Influence of brine leakage on frozen wall development in offshore sand layer when active freezing: A numerical study

Abstract

Brine leakage after freezing pipe fracture when active freezing will cause local structural defects or even failure of frozen wall. A water-heat-solute coupled model that includes a modified Michalowski model considering both temperature and salt concentration was proposed to simulate the freezing construction in offshore sand layer. It was verified by the artificial freezing model tests of saturated saline sand under seepage. The structural defects of frozen wall were observed at the boundary between straight and arch walls on the upstream. The range of the structural defect and the closing time of frozen wall both rise with larger pressure head. The brine leakage was then simulated to evaluate the effects of both pressure head and fracture range of freezing pipe on the structural defect of frozen wall. As indicated by the normalized unfrozen water content contour, there are obvious flaws in determining whether the frozen wall is closed only by the average temperature when brine leakage. A characteristic index, the area ratio of structural defect of frozen wall, was derived from the normalized unfrozen water content contour. The structural defect results from brine leakage when the pressure head is below 2.0 m, otherwise from both brine leakage and groundwater seepage. It is recommended that in addition to monitoring temperature during active freezing, additional moisture monitoring devices should be installed to prevent brine leakage hazards.