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The number of boreholes depends on site area, geological variability, and the sensitivity of the structure. As a starting point, Eurocode 7 suggests at least 3 boreholes for smaller sites, with spacing of 15–40m for buildings and 25–50m for roads. On highly variable sites or where geological discontinuities are suspected, closer spacing or additional methods such as geophysics may be recommended. We will advise an appropriate investigation layout based on desk study findings and your project brief.

Borehole depths depend on the structure and ground conditions. For typical two to four-storey buildings in Accra and Kumasi, depths of 8–15m are common. For high-rise buildings requiring deep pile foundations, depths of 20–35m are typical. For road investigations, 3–6m is usually sufficient for pavement design. We always aim to penetrate at least 1.5× the proposed foundation depth into competent material, or to a point where the stress influence from the structure becomes negligible.

A Geotechnical Investigation Report (GIR) presents the factual results of ground investigation — borehole logs, laboratory test results, and field observations — without engineering interpretation. A Geotechnical Design Report (GDR) takes that data and applies engineering analysis to provide design recommendations — bearing capacities, pile lengths, slope stability factors of safety, and so on. Most clients require both, and EC7 distinguishes them formally. Smecon can produce either or both depending on the project stage.

Mobilisation typically takes 3–7 days from instruction. Field investigation duration depends on scope: a residential site investigation (4–8 boreholes to 10m) usually takes 3–5 days on site. A major road investigation may take 3–6 weeks. Laboratory testing and report preparation typically adds 2–4 weeks after fieldwork completion. Smecon provides a programme at the outset and updates clients weekly. We can expedite delivery for time-critical projects on request.

Pile foundations are typically preferred when: the near-surface soils are too weak to support shallow foundations economically; settlement of a shallow foundation would be unacceptably large; the structure applies very high loads (multi-storey buildings, bridges); the site has variable ground conditions that would cause differential settlement; or when proximity to other structures precludes excavation. In coastal Accra, soft alluvial deposits frequently make piling the most cost-effective solution. Our investigation findings will always identify whether piling is warranted.

The most common ground-related causes of building cracking in Ghana are: differential settlement from variable sub-soils (especially where fill material underlies part of a building); heave or shrinkage of expansive (montmorillonitic) clay soils due to moisture changes; inadequate foundation depth or bearing pressure; erosion of foundation support from poor drainage; and inadequate investigation prior to construction. We provide forensic investigation and remediation advice for distressed structures, and recommend preventive investigation before construction.

CBR (California Bearing Ratio) is a measure of the relative strength of a soil or pavement material compared to a standard crushed stone. A subgrade CBR of 3% is weak; 8% is moderate; 15%+ is strong. It directly determines the required thickness of pavement layers above the subgrade — a weaker subgrade needs a thicker pavement structure. Overestimating CBR leads to premature pavement failure; underestimating it leads to unnecessarily expensive over-design. Our soaked CBR tests, performed at the expected field moisture content, give the most conservative and appropriate design value.

Requirements vary depending on the development authority and project type. Ghana's development control regulations require a geotechnical assessment for major developments, multi-storey buildings, and infrastructure projects. For EIA-required projects, a geotechnical chapter is a standard component. Even where not formally required, providing a geotechnical report demonstrates due diligence and reduces the risk of costly ground-related issues during construction. Smecon can produce concise feasibility-level reports suitable for planning submission, or detailed investigation reports for detailed design.