Water film in liquefied sand and its effect on lateral spread

A 1D saturated sand layer of 2 m in thickness, in which a silt seam is sand wiched, is liquefied by an instant shock. It is found that a water film is easily formed beneath the silt seam with a thickness as thin as a few milli meters just after liquefaction in loose sand and that the film lasts longer than the post-liquefaction settlement. The effect of the water film on por e-pressure distribution and sand settlement is intensively studied. Ig shak e table tests are then carried out for 2D models with or without seams of s ilt within a saturated sand layer. In the former case, water films formed b eneath silt seams just after liquefaction enable the soil mass above them t o glide due to an unbalanced force along the water films, not only during b ut also after shaking. In the latter case, the soil deforms continuously, m ostly during shaking, and stops afterward. Thus, a significant effect of wa ter films formed beneath thin, low-permeability sublayers in a liquefied lo ose sand, on the failure mode and timing in lateral spread, is clearly demo nstrated by these simple model tests.