深水海洋环境下砂土换填地基振冲加固应用研究

Vibroflotation method for foundation treatment of replaced sandy soil in deepwater marine environment

海洋环境特殊、场地条件较陆地更加复杂,水深超过20 m地基无料振冲加固尚无工程实践、技术标准、工艺参数借鉴与参考,现行有关振冲的规范与技术标准主要针对陆地地基,且基于早期、装备相对落后的工程经验认识。在科特迪瓦阿比让港口水深20~25 m条件下对原状地层进行基槽开挖、中粗砂换填,并采用100,180,230 kW的振冲器对换填砂层进行无填料振冲加固处理,分析常用振冲器在深水海洋环境下容易出现的问题,探讨深水海洋环境下换填砂土地基的单次加固深度、施工效率、加固效果、工艺参数等。结果表明:①海洋环境中振冲器容易出现脱焊或断裂、腐蚀而加速损坏、难以振冲至预定深度等问题,应慎重选择合适的振冲设备;②水深对振冲器加固深度影响十分显著,100,180,230 kW振冲器的单次加固深度分别为4~6 m,6~8 m,8~10 m,明显低于同等条件下陆地地基加固深度;③单个振冲孔的水平加固面积作为施工效率的评价标准,180 kW较100 kW振冲器的施工效率高56%,230kW较100 kW的施工效率高125%;④深20~25 m、振冲器功率100~230 kW、处理厚度10~19 m、水平间距2~3.5m、留振时间30s等阿比让港口的振冲基本工艺参数,可为今后"一带一路"港口工程、岛礁吹填等海洋工程地基加固处理提供参考。

The marine environment is special,and its geotechnical site conditions are more complex than those on land.There have been no engineering practices,technical standards and technological parameters for reference in the foundation treatment of vibration-impact method with a water depth of more than 20 m.The current codes and technical standards of vibration-impact method are mainly applicable to land foundations,based on the engineering experience of early stage and relatively backward equipments.The excavation of foundation trench and the replacement of medium-coarse sand are carried out on the undisturbed soil layer under water depths of 20~25 m in Abidjan Port,and the vibration-impact machines of 100,180 and 230 kW are used to treat the replaced sand layer.The issues of common vibrator problems in deepwater marine environment are analyzed,and the vibration-impact depth,construction efficiency,foundation treatment effect and technological parameters of vibration-impact method in deep-water marine environment are discussed.The results indicate that:(1)In the marine environment,the vibrator is easy to detach,or break,or corrode,and it is difficult to penetrate to a design depth,so the appropriate vibration-impact equipments should be carefully selected.(2)The depth of water has a significant influence on the foundation treatment depth of vibration-impact method.The foundation treatment depths of 100,180 and 230 kW-vibrator is 4~6,6~8 and 8~10 m,respectively,which are significantly lower than those of land foundation under the same conditions.(3)Taking the horizontal treatment area of foundation as the evaluation standard of construction efficiency,the construction efficiency of 180 kW-vibrator is 56%higher than that of 100 kW,and the construction efficiency of 230 kW-vibrator is 125%higher than that of 100 kW.(4)The parameters of vibration-impact method in Abidjan port,such as water depths of 20~25 m,vibrator powers of 100~230 kW,treatment thicknesses of 10~19 m,horizontal spacings of 2~3.5 m,vibration retention time of 30 s,can provide reference for the foundation treatment of marine geotechnical engineering in countries along"Belt and Road Initiative"in the future.