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

Meiyun Tang,Chenxi Wang,Yonggang Jia,Hanlu Liu,Shaotong Zhang

doi:10.3390/jmse9030270

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.

Highlights

The high-concentrated sediments from the middle and lower reaches of the Yellow River deposited rapidly at the estuary, forming an underwater delta with high excess pore water pressure [1]
To study the critical hydraulic gradient for seepage failure of newly deposited seabed in the Yellow River Delta (YRD), we carried out comparative experiments with an improved annular flume by simulating the seepage failure process of the seabed with different consolidation times
(1) Making the vertical seepage path smaller than the horizontal seepage path successfully realized the seepage failure occurring in the middle of the seabed, avoiding the boundary effect

Summary

Introduction

The high-concentrated sediments from the middle and lower reaches of the Yellow River deposited rapidly at the estuary, forming an underwater delta with high excess pore water pressure (i.e., under consolidated) [1]. About 30–40% of these sediments deposited near the river mouth [2], forming a very active sedimentary area near the mouth, i.e., the tidal sensitive zone In this zone, a large amount of sediment is intercepted to form a plastic seabed at high tides and is eroded and transported into the sea at low tides [3]. A large amount of sediment is intercepted to form a plastic seabed at high tides and is eroded and transported into the sea at low tides [3] In this way, the nearshore seabed of the Yellow River Delta (YRD) is repeatedly redeposited. It is of great significance to determine the critical hydraulic gradient for seepage failure for maintaining the safety of offshore engineering and structures

Results

Discussion

Conclusion