Coefficient of consolidation from non-standard piezocone dissipation curves

It has been observed in piezocone dissipation tests that the measured pore water pressure may initially increase and then decrease with time. This phenomenon has been designated as “non-standard” dissipation. For cone penetrometers with the filter element used for measuring pore water pressure located at the shoulder of the cone, the results of numerically simulated cone penetration and pore pressure dissipation indicate that the “non-standard” dissipation curves are mainly caused by (a) shear-induced dilatancy of overconsolidated clays or dense sandy soils around the cone and (b) possible unloading effects for soil elements moving from the vicinity of the face to the shoulder of the cone. Using the results of an uncoupled radial consolidation analysis, an empirical method has been established for interpreting the field value of the horizontal coefficient of consolidation (ch) from “non-standard” dissipation curves. The proposed method has been applied to the numerically simulated “non-standard” dissipation predictions as well as the results of some field cases available in the literature. It is concluded that the values of ch evaluated from the proposed method are more representative of the field values than those evaluated using available alternative methods.