This paper discusses the potential for using variable rate penetration tests as a means of assessing the consolidation coefficient for fine-grained soils. Previous testing has shown that the penetration resistance increases as the rate of penetration decreases, owing to partial consolidation in the soil ahead of the advancing probe. This led to the idea of reducing the penetration rate over a short interval during a standard (rapid) test, in order to identify the velocity at which consolidation effects become significant. By matching that point against a normalised backbone curve of penetration resistance versus non-dimensionalised velocity, the consolidation coefficient, cv, of the soil may be deduced. To explore this idea, a series of penetration tests in kaolin clay were undertaken on a drum centrifuge at the University of Western Australia (UWA), using a cylindrical T-bar penetrometer. A backbone curve was first established using constant penetration rate tests, but with velocities covering nearly 3 orders of magnitude. Then, a series of ‘twitch’ tests were undertaken, where the velocity was successively halved over 8 steps, from a high value (corresponding to undrained conditions) down to 0.4% of the initial value, with the penetrometer being advanced by either 1 or 2 diameters in each step. Comparison of the normalised penetration resistance with the backbone curve provided an estimate of the coefficient of consolidation, which was compared with independent estimates from oedometer tests. The tests gave very encouraging results, with the potential for the value of cv to be estimated within an error band of ±20%.

The paper addresses analysis techniques and design parameters for suction caissons in clay for loading conditions ranging from horizontal to vertical. A three-dimensional upper bound approach is described for caissons undergoing significant horizontal motion or rotation, and the relative accuracy of the analysis is assessed through comparison with independent semi-analytical 3-dimensional finite element analyses. For vertical loading, design parameters for shaft friction and end-bearing are deduced from results of physical model tests, for both sealed and unsealed caissons and for short-term and long-term loading. Interaction between horizontal and vertical loading is discussed, and aspects such as strength anisotropy of the soil, mis-alignment of the caisson (vertically and in plane), and orientation of the applied load are considered.

Physical modelling in geotechnical engineering is used extensively, in spite of the high investment costs for experimental facilities and the contrasting decline in computing costs. The paper discusses why physical modelling is still needed, and the manner in which it may be used in conjunction with numerical analysis to develop the simple conceptual models that are used for the major part of design. Two example problems are discussed, one in relation to scale effects when dealing with interface shearing involving dilation, and one in the area of penetration testing. In both cases, physical modelling is shown to reveal limitations in analytical models. An approach for in situ determination of the consolidation coefficient, by means of variable rate penetration testing, is described.