Building on borrowed ground – a story of karst landscapes

Building a house is often described as “laying a foundation for the future.” In some parts of Lusaka, that phrase carries a little more suspense than most people bargain for. Beneath the city lies not just soil and rock, but a geological trickster - a product of a karst landscape. A karst landscape is formed from soluble dolomite and limestone. As highlighted in “Lusaka and its Environs: A Geographical study of a planned capital city in tropical Africa” published in 1986 by the Zambia Geographical Association, these rocks slowly dissolve when rainwater, slightly acidic by nature, seeps into the ground. Over time, this process creates hidden cavities, underground channels, and voids that quietly reshape the land from below.

Think of it as nature running its own underground construction project, except that it specialises in removing support rather than adding it. Water does not linger on the surface here; it slips through cracks and fractures, widening them gradually. What begins as tiny fissures can evolve into sizeable hollows. Eventually, the ground above may lose its strength and collapse, producing what we dramatically (and accurately) call sinkholes. They are not just holes. They are the visible reminders of a long, invisible geological process.

Building in such an environment can mean unstable foundations, sudden ground subsidence, and structural damage that appears as cracks, tilting walls, or doors that refuse to close politely. In worst-case scenarios, the ground may simply ‘eat itself’.

Add to that the issue of groundwater. In a landscape where water moves underground like cars in a Formula 1 race, any contamination travels just as efficiently.

So, should one abandon dreams of homeownership in karst landscapes? Not quite. The land may be unpredictable, but human ingenuity has a few tricks of its own. The first line of defence is knowledge. Before a single brick is laid, thorough geological and geotechnical investigations should be carried out. These studies help identify weak zones, cavities, and fracture lines. This essentially gives builders a ‘peepshow’ of what lies beneath.

Fact is. Laying a foundation in karst areas is not your average, one-size-fits-all affair. Techniques such as deep piling, reinforced slabs, and flexible structural designs can help buildings adapt to minor ground movement without serious consequences. Good drainage is equally important. Keeping excess water away from foundations prevents further dissolution of the rock below.

In addition, urban planning is non-negotiable in karst landscapes. Enforcing zoning regulations and restricting development in high-risk areas can save future homeowners a great deal of trouble—and expense. Meanwhile, public awareness ensures that early warning signs, like unexplained cracks or ground depressions, are taken seriously rather than dismissed as the work of my beloved grandmother’s boyfriend – the renowned wizard from Shangombo.

In the end, building in karst landscapes in an abyss of knowledge is simply building on borrowed ground. It is less about avoiding risk entirely, but more about respecting the ground beneath your feet. After all, when the earth itself has a sense of humour, it is best to build with both caution and a touch of humility.

Scientia est potential.