锯末混合土场地模型振动台试验研究

在北京工业大学九子振动台台阵系统上开展了一系列锯末混合土场地模型试验,试验中模型箱采用装配式连续体刚性模型箱,其尺寸为7.7 m(长)×3.2 m(宽)×1.2 m(高),输入地震动时程采用El Centro地震动记录和天津地震动记录,地震动输入方向为水平横向和水平纵向。通过场地模型振动台试验,验证了设计的模型箱的较小的"边界效应"影响程度,同时考察了锯末混合土场地模型的动力特性及其变化规律。对部分试验结果,包括场地反应的地震动峰值加速度及其动力放大系数、加速度时程及其频谱,进行了具体分析。试验结果表明:本次使用的装配式连续体刚性模型箱边界效应处理效果良好,同一水平面上不同部位土体反应的加速度仅有较小差异;随着地震动输入强度的增大,同一测点反应的峰值加速度总体上在增大,但其加速度动力放大系数总体上呈现减小的趋势,反应的频谱组成从较高频率向较低频率移动。这些结果说明,随着地震动输入强度的增大,土体由于刚度发生变化而相对变软,土体模量逐渐降低。

Shaking table tests on sawdust-mixed clay site

A series of shaking table tests on a sawdust-mixed clay site model are conducted under uniform earthquake excitation using the shaking table testing system with 9 sub-tables in Beijing University of Technology. The tests are performed using a rigid prefabricated continuous model box with dimensions of 7.7 meters long, 3.2 meters wide and 1.2 meters high. The test system is subjected to strong ground motions from El Centro record and Tianjin record. Through the horizontal longitudinal and horizontal transverse free-field shaking table tests, the boundary effect of the model box is investigated, and its dynamic characteristics and variation laws are given. The partial test results are analyzed, including the peak ground accelerations and their amplification factors, acceleration time histories and their Fourier spectra for the site responses. The test results indicate that the boundary effect of the model box is small because there is only a slight difference in the accelerations of site responses at the same elevation. With the increase of intensity of the input ground motion, the peak ground acceleration of the site response at the same test point increases, but its acceleration amplification factor decreases, and the main frequency components move from high to low frequency. It means that the soil becomes softer and the soil modulus decreases gradually with the increase of the intensity of input ground motion.