Significance of nonlinear soil-structure interaction (SSI) on the seismic performance of micropiles-retrofitted pile foundations

多年来，各种抗震改造技术和策略被开发和应用，以确保在抗震设计规范修订之前建造的现有桥梁的抗震性能。然而，在进行改造时，人们往往把重点放在桥墩上，而对基础的关注却较少。在如此关注基础的众多原因中，有一个原因可以归因于改造基础的相对鲜为人知的抗震性能。在2016年熊本地震中，即使桥墩进行了抗震加固，桥梁基础也出现了破坏，突出了基础抗震加固的必要性。在实际的地基改造中，微桩比传统桩具有更大的优势。然而，考虑非线性土-结构相互作用（SSI）影响的微桩加固基础在动力荷载作用下的性能仍是未知的。为此，考虑了静、动荷载作用下的微桩加固桩基础1g模型试验。结果被量化为运动相互作用因素和横向桩顶阻抗函数。考虑了基于相似律的1/20地基改造模型。土壤选用干岐阜砂。

Various seismic retrofitting techniques and strategies have been developed and employed over the years to ensure the seismic performance of existing bridges built prior to the revision of seismic design codes. For retrofitting, however, focus is often given to the bridge piers while lesser attention is paid to the foundations. Out of the many reasons for such attention to the foundations, one can be attributed to the relatively lesser-known seismic performance of the retrofitted foundations. Damage seen in 2016 Kumamoto earthquake revealed the failure of a bridge foundation even though the pier of the bridge was seismically retrofitted, highlighting the necessity of seismic retrofitting of foundations. In practice, for foundation retrofitting, micropiles are often preferred over the traditional piles for its several merits. The behavior of micropiles-retrofitted foundations considering the effects of nonlinear soil-structure interaction (SSI) under dynamic loading, however, is still largely unknown.To this end, 1g model testing of micropiles-retrofitted pile foundations embedded in soil is considered under a range of static and dynamic loads. Results are quantified in terms of kinematic interaction factors and lateral pile-head impedance functions. A 1/20 model of retrofitted foundation based on the law of similitude is considered. For soil, dry Gifu sand is selected.