饱和度对平面P波入射下自由场地地震反应的影响分析

Effects of saturation on free-field responses of site due to plane P-wave incidence

场地土的特性是影响场地地震反应的重要因素。以往自由场地震反应分析中常假定场地土为单相介质或两相饱和多孔介质,而在实际工程中,常会遇到非饱和土的相关问题。目前对非饱和土波动特性的研究尚处于起步阶段,关于土体饱和度的变化对自由场地地震动的影响亦只针对准饱和土(饱和度Sr≥90%)的情况。为研究Sr<90%时,饱和度变化对自由场地地震动的影响,建立了非饱和土自由场地地震反应分析模型,在现有的非饱和多孔介质波动方程的基础上,对平面P波入射情况下场地中的波场进行分析,根据场地边界条件,求得到平面P波入射情况下非饱和土自由场地地震地面运动的解析解答,通过计算,系统地分析了入射角度、频率、土层刚度、孔隙率不同时,土体饱和度变化对非饱和土自由场地地震地面运动的影响,得到了非饱和土自由场地地震反应的一般规律。

The property of the soil in free field is an important influencing factor for the free field seismic response. In the existing studies the soil at local site is supposed to be the single-phase medium or saturated porous medium. But in fact, it consists of solid phase, liquid phase and gas phase sometimes, and presents the porous and multi-phase characteristics. The researches on the wave characteristics of unsaturated soils are still at the initial stage. The analysis about the effects of saturation on free-field responses of site is also limited under the condition of Sr≥90%. To analyze the effects of saturation on free-field responses of site when Sr〈90%, the free field model for unsaturated soils is established, and the wave fields in the free field of unsaturated soils under the P-wave incidence are analyzed. According to the boundary conditions, the undetermined coefficients of the waves are determined, and then the analytical solutions to the free site seismic ground motion of unsaturated soils are gained in the case of P-wave incidence. On the basis of analytical solutions, the effects of saturation on the free field seismic responses under different incident angles, wave frequencies, soil rigidities and porosities are analyzed. Some general rules of the seismic responses of the free site of unsaturated soils are obtained.