Instrumentation of a bebo arch constructed at byron bay, New South Wales

The bebo arch constructed at byron bay NSW in July 1985 performed extremely well under soil load and vehicle load test conditions. The 9 m span arch with a wall thickness of 250 mm deflected no more than a fraction of a millimetre under soil loading and about a millimetre under vehicle loading. Considerably greater movements (up to 2 mm) were measured during the fill period but the greater part of these movements can be attributed to contraction of the system due to temperature change. Because the movements associated with structural loads were extremely small, the soil structure interaction was not significant for this relatively stiff and small span arch. Such an interaction process can only become significant when sufficient deflection of the structure takes place to mobilise some of the available shear strength and compressive strength of the soil. It is likely that a considerable margin of safety exists and that a somewhat thinner walled structure would utilize more of the backfill resistance. However, the arch thickness of 250 mm was chosen for stiffness in handling cover requirements to reinforcement and to permit standardization in thickness for spans up to 12 m or more.