Penetrometer Testing: Effect of Partial Consolidation on Subsequent Dissipation Response

Partial drainage during a penetration test increases the penetration resistance, and also affects the excess pore pressures generated and the form of any subsequent dissipation test. This complicates interpretation of such tests, particularly in soils of intermediate consolidation characteristics, because it is difficult to obtain an accurate estimate of the coefficient of consolidation from which to assess the degree of consolidation during penetration. The effect of partial consolidation during penetration on subsequent dissipation tests is investigated here through a number of model piezocone and piezoball tests conducted in a single soil sample under centrifuge conditions. Backbone curves of penetration resistance and excess pore pressure are devised, and comparisons are made of the form of the dissipation response for the two types of penetrometers and for two different pore pressure monitoring positions on the piezoball. Different methods are proposed for assessing the degree of consolidation during the penetration phase, thus allowing the consolidation coefficient to be estimated with reasonable accuracy. Advantages of monitoring pore pressure at two different locations on the piezoball are argued.