INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS Int. J. Numer. Anal. Meth. Geomech. 2008; 32:289–306 Published online 16 May 2007 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/nag.628 Effects of frictional forces acting on sidewalls of buried box culverts Junsuk Kang 1, ‡ , Frazier Parker 1, § , Young J. Kang 2, § and Chai H. Yoo 1, ∗, †, § 1 Department of Civil Engineering, Auburn University, Auburn, AL 36849-5337, U.S.A. 2 Department of Civil Engineering, Korea University, Seoul 136-713, Korea SUMMARY The effects of frictional forces acting on the sidewalls of buried box culverts are presented as determined with finite element method (FEM) and detailed soil modelling. The possibility of reducing earth pressure on deeply buried concrete box culverts by the imperfect trench installation (ITI) method has been contemplated during the last several decades. There have been limited research results published primarily regarding the qualitative aspect of load reduction in ITIs. It was found during the course of this study that significant frictional forces develop along the sidewalls of box culverts and adjacent sidefills in ITIs. Current American Association of State Highway and Transportation Officials provisions do not consider these frictional forces, but they cannot be neglected in ITIs, as their effect is dominant. An optimum geometry for the soft zone in ITIs is presented to maximize earth load reductions. The soil–structure interaction at the box culvert–soil interface was found to have a significant effect on total earth pressure acting on the bottom slab. Predictor equations for earth load reduction rates were formulated for ITIs incorporating the optimum soft zone geometry based on the FEM. Copyright 2007 John Wiley & Sons, Ltd. Received 9 October 2006; Revised 22 January 2007; Accepted 5 April 2007 KEY WORDS: box culverts; embankment; finite element method; imperfect trench; frictional force; soil–structure interaction INTRODUCTION The soil pressure exerted on buried concrete box culverts is significantly affected by installation practices, soil properties, and the geometry and stiffness of the structure. The current American Association of State Highway and Transportation Officials (AASHTO) procedure [1] for computing ∗ Correspondence to: Chai H. Yoo, Department of Civil Engineering, Auburn University, Auburn, AL 36849-5337, U.S.A. † E-mail: chyoo@eng.auburn.edu ‡ Ph.D. Candidate. § Professor. Contract/grant sponsor: Alabama Department of Transportation; contract/grant number: 930-592 Copyright 2007 John Wiley & Sons, Ltd.