Correcting indirect strain measurements in laboratory uniaxial compressive testing at various scales


Various devices can directly or indirectly measure strain and record the deformational response of rock materials in uniaxial compressive strength tests. Strain gauges glued to specimens directly measure electrical resistance, while displacement sensors, typically linear variable differential transformers (LVDTs), indirectly measure linear displacements. However, no guidance is available regarding how to position the LVDTs to accurately measure axial or radial strain. A common practice is to measure axial strain with displacement sensors on the basis of the reduction in span between steel platens in relation to specimen height. If the deformational response for axial strain measured using strain gauges and displacement sensors is compared, however, it may be that neither maximum axial strain nor elastic constants are the same. This paper describes an approach to correcting platen-to-platen displacement measurements based on energy calculations at different scales in Olkiluoto gneissic rock specimens, with control specimens tested by combining strain gauge and displacement sensor measurements. It is suggested that the approach may be adaptable to other rocks.

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Posiva Oy (Helsinki) is acknowledged for publication permission of partial findings associated with the development of the research project entitled “Scale effect of intact Olkiluoto gneissic rocks through uniaxial compressive testing and geophysical measurements” by the University of Vigo.

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Correspondence to Leandro R. Alejano.

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Alejano, L.R., Arzúa, J., Estévez-Ventosa, X. et al. Correcting indirect strain measurements in laboratory uniaxial compressive testing at various scales. Bull Eng Geol Environ (2020).

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  • Rock mechanics
  • Rock testing
  • Uniaxial compressive strength tests
  • Strain measurements
  • Deformability
  • Elastic Modulus