Characteristics of Elastic Waves According to Cementation of Dissolved Salt

Abstract

Natural cementation influences the mechanical behavior of granular media. The goal of this study was to investigate the phenomenon of the low strain stiffness of granular media during precipitation and cementation of dissolved salt in the pore fluid. Granular specimens of glass beads with three different sizes (0.26, 0.5, and 1.29 mm) were cemented by NaCl aqueous solutions (0, 0.1, 0.50, 1.0, and 2.0 mol L-1). The small-strain stiffness was investigated by measuring compressional (P) and shear (S) waves using bender elements and piezo disk elements during the cementation process. The change of P-and S-wave velocities during cementation due to drying shows three distinct stages based on the degree of saturation, S: (i) S-wave velocity increases, but P-wave velocity decreases at a degree of saturation of 100 to similar to 90%; (ii) the elastic wave velocities are stable at 90 to similar to 10% saturation; and (iii) the elastic wave velocities dramatically change (increase and decrease) at a degree of saturation of 10 to similar to 0% due to salt cementation and capillary force. Without cementation, the three grain size particles are controlled by capillary forces. The cementation occurs at contact points of particles for low salt concentrations and at both pores and contact points for high salt concentrations. The measured small-strain stiffness agreed with the predicted stiffness based on the micromechanical model. This study demonstrates the elastic wave characteristics of granular media in a vadose zone according to the cementation of dissolved salt.