Impacts of Consolidation Time on the Critical Hydraulic Gradient of Newly Deposited Silty Seabed in the Yellow River Delta

Abstract

The silty seabed in the Yellow River Delta (YRD) is exposed to deposition, liquefaction, and reconsolidation repeatedly, during which seepage flows are crucial to the seabed strength. In extreme cases, seepage flows could cause seepage failure (SF) in the seabed, endangering the offshore structures. A critical condition exists for the occurrence of SF, i.e., the critical hydraulic gradient (icr). Compared with cohesionless sands, the icr of cohesive sediments is more complex, and no universal evaluation theory is available yet. The present work first improved a self-designed annular flume to avoid SF along the sidewall, then simulated the SF process of the seabed with different consolidation times in order to explore the icr of newly deposited silty seabed in the YRD. It is found that the theoretical formula for icr of cohesionless soil grossly underestimated the icr of cohesive soil. The icr range of silty seabed in the YRD was 8–16, which was significantly affected by the cohesion and was inversely proportional to the seabed fluidization degree. SF could “pump” the sediments vertically from the interior of the seabed with a contribution to sediment resuspension of up to 93.2–96.8%. The higher the consolidation degree, the smaller the contribution will be.

Structure–Seabed Interactions in Marine Environments

“…Nine (9) papers are included in this Special Issue: one review article [1] and eight research articles covering two main themes-(1) the mechanisms of marine sediments in the Yellow River Delta [2] and a field study [3] and (2) structure-seabed interactions in the vicinity of tunnels [4,5], spudcans [6], pile foundations [7], breakwaters [8], and pipelines [9]. More details on each contribution are summarized here.…”

“…The nearshore seabed of the Yellow River Delta (YRD) is repeatedly re-deposited and excess pore-water pressure and upward seepage appear in the newly deposited seabed. Tang et al [2] reported a series of laboratory experiments carried out on the newly deposited sediments in the Yellow River Delta in their O-tube flume. They focused on the critical hydraulic gradient for seepage failure, which has a significant effect on the erosion and re-suspension of sediments.…”

Field measurement of the erosion threshold of silty seabed in the intertidal flat of the Yellow River Delta with a newly-developed annular flume

“…Currently, there is no large in-situ annular flume that combines wave and current. However, some researchers have developed a laboratory annular flume with coupled seepage and scour to investigate the influence of wave-induced seepage on sediment erodibility (Zhang S. et al, 2018;Tang et al, 2021). Therefore, there is an urgent need to develop a large in-situ annular flume that combines wave-current action to investigate the influence of wave-induced seepage on the erodibility of the seabed.…”