Testing the Modified Iowa Formula to Calculate the Deflection of Two Flexible Pipes Buried in Sand into One Trench under Live Loads

The Iowa formula is one of the most traditional methods used to estimate the deflection of a buried flexible pipe. Separate sewer system pipelines, set in one trench, can be found at intersections these in one trench often located at crossroads. The traditional Iowa formula however, does not account for the deformation of two pipes placed in one trench, this information critical for road and other infrastructure design. This paper presents the results from testing a new method to set up separate sewer pipelines when buried in parallel in sand. The results have been used to validate an improvement to the Iowa method used to calculate the deformation of flexible pipes set in one trench, one over the other, or when the pipes intersect at different levels, again within one trench. The improved method was tested by lab experiments through the application of a series of loads on two pipes laid in one trench, using a hydraulic rig to simulate road traffic (live loads), this compared to the results when setting one pipe in a trench. Two PVC pipes and the soil properties of the trench were examined. The results have been compared to experimental data, the two pipe system integrity validated against the standard requirements for flexible pipes buried in soil.