Structural and geotechnical interpretation of strain gauge data from laterally loaded reinforced concrete piles

Abstract

Four instrumented sites, with a total of 14 instrumented piles, have been analysed to understand the structural behaviour of the piles and the geotechnical behaviour of the stabilised slopes. Vibrating wire strain gauges are used for the calculation of the bending moment applied to the piles, while inclinometers are used to measure the displacements. A review of the instrumentation has been carried out and a methodology for processin and analysing strain gauges data has been developed. Concrete is a material with a complex behaviour. Shrinkage, creep, cracking, temperature variations, strength and modulus of elasticity of concrete are critically analysed to understand their influence on the concrete pile behaviour and on the function of the strain gauges. The results show that creep and shrinkage effects can be neglected in underground reinforced concrete structures in saturated clay, while cracking effects and temperature variations have to be analysed case by case. A correction method has been developed to consider the difference between the coefficient of thermal expansion of the strain gauges and that of the concrete. Two types of pile have been analysed, standard reinforced concrete piles and circular concrete-filled steel tubular piles. A review of their behaviour in bending that considers the development of cracking is presented. Two methods for the calculation of bending moment in the piles have been developed taking into account realistic stress/strain curves and the effects of concrete cracking. The bending moment results are compared with the inclinometer profiles using an improved version of an existing curve fitting method. The comparison shows good agreement between the two instrument results. A critical analysis of the pile/soil behaviour has been carried out comparing the results from the instrumented sites with theoretical mechanisms for landslide stabilising piles presented elsewhere. The results show a good match with the theoretical mechanisms as well as showing that the slopes have been successfully stabilised. Other observations have been made during analysis of the monitoring data. These include the seasonal effects of climate and vegetation on stabilised slopes and the structural effect of the external grout ring in laterally loaded circular concrete-filled steel tubular piles

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ORCID for W. Powrie: orcid.org/0000-0002-2271-0826

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