Upgrading disk transducer to measure elastic waves on coarse-grained granular materials: development and performance revelation

This paper describes a recently developed technique of evaluating elastic properties of geomaterials in the large size triaxial apparatus enabling to propagate elastic waves even in coarse-grained geomaterials. A flat surface transducer of 80 mm in diameter has been developed embedding four pairs of compressional and shear wave measuring piezoceramic elements. The assemblage of piezoceramics, interpretation of results, verification of performance and applicability are corroborated. It has been shown that an accumulated strength of numerous piezoceramics in form of a single transducer significantly improved the integrity of the transducer enabling to evaluate elastic wave velocity in a large size the triaxial specimen of 230 mm × 230 mm × 500 mm. An investigation on three sorts of granular materials; fine, (d₅₀ = 0.2 mm), medium, (d₅₀ = 1.7 mm) and coarse, (d₅₀ = 12 mm) is carried out. Small strain stiffness of tested geomaterials is evaluated by newly developed large-size disk transducer method and small-strain cyclic loadings. Stiffness measured by both static and elastic wave measurement is confirmed to be followed similar trends. The large size disk transducer evinces the competent performance showing the stiffness evaluated by this method scattered within 20% of the stiffness achieved by a static method and compared with available previous researches as well.