A fundamental Study on stability of under ground large structures subjecting buoyant forces

近年来，由于土地空间的短缺，日本沿海地区得到了开发，建筑物的规模越来越大。地下水位高的地区的大型地下建筑物可能会受到很大的浮力。本文通过一系列的离心机试验，研究了地下结构的深度、大小、形状、柔度和加载速率对地基稳定性的影响。并用上限法和有限元方法进行了稳定性分析。得出了以下结论：(1)砂土中建筑物的极限抗拔能力随着覆盖层深度与宽度之比的增大而迅速增大。极限平衡法计算的极限承载力与实测极限承载力吻合较好。(2)隧道的柔性对隧道衬砌的周向应力有较大影响，相对柔性的隧道可以在水平方向上增加隧道宽度，从而得到相对均匀的周向应力分布，而刚性隧道的周向应力主要集中在弹簧附近。

Because of shortage of land space, coastal areas in Japan have been developed and scale of structures become larger and larger in recent years. Large under ground structures in areas of high ground water table might be subjected to large buoyant forces. In this study a series of centrifuge tests were carried out to investigate the influences of depth, size, shape, and flexibility of under ground structures and loading rate on the stability of ground. Stability analyzes are also carried out by using the upper bound method and finite element method. Following conclusions were found ;(1) The ultimate uplift capacity of structures in sand increases rapidly with increasing in a ratio of depth of cover to width of structures. Calculated ultimate capacity from limit equilibrium method using observed failure mechanism agree well with that measured.(2) A flexibility of tunnel influences considerably on circumferential stress of tunnel lining ; relatively flexible tunnel could increase its width horizontally, which results in relatively uniform circumferential stress distribution while circumferential stress concentrates on around springline of rigid tunnel.