Performance of Induced Trench Culverts in New Brunswick

The induced trench method of culvert construction has been in use for over 80 years. In this construction, a compressible layer is placed directly above a rigid culvert to induce positive arching. The design is based on the research work done by Marston and Sprangler in the 1920’s and 1930’s. In spite of its long history, the induced trench method of design and construction is viewed with skepticism because of many simplifying assumptions used in the design method. The latest edition (2000) of the American Concrete Pipe Association Handbook has deleted this method reflecting the current reservations about this method of construction. In response to some of these recent concerns, an inspection program was implemented by the New Brunswick Department of Transportation (NBDoT) in the summer of 2001 to assess the performance of induced trench installations. Each installation was visually inspected for signs of structural distress or any other signs of failure. In this paper, the results of this inspection and analysis of the resulting data are presented. It is concluded that induced trench construction results in a significant savings and the design methods and construction details used by NBDoT result in buried conduits which satisfy serviceability limit states.