水中巨型沉井冲刷试验与数值计算对比分析

Comparative Analysis of Scouring Test and Numerical Calculation for Giant Open Caisson in Water

针对模型试验和数值计算在研究桥墩冲刷过程中存在的不足,尤其是淤泥质粉质黏土冲刷过程中存在的问题,结合常泰长江大桥5号墩水中沉井实际工程地质条件,开展地质不分层、分层工况下物理模型试验与数值计算的对比分析。研究结果表明:物理模型试验和数值计算的最大冲刷深度均随流速的增大而增大,且在同一原型流速下,物理模型试验的最大冲刷深度大于数值计算的最大冲刷深度;原型流速1.5m/s作用下,基本可将表层粉砂层冲掉,粉质黏土层基本无冲刷;原型流速2.5m/s作用下,最大冲刷深度未到粉质黏土层底标高,粉质黏土层阻冲刷效果明显;地质不分层条件下,物理模型试验和数值计算的冲刷形态相似;地质分层较大流速作用下,物理模型试验中沉井两侧未形成明显淤积,而数值计算中沉井中部和尾部两侧淤积明显;数值计算的冲刷结果更加贴合实际,而物理模型试验的冲刷结果相对保守。

Aimed at the shortcomings of model test and numerical calculation in the study of pier scouring process,especially for the scouring of the silty clay,combined with the actual engineering geological conditions of the underwater open caisson of No.5 pier of Changtai Yangtze River Bridge,this paper compares and analyzes the physical model test and numerical simulation with non⁃layered and layered conditions.It is found that the maximum scouring depth of the physical model test and numerical simulation increases with the increase of the flow velocity,and the maximum scouring depth of the physical model test is greater than that of the numerical calculation for the same prototype flow velocity.The surface silt layer can basically be washed away under the flow velocity of 1.5m/s,while the silty clay layer keeps as it is.The maximum scouring depth does not reach the bottom of the silty clay layer under the flow velocity of 2.5m/s,and the silty clay layer has obvious anti⁃scouring effect.The scouring patterns of physical model tests and numerical calculations are similar under non⁃layered condition.There is no obvious siltation on both sides of the open caisson in the physical model test under the higher flow velocity,while the siltation on both sides of the middle and tail of the open caisson is obvious in the numerical simulation.The scouring results of numerical calculations are more in line with reality,while the results of physical model tests are relatively conservative.