Complex Conductivity and Shear Wave Velocity Responses of Sand-Calcite Mixture

Abstract

Size and distribution of precipitated particles significantly influence the efficiency of ground improvement by introducing fine particles in the original soil matrix mechanically, chemically, or biologically. However, direct measurement of these fine particles poses challenges to the existing non-destructive methods. Recent advancement in low-frequency (0.01–100 Hz) complex conductivity showed promising results in obtaining the size and accumulation pattern of fine particles distributed in coarse-grained soils. In this study, low-frequency complex conductivity measurements were conducted to monitor the spectral induced polarization (SIP) responses of Ottawa 50–70 sand mixed with eggshell powder at sieve size between No. 80 and 140. Vertical stresses of 5, 25, 50 and 100 kPa were progressively added to the sample. Shear wave velocity (V_s) was also monitored by bender element technique. Relaxation frequency of imaginary conductivity increased with the increment of vertical stress, which was attributed to crack generation of eggshell as vertical stress increased. The calculated particle size at 5 kPa from complex conductivity measurement was close to the size of eggshell powder used, suggesting the accuracy of the prediction of SIP method. Shear wave velocity detected increment of stiffness of the mixture as stress increased.