Matthieu Blanc

Arching and Deformation in a Piled Embankment: Centrifuge Tests Compared to Analytical Calculations

AbstractMeasured loads in centrifuge tests on piled embankments were compared with values calculated by three analytical arching models. The Zaeske and Van Eekelen models use sets of arches that give the direction of the load transfer, and result in an increasing load on the soft soil with increasing embankment thickness or surcharge load, which matches the measurements. The Svano model, however, assumes that the load on the soft soil remains constant with increasing embankment thickness or surcharge load, thereby being transferred directly to the piles. Therefore, the Zaeske and Van Eekelen models match the measurements better than the Svano model. The Van Eekelen model slightly overestimates the pile efficiency for relatively thin embankments, but matches the measurements better than the Zaeske model for increasing embankment thickness or surcharge load.

Effect of Seabed Trenching on the Holding Capacity of Suction Anchors in Soft Deepwater Gulf of Guinea Clays

Seabed trenching, related to large motions of relatively taut deepwater mooring systems in the long Gulf of Guinea swell, can reach the suction anchor and the chain padeye depth, thus raising serious concerns about the holding capacity of the suction anchors and the safety of the mooring systems. The potential reduction of the anchor capacity, estimated by means of 3D finite element (FE) calculations, needs to be verified by means of testing, and this is the objective of the study presented here. The paper describes the IFSTTAR geotechnical centrifuge test facility and the model soil preparation procedure for obtaining large open trenches with natural deepwater Angola clay in the swinging centrifuge. The scope of the study includes a number of holding capacity tests on suction anchors without trenches (reference cases) and with large trenches reaching the suction anchor and padeye depth. Tests were performed under vertical and inclined loading (actual case of taut deepwater moorings with significant vertical loading component), with the measurement of pore pressures at different levels below the anchor tip for verifying the effect of the trench on the reverse end bearing (passive suction) capacity. The centrifuge test results are compared with Plaxis 3D FE calculations for the purpose of comparison with previously published results. The preliminary results presented show that the REB capacity is mobilized, even with large trenches reaching the anchor and padeye depth. It is also confirmed that Plaxis 3D FE modelling offers a reliable tool for the assessment of the post-trench holding capacity of the suction anchors.