1. American Association of State Highway and Transportation Officials (AASHTO). AASHTO LRFD Bridge Design Specifications (3rd edn). AASHTO: Washington, DC, 2004.
2. . The theory of loads on pipes in ditches and tests of cement and clay drain tile and sewer pipes. Bulletin 31. Iowa Engineering Experiment Station, Ames, IA, 1913.
3. The theory of external loads on closed conduits in the light of the latest experiments. Bulletin 96. Iowa Engineering Experiment Station, Ames, IA, 1930.