Negative skin friction of piles installed in dredged slurry after being reinforced by the vacuum preloading method

Negative skin friction (NSF) is an undesirable effect of piles observed in the dredged slurry of coastal reclamation areas. Herein, a testing framework was developed to investigate the pile NSF development pattern in the Wenzhou dredged slurry treated using the vacuum preloading drainage reinforcement (VPLDR) method. The vacuum pressure (VP) loss in field projects can cause variations in pressures in the treatment area and the VPLDR duration. A method to quickly quantify the treatment effectiveness of VPLDR is needed to ensure consistency. Two VPLDR cases with varying negative vacuum pressures (NVPs) and duration time were implemented to determine the main operating strategy for controlling the artificial consolidation effect. The pore water pressure (PWP) of soil was found to be associated with the undrained shear strength (Su) and was the primary indicator of the VPLDR effectiveness. The moisture content and water discharge only slightly influenced the Su magnitude. The equivalent reinforcement effect was achieved in the field VPLDR treatments by maintaining a constant PWP. Four tests on the model pile subjected to ground surcharge loading were conducted to study the NSF under various soil specimens and axial loading. NSF was observed in piles with surcharge loading and was reduced significantly in the reinforced slurry by the VPLDR. The surcharge-induced pile settlement can be decreased further with a small level of pile top load. The appropriate VPLDR and top load can weak the NSF caused by stacking. Therefore, these factors should be considered during pile construction in reclamation areas to restrain NSF.