Design Loading on Deeply Buried Box Culverts

The current American Association of State Highway and Transportation Officials (AASHTO) standard specifications for highway bridges and AASHTO LRFD bridge design specifications stipulate the computation of the design load on the box culvert primarily based on research by Marston and Spangler. Although this procedure may be applied conservatively for most ordinary culverts, an opportunity exists to evaluate a more realistic soil-structure interaction behavior based on modern finite element analyses of deeply buried concrete box culverts. The Duncan soil model, represented by hyperbolic stress– strain curves, has been used for properties of backfill and in situ soil. The backfill heights are varied from 15.2  to  61.0  m (50–200  ft) for the embankment condition and 15.2–45.7  m (50–150  ft) for the trench condition. An optimum combination of parameters has been identified for use in the imperfect trench installation method. The data from several hundred hypothetical models with various parameters under three typical installation methods, i.e., embankment, trench, and imperfect trench installation are characterized and quantified using regression analysis.