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

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.