海洋地质与第四纪地质

永暑礁表层为松散的生物砂砾堆积,表层以下为礁灰岩,夹有2个沉积间断面。礁体呈岩盆结构,从外向内胶结程度依次降低。在综合研究了永暑礁自然环境特征、地层岩性以及岩体结构特征的基础上,认为永暑礁整体稳定性良好,不会发生整体倾覆的现象,浅层土体也不会发生剪切、滑移等工程地质问题。并利用非线性弹性本构模型,对永暑礁礁体地基与边坡在不同应力作用下发生变形与破坏的过程及机理进行了探讨,研究结果认为,在外部应力作用下,珊瑚礁内的应力状态将发生变化,局部出现应力集中,边坡出现拉应力。200kPa的荷载使礁体边坡产生的水平位移小于1cm,岩体边坡仍是稳定的,但最大垂直位移达到1 8cm,有可能出现珊瑚砂的整体剪切破坏。

Yongshu Reef is an opentyped atoll, its reef flat may be divided into three geomorphic units: outer reef flat, middle reef flat and inner reef flat.The seaward slope is steep in the upper section and gentle in the lower section, and has six underwater terraces. The surface of the reef is made up of loose organic sand underlain by reef limestone with two sedimentation hiatus in between. The rockmass is in a basin structure and its cementation weakens from the outer flat to the inner. On the basis of analyzing the natural environment, strata and rockmass structure of Yongshu Reef, the authors studied its whole stability and believed that the reef was stable and overturning and shearing would not happen. We also discussed the process and mechanism of deformation as well as failure of foundation and slope under different stress situations using nonlinear elasticity constitutive model. The results show that the inner stress condition will be changed and stretching stress appears on the slope. The horizontal displacement is smaller than 1 cm and the slope is still stable under 200 kPa. But the vertical displacement of the foundation can reach 18 cm and shear failure of coral sands may happen.