Experimental study on mitigation of damage induced by lateral displacement of liquefied subsoil

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The present study aims at developing a mitigation measure by which liquefaction-induced deformation of embankment is reduced to an acceptable magnitude. This measure is intended to be practiced in such a situation as densification and other prevention of liquefaction are not feasible. Shaking table tests were conducted on models of embankment resting on liquefiable sandy deposit. Firstly, two rows of sheet pile walls were installed at the foot of the embankment so that lateral spread of foundation sand might be mitigated by the stiffness of sheet pile walls. Although this idea worked well when the frequency of shaking was high, still there observed certain extent of subsidence in the embankment due to minor amount of boiling sand near the wall as well as consolidation settlement of foundation sand.Low frequency shaking demonstrated the problem of sheet pile wall measure. Since the displacement of wall was large, cracks opened near the wall and a large amount of sand boiled out from there, leading to significant subsidence of the embankment. This problem was overcome by placing additional berm above the walls in order to prevent boiling. This idea was shown to be satisfactory in a shaking table test. Special sheet pile walls were attempted which had drainage capability. When the drainage was attached beneath the slope of embankment, pore pressure was reduced near the surface and a rigid soil block was formed therein.This soil block prevented the aforementioned boiling of sand and reduced subsidence. On the contray, sheet pile walls installed from the top of an embankment with tie-rod connection at the top did not worked well because the unprotected slope failed and consequently the sheet pile walls distorted substantially.