Assessment of SSI effects on stiffness of single and grouped helical piles in dry sand from large shake table tests
Assessment of SSI effects on stiffness of single and grouped helical piles in dry sand from large shake table tests
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DOI：
10.1007/s10518-021-01241-7
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发表时间：
2021-10
影响因子：
4.6
通讯作者：
A. Fayez;M. E. El Naggar;A. Cerato;A. Elgamal
中科院分区：
文献类型：
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作者：
A. Fayez;M. E. El Naggar;A. Cerato;A. Elgamal
进行了全尺寸振动台试验，以评估单根和成组螺旋桩的抗震性能。将具有不同属性（包括长度、半径和螺旋数量）的八根圆形和一根方形螺旋桩以及一根打入的圆形桩安装在干燥沙中，封闭在位于振动台上的层状土剪切箱中。根据不同振动事件期间收集的数据，评估了沙床的动态特性及其固有频率以及单个和成组螺旋桩-土系统的固有频率。还研究了不同桩构型以及连续振动对沙床和桩土系统固有频率的影响。研究发现，随着螺旋数量的增加，土体的扰动增加，从而导致桩土刚度和固有频率降低。由于桩土刚度下降以及靠近地表的桩身周围形成间隙，连续晃动导致单桩和群桩的固有频率降低。桩的自由长度显着降低了单根和成组螺旋桩的刚度，间隙开口进一步增加了自由长度，从而进一步降低了刚度和固有频率。在螺旋桩基础的抗震设计中必须考虑这些影响。此外，单桩和群螺旋桩的地震响应受共振条件影响较大，导致土体发生较大变形，桩-土体系刚度显着降低。还证明，DYNA6 软件可以通过考虑土壤刚度的退化和间隙张开来正确预测单桩和群桩的行为。
Full-scale shake table testing was conducted to evaluate the seismic performance of single and grouped helical piles. Eight circular and one square helical piles with different properties including length, radius and number of helices, as well as one driven circular pile were installed in dry sand enclosed in a laminar soil shear box that was situated on the shaking table. Dynamic properties of sand bed and its natural frequencies as well as natural frequencies of single and grouped helical pile-soil systems were evaluated from the collected data during different shaking events. The effects of different pile configurations as well as successive shakings on the natural frequencies of the sand bed and pile-soil systems were also investigated. It was found that the soil’s disturbance increased as number of helices increased, which resulted in reduced pile-soil stiffness and natural frequency. Natural frequencies of single piles and pile groups decreased due to successive shakings owing to the degradation in the pile-soil stiffness and gap forming around pile shafts near the ground surface. The pile’s free length significantly reduced the stiffness of single and grouped helical piles and gap opening further increased the free length and hence resulted in additional reduction in stiffness and natural frequencies. These effects must be considered in seismic design of helical pile foundations. Furthermore, the seismic responses of single and grouped helical piles are greatly affected by the resonance condition, which causes large soil deformations and significant reduction in the stiffness of the pile-soil system. It was also demonstrated that the software DYNA6 could predict the single and grouped piles behaviour correctly by accounting for degradation of the soil’s stiffness and gap opening.