Expansive soil becomes weaker when it absorbs water, affecting the stability of slopes. By using computer software to analyze how rainwater seeps into the soil, researchers found that rain mainly impacts shallow areas of the slope. Slopes with low permeability are more affected by rainwater, but short-term rainfall doesn't cause widespread damage. The slip surface of the slope is usually in the top layer, showing shallow slipping. This study provides useful information for building and protecting slopes made of expansive soil.