When a pipe culvert is constructed on or near the natural ground surface and covered by a highway fill or embankment, the weight of the embankment compresses and consolidates the foundation soil, settlement occurs, and the culvert subsides and sags below the original grade line. Experience has shown that culverts which become clogged with silt and debris, become disjointed and faulted, leak, become undermined, and endanger the stability of the embankment. These and other damages attendant to settlement restrict the flow of water, prevent adequate inspection of the structure, and may eventually require extensive maintenance or complete replacement of the structure. Some of this damage may be avoided by placing the culvert on cambered grades--that is, by installing the culvert with its flow line somewhat above its normal or desired elevation along the central portion of its length. This idea anticipates that settlement under the load of the embankment will, in time, lower the flow line to the desired straight grade.

The project reported in this paper was undertaken to develop a simplified criterion which would permit the inclusion of camber as a routine design feature in highway culvert installations. The work was based on the theory of consolidation and consisted of consolidation tests and prediction of settlement profiles under proposed embankments, the installation of these culverts cambered according to the predicted settlement profiles, and the observance of the settlements during and following the completion of the embankments. Fairly close agreement between the predicted and observed settlements invited serious speculation as to the possibility of estimating camber, within reasonable limitations, from typical void ratio-pressure curves obtained from typical or average soils.

Report Date


Report Number

No. 209

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