When I first became interested in structural engineering, I thought engineers would spend most or even all their time working on the designs for the components. I assumed that the strength of structural elements like beams and columns mattered more than anything else. However, when I visited a construction site, I noticed that engineers were closely observing and taking measurements of the soil long before any construction began. Their scrutiny with the soil made me realize how important the site itself is in the construction of buildings.

Every structure transfers its weight into the ground due to gravity. If the soil is soft and cannot support the structure, it would experience severe structural damage. Geotechnical engineers specialize in studying the properties of soil at construction sites. By taking numerous different measurements, they can determine the soil quality and whether it is safe to build on or if other procedures need to be done before construction can start. Engineers use tactics like mechanical compression or chemical stabilization to compact soil and strengthen it. Using large machines, they press down on the soil, squeezing out air gaps and making it stronger. They could also chemically strengthen the soil by adding additives like lime, cement, or polymers to increase the load-bearing capacity and reduce the plasticity of the soil.

The Leaning Tower of Pisa serves as a historical reminder of what happens when soil strength is ignored. The tower was built on soft, moist soil, and engineers didn’t compact it before construction began. Once the upper floors were built, the tower began to sink as the soil under it settled deeper under the pressure. Efforts to straighten the tower included counterweights on the opposite side, and strengthening the foundation. However, engineers were unable to restraighten the tower, leaving it permanently leaning, all because the soil wasn’t strong enough. It serves as a reminder to engineers that no matter how structurally sound a building may be, without a proper soil bed to rest on, there is a high risk of collapse.