A Study on the Deformation Characteristics of Foundation Ground reinforced with Micropiles.

本研究的目的是阐明砂地基上微桩基础承载力的机理。进行了一系列模型加载试验，对微桩加固基础进行竖向和倾斜荷载试验。对微桩基础的性能进行了观察和比较。重点研究了砂土相对密度、微桩长度和刚度、微桩数量和微桩倾角对地基承载力的影响。从试验结果中得出的关于地基与群微桩相互作用的结论总结如下：-认识到群微桩对微桩加固地基提高承载力的显著作用。这种效果在密集、膨胀的地面上更加突出。—由于基础与群微桩相互作用，使基础下地基材料受到约束，围压和抗剪强度升高。-为了调动相互作用的围合效应，地基材料的剪胀性、足够的微桩数量和微桩的抗弯刚度是必不可少的。在竖向荷载作用下，群微桩对承载力的提高在一定的基础沉降下出现。在倾斜荷载情况下，由于缺乏基础基础压力，通常情况下无法识别承载力的提高。——发现初始基压是稳定提高承载力必不可少的条件。因此，在微桩上施加预张力和相应提高基底压力是微桩抗震基础施工的有效措施。

The aim of this study is to clarify the mechanism of bearing capacity of Micropile Foundation on sand ground. A series of model loading tests were conducted, where the footing reinforced with a group of micropiles were subjected to vertical and inclined loads. The behavior of the Micropile Foundation was observed and comparatively examined. The effects of the relative density of sand ground, the length and stiffness of micropile, the number and inclination of micropiles on the bearing capacity were focused. The conclusion concerned with the interaction between footing and a group micropiles derived from the test results is summarized as follows ;- The significant effect of group micropile was recognized on the improvement of bearing capacity by the reinforcement of foundation ground with micropiles. The effect was emphasized in dense, dilatant ground.- Due to the interaction between footing and group micropiles, the ground material beneath the footing is confined, and the confining pressure and shear strength raised.- To mobilize the confining effect of the interaction, dilatancy of ground material, sufficient number of micropiles and bending stiffness of micropiles are dispensable.- In the case of vertical load, the improvement of bearing capacity by group micropiles appeared under the certain amount settlement of footing. In the case of inclined load, the improvement of bearing capacity was not recognized under the ordinary condition due to the lack of base pressure of footing.- It was found that initial base pressure is indispensable for the stable improvement of bearing capacity. Then the application of pre-tension on the micropiles and a complimentary rise in base pressure is effective measure for the construction of earthquake resistant micropile foundation.