A parkable piezoprobe for measuring cv at shallow depths for offshore design

Abstract

The coefficient of consolidation (cv) at shallow depth is an important parameter for the design of many offshore facilities, particularly pipelines. This paper sets out the concept, operation and interpretation of a new simple tool for measuring cv in situ at shallow depths. This tool is a large cylindrical penetrometer with a hemispherical tip, which is embedded statically under self-weight, for example from a winch. After embedment, the tool is ‘parked' – not requiring support from a drill-string – and the pore pressure dissipation is monitored. This ‘parkable' feature allows the tool to be added to conventional drilling or penetrometer systems and used in parallel. The operation of the tool has been simulated using large-deformation finite-element analysis with the Cam Clay plasticity soil model. Results in the form of the normalised undrained penetration response and pore water pressure dissipation–time history are presented. The penetration response indicates the weight requirement of the device. The dissipation curves allow cv to be determined from field measurements of pore pressure.