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Abstract:Conduit structures dealing with hydraulic drainage needs in the Louisiana highway system include pipe culverts, pipe arch culverts, storm drains, sewers, etc. Although the Louisiana Department of Transportation and Development (LADOTD) has standard specifications for furnishing and installing these conduit structures to guarantee their proper functions, unexpected pavement surface dips still occur at some locations of highway cross-drain culverts and cause the deterioration of pavement ride comfort. The goal of this study was to develop recommendations for design and construction procedures to eliminate such pavement surface dips above highway culvert crossing structures.
Researchers conducted a literature search and field investigation on existing pavements at various cross-drain locations with and without the pavement surface “dip” problem. In addition to conventional laboratory tests, full-scale trench backfill tests at the Louisiana Transportation Research Center’s (LTRC) Pavement Research Facility (PRF) site evaluated different backfill materials in a controlled environment. Four construction projects accommodated field trench backfill testing sections with various backfill materials to further verify the findings obtained previously. The field testing sections used concrete pipes varied in size from 36 to 54 inches. Using different field compaction equipment and methods, the study explored and evaluated factors that influence the quality of highway cross-drain trench backfill. Relevant cost information is also included for future reference.
The results from this study indicate that pavement surface dips at highway cross-drains on Louisiana highways involve many complex factors. The field probing tests revealed that the occurrence of the pavement dip depended largely on the relative stiffness of trench backfill materials with respect to their adjacent natural soils. The occurrence and magnitude of pavement surface dips depended also on other factors such as the stiffness of the pavement structure and truck traffic loading, etc. When a dip occurred at the surface, the trench backfill underneath was weaker than adjacent subgrade soils. Construction environment, contractors’ workmanship, backfill materials, and compaction are the major factors controlling the quality of trench backfill compaction. Sand used in Louisiana is not a good backfill for highway cross-drains due to its very poor gradation and difficulty in compaction. Alternatives such as crushed limestone and flowable fill should be used for highway cross-drains because of their good performance after placement. The DCP device can be useful in evaluating the quality of trench backfills. LADOTD has implemented the results from this study by modifying the current specifications and standard design detail plans to accommodate the complicated field construction conditions.
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