Bridge piers within moving water are exposed to an additional failure mechanism known as scour. Upon the scour depth reaching the foundation of the pier, the structural integrity of the pier, and consequently the bridge, can be jeopardized. Bridge pier scour is the result of a three-dimensional flow separation consisting primarily of the horseshoe vortex, flow acceleration along the sides of the pier, and wake vortices. There are numerous factors that can affect bridge pier scour, of which many of them have been studied extensively. However, there are still some factors where the knowledge base is limited: one example is the presence of an ice cover around bridge piers. In order to reduce the risk of failure induced by scour, regardless of the cause, a preferred option is to use scour countermeasures. However, an ideal countermeasure does not exist. Therefore, the purpose of this research is to design and test an improved bridge pier scour countermeasure, while also better understanding the effects an ice cover has on scour. Achieving a new countermeasure design consisted of a hybrid approach that combined both numerical and experimental modelling. The numerical model was used in an iterative manner to expedite the design process, as well as to reduce experimental costs. Upon testing and improving the initial collar design numerically, physical models were constructed for the purpose of testing experimentally. Experimental tests were performed at a 1:30 scale in the presence of a sand bed. The same experimental setup was used to investigate bridge pier scour under an ice cover, except a rigid structure was constructed to replicate an ice cover. The artificial ice cover possessed either a smooth or a rough underside and was installed in such a way to replicate a floating or fixed (pressurized) ice cover. The purpose of the new countermeasure design was to improve on the flat plate collar by guiding the horseshoe vortex in a novel manner. By doing so, the quantity of erosive forces contacting the bed was greatly reduced. In order to reach a final design, a series of prototype designs were tested, and are outlined in this thesis, as they provide valuable insight into the scour problem. The final countermeasure design resembles a contoured collar but is made of riprap, where it was found to reduce the scour depth and volume by 81.0% and 92.3%, respectively, while using 18% less riprap than the conventional flat riprap countermeasure. Upon investigating scour in the presence of an ice cover, it was found that the quantity of scour increases as the ice cover becomes rougher and as the flow becomes more pressurized beneath. Specifically, the scour depth under the rough ice cover and the most pressurized condition increased by 412%. It was demonstrated that implementing any device which increases the width of the pier has inherent limitations for reducing scour. Instead, having a depression around the pier, especially made of riprap, such that it is flush with the bed and can help guide the horseshoe vortex, was found to greatly reduce scouring. Furthermore, it was observed that the presence of any ice cover on the surface of the water generates greater pier scour, therefore necessitating that ice cover always be taken into consideration when designing bridges in cold climates.

Sediment material around the base of a bridge pier is moved by the flow velocity and associated turbulence. This phenomenon is generally termed as local scour and can lead to undermining the structure and increase its possibility of failure. Numerous factors can affect bridge pier scour and they have been investigated for decades. Debris jams, one of these factors, could significantly contribute to bridge failure as some field examples and experimental investigations pointed out. Woody debris accumulation on the front of either single or multiple bridge piers can result in deeper pier scour and extra load exerted on the pier. Several studies have already investigated the influence of woody debris on pier scour in terms of static woody debris. In addition, HEC-18 (2012) also proposed a design code to estimate scour depth in the presence of woody debris jam. However, in these studies, the woody debris jam was considered to be static, whereas a woody debris jam accumulates piece by piece, growing to a debris jam with a shape most akin to a half-cone, and then may even eventually break up and be carried in pieces downstream. Therefore, this research investigated the evolution of the loading onto and scouring around a bridge pier in the presence of dynamic debris jams. In this study, the temporal evolution of the bridge pier scours was monitored during the development of dynamic debris jams. Experimental modeling was conducted to explore the influence of dynamic debris jam on bridge pier scour using a scale of 30 by employing both dowels and seedling trees. It was found that the dynamic debris jam of dowels could last 10-20 minutes and reach a critical size, then fail and subsequently reform. In addition, the first debris jam had an obvious influence on scour depth which correlated to the blockage generated by the debris jam; however, the influence of the subsequent debris jam depended on its size compared to the previously formed one. For the dynamic debris jam using seedling trees, the debris jam lasted for a longer time once it formed, and it could lead to twice the maximum scour depth compared to that generated in the absence of the debris jam, which is the same with dowels debris jam. In addition, the hydraulic head induced by the debris jam was correlated to the blockage of the debris jam and the flow Froude number irrespective of whether the dynamic debris jam was made of dowels or seedling trees. Additionally, blank control tests in the absence of a debris jam were used along with previous data gleaned from the literature to develop and test new multigene genetic programming (MGGP) models for the temporal evolution of scour. The MGGP model, using the non-dimensional variables from the empirical equations, can reach a better accuracy than the empirical equations, which indicates the ability of the model to optimize the empirical equations. The temporal evolution of load exerted onto the bridge pier with a dynamic debris jam was also measured. Experimental tests were performed to investigate the additional debris jam drag force exerted onto the bridge pier using both dowels and seedling trees in the presence of a fixed flume bed. Likewise, the dynamic debris jam of dowels lasted for about 10-20 mins, while those formed by the seedling trees, once formed, could last over 50 mins. The investigation demonstrated that the drag coefficient of the seedling trees jam was higher than that of the dowels jam. More importantly, a spike in the drag force was also observed irrespective of whether the jams were formed by dowels or seedling trees. Detailed investigation of the flow field around the debris jam and pier provided insight into the mechanics of debris jams. Three half-cone-shaped debris jams of the same dimensions were designed and built. The three jams were fabricated using: a) 20 cm long dowels, b) 30 cm long dowels, or c) a 3D printer. For each jam, four sections were measured using an Acoustic Doppler Velocimeter (ADV). The results indicated that the flow fields around the 20 cm length dowel jam and the 30 cm length dowel jam were similar. In addition, the section behind the pier and debris jam showed divided zones termed herein as the accelerated high-velocity zone, the high shear transition zone, and the wake dead zone. As for the drag coefficient, the 20 cm length dowels jam and 30 cm length dowels jam shared a very close magnitude of 1.7, but the drag coefficient of the 3D printer debris jam was only 0.88 which indicated the debris jam built by individual pieces behaved differently than the block jam.

