow the use of thermoplastic pipe in TxDOT construction projects . This standard specification must address issues such as the minimum cover required , maximum fill heights to be allowed and allowable backfill materials and field compaction procedures . Such alternative installation methods : (a ) should ensure integrity of the pipe system during both their installation and long -term service , (b ) utilize backfill material that is readily available statewide , (c ) must be cost effective , and (d ) applicable to a broad range of soil conditions . One of the main objectives of the research is to develop specifications for backfill type and compaction in such a manner that density checks , backfill compaction control , or pipe deflection measurements to verify proper installation would not be needed . |