Expressway embankments have collapsed in many locations in Japan recently because of torrential rains and earthquakes striking the areas. Because the soil from collapsed embankments contains much water, we have assumed that penetrating rain and groundwater affected the embankments, in some way, and led to the collapse. To reinforce the slopes and prevent such disasters, we have dug slits where are excavated at the foot of the slope and filled with crushed stones to reduce the water content ratio of the slope. To verify the effectiveness of this measure, we have conducted the following two tests. First, we conducted laboratory tests, changing the water content ratio, to examine the changes in the strength characteristics of the embankment soil. This test confirmed that soil strength weakens as the water content increases, even if compaction of the soil remains the same. For the second test, we made a 1/50-scale model embankment and carried out large-scale dynamic centrifugal force loading tests to verify the reinforcement effects of this measure. The test confirmed that embankments reinforced with the drainage works held down deformation to half of that of embankments which were not reinforced.