Decommissioning of mudmats with the aid of thermally induced pore pressure

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4. Decommissioning of mudmats with the aid of thermally induced pore pressure

Mudmats are offshore shallow foundations used to support subsea equipment resting on the seabed. After the end of exploration activities in a given field, in order to meet environmental requirements, these structures shall be recovered from the seabed in a procedure known as decommissioning. During these operations, this structure is pulled out from the seabed using a crane barge. In the course of the pull out operation, excess of negative pore pressure, i.e., suction, develops at the foundation-soil interface. This suction makes decommissioning operations more expensive and challenging. This circumstance calls for a way to reduce the suction to make such operation feasible. A proposed methodology not yet investigated is to heat the soil under these foundations. It is inspired by the results presented in the literature that show the undrained heating produces a positive excess of pore pressure. Therefore, this study aims to test the hypothesis of reducing the suction by generating positive pore pressure during heating. For this study, triaxial tests in Brazilian marine clay are carried out with heating under non-hydrostatic stress conditions. Reduced physical modelling tests of shallow foundations are also carried out in the geotechnical centrifuge. These foundations are subjected to pull out loads while the underlying soil is heated. The triaxial tests show that considerable pore pressure values are induced in the clay for thermal variations of 35°C, in addition, thermal failure was observed. Centrifuge tests reveal that the heating procedure is capable of significantly reducing suction depending on the applied pull out load level.

5th European Conference on Physical Modelling in Geotechnics (ECPMG2024)

Onshore and offshore foundation systems