The variation of hardness and permeability by deep tillage on embankment in the coastal forest restoration project

Abstract

After the Great East Japan Earthquake, an embankment was built along the coast as a planting base by the Coastal Forest Restoration Project. It is feared that a rain pool and the hardness in a part of embankment inhibits the growth of planted trees. Thus, deep tillage has been conducted on the embankment. The effect of deep tillage and its sustainability were investigated in Natori city, Miyagi Prefecture, Japan. Deep tillage was carried out by an excavator with a skeleton bucket. Hardness and permeability were measured by a Hasegawa-type soil penetrometer and the constant level method, respectively. This deep tillage softened the embankment and increased its permeability. After 3 to 6 months, the embankment became hard again at a depth of 0-10 cm. In contrast, the embankment remained soft below 10 cm deep, indicating that the effects of deep tillage were sustained at that depth for 6 months.