CANDE is one of the most commonly used programs for analysis of buried pipe; however, CANDE is limited to applications with small deflections. This limitation is typically not problematic, but there are some instances in which analysts may be interested in large-deflection behavior. This limitation led to the consideration of other analysis tools. In this study ANSYS, a general finite element program, was used to model the soil-pipe system. Small- and large-deflection theories of ANSYS were used in the analysis of several case studies, and the results were compared with those of CANDE. Also, a code was written to run within ANSYS to include the following soil constitutive models: the hyperbolic tangent modulus with both power and hyperbolic bulk modulus. Results obtained using ANSYS with the modified soil models were in good agreement, with less than 10% difference, except in one case: CANDE results for 6.1 m of soil cover above the springline for 610-mm pipe diameter with SM and ML soils. Use of large-deflection theory resulted in an insignificant effect, less than 5%, when compared with ANSYS small-deflection theory results for soil heights up to 6.1 m above the springline, which proves that small-deflection theory is adequate for these cases. Comparing CANDE and ANSYS for 1,200-mm-diameter polyethylene (PE) pipes with experimental results showed that ANSYS more accurately describes the PE pipe behavior for cases of 9 m of soil cover or more and that large-deflection theory describes the PE pipe behavior better than small-deflection theory for a vertical deflection of 4% or more. The pipe material effect was investigated by comparing the results of ANSYS small- and large-deflection theories for both PE and polyvinyl chloride pipes. The difference between the small- and large-deflection theories for both pipe materials becomes significant, more than 10%, at a vertical deflection of 4%.
Abstract