Some remarks on the assessment of P-wave velocity in laboratory tests for evaluating the degree of saturation

This work stems from the need to validate a technique for a reliably measurement of the degree of saturation (Sr) in deposits composed of sandy soils to improve their liquefaction resistance. The estimation of the degree of saturation of soil can be conducted by assessing the P-wave velocity (Vp), due to it values sharply increase near to the full saturation condition. P-wave measurements are comparable for in situ and laboratory procedures, offering prominent advantages for practical implementation. This paper presents a series laboratory results obtained from bender element tests conducted on a partially saturated monogranular sand. As a first approach, these tests were interpreted in the time-domain, showing how the interferences among the generated waves can significantly affect results and mask the actual degree of saturation in the specimen. However, a new processing of the output signal was carried out in the frequency-domain to accurate identify the wave propagation time. Moreover, results are discussed to investigate the mutual relationships between the Vp with Sr and Skempton’s B parameter. Finally, an experimental correlation between Vp and Sr is obtained, considering the strain level dependency of the soil behaviour, which can be adopted to interpret the results of in situ tests.