CLASSES OF UNDERGROUND CONDUITS. Underground conduits are divided into 2 major classes, known as ditch conduit and projecting conduit, the classification based on the construction or environmental conditions which influence the load. Projecting conduits are further subdivided into positive projecting conduits and negative projecting conduit.
DEFINITIONS. A ditch conduit is define as one which is installed in a relatively narrow ditch dug in passive or undisturbed soil and which is then covered with earth backfill. Ex : sewers, drains, water mains, and gas mains. A positive projecting conduit is one which is installed in shallow bedding with its top projecting above the surface of the natural ground and which is then covered with an embankment. Ex : Railway and highway culverts. A negative projecting conduit is one which is installed in a relatively narrow and shallow ditch with its top at an elevation below the natural ground surface and which is then covered with an embankment. This is a very favorable method of installing a railway or highway culvert, since the load produced by a given height of fill is generally less then it would be in the case of a positive projecting conduit. This method of construction is most effective in minimalizing the load if the ditch between the top of the conduit and the natural ground surface is backfilled with loose uncompacted soil.
DEFINITIONS. A ditch conduit is define as one which is installed in a relatively narrow ditch dug in passive or undisturbed soil and which is then covered with earth backfill. Ex : sewers, drains, water mains, and gas mains. A positive projecting conduit is one which is installed in shallow bedding with its top projecting above the surface of the natural ground and which is then covered with an embankment. Ex : Railway and highway culverts. A negative projecting conduit is one which is installed in a relatively narrow and shallow ditch with its top at an elevation below the natural ground surface and which is then covered with an embankment. This is a very favorable method of installing a railway or highway culvert, since the load produced by a given height of fill is generally less then it would be in the case of a positive projecting conduit. This method of construction is most effective in minimalizing the load if the ditch between the top of the conduit and the natural ground surface is backfilled with loose uncompacted soil.
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