Discrete element analysis of uplift and lateral capacity of a single pile in methane hydrate bearing sediments

Methane hydrate (MH) is extensively found in outer continental margins where offshore infrastructures with pile foundations are also common. The presence of MHs significantly alters the mechanical properties of the host marine sediments, and therefore affects the behavior of piles inside. This paper presents an attempt to investigate the performance of a single pile in methane hydrate bearing sands in seabed using the distinct element method. A novel bond contact model was employed for sandy grains cemented by MHs at contacts, and calibrated from the triaxial compression tests on synthetic specimens of methane hydrate bearing sands. The response of the pile subjected to axial pullout loads and lateral loads was simulated under different subsurface conditions characterized by different saturation levels of MHs. The results show that the presence of MHs increases the uplift capacity of the pile by changing the failure mode of the soils from the perimeter failure to the conical failure. The uplift capacity of the pile significantly deteriorates as a result of de-bonding, while the onset of the rapid de-bonding triggers the softening of the uplift load. In addition, the lateral capacity of the pile largely increases due to the presence of MHs. The pile in methane hydrate bearing sands is considered flexible rather than rigid as a result of the increased deformation modulus of soils due to MH cementation between particles. The lateral load–displacement diagram of the pile in methane hydrate bearing sands is not as smooth as that in clean sands with an abrupt drop associated with the onset of de-bonding.