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

多年来，为了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，已经开发并采用了各种抗震加固技术和策略。然而，对于改造，重点往往是给予桥墩，而较少注意的基础。出于对基础的关注的许多原因，其中之一可以归因于改造基础的相对鲜为人知的抗震性能。2016年熊本地震中的损坏显示，即使对桥梁的桥墩进行了抗震改造，桥梁基础也发生了故障，这突出了基础抗震改造的必要性。在工程实践中，微型桩由于其诸多优点，常被用于地基加固。然而，考虑非线性土-结构相互作用（SSI）影响的微型桩加固基础在动力荷载作用下的行为还很不清楚，为此，考虑了埋置在土壤中的微型桩加固基础在一定范围的静、动荷载下的1g模型试验。结果量化的运动相互作用因素和横向桩头阻抗函数。根据相似原理，考虑了1/20地基加固模型。对于土壤，选择干燥的岐阜砂。

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.