Why Early Site Investigations Matter

We’ve seen projects stalled or even abandoned when late-stage geotechnical surprises (such as weak soils, waterlogging, buried waste or rock) add huge costs or design constraints.

A thorough site investigation (consisting of both desk study and intrusive sampling) gathers the hard data to confirm or rule out risks and protect the project from unforeseen costs, planning delays, or environmental liabilities.

In short, the best time to understand ground conditions is before buying land or submitting detailed plans, not after a problem appears.

What is a Site Investigation?

A site (ground) investigation is the process of collecting and interpreting data about the ground beneath a proposed development. It typically starts with a desk study, reviewing geological maps, old site plans and history, and proceeds to physical testing of soils and groundwater.

In practice, our site investigations follow a staged approach:

• Phase 1 (Desk Study): Gather all existing information (site records, borehole logs, geology maps, historical land use) to identify potential risks.
• Phase 2 (Intrusive Investigation): Drill boreholes and dig trial pits to sample soils, groundwater and any contaminants in situ. Standard methods include cable-percussion or rotary drilling, window sampling, and excavation of pits for shallow layers.
• Laboratory Testing: Send collected soil, rock and water samples for tests (strength, density, contaminants, ground gases, etc.) to quantify hazards.
• Phase 3 (Further Field Work): If needed, return to the site (detailed pits, monitoring, additional drilling) based on initial findings.
• Phase 4 (Reporting): Compile an interpretive report that assesses bearing capacity, settlement, contamination and water issues. Engineers then use this to design foundations, earthworks and drainage.

Well-planned investigations save money by giving engineers the data they need to optimise design. For example, defining the exact location of weak soils can reduce the extent of expensive stabilisation layers or imported fill, potentially cutting earthwork volumes by a significant amount and offsetting the cost of the investigation. In short, you pay for an investigation one way or another.

• Expansive (Clay) Soils: Clay-rich soils can swell when wet (heave) or shrink when dry (subsidence). The British Geological Survey warns that shrink–swell soils are one of the most costly and globally widespread geological hazards, with damages running into billions of pounds annually. In the UK, clay movement famously caused £540 million in damage after just the 1991 drought, and insurers report tens of millions in subsidence claims each year. For new developments on clay, special precautions are needed: foundations must be designed for vertical pressure and lateral heave (often needing larger footing depth or compressible layers), and lightweight internal finishes. Failing to do so leads to cracking and structural damage, costly to fix. In practice, even if the ground appears ‘firm’ at one time, seasonal moisture changes (or tree removal!) can trigger heave later. Without a site investigation to reveal clay layers, a project may need last-minute heave protection measures for every unit.
• Permeable Soils: Conversely, very porous soils or karst (limestone) allow water to flow freely, raising risks of flooding. A permeable subsoil under a basement means there’s no easy way to make it watertight except full tanking (a waterproof envelope). Any cut foundation wall will need continuous membranes. If not anticipated, this adds cost; if not done, buildings face chronic damp. As one waterproofing guide advises, relying on simple drainage systems in high-permeability ground is ill-advised, meaning a full tanking strategy is usually needed.
• Shallow Bedrock: Hard rock layers near the surface may sound good (high strength), but they dramatically increase excavation cost. Breaking out rock also slows work and demands specialist plant.