Geological drilling
Pre-construction site investigation: soil study, sampling and data for the geotechnical report.
Before a building, road or plant is built, the bearing capacity of the ground, the groundwater level and the layering must be known. Geological boreholes provide this. The work is called a geotechnical site investigation and is a required stage of design: the type, depth and cost of the foundations follow directly from its results.
Who it is for
- Design firms and architects — the geotechnical report for the project.
- Contractors — multi-storey buildings, housing estates, shopping centres.
- Industry and infrastructure — plants, warehouses, tanks, roads, bridges, pipelines.
- Private clients — a large house or a difficult plot (a slope, waterlogged ground, made ground).
What it establishes
- the type, thickness and order of the soil layers;
- physical and mechanical properties: density, moisture, strength, compressibility;
- the groundwater level and how it may change with the seasons;
- how aggressive the water and soil are to concrete and steel;
- hazards such as collapsible, swelling, saline or made ground.
In seismic areas the same data sets the ground's seismic category.
Samples and tests
Disturbed samples are taken to identify the soil type and composition. Undisturbed samples are recovered with a special sampler that keeps the natural structure, and are used in the laboratory for strength and consolidation tests. A water sample is taken where groundwater is met.
Where the design calls for it, in-situ tests are run in the borehole, such as the standard penetration test (SPT), which gives density and strength with depth.
Number and depth of boreholes
The number of boreholes depends on the size and importance of the structure; the depth depends on the foundation type and load. Each hole must pass through the full thickness of ground the foundation affects. As an example:
| Project | Boreholes | Depth |
|---|---|---|
| Private house | 2–3 | 8–12 m |
| 5–9 storey building | 4–6 | 15–25 m |
| High-rise on piles | 6 or more | 30–50 m |
The exact scope is set by the designer or geologist in the brief. If there is no brief yet, we can help prepare one.
Work sequence
- Receiving the brief and the borehole layout.
- Setting out the holes on site and checking for buried services.
- Drilling, logging the section, taking samples.
- Recording the groundwater level when struck and once it settles.
- Grouting the holes and cleaning up the site.
- Delivering samples to the laboratory and handing over data for the report.
When you get in touch, send the site address, the type and height of the building, the planned foundation and the brief if you have one.