Riverbed deformation around multiple pile bridge piers under ice-covered conditions - experimental study in a large-scale flume and numerical simulation

在加拿大，一些地区的冰盖可以持续长达六个月。覆冰条件下，最大流速位置比明流条件下更靠近河床。因此，有覆冰桥墩周围的河床冲刷深度大于无覆冰桥墩。过度的冲刷会对桥墩基础造成损害，例如1966年公元前史密瑟斯的16号高速公路大桥坍塌和2018年布鲁斯港的大桥坍塌。拟议的研究将有助于我们更好地了解冰盖下不同尺寸、形状和布置的多个桥墩周围的局部冲刷过程。这项研究将为土木工程师提供可靠的结果，可用于修改考虑冰盖影响的桥梁设计指南。 这项研究将解决一些 科学文献中的重要空白，包括：(A)评估多个码头周围的局部冲刷过程 在冰盖下，(B)调查 多墩的尺寸、形状和布置对局部冲刷的影响 冰盖下的过程，(C) 建立描述冲刷过程与水流关系的方程 强度、颗粒大小、覆盖条件、多个桥墩的布置以及 冰盖下压缩的马蹄涡，以及(D)开发一个模拟局部冲刷的数值模型 在冰盖下的多个码头周围作业。 广泛性 试验将在80米长的大型水槽中进行， 宽2米，深1.3米。五种不同的非均匀沙子将是 使用。将使用聚苯乙烯泡沫塑料作为模拟冰盖(光滑、粗糙和 非常粗糙)。对明流和覆冰条件下的实验数据的分析将 关注无量纲变量，如剪切雷诺数、屏蔽 参数与桥墩 尺寸。将建立公式来确定冰盖下的冲刷深度。 模拟冲刷过程将包括模拟强耦合系统，包括流场、泥沙输运和 床层形态。数值模式将包括 三个模块：一个用于流场模拟的流体动力学模块 在多个桥墩周围，有一个泥沙模型用于悬移 泥沙输运，以及一个河床变化模块，以考虑到 床面地形。 局部冲刷的数值研究 本文还将围绕多个桥墩展开研究。一 多桥绕流数值模拟的重点是什么？ 桥墩是为了解决基础设施周围的涡流系统。要解决这个问题 涡旋系统，非定常RAN(雷诺平均NavierStokes方程)或大涡模拟将被用于 解决马蹄形涡旋。标准k-epsilon湍流模型将是 首次用于多桥墩绕流的数值模拟 在冰盖下。基于RNG的k-epsilon湍流模型也将用于 模拟。

In Canada, ice cover can last up to six months in some regions. Under ice covered conditions, the location of maximum flow velocity is closer to the riverbed than during open flow conditions. Thus, riverbed scour depth around bridge piers under ice cover is greater than in the absence of ice cover. Excessive scour can cause damage to bridge pier foundations, such as occurred with the collapse of the Highway 16 bridge in Smithers, BC in 1966 and the bridge collapse in Port Bruce, ON in 2018. The proposed research will help us better understand local scour processes around multiple piers with different dimensions, shapes and arrangements under ice cover. This study will provide civil engineers with reliable results that can be used to modify bridge design guidelines that take the impact of ice cover into consideration. This research will address some important gaps in the scientific literature, including, (a) assessing local scour processes around multiple piers under ice cover, (b) investigating the impacts of the dimension/shape/arrangement of multiple piers on local scour processes under ice cover, (c) establishing equations describing the dependence of scour processes on flow intensity, particle size, cover conditions, arrangement of multiple piers, and compressed horse-shoe vortex under ice cover, and (d) developing a numerical model for simulating local scour processes around multiple piers under ice cover. Extensive experiments will be carried out in a large scale flume which is 80-meters long, 2-meters wide and 1.3-meters deep. Five different non-uniform sands will be used. Styrofoam sheets will be used as simulated ice cover (smooth, rough and very rough). Analyses of the experimental data under both open-flow and ice-covered conditions will focus on non-dimensional variables, such as shear Reynolds number, Shields parameter and bridge pier dimensions. Equations will be established to determine the scour depth under ice cover. Modeling the scour process will include modeling a strongly coupled system involving flow field, sediment transport and bed morphology. The numerical model will consist of three modules: a hydrodynamic module for the simulation of the flow field around multiple piers, a sediment module for the modeling of suspended sediment transport, and a bed variation module to account for the change in the bed topography. Numerical studies of the local scour around multiple bridge piers will also be undertaken in the present research. One of the priorities for the simulation of flow fields around multiple bridge piers is to solve the vortex systems around the infrastructure. To solve the vortex systems, either unsteady RANS (Reynolds-averaged NavierStokes equations) or Large Eddy Simulation will be used to resolve the horseshoe vortex. The standard k-epsilon turbulence model will be used first in the simulation for the flow field around multiple bridge piers under ice cover. The RNG-based k-epsilon turbulence model will also be used in the simulation.