ABSTRACT
The piezocone (CPTU) offers a quick and repeatable investigation tool with instantly available high-resolution data. For these reasons it is both technically and commercially attractive to further instrument the CPTU to acquire additional measurements with more sensors either within the cone itself or as add-on modules behind the cone. Many ideas for further instrumentation of the CPTU have been conceptualised or tested but one that could offer direct benefit for offshore wind turbine foundation design is the Cone Pressuremeter (CPM). This in situ tool includes a pressuremeter module behind the standard cone that can measure ground displacement or expansion as a function of pressure applied during the loading, unloading and reloading of the surrounding soil when penetration is paused. From these measurements a number of soil parameters may be interpreted including the stiffness degradation (G/G0) of the soil when combined with reliable in situ or laboratory measured G0 values. With increasingly larger wind turbines being used and deeper water sites selected for construction, soil stiffness is an increasingly critical input for the design of many offshore wind turbine foundations. CPM testing has been trialed in the field onshore at a glacial till site and a medium to very dense sand site. The results of the CPM are compared in this paper to site specific results for the self-boring pressuremeter and advanced laboratory-based alternatives. The practical considerations of using the CPM offshore in seafloor mode are also reviewed.
