Effectiveness of sandy soil densification method by simultaneous use of vacuum drainage and soil particles redistribution

摘要

In order to increase a density of sandy ground for a purpose to mitigate a risk of liquefaction, it is effective to mechanically rearrange the soil structure as well as to drain excess pore water simultaneously. As the methods to rearrange the soil structure, three methods were undertaken, i.e., 1) applying cyclic loads, 2) vibrating and 3) mechanical disturbance by mixing blade. Two kinds of sands were used in laboratory tests. One was clean sand with D_(r) = 51% (initial) and F_(c) = 0%, and the other was mixed sand with D_(r) = 60% (initial) with F_(c) = 30%. Cyclic loading tests were carried out using cyclic tri-axial testing equipment. Both a vibration model test and a mechanical disturbance model test were carried out using sand specimens of 30cm in diameter and 80cm in height, with vacuum pressure of -60kN/m~(2). From the result of the tests, it was clarified that a densification from D_(r) = 51% to D_(r) = 73 - 94% for clean sand and from D_(r) = 60% to D_(r) = 83 - 107% for mixed sand were possible with these methods.