Experimental study on marine slurry dewatering using a siphon assisted prefabricated horizontal drain system

In coastal engineering, the process of marine slurry dewatering with high water content is crucial. Continuous vacuum pumping is effective for dewatering high-water-content marine slurry but is sensitive to air leakage and requires sustained active suction. This study experimentally evaluates siphon-assisted and vacuum-siphon prefabricated horizontal drain (PHD) systems using marine slurry with an initial water content of approximately 75%. The experimental program included vacuum-PHD, siphon-PHD, siphon-PVD, membraneless siphon-PHD, and vacuum-siphon-PHD configurations, together with pure-water pumping tests and analytical back-calibration. At 325 h, the cumulative drained-water masses of the vacuum-siphon-PHD and siphon-PHD systems were 12.28% and 22.13% lower, respectively, than that of the vacuum-PHD system, confirming the higher short-term efficiency of active vacuum pumping. However, the vacuum-PHD test terminated at 325 h because of air leakage, whereas the coupled system remained effective for approximately 1000 h and reached a final cumulative drained-water mass of 4358 g, 28.1% higher than the 3402 g obtained in the vacuum-PHD test. Among the tested nominal pressure allocations, Case 8, consisting of a −40 kPa vacuum set point and a 4.0 m siphon head, produced the highest final cumulative drained-water mass of 4716 g and the largest average settlement of 65.8 mm. The membraneless configuration showed comparable early cumulative outflow but weaker pressure transmission, smaller settlement, and higher final water content than the sealed system. Analytical calibration indicated that a nominal siphon head of 6.5 m corresponded to an equivalent suction of approximately 50-53 kPa rather than a sustained suction of −65 kPa. These results demonstrate the potential of siphon assistance to extend drainage duration and reduce reliance on high-level active vacuum. This study provides a laboratory basis for further development and field validation of vacuum-siphon coupled drainage systems.