Instrumented concrete pile tests – part 2: strain interpretation

The incorporation of strain gauges (traditionally electrical resistance and vibrating wire gauges but increasingly fibre optic sensors) within concrete piles enables an enhanced understanding of the shear stress distribution along the pile shaft and the bearing resistance at the pile base. This paper provides a roadmap for practitioners to negotiate the challenges associated with strain interpretation in concrete piles. Key lessons from the paper relate to residual loads, temperature effects during curing, pile bending, strain-dependent modulus, unload–reload loops and creep strains during loading. Guidance is drawn from a combination of techniques advocated in the literature, examples from the authors’ experiences of various instrumented concrete pile types and case histories reported by others.