南海珊瑚砂地基承载力模型试验研究

Model test on bearing capacity of coral sand foundation in the South China Sea

珊瑚砂是一种工程性状特殊的土,研究珊瑚砂的承载性能对南海岛礁建设具有重要意义。通过自制平板载荷室内模型装置量化研究珊瑚砂密实度、级配及载荷板的形状、尺寸对珊瑚砂地基承载力影响,并对比了珊瑚砂与石英砂承载力的差异性。试验表明:比对相同密实度的石英砂,珊瑚砂颗粒形态扁平的特征突出、棱角分明,致使内摩擦角增大,也相应引起承载力提升。同荷载下沉降量比前者小得多,且基础对承载力的尺寸效应也明显大于石英砂。而珊瑚砂地基土的应力水平依存系数与相对密实度呈线性相关,内摩擦角受级配影响显著,建立了地基承载力系数Nγ与内摩擦角φ之间的关系式。珊瑚砂地基的承载力随载荷板尺寸的增大而增大,方形基础下珊瑚砂地基的承载能力明显高于同面积的圆形基础,且尺寸效应发挥得更明显,说明基础型式在实际工程中有提升承载力的实用意义。在梅耶霍夫公式的基础上提出了适用于珊瑚砂的地基承载力修正公式,提高了珊瑚砂承载力计算结果的准确性。

Coral sand is a type of soil with special engineering properties.It is of great significance to study the bearing capacity of coral sand for construction of islands and reefs in the South China Sea.The influence of density and gradation of coral sand,shape and size of load plate on the bearing capacity of coral sand foundation were quantitatively studied by self-made indoor model device of plate load,and bearing capacities of coral sand and quartz sand were compared.Test results show that,compared with quartz sand with the same density,coral sand has prominent flat features and sharp edges and corners,which leads to an increase of internal friction angle and further leads to an increase of its bearing capacity.Settlement under the same load is much smaller than that of the former,and size effect of foundation on bearing capacity is obviously greater than that of quartz sand.However,dependence coefficient of stress level of coral sand foundation soil is linearly related to its relative density,and internal friction angle is significantly affected by gradation.Relationship between bearing capacity coefficient of foundation Nγand internal friction angleφis established.At the same time,the bearing capacity of coral sand foundation increases with the increase of load plate size,and the bearing capacity of coral sand foundation under square foundation is obviously higher than that of circular foundation with the same area,and size effect is more obvious,which shows that the foundation type has practical significance on improving the bearing capacity in practical engineering.Based on the Meyerhof formula,a modified formula of foundation bearing capacity for coral sand is also proposed,which improves the accuracy of calculation results of bearing capacity of coral sand.