Development of large size Disk Transducer to evaluate elastic properties of coarse granular materials

A new type of Disk transducer with the size of 80 mm diameter has been developed by assembling p-type piezo ceramic elements and s-type piezo ceramic elements, in order to carry out the elastic wave study of small to large grain size geomaterials. It has been proved that by using multiple numbers of piezo ceramic elements, development of required size of wave measurement device (i.e. disk transducer) is possible. To clarify the workability of such disk transducer, elastic properties of Toyoura sand (D50 = 0.20mm) were evaluated by three sorts of method (i.e. static method, disk transducer method and Trigger accelerometer method) by using the large triaxial apparatus with the rectangular prismatic specimen of 50cm*23cm*23cm. All tested sample were in completely dry condition. Applying 11 number of very small strain (i.e. strain less than 0.001%) cyclic loading young's modulus and Poisson's ratios were derived and shear modulus were calculated. Both the axial and radial strain was locally measured by local deformation transducers. Newly developed large size disk transducer has been used to evaluate the elastic properties by wave measurement method. Trigger Accelerometer method was also used to compare the elastic wave properties obtained by elastic wave propagation method. To prove the reliability, consistency and further application on the geotechnical engineering study elastic properties measured by newly developed disk transducer method were compared with previous research and the stiffness found to be fallen in similar range within allowable scatters.