Assessment of the GAP-SENSOR Use for Measuring Maximum Shear Modulus in Layered sandy and Gravelly Dacite Materials

Among dynamic parameters, the maximum shear modulus and damping ratio of the materials has the great importance in the dynamic analyses. In this paper, the high frequency GAP-SENSORs (20 kHz) is used to measure shear wave velocity of the sandy and gravelly Dacite materials in the cyclic triaxial equipment. The test procedure is as follows: firstly, a weak impact on the top cap triaxial specimen is induced. The induced low horizontal and vertical displacements time histories (strain in the range 10-6) are recorded using data logger with rate of 100,000 samples per secent for each channel. Then by traveling time and distance between two GAP-SENSORs, wave velocity is measured. Finally, by calculating the poison ratio via horizontal and vertical strains, the maximum shear modulus of the material is calculated. The results indicate that the value of wave velocity is increased by increasing confining pressure, and their values are dependent on particle size. Also, using the reduced vibration amplitude technique at different levels of specimen, damping ratio value is calculated by temping method. By comparing the results of shear modulus and damping ratio using local measurement of axial strain (with GAP-SENSORs in the cyclic triaxial) at small strain level with the results of the proposed method, cofirmed the high precision of the innovative used method.