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

本研究的目的是开发一种缓解措施，通过这种缓解措施，路堤的变形减小到可接受的程度。该措施旨在在致密化和其他液化预防措施不可行的情况下实施。对软土桑迪存款层上路堤模型进行了振动台试验。首先，在路堤底部设置两排板桩墙，以利用板桩墙的刚度减缓地基砂的侧向扩散。虽然这种方法在高频率振动时效果较好，但由于墙附近有少量的沸腾砂和地基砂的固结沉降，路堤仍有一定程度的沉降，低频振动表明板桩墙措施存在问题。由于墙位移较大，墙附近出现裂缝，大量砂土从墙内涌出，导致路堤明显下沉。这个问题通过在墙壁上方放置额外的护堤来解决，以防止沸腾。在振动台试验中证明了这一想法是令人满意的。尝试了具有排水能力的特殊板桩墙。当排水装置附着在路堤边坡下时，靠近表面的孔隙压力降低，并在其中形成刚性土块，该土块防止了上述砂的沸腾并减少了沉降。与此相反，从路堤顶部安装的板桩墙在顶部与拉杆连接没有很好地工作，因为未保护的斜坡失败，因此板桩墙变形显著。

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.