饱和软土自由场地地震反应特性振动台试验

Shaking Table Tests on the Seismic Response Characteristicsof a Free Field in Saturated Soft Soil

摘要:

为了解软土自由场地地震反应特性，开展饱和软土自由场地地震反应特性大型振动台模型试验。分别从模型体系自振特性、震陷位移及不同土层深度测点的加速度、动孔压比等动力响应指标方面，较为深入和全面地分析饱和软土自由场地地震反应规律、破坏机理。同时还分析模型箱的"边界效应"以验证试验土箱的合理性、有效性和测试仪器性能，并由此进一步确定模型地基有效工作区域。研究表明：（1）地震动作用下，饱和软土自由场地特征频率降低，阻尼增大；（2）饱和软土自由场地对水平输入地震波具有短周期滤波、长周期放大效应，且强震作用下地基失效并表现为减隔震作用；（3）饱和软土自由场地动孔压比优势区域位于浅埋土层，并随着输入地震动强度的增大，该区域动孔压比优势逐渐减弱。该研究可为非自由软土场地试验研究提供必要的技术经验。

Abstract:

This work investigated the seismic response characteristics of a free field in soft soil through a large-scale shaking table test. The seismic response characteristics and failure mechanism of the soft-soil free field were studied from several aspects, i.e., the natural vibration characteristics and subsidence displacement of the model system and the acceleration and dynamic pore pressure ratio of measurement points at different soil depths. The boundary effect of the laminar shear model box was also analyzed to verify the rationality and effectiveness of the soil box system and to test instrument performance. The effective working area of the model foundation was then further determined. Study results showed the following:(1) The characteristic frequency of the saturated soft-soil free field decreased and the damping ratio increased under seismic load. (2) The saturated soft-soil free field exerted short-term filtering and long-term amplification effects on horizontal input seismic waves. Moreover, under strong seismic loads, the failure foundation absorbed and isolated shock. (3) The peak pore pressure ratio of the saturated soft-soil free field was located in a shallow buried soil layer. The advantage of dynamic pore pressure ratio in this area gradually weakened as the input ground motion intensity increased. This research can provide the necessary technical experience for experimental studies on non-free-field soft soil.