西北季节性冻土场地地震反应特性研究∗

Seismic Response Characteristics of Seasonally Frozen Soil Sites in Northwest China

摘要:

我国西北地区被季节冻土全覆盖，且近年来该区域地震频发。为研究我国西北地区季节性冻土场地的地震反应特性，开展了季节性冻土场地振动台试验，并建立了不同冻结深度的三维实体有限差分模型，对比分析了不同地震激励作用下的季节性冻土场地的地震反应特征和土体的动剪应力—动剪应变规律。结果表明：在地震激励下，冻土层的存在虽然有效抑制了地震动能量，但冻结期场地的水平位移与非冻结期相比明显较大，且竖向位移呈显著的层状震陷特征；冻土场地的峰值放大系数呈先增大后减小然后再增大的规律，并且冻土层深度越大其峰值放大系数越小。此外，通过土体的动剪应力—动剪应变关系可以发现，冻土场地地震反应具有明显的非线性特征， 且冻土层的存在对地震能量具有一定的削弱作用。

Abstract:

Seasonally frozen soil covers the whole area of Northwestern China where earthquakes have happened frequently in recent years. In order to study the seismic response characteristics of seasonally frozen soil sites in Northwestern China， shaking table tests of seasonally frozen soil sites were carried out， and three-dimensional solid finite difference models with different freezing depths were established. Seismic responses and soil dynamic shear stress-strain relationship under different seismic excitations were analyzed. Results showed that the existence of the frozen soil layer effectively restrained the ground motion energy， while the horizontal displacement of the site in frozen status was larger than that in unfrozen status. Besides， the vertical displacement showed a significant layered seismic settlement. The peak amplification coefficient of the seasonally frozen soil first increased， then decreased and finally increased again. It was found that the thicker the frozen layer， the smaller the peak amplification coefficient. In addition， the dynamic shear stress-strain relationship of soil exhibited obvious nonlinearity， and the frozen soil layer can dissipate the seismic energy during earthquakes.