Application of Piezoceramic Elements for Determining Elastic Properties of Soils

Elastic modulus and Poisson’s ratio of soils are two important parameters required for safe design of various civil engineering structures. The elastic modulus and shear modulus of the soils are generally obtained from the resonant column, torsional shear tests and geophysical methods. Though, from these parameters the Poisson’s ratio can be determined, these tests are quite elaborate, cumbersome, time consuming and require skilled manpower particularly for data interpretation. Moreover, direct determination of the Poisson’s ratio by employing micro-strain gauges, which measure axial and lateral strains using Wheatstone bridge circuits, is difficult for soils due to the problems associated with their fixing on the surface of the sample. Under these circumstances, application of piezoceramic elements, which can generate shear and compression waves, seems to be an excellent alternative. Using these wave velocities, the Poisson’s ratio can be computed easily and precisely. However, how this (computed) value of the Poisson’s ratio compares vis-à-vis that obtained from the conventional triaxial tests (i.e., strain controlled uniaxial compression tests), which yield stress–strain relationship, needs to be established. With this in view, investigations were conducted on soils of different types (clays and sands) in their disturbed and undisturbed forms by resorting to piezoceramic tests and the triaxial tests. Details of the methodology are presented in this paper and it has been demonstrated that application of piezoceramic elements yields the Poisson’s ratio and the elastic modulus of the soils quite easily, particularly for the soft clays and sands.