A comparison of devices for measuring stiffness in situ.

Abstract

The variability between devices that measure the stiffness of a road foundation in situ and their\naccuracy are important considerations for the introduction of such field assessment methods into the\nconstruction monitoring process. The aim of this paper is to present the significant findings of recent research\ninto the comparability of four such stiffness devices. Results have been obtained from commercial\nconstruction sites and large-scale field trials covering a wide range of material type and stiffness. In\naddition, controlled tests on a synthetic rubber were carried out to investigate repeatability, as well as a study\nto investigate the stress dependency of the computed stiffness values.\nThe results show significant variations in the correlation coefficients, which were shown to be dependent\nupon material type and construction methods. Conclusions are drawn with regard to the efficacy and\naccuracy of the four stiffness measuring devices and proposals made concerning their suitability for the range\nof site construction conditions and materials.