Nowadays, geotextile reinforced soil walls are being used more often, and with that, the number of reports on the deformation of these soil walls is on the rise. But we do not yet fully understand what happens to the reinforcement material within the embankment when deformation occurs. To find out, the authors have studied density, water content ratio, velocity of elastic wave, and strength of reinforcement material of the deformed embankment interior, where the mudstone reinforcement wall was rebuilt after it had been damaged. Studies showed that penetrating groundwater and rain had weakened the mudstone used to construct the embankment, causing deformation. We also confirmed that some parts of the reinforcement material were much fragile and showed considerably lower deformation capacity compared with the new reinforcement material. These findings indicate the possibility of lowered strength and deformation capacity of reinforcement material within the damaged geotextile reinforcement soil wall.