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 sandwiched, 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 millimeters just after liquefaction in loose sand and that the film lasts longer than the post-liquefaction settlement. The effect of the water film on pore-pressure distribution and sand settlement is intensively studied. Ig shake table tests are then carried out for 2D models with or without seams of silt within a saturated sand layer. In the former case, water films formed beneath silt seams just after liquefaction enable the soil mass above them to glide due to an unbalanced force along the water films, not only during but also after shaking. In the latter case, the soil deforms continuously, mostly during shaking, and stops afterward. Thus, a significant effect of water films formed beneath thin, low-permeability sublayers in a liquefied loose sand, on the failure mode and timing in lateral spread, is clearly demonstrated by these simple model tests.