Deep Compaction Using Vibratory Pile Hammers-PDF

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The paper describes a deep vibracompaction method developed by PND for improving loose, saturated granular soils, especially beneath marine bulkheads and other structures. Earlier vibratory-hammer methods produced inconsistent results because they did not effectively transfer energy into surrounding soil. PND’s improved system pairs a high-powered vibratory pile hammer (at least 500 hp) with an H-pile probe fitted with welded angles that help move soil laterally as the probe is raised and lowered.<br /><br />Vibration temporarily destabilizes saturated granular soil, allowing particles to settle more densely as excess pore-water pressure dissipates. Repeated probing also draws fill into the resulting voids. The method is best suited to granular soils with limited fines. In fine-grained soils, immediate densification is slower; adding coarse granular fill instead forms columns that increase bearing capacity and act as vertical drains, supporting longer-term consolidation.<br /><br />At the Port MacKenzie project in Alaska, contractors treated 1,792 probe locations to an average depth exceeding 40 feet. Average production was 27 probes per day. Post-treatment standard penetration test values in gravelly sand increased by about 2.5 times: from N60 14 to 36 above the groundwater table and from 26 to 66 below it. The below-water-table result was considered sufficient for liquefaction stability. Hard seabed clays showed no significant strength change.<br /><br />The authors report successful applications in various granular fills and structures, including open-cell bridge abutments and docks. They conclude that deep vibracompaction can improve safety and reduce costs in seismic areas with loose soils, while noting that fine-grained soils respond differently and may require time to consolidate.

Keywords

deep vibracompaction

granular soils

vibratory pile hammer

H-pile probe

pore-water pressure

soil densification

Port MacKenzie

SPT N60

liquefaction stability

seismic improvement