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The parkable piezoprobe is a site investigation tool for measuring the coefficient of consolidation, in situ offshore, at shallow embedment depths. The device applies a similar bearing pressure to subsea infrastructure so it reaches a comparable self-weight penetration when ‘parked’ at the seabed, representative of an unburied pipeline. Instrumentation on the device allows the dissipation of penetration-induced excess pore pressure to be recorded at various locations on the surface. From these dissipation responses the coefficient of consolidation can be inferred, which is a key parameter in the design of many offshore structures founded in surficial soil, such as pipelines or shallow foundations. The intent is that this device is deployed from a seabed frame, while other activities such as penetrometer testing or sampling take place in parallel. This paper presents robust interpretation methods for the parkable piezoprobe by using a combination of centrifuge experiments and large deformation finite-element analyses. The centrifuge tests demonstrate that the penetration response of the parkable piezoprobe is adequately captured by existing bearing capacity models, allowing the optimum device weight to be identified. A comprehensive interpretation method is then developed for the dissipation stage. This yields accurate estimates of the coefficient of consolidation, even for cases where there is no prior knowledge of the soil parameters or the depth to which the device embeds under its own self-weight.

The parkable piezoprobe is a site investigation tool for measuring the coefficient of consolidation, in situ offshore, at shallow embedment depths. The device applies a similar bearing pressure to subsea infrastructure so it reaches a comparable self-weight penetration when ‘parked’ at the seabed, representative of an unburied pipeline. Instrumentation on the device allows the dissipation of penetration-induced excess pore pressure to be recorded at various locations on the surface. From these dissipation responses the coefficient of consolidation can be inferred, which is a key parameter in the design of many offshore structures founded in surficial soil, such as pipelines or shallow foundations. The intent is that this device is deployed from a seabed frame, while other activities such as penetrometer testing or sampling take place in parallel. This paper presents robust interpretation methods for the parkable piezoprobe by using a combination of centrifuge experiments and large deformation finite-element analyses. The centrifuge tests demonstrate that the penetration response of the parkable piezoprobe is adequately captured by existing bearing capacity models, allowing the optimum device weight to be identified. A comprehensive interpretation method is then developed for the dissipation stage. This yields accurate estimates of the coefficient of consolidation, even for cases where there is no prior knowledge of the soil parameters or the depth to which the device embeds under its own self-weight.

Experimental data from loading tests of model circular footings on soft normally consolidated clay are presented. The experiments were carried out on a drum centrifuge at a radial acceleration level equivalent to 100 times Earth's gravity, ensuring conditions of stress similitude between the model and the prototype scale. The aim of the experiments was to compare the undrained response of different offshore foundations to the same loading conditions. Two different types of foundation were targeted for investigation: spudcans and suction caissons. The spudcan, typically an inverted shallow cone, is the traditional footing for mobile drilling units (also known as jack-up rigs). An alternative foundation concept that is being increasingly considered is that of foundations skirted about the perimeter and installed by suction. A loading arm that incorporated an internal hinge was used so that combinations of load appropriate to the foundations of jack-up units could be applied to the models. Although it was anticipated that, by using skirted foundations there would be increased moment capacity, this was not found to be the case (for the caisson skirt length and soil strength profile investigated). However, there was a stiffer response and additional horizontal capacity at the foundation level. Significantly the use of skirted foundations allowed for a greater combined loading capacity under tensile vertical loads. The results have been interpreted within the framework of strain-hardening plasticity theory, and comparisons with existing yield surfaces are detailed.