IMPROVEMENT AND APPLICATION OF A P-WAVE MEASUREMENT SYSTEM FOR LABORATORY SPECIMENS OF SAND AND GRAVEL

抄録

A compression (P-) wave velocity measurement system was improved to evaluate vertical small strain Young's modulus of sand and gravel specimens. The wave was generated using a multi-layered piezoelectric actuator attached to the top cap of a triaxial cell specimen and received with two piezoelectrical accelerometers at two different positions on the specimen's side. This system includes use of a peak to peak travel time based on excitation records that were triggered by single pulse or sinusoidal wave and stacked for 128 times. The vertical Young's moduli (E_d) obtained by using this dynamic measurement were then compared with the statically measured vertical Young's moduli (E_s) that were evaluated by conducting small unloading/reloading cycles on the same specimen. Two series of tests using medium and large size specimens, respectively, were conducted on three kinds of material namely Toyoura sand (D₅₀=0.23 mm), sieved Chiba gravel (D₅₀=3 mm) and original Chiba gravel (D₅₀=6 mm). No significant effect of specimen size was observed on E_s and E_d of Toyoura sand. E_d was found larger than E_s in all three types of materials while the difference between the two was not the same. Combined effects of the dry density and the wavelength in the dynamic measurement were then discussed.