Soil and geological conditions can vary greatly, even between neighbouring properties. Where one site has firm, relatively uniform soil, another might have loose fill or changing groundwater conditions. This is why visible symptoms don't always tell the full story.
A crack doesn't necessarily mean that there's a major problem with the foundation of a building. But it is hard to make good decisions when movement is suspected without knowing what's happening under the structure.
A geotechnical report is an assessment of the ground conditions that answer practical questions about the soil, rock, groundwater and geological features, all of which affect construction or foundation stability.
According to Pinnacle Structural Repair Specialists, understanding these underlying conditions is important when determining why a building is moving or how suitable a site is for construction.
A geotechnical investigation can involve hand augering, boreholes, soil sampling, laboratory testing and geological mapping. The exact scope depends on the property and the nature of the concern.
The findings are brought together to create a site-specific picture of the ground. This information is useful before a new building or as part of a foundation assessment where an existing property is showing signs of movement.
A soil test will determine what type of material exists on a property and classify it. The test also provides information about its strength, moisture content, load-bearing characteristics and settlement potential.
Some soils compress when a load is placed on them. Others expand when wet and shrink as they dry. A soil investigation reveals differences between underground layers, including weaker material beneath apparently firm surface soil.
These characteristics are important to understand because a foundation transfers the weight of a building into the ground. If the ground settles or moves unevenly, different parts of the foundation may behave differently.
This doesn’t mean that one type of soil automatically makes a property unsafe, but factors like the design of the building, the depth of the affected soil and the conditions at that specific site all play a role.
Water can be very important for the stability of the ground. Groundwater assessment tells you about underground seepage and how the moisture interacts with the surrounding soil.
Leaking pipes or changing groundwater conditions can soften certain soils or contribute to repeated cycles of expansion and contraction. This is particularly relevant as South Africa works to address ageing water infrastructure and high levels of water loss. In some cases, water also washes fine material out of the ground.
In South Africa, where properties are exposed to heavy seasonal rainfall, dry periods, coastal conditions or highly variable soil profiles, these considerations are especially relevant. The source and effect of the moisture must be investigated rather than assumed.
A geotechnical report identifies the property's settlement, property subsidence, expansive soils, erosion, unstable ground or difficult groundwater conditions. The report could also highlight underground voids or geological hazards that need further investigation.
For a property with cracks or sticking doors and windows, this information helps professionals look beyond the visible symptoms. These signs can have several possible causes and do not, on their own, prove foundation failure.
The results of a geotechnical investigation can assist in making decisions regarding site preparation and foundation design. For existing buildings, a report can help you decide whether to consider options like better drainage or underpinning foundations.
There is no single repair that suits every case. Underpinning may be appropriate for one property but unnecessary or ineffective for another. Diagnosis before intervention prevents spending money on repairs that address the crack but not the cause.
Geotechnical findings should therefore be considered alongside a structural assessment by suitably qualified professionals. Together, these investigations distinguish between superficial defects and movement linked to the supporting ground.
