Laboratory tests of measurement systems in pile shafts

The article describes the results of laboratory tests of reinforced concrete pile sections instrumented with several measurement systems. Compression tests were carried out on three 300-mm-by-1.2-m cylindrical pile elements, reinforced with an IPE140 steel profiles. The elements were equipped with vibrating wire sensors for measuring strains and stresses in concrete, and two elements had additional fibre optic cables installed for measuring strains. During the tests, external measurements were also made for axial force and longitudinal deformations of the elements. The aim of the research was to compare the measured values of all the internal and external systems and to evaluate the reliability of internal systems. The analysis of the measurement results showed generally good reliability of strain measurements using local vibrating wire sensors and extensometers and especially fibre optic sensors. Measurements of stresses in concrete using an internal vibrating wire sensor were unfortunately much less reliable. The reasons for the reduced reliability of the stress measurements are discussed and a correction coefficient is proposed. The conclusions state that the research and its results are valuable and useful for measuring and monitoring of foundation piles and columns purposes.