Dynamic liquefaction of shear zones in intact loess during simulated earthquake loading
Dynamic liquefaction of shear zones in intact loess during simulated earthquake loading
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DOI：
10.1007/s10346-016-0746-y
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发表时间：
2017-06-01
期刊：
影响因子：
6.7
通讯作者：
Petley, D. N.
中科院分区：
文献类型：
--
作者：
Carey, J. M.;McSaveney, M. J.;Petley, D. N.
2010-2011 年新西兰坎特伯雷地震序列使该地区黄土覆盖的斜坡暴露于非常高水平的地震激发（当地测量为 >2 g）。很少有黄土边坡表现出永久性的局部下坡变形，而且大多数黄土边坡仅表现出有限的累积位移。对从最近活动的斜坡之一收集的完整和重塑的黄土样本进行了一系列创新的动态背压剪切盒测试，复制了不同简化水平地震激励下的现场条件。在每次测试期间，测量样品失效时产生的强度降低和超孔隙水压力。测试结果表明，虽然可能发生动态液化，但一个关键因素可能是大地震发生时黄土基本上不饱和。由于材料的岩土工程特性变化很大，测试中完整黄土样品的失效是复杂且多变的。由于地震激发导致孔隙水压力增加，导致一些黄土样品由于动态液化而迅速失效，从而引发强度的快速损失，从而导致抗剪力的损失。在最初的破坏之后，孔隙压力随着持续的地震激发而消散，并且样品固结，导致部分剪切强度恢复。一旦超孔隙水压力消散，变形就会继续处于临界有效应力状态，体积不会进一步变化。然而，重塑的和较弱的样品不会液化，而是体积立即减小，伴随着样品固结时孔隙压力的缓慢且更持续的增加。此后，多余的压力消散，变形继续处于临界状态。这种复杂的行为解释了为什么尽管地面震动异常强烈，但位移却有限且缺乏跳动：在自由排水的斜坡中不太可能发生动态液化。然而，动态液化仍然是解释一些低角度坡脚处黄土破坏的合理机制，这些坡脚的黄土中存在永久地下水位。
The 2010-2011 Canterbury earthquake sequence in New Zealand exposed loess-mantled slopes in the area to very high levels of seismic excitation (locally measured as >2 g). Few loess slopes showed permanent local downslope deformation, and most of these showed only limited accumulated displacement. A series of innovative dynamic back-pressured shear box tests were undertaken on intact and remoulded loess samples collected from one of the recently active slopes replicating field conditions under different simplified horizontal seismic excitations. During each test, the strength reduction and excess pore water pressures generated were measured as the sample failed. Test results suggest that although dynamic liquefaction could have occurred, a key factor was likely to have been that the loess was largely unsaturated at the times of the large earthquake events. The failure of intact loess samples in the tests was complex and variable due to the highly variable geotechnical characteristics of the material. Some loess samples failed rapidly as a result of dynamic liquefaction as seismic excitation generated an increase in pore water pressure, triggering rapid loss of strength and, thus, of shear resistance. Following initial failure, pore pressure dissipated with continued seismic excitation and the sample consolidated, resulting in partial shear strength recovery. Once excess pore water pressures had dissipated, deformation continued in a critical effective stress state with no further change in volume. Remoulded and weaker samples, however, did not liquefy and instead immediately reduced in volume with an accompanying slower and more sustained increase in pore pressure as the sample consolidated. Thereafter, excess pressures dissipated and deformation continued at a critical state. The complex behaviour explained why, despite exceptionally strong ground shaking, there was only limited displacement and lack of run-out: dynamic liquefaction was unlikely to occur in the freely draining slopes. Dynamic liquefaction, however, remained a plausible mechanism to explain loess failure in some of the low-angle toe slopes, where a permanent water table was present in the loess.