A retaining wall that has a strut in compression for soil stability is known as what?

A retaining wall that features a strut in compression for soil stability is termed a buttress. Buttresses are structural elements that provide support and stability to a wall, particularly in the context of earth-retaining structures. When soil pressure against a retaining wall increases, the buttress helps manage this lateral force by transferring the load and creating a compressive force in the strut. This design enhances the wall's ability to resist soil movement and prevents potential failure due to overturning or sliding.

In contrast, while an arch is a curved structure that can distribute loads effectively, it doesn’t apply directly to retaining walls. A column is a vertical structural element designed primarily to support weight from above, and a pillar is typically a freestanding structure that can also bear loads but does not have the same specific use as a buttress in retaining wall applications. The unique structural function of a buttress in maintaining stability makes it the correct terminology in this scenario.