The case of Mombasa airport was baffling – a JICA geological expert on the Dongo Kundu road construction site noticed what looked like sinkholes on the slopes rising up the airport hill brow. Staff at the airport had also found holes in the grassy berm along the runway and even filled some with rubble. They became worried because the holes were developing and increasing in number. The airport management worried that sinkholes could be developing under the runway and one day the ground may just give in under a landing flight.
The engineering consultants on the airport rehabilitation project called us in to solve the mystery of the sinkholes and if indeed, there could be some under the runway.
After 2 weeks of 2D electrical resistivity tomography conducted mainly by night due to a busy runway during the day, we solved the riddle. The holes seen were not classic limestone-cavern type sinkholes, but were the product of tunnel erosion.
Now, tunnel erosion is a drainage problem and not a chemical solution problem as it is with traditional sinkholes. We were able to formulate a drainage solution suitable for the unique lithological conditions at the airport and hand it over to the design engineers.