What is the main structural function of counterfort walls?

Counterfort walls are structural systems primarily used to retain soil and withstand lateral earth pressures, particularly in situations involving steep or high retaining walls. The main structural function of a counterfort wall is to resist flexure and overturning. This is accomplished through the use of vertical tension ribs, which connect the wall to the base slab.

By incorporating these ribs, counterfort walls enhance their ability to withstand bending moments and shear forces created by the lateral pressure exerted by the retained soil. The tension ribs help to distribute those forces more effectively and provide additional resistance against overturning moments that may occur due to the weight of the retained material pushing against the wall.

While counterfort walls do have capacities that contribute to sliding resistance, compression strength, and the ability to support shear loads, their primary and most critical function lies in effectively managing flexural stresses and preventing overturning, which is why the function described in the correct answer is essential for their design and utilization in civil engineering applications.