Experimental studies on compaction of quartz – smectite mixtures and the response of porosity, density, P-wave velocity

Abstract:

The density (ρ), porosity (φ) and P-wave velocity (V_p) of quartz – smectite mixtures were systematically measured as a function of pressure from 10MPa to 450 MPa on oedometer at room temperature. A new approach was developed to determine total porosity of materials as function of loading. The total porosity can divided into two portions, compliant porosity (φ_c(P)) and framework one (φ_r(P)). The former is well fitted by exponential function and reaches zero at the pressure P_cp – “compliant pore closure pressure”, and the latter described by a linear function. An interesting and startling phenomenon is that framework pores can survive in specimens beyond 450 MPa, even higher than 1000MPa. ρ and V_p linearly increase with pressurization at pressures beyond P_cp, however, the pressure derivatives of density (D_ρ) and of velocity (D_v) are at least one order of magnitude higher than the counterparts of crystallized rocks. We attribute these higher values (D_ρ and D_v) to the existence of pores within specimens even when pressure reaches 450 MPa.