Performance of small-scale offshore mudmat foundation under uplift and compression loading

Abstract

Oil and gas exploration infrastructure installed at the seabed must be decommissioned once the production activities are over. The present study aims to assess the seabed shallow foundation structures (mudmats) behavior by conducting small-scale model tests. These experiments focused on investigating the development of porewater pressure at the foundation base, identifying failure mechanisms, and assessing the influence of loading rate on uplift capacity of the foundation. The soil profile was characterized using one-dimensional consolidation tests, as well as small-scale vane shear, T-bar penetration, and ball penetration tests. Three test configurations were carried out: pullout extraction tests, foundation compression bearing capacity, and a combination between the two previous types. Stress–displacement and pore pressure–displacement curves for pull-out extraction tests were similar in shape but inversely proportional, which shows that suction contributes to sustaining the bond created between the soil and the mudmat foundation. Suction development was directly proportional to the test rate. These findings demonstrate that decommissioning processes must have adequate controls and avoid high-speed extractions rates. The outcomes of foundation compression bearing capacity tests indicated increases in stress and pore pressure corresponding to increases in loading rate. Foundation pull-out extraction after compression tests attained normalized displacement at the peak stress failure higher that the other test types.