中粗砂中吸力锚的负压沉贯模型试验研究

Model tests on penetration of suction anchors in medium-coarse sand

吸力锚是海洋工程中广泛采用的一种基础形式。其沉贯能力(即达到预定海床位置)是其承载力达到设计要求的重要保证。国内外针对吸力锚在细砂、粉土和黏土中的沉贯性进行了较多理论及模型试验研究,但对中粗砂研究相对较少。分别针对不同水位深度和不同抽吸速度条件,对吸力锚在中粗砂中的沉贯性进行了大量模型试验研究和分析,得到了负压与沉贯深度的关系。通过沉贯方案对比,得出了吸力锚负压沉贯的最佳试验条件。通过有机玻璃吸力锚对比沉贯试验,直观展示了沉贯过程中吸力锚中"水塞"和"土塞"的形成过程。吸力沉贯与压力贯入对比试验表明,负压导致的渗流显著降低了吸力锚的沉贯阻力,是中粗砂中得以沉贯的主要原因。基于试验成果,提出了模型试验条件下,吸力锚沉贯计算的理论公式。

Suction anchors are widely used in offshore engineering for fixing platforms, offshore wind turbines and mooring floating facilities. Penetration of suction anchors, i.e., driven into a desired position in the seabed by the suction, is a key factor for the design. It is necessary for the bearing capacity to meet the needs. Researchers have focused their attention on the installation in the fine sand in a medium or dense state, silt and clay. This study shows that it is feasible for the penetration of suction anchors in the natural medium-coarse sand. Model tests are carried out to investigate the behavior of the penetration of steel suction anchors in medium-coarse sand by varying water levels and pumping speeds. The relation between the suction and the penetration depth is obtained. By comparing different installation approaches, the optimized method to achieve the maximum penetration depth is put forward. The formation of water/soil plug is observed by using Perspex suction anchors, and reasons for preventing the penetration of suction anchors are analyzed. Compared with the jacking tests, the seepage induced by vacuum plays a vital role in assisting the suction anchors to achieve the penetration in the medium-coarse sand. Finally, an approach is developed to calculate the required suction under a desired penetration depth on the basis of the model tests.