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 (1g) 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 (SoFSI) laboratory, University of Bristol. The thermal load was modelled as a cyclic displacement history of 1.2 cm (constant) amplitude imposed via a hydraulic actuator, corresponding to a maximum drift of approximately 4 x 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 simulations; the model has shown to capture reasonably well the densification of the sand and successfully mimic the observed lateral earth pressure and bending moment distribution with number of cycles.