单向流作用下黏土中单桩基础冲刷试验研究

Experimental study on scouring of monopile foundation in clay under unidirectional flow effect

我国东南海域广泛分布黏土海床,针对单向流作用下黏土海床中单桩基础的局部冲刷问题,开展了5组不同水深和流速的室内水槽试验,并通过在模型桩内布设摄像头,实时监测捕捉桩周冲刷深度随时间的变化特征,分析黏土中单桩局部冲刷发展规律。结果表明:黏土冲刷的稳定时间与砂土冲刷相类似,冲刷坑的形状发展也较为相似,但是黏土海床冲刷坑的底部边界相对粗糙,这主要是由于黏土黏聚力所致;随着桩前入射流速的逐渐增加,桩周最大冲刷点的位置呈现出从桩侧向桩后发展的趋势;当水深和入射流速较大时,水流除了在桩周形成大范围的冲刷浅坑之外,还会在桩后1倍桩径(1D)处形成直径大约为1D的冲刷深坑;冲刷深坑的边界会延伸到单桩桩周,致使部分埋置桩身暴露,这很可能导致桩基承载力的降低。

Aiming at the problem of the local scouring of the monopile foundation in clay seabed under the effect of unidirectional flow,five sets of indoor flume experiments with different water depths and flow rates are carried out,and then the changing characteristics of the scouring depth around monopile depending on time is captured with the relevant real time monitoring through the camera installed inside the model pile body,from which the law of the local scouring development of the monopile in clay is analyzed.The result shows that the stabilizing time of clay scouring is similar to that of the sandy soil,while both the developments of the scouring pit shapes are more similar as well.However,the bottom boundary of the scouring pit in clay seabed is relatively rough,which is mainly caused by the cohesive force of clay.Following with the gradual increase of the incident flow velocity before the monopile,the location of the maximum scouring point around the pile exhibits a trend of the development from the pile side to the pile back.When both the water depth and the incident flow velocity are larger,the water flow is to form a deep scouring pit with the diameter of about 1D at the location of 1D to the pile back in addition to forming a wide range of scouring shallow pits around the pile.The boundary of deep scouring pit is to extend to the circumference of the monopile and then makes a part of the pile body be exposed,which can possibly lead to the decrease of the bearing capacity of the pile foundation.