群桩冲刷及抛石级配与厚度对防护效果的影响

水下群桩不可避免地发生局部冲刷而使桩基埋深减小,影响上部结构的安全,因此,群桩冲刷及其防护措施十分值得研究.通过实验室水槽试验和结果分析,研究了井字形排列群桩的间距与冲刷深度变化的关系,进而研究抛石颗粒的级配及抛石层厚度对冲刷防护效果的影响.研究发现,桩间净距的增大可使群桩局部冲刷深度减小,与桩间零净距相比,当达到临界...

Scour at pile groups and effects of riprap gradation and thickness on the scour reduction

Local scouring inevitably follows at underwater pile groups, which reduces the buried depth of the pile foundation and affects the safety of the upper structure. Therefore, the preventing scour measures for pile groups are worth studying. This work focused on the variation of scour at pile groups in the square array with spacing of piles, as well as the impact of particles grading and thickness of riprap layer on the effect of erosion reduction. Laboratory flume experiments were conducted and the observation data were analyzed. The study found that increasing the spacing between piles the local scour depth at pile groups can be reduced in a limited range. A maximum spacing of which is related with pile Froude number appears when the equilibrium scour depth can be reduced by 50%~60% compared with zero spacing of four piles. During the first 30% of the scouring process,the scour rate is about 30%~50% of less than that at a single pile. The maximum equilibrium scour depth is located in front of the front row of piles. Riprap composed of non-uniform particles with smaller riprap thicknesses can achieve better prevention efficiency than that of uniform ripraps. An optimal riprap gradation and riprap thickness are impacted by multi-factors, such as hydrodynamic force, pile diameter, bed sand, and so on, which is worth studying further to meet the demands of design countermeasure of scour reduction.