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

近年来，由于土地空间的紧张，日本沿海地区得到了开发，建筑规模越来越大。地下水位较高地区的大型地下结构可能会受到较大的浮力作用。本文通过离心试验研究了地下结构的深度、尺寸、形状、柔韧性和加载速率对地面稳定性的影响。采用上界法和有限元法对结构进行了稳定性分析。得出以下结论：(1)砂土中构筑物的极限上拔能力随着构筑物覆盖深度与宽度之比的增大而迅速增大。用极限平衡法根据观察到的破坏机制计算出的极限承载力与实测值吻合较好。(2)隧道柔性对衬砌周向应力影响较大；相对柔性隧道可以在水平方向上增加隧道宽度，使隧道的周向应力分布相对均匀，而刚性隧道的周向应力集中在弹性线附近。

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.