The modified suction caisson(MSC) is a novel type of foundation for ocean engineering, consisting of a short external closed-top cylinder-shaped structure surrounding the upper part of the regular suction caisson(RSC). The MSC can provide larger lateral bearing capacity and limit the deflection compared with the RSC. Therefore, the MSC can be much more appropriate to use as an offshore wind turbine foundation. Model tests on the MSC in saturated sand subjected to monotonic lateral loading were carried out to investigate the effects of external structure sizes on the sand surface deformation and the earth pressure distribution along the embedded depth. Test results show that the deformation range of the sand surface increases with the increasing width and length of the external structure. The magnitude of sand upheaval around the MSC is smaller than that of the RSC and the sand upheaval value around the MSC in the loading direction decreases with the increasing external structure dimensions. The net earth pressure in the loading direction acting on the internal compartment of the MSC is smaller than that of the RSC at the same embedded depth. The maximum net earth pressure acting on the external structure outer wall in the loading direction is larger than that of the internal compartment, indicating that a considerable amount of the lateral load and moment is resisted by the external skirt structure.
相对密实度是影响砂土力学性质的重要指标,密实的砂土呈现强度软化,松散的砂土却呈现强度硬化,而测定最大、最小孔隙比是计算相对密实度的前提。砂土的最小及最大孔隙比是通过直接测定的相应最大、最小干密度换算得到的,但目前常忽略了试验方法对其试验结果的影响,也忽略了黏粒含量对砂样密实度的影响。现取细、中、粗砂3种砂样,进行了干密度测试试验并测定了不同黏粒及黏粒掺量下砂样的最大、最小孔隙比。研究结果表明：采用量筒慢转法测量砂土最小干密度较为合理;采用振动锤击法测定砂土最大干密度时,建议细砂采用容积为250 m L击实筒,中、粗砂采用1000 m L击实筒;掺入粉粒、黏粒后砂样的最小孔隙比均随黏粒掺量（≤30%）增加而减小,且两者之间存在一定的线性关系;砂样最大孔隙比随粉粒、黏粒掺量增加逐渐减小,而随高岭土黏粒掺量增加呈缓慢增大趋势。
