What effect does increasing soil compaction have on a retaining wall's stability against sliding?

Increasing soil compaction positively affects a retaining wall's stability against sliding. When soil is compacted, the particles are arranged more closely together, which increases the soil's density and overall shear strength. This increased shear strength enhances the frictional resistance between the wall and the soil behind it, effectively reducing the likelihood of sliding.

Furthermore, compacted soil provides better lateral support to the wall because it creates a more stable and cohesive mass that can resist lateral earth pressure. This is particularly important for retaining walls, which rely on the pressures exerted by the soil to maintain their position and function. In addition to increasing stability, well-compacted soil can absorb and redistribute loads more effectively, minimizing the risk of structural failure due to sliding.

The other options do not adequately address the physical effects of soil compaction on stability. While it is conceivable that soil compaction could have negligible effects or alter other characteristics, the predominant effect is the enhancement of stability due to increased friction and reduced sliding potential. Thus, the correct understanding is that increasing soil compaction directly increases the stability of a retaining wall against sliding.