The monotonic and cyclic shear behaviour of a volcanic soil Shirasu as a reclamation material was investigated in the present study. Shirasu usually has a high coefficient of uniformity and contains typically 20–30% non-plastic fines formed from the crushed remains of larger particles. A series of monotonic and cyclic triaxial tests was carried out on samples of Shirasu to assess the influence of the fines on the monotonic shear and liquefaction susceptibility. Tests were performed on both the original particle size distribution and soil which had the fines washed out. The existence of the fines was shown to dictate the mechanical properties of Shirasu when used as a fill material.
In 1995 during the Great Hanshin earthquake, reclaimed areas filled with masado underwent major liquefaction damage. Since this earthquake event, Masado, a decomposed granite has been recognised as a material susceptible to liquefaction and many tests have been performed to establish the conditions under which it would liquefy. In addition to the igneous decomposed granites, Japan also has large areas covered by crushable volcanic ash sediments. These are particularly predominant in the south of Kyushu, particularly in Kagoshima prefecture where they are known as Shirasu. These ash deposits are frequently exposed as soft rock escarpments which are mined for use in reclaimed land fill. It is frequently pumped from inland locations as a slurry to form a loose saturated fill. In the 1968 Ebino earthquake sand boiling due to liquefaction was observed on the plains and river terraces formed from Shirasu and subsidence of bridge piers was reported. In March and May 1997 structural damage due to liquefaction was observed in the Kagoshimaken Hokuseibu earthquake in areas of coastal land reclamation at Akune harbour and Izumi and inland at Iriki.
