The depth vibrator itself is a steel lance, roughly 3–4 metres long, with eccentric weights spinning at 1800 rpm inside a sealed casing. In Swords, where the glacial sands beneath the Broadmeadow valley can extend 15 metres deep, we typically mobilise an electric-driven V23 or V32 unit suspended from a crawler crane. The vibrator is lowered under its own weight, fluidised by water jets at the tip. Compaction starts from the bottom, lifting in 0.5-metre increments. We measure amperage continuously because in the loose alluvial deposits near the Ward River, the power draw tells you more about densification than any surface observation. Unlike dynamic compaction, there is no crater and no flying debris—just a clean, systematic grid of probe points that densifies the soil mass from the inside out.
In Swords’ glacial sands, amperage logs from the vibrator give a real-time signature of densification—no need to wait for lab results to confirm the improvement.
Frequently asked questions
What soil types in Swords are suitable for vibrocompaction?
The technique works best on clean sands and silty sands with fines content below 15–20 %. Much of Swords sits on glacial sands and gravels that respond well. However, zones with soft silty clay lenses or buried organic material need careful assessment—vibratory energy does not densify cohesive soils. We always cross-reference borehole logs to identify any interbedded layers that could limit the treatment effectiveness.
How do you verify that the ground improvement has worked?
Our primary verification tool is the CPT, run at selected locations within the treatment grid. We compare cone resistance (qc) and friction ratio before and after compaction. For a typical Swords project, we aim for a post-treatment qc increase of at least 2–3 times the pre-treatment value. Additional checks may include SPTs or pressuremeter tests if the design requires deformation modulus values.
How close to existing buildings can vibrocompaction be carried out?
We normally maintain a minimum stand-off distance of 3–5 metres from existing structures, depending on their condition and foundation type. The vibrations attenuate quickly in sand, but for sensitive or heritage buildings in Swords’ older village centre, we monitor peak particle velocity with geophones and adjust the vibrator frequency if needed.
What is the typical cost range for a vibrocompaction design and verification package?
For a medium-sized residential or commercial site in Swords, the combined design, supervision, and post-treatment CPT verification package typically falls between €1,280 and €4,820. The spread reflects site size, depth of treatment, and the number of verification locations required. We provide a fixed-price proposal after reviewing the ground investigation data.
Can vibrocompaction reduce the risk of liquefaction in Swords?
Yes—this is one of the key drivers for using the technique in areas underlain by loose saturated sands. By raising the relative density above 70–75 %, the sand gains enough confinement to resist pore pressure build-up during seismic shaking. We evaluate liquefaction potential using CPT-based methods (Youd & Idriss) and design the grid to achieve the target factor of safety required by Eurocode 8.
