LAUSR

Abstract Substantial research has been conducted on single flexible pipes buried in a trench. In contrast, the objective of this study is to determine the structural performance of two buried flexible sewer pipes positioned one over the other in a single trench. An innovative configuration is designed, based around the use of an innovative manhole structure which can accommodate both foul and surface water, to solve the challenges associated with constructing separate sewer systems in narrow streets while providing additional space for other infrastructure services. The behaviours of the two flexible pipes were tested using a 3D finite element (FE) model validated with experimental data from a laboratory investigation. A modified Drucker–Prager cap soil constitutive model was used to simulate the elasto-plastic soil behaviour. The results show that this approach comprising the use of a large-diameter flexible pipe set above a small-diameter flexible pipe mitigates the strain on the smaller pipe and decreases the total deflections of both pipes and the soil.