It is one of the most common mistakes in construction: a developer commissions structural drawings before commissioning a soil investigation. The structural engineer designs a foundation system based on assumed conditions. Ground breaks. Then comes the rude awakening — black cotton soil where firm ground was expected, or a water table far higher than anticipated.

At Abba & Wandu Engineers, we treat the geotechnical assessment not as a regulatory formality but as the foundation of every foundation we design.

What a Soil Investigation Tells You

A proper geotechnical investigation delivers several critical data points that directly inform structural decisions:

  • Bearing capacity: How much load the soil can carry per unit area — directly determines footing sizes and types.
  • Soil profile: The sequence of soil layers from surface to the design depth.
  • Water table depth: Affects foundation type selection, waterproofing requirements, and excavation methodology.
  • Expansive soils: Black cotton soil swells when wet and shrinks when dry — a foundation that ignores this will crack, tilt, or fail over time.
  • Settlement potential: How much the soil will compress under load, and whether that compression will be uniform or differential.

The Cost of Skipping It

We have been called onto projects where soil investigations were skipped to save money. In every case, the cost of remediation far exceeded what a proper investigation would have cost at the outset.

A soil investigation that costs KES 150,000 can prevent a remediation bill of KES 5 million. It is never optional.

How We Use Soil Data in Our Designs

Once we have the geotechnical report, our structural team uses the bearing capacity values to size pad footings, strip footings, or raft foundations. For sites with poor near-surface soils, we may specify pile foundations that transfer loads to deeper, competent strata.

For expansive clay sites — common across the Nairobi region and the Rift Valley — we use stiffened raft foundations designed to bridge over differential movement, combined with void formers under ground beams that allow the soil to heave without loading the structure.

The soil investigation is not the first step in construction. It is the first step in engineering. Everything else follows from it.