季节性冻土和多年冻土对场地地震反应的影响

INFLUENCE OF PERMAFROST AND SEASONALLY FROZEN SOIL ON SEISMIC RESPONSES OF SITES

季节性冻土和多年冻土的存在,对场地的地震反应将产生一定的影响。根据一维波动理论,应用水平层状场地地震反应的等效线性化有关程序,对季节性I,II类场地的冻土区和多年冻土区在不同地震波作用下的反应进行计算,分析冻土层的变化对场地地震反应的影响。计算结果表明:在季节性冻土区,冻土层使自由场地的地面峰值加速度减小,且随冻土地温降低,冻土厚度增大、地面的加速度减小。对II类场地的冻土层影响大于I类场地;在多年冻土区,冻土层厚度越大,II类场地的地面加速度越小,而在I类场地上没有此规律。多年冻土上界以上为融土时,地表面的加速度峰值比上界以上为季节性冻土时要大。

The seismic responses of site will be influenced to certain extension when seasonal frozen soil and permafrost exist. According to one-dimensional fluctuation theory, the seismic responses field of Classes Ⅰ and Ⅱ in permafrost and seasonal frozen soils are calculated under multifarious earthquakes by using equivalent linearization program of plane-stratum earthquake response. The influences of seismic responses in field are analyzed due to the thickness change of frozen soil layer. Ⅰt indicates that in seasonal frozen regions, the peak value of ground surface acceleration decreases when seasonal frozen soil exists; and its acceleration peak value decreases with decrease of temperature of frozen soil and with increase of thickness of frozen soil. The influences of frozen soil/site of Class Ⅰ are greater than that of Class Ⅱ. The calculated results also show that in permafrost, the deeper of frozen soil layer is, the more decrescent of the site ground acceleration peak value for site of Class Ⅱ is. However, the rule is not suitable for site of Class Ⅰ. When the overlay of permafrost is thawy soil, the acceleration peak value is greater than that when the overlay permafrost changes into frozen soil.