Effect of cyclic thermal loading on the behaviour of integral abutment bridges: a large-scale experimental study in a soil pit

We investigate abutment–backfill interaction in integral bridges (IBs) under thermal loading over a large number of cycles for a 120-year life span as specified by modern design codes. To better understand the associated mechanisms and assess the performance of IBs within their entire life cycle, a large-scale (1 g) physical model, comprising a 3 m tall concrete wall retaining 35 m³ of dry uniform sand, was built and tested in the soil pit of the Soil Foundation Structure Interaction laboratory at the University of Bristol. The thermal load was modelled as a cyclic displacement history of constant amplitude imposed via a hydraulic actuator, corresponding to a maximum drift of 4.8 × 10^–3 . The maximum passive soil resistance increases monotonically, especially during the first 40 loading cycles, at a decreasing rate. Motivated by the inability of available design formulae to capture the pressure built-up over the entire life cycle of the bridge, an adaptive numerical spring model is developed, employed first for the design of the experiment and subsequently for the numerical simulation of the test; the model has shown to capture reasonably well the densification of sand and successfully mimic the observed lateral earth pressure and bending moment distribution with number of cycles.