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

近年来，由于陆地空间的不足，日本沿海地区得到了开发，建筑物的规模越来越大。在地下水位高的地区，大型地下结构可能会受到很大的浮力。本文通过一系列的离心试验，研究了地下结构的深度、尺寸、形状、柔度以及加载速率对地基稳定性的影响。采用上限法和有限元法对该结构进行了稳定性分析。研究结果表明：（1）砂土中结构物的极限抗拔承载力随着结构物深宽比的增大而迅速增大;采用极限平衡法计算的极限承载力与实测结果吻合较好。(2)隧道的柔性对隧道衬砌的环向应力影响较大，相对柔性的隧道可以增加其横向宽度，从而使环向应力分布相对均匀，而刚性隧道的环向应力集中在弹接线附近。

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.