Physical modelling of lateral sand–pipe interaction

This paper presents a series of physical modelling tests performed to measure the resistance developing during lateral dragging of a rigid pipe buried in loose to very dense dry sand. The experiments were performed in a small-scale prototype developed to model sand–pipe interaction during relative ground movement episodes while accurately controlling the density and uniformity of sand around the pipe. Digital imaging and particle image velocimetry equipment are integrated with the rig, so as to track the evolution of the failure surface developing in sand with increasing pipe displacements. Auxiliary components of the rig allow investigation of the effects of pipe kinematic constraints and embedment method on the results obtained. Accordingly, the measurements obtained with the developed prototype are compared against results from similar studies, with the intention of shedding some light on the scatter observed in published data, and on the provisions from different pipe stress analysis guidelines. It is shown that current simplified methods may underestimate the lateral reaction developing on pipes in very dense sand beds, and analysis models built around these methods may under-predict pipe strains. To alleviate this, a modified expression is proposed for estimating the peak reaction of lateral elastoplastic soil springs, and an upper bound of this reaction is provided for design purposes.