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Seismic Tomography Surveys in Celbridge: Refraction and Reflection for Site Characterisation

Practical geotechnics, field-tested.

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Many sites around Celbridge sit right on the edge of the Carboniferous limestone that defines the bedrock along the Liffey valley, and that boundary creates more variation in shallow rock quality than most people realise. A standard desk study won't tell you whether the limestone is pinnacled, karstified, or buried under a few metres of silty till. The seismic tomography survey maps those transitions directly, giving you a continuous velocity profile that exposes weak zones, fracture corridors, or solution features before they become a problem during excavation. We run both refraction and reflection arrays depending on what the site geometry allows, and when karst is suspected we combine the resistivity survey to cross-check low-velocity anomalies against electrical contrasts, which is a practical way to separate a water-filled cavity from a weathered clay seam without extra boreholes.

A seismic tomogram lets you trace the rockhead surface continuously across a site, rather than guessing between borehole points where it could dip or fault.

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Celbridge grew fast through the 1990s and 2000s, and much of the later development pushed onto ground that earlier builders had avoided because of poor drainage or shallow rock concerns. That history means a surprising number of sites here have undocumented fill over natural soft ground, and seismic velocity contrasts across those interfaces are sharp enough to produce clear refracted arrivals even with a short spread. Our approach pairs a 24-channel seismograph with a weight-drop or accelerated hammer source, which works well in urban noise conditions and avoids the permitting requirements of explosives. Processing follows first-break picking and iterative ray tracing, and we always run a reciprocal check on the shot gathers to catch timing errors before they propagate into the tomogram. For deeper targets, like mapping the limestone-shale contact below 25 metres, the reflection component becomes essential and we switch to a common mid-point acquisition geometry that stacks out surface-wave noise. The result is a 2D velocity section that you can take directly into your ground model, and it often reduces the number of boreholes needed to characterise a site when paired with a targeted SPT drilling programme on the anomalous zones.
Seismic Tomography Surveys in Celbridge: Refraction and Reflection for Site Characterisation
Technical reference — Celbridge

Site-specific factors

A mistake we see repeatedly around Celbridge is assuming that a handful of boreholes on a two-hectare site will catch every karst feature or buried channel. The limestone here can dissolve along joint planes into narrow, vertically oriented pipes that a single rotary borehole will miss by half a metre, and that missed cavity might sit right under a pad footing. Seismic tomography spans the gap between point data and spatial coverage because it measures a physical property — P-wave velocity — that drops sharply in broken or voided rock, and the survey line can be walked across the exact footprint of the proposed foundations. When a velocity section shows a bullseye low-velocity anomaly at 6 metres depth that lines up with a surface depression on the site walkover, you have a target to investigate further rather than a post-excavation surprise that triggers a redesign. Skipping this step on karst-prone ground is a risk that costs multiples of the survey fee in delay claims.

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Explanatory video

Regulatory framework

ASTM D5777-18 (Standard Guide for Using the Seismic Refraction Method), ASTM D7128-18 (Standard Guide for Using the Seismic Reflection Method), ISRM Suggested Methods for Seismic Testing, Eurocode 8 (EN 1998-1:2004) for site classification via Vs profiles

Reference parameters

ParameterTypical value
MethodSeismic refraction and reflection tomography
Source typeAccelerated weight drop or sledgehammer on plate
Recording system24-channel seismograph, 4.5 Hz geophones
Typical spread length46–115 m depending on target depth
Depth of investigation (refraction)15–25% of maximum spread
Depth of investigation (reflection)10–50+ m depending on geometry
Data processingFirst-break picking, reciprocal QC, ray-trace inversion
Deliverable2D P-wave velocity section in SEG-Y and CAD formats

Frequently asked questions

How long does a seismic tomography survey take on a typical Celbridge site?

For a single refraction line of about 70 metres with a two-person crew, field acquisition takes around two to three hours including setup and calibration. Processing and interpretation add another two to three working days before you receive the final velocity section and report. Reflection surveys take longer in the field because of the tighter geophone spacing and higher shot density, so a full day on site is more typical.

Can you run a seismic survey on a site next to the M4 or in a residential estate without disturbing neighbours?

Yes. We use a weight-drop source rather than explosives, which produces a short, thud-like impulse that does not carry far. In residential areas around Celbridge we coordinate start times to avoid early mornings and always notify adjacent properties beforehand. The 24-channel spread uses cables along the ground and does not require any permanent installation.

What does a seismic tomography survey cost for a site in Celbridge?

For a single refraction line with full processing and interpretation, budgets typically range from €2,640 to €5,120 depending on the spread length, number of shots, and whether reflection coverage is also required. We provide a fixed-price quotation after reviewing the site plan and investigation objectives, so there are no surprises.

How do you tell the difference between a water-filled cavity and a soft clay layer on the tomogram?

Both appear as low-velocity zones on a P-wave section, so we cross-reference the seismic data with an electrical resistivity line over the same profile. A water-filled void will show a strong resistivity contrast, while a clay-filled depression or weathered zone tends to have a more muted response. Combining the two geophysical methods gives much higher confidence in the interpretation than either one alone.

Is seismic tomography accepted by the planning authority for site characterisation in County Kildare?

It is. Seismic refraction and reflection data are routinely submitted as part of site investigation reports for planning applications across Kildare, particularly where the ground model needs to demonstrate bedrock depth, karst risk assessment, or rippability for earthworks design. We can include the processed SEG-Y files and a summary interpretation signed by the responsible geophysicist for direct inclusion in your planning package.

Location and service area

We serve projects across Celbridge and surrounding areas.

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