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1 前言 最近,日美合作研究会议录提供了大量有关平缓坡面上诱发的地面位移的案例资料。例如:(a)1964年新泻地震中,新泻市大泻区在平均坡度仅为0.5％的4m厚可液化土层上,发生了向着Tsusen河方向的超过6m的地表位移(Yasuda等,1989);(b)在上Van Norman水库西岸,覆盖有最大厚度为6m的可液化冲积土层,1971年费尔南多地震的结果,在其基底坡度为1°到2°的人工填土层上,发生了达3.0m的地表位移(O’Rourke等,1989)。Sasaki等(1992)和Towhata等(1992)提供的振动台试验,已经阐明了这些案例提出的若干问题:由于重力作用,向下坡方向产生了永久位移;侧向位移在液化层表面最大,而在基底则可以忽略;未饱和表层与液化下层一块移动,而其界面没有滑动。 因此说明地面位移乃是饱和表层下面软弱层中剪应变的结果,而不是由于形成了不连续滑动面。然而,正如作者们自己指出的那样,无法使用1g的振动台模型去研究逐个瞬间的移位;在重现原位性状方面,孔隙压力比消失得太快,因而模型在软化状态下没有足够的时间来发展大位移(Sasaki等,1992)。 Steedman(1989)概述了用离心模拟研究包括超孔隙压力、组合应变与刚度以及强度退化效应的重要性。Bolton有关峰值剪切抗力的工作揭示了在1g条件下模拟所产生的两个最重要的误差,这些误?
1 INTRODUCTION Recently, Japan-United States Cooperative Study Proceedings provided a wealth of case information on ground-induced displacement over flat slopes. For example: (a) In the Niigata earthquake of 1964, a surface displacement of more than 6 m in the direction of the Tsusen River occurred on a 4-m liquefiable soil with an average slope of only 0.5% in Daiei District, Niigata City (Yasuda et al. 1989); (b) on the west bank of the Van Norman reservoir, covered with alluvial alluvial alluvium of up to 6 m in thickness, as a result of the 1971 Fernando Earthquake, on artificial fill with a base gradient of 1 ° to 2 °, Surface displacement up to 3.0 m occurred (O’Rourke et al., 1989). Shaking table tests provided by Sasaki et al. (1992) and Towhata et al. (1992) have elucidated several of the problems posed by these cases: permanent displacement to the downhill due to gravity; lateral displacement to the surface of the liquefaction layer maximum and In the substrate can be ignored; Unsaturated surface and the lower layer of liquefaction move without sliding interface. Therefore, it shows that the ground displacement is the result of the shear strain in the weak layer below the saturated surface, not due to the formation of discontinuous sliding surface. However, as the authors themselves point out, it is not possible to use a 1g shaker model to study the displacement moment by moment; the pore pressure ratio vanishes too quickly in reproducing the in situ character, so the model does not have enough Time to develop large displacements (Sasaki et al., 1992). Steedman (1989) outlines the importance of using centrifugation simulations to study effects including excess pore pressure, combined strain and stiffness, and strength degeneration. Bolton’s work on peak shear resistance revealed two of the most important errors in simulations at 1g.