Influence of Cover Soil Depth on the Load Rating of Reinforced Concrete Box Culverts

This paper describes the influence of cover soil depth on the load rating of the designs of multibarrel, cast-in-place (CIP) reinforced concrete (RC) box culverts and highlights implications for the load rating and design of culvert structures. The basics of culvert load rating are discussed and are followed by a history of culvert design policy and the challenges created by the use of culvert standard designs. A population of Texas Department of Transportation CIP RC standard culvert designs developed between 1930 and 1980 was load rated by using AASHTO policy guidance and a two-dimensional model of direct stiffness structural demand for a full range of cover soil depths. This analysis resulted in a set of 1,081 relationships of load rating versus cover soil depth. Three typical relationships of rating versus depth are illustrated and described in detail. The distribution of characteristic relationships of rating versus depth on the basis of culvert geometry, design cover soil depth, and design era is explored. Cover soil depth is shown to be a critical parameter that must be explicitly considered for the intelligent load rating and design of RC box culverts.