Scour at bridge piers is considered as a significant safety hazard. Hence, scour countermeasure design plays a critical role to hinder the scour potential at bridges. The selection methodology for a scour countermeasure varies with respect to site conditions, economy, availability of material and river characteristics. The aim of this study is to review the literature on this topic to gather universally accepted design guidelines. A user-friendly computer program is developed for decision-making in various sequential steps of countermeasure design against scouring of bridge piers. Therefore, the program is eventually intended to select the feasible solution based on a grading system which deals with comparative evaluation of soil, hydraulic, construction and application aspects. The program enables an engineer to carry out a rapid countermeasure design through consideration of successive alternatives. A case study is performed to illustrate the use of this program.

The bridge scour depths in cohesive soil have been predicted using the scour equations developed for cohesionless soils due to scarce of studies about cohesive soil. The scour depths predicted by the conventional methods will result in significant errors. For the cost effective design of bridge scour in cohesive soil, the Scour Rate In COhesvie Soil (SRICOS) for the singular circular pier in deep water condition was released in 1999, and has been developed for complex pier and contraction scour. The present study is the part of SRICOS-EFA method to predict the history of contraction scour, and local scours, such as abutment scour and pier scour. The main objective is to develop the prediction methods for the maximum and the uniform contraction scour depth, the maximum pier scour depth and the maximum abutment using flume test results. The equations are basically composed with the difference between the local Froude number and the critical Froude number. Because the scour happens when the shear stress is bigger than the critical shear stress, which is the maximum shear stress the channel bed material can resist from the erosion, and continues until the shear stress becomes equal to the critical shear stress. All results obtained from flume tests for pier scour have been conducted in Texas A&M University from 1997 to 2002 are collected and reanalyzed in this study. Since the original pier scour equation did not include soil properties. The effect of water depth effect, pier spacing, pier shape and flow attack angle for the rectangular pier are studied and correction factors with respect to the circular pier in deep water condition were newly developed in present study. For the abutment scour, a series of flume tests in large scale was performed in the present study. Two types of channel - rectangular channel, and compound channel - were used. The effect of abutment length, shape and alignment of abutment were studied and the correction factors were developed. The patterns of velocity and of scour were compared, and it was found that the maximum local scour occurred where the maximum turbulence was measured. For the contraction scour, the results obtained from a series of flume tests performed in 2002 and a series of flume tests for the abutment scour in the present study are analyzed. The methodologies to predict the maximum contraction scour and the uniform contraction scour in the compound channel was developed. Although all prediction methods developed in the present study are for the cohesive soils, those methods may be applicable to the cohesionless soils because the critical shear stress is included in the methods. All prediction methods were verified by the comparison with the databases obtained from flume test results and field data.

Yes / Pier scour has been extensively studied in laboratory experiments. However, scour depth relationships based on data at the laboratory scale often yield unacceptable results when extended to field conditions. In this study, non-uniform gravel bed laboratory and field datasets with gravel of median size ranging from 2.7 to 14.25 mm were considered to predict the maximum equilibrium scour depth at cylindrical piers. Specifically, a total of 217 datasets were collected: 132 from literature sources and 85 in this study using new experiments at the laboratory scale, which constitute a novel contribution provided by this paper. From the analysis of data, it was observed that Melville and Coleman's equation performs well in the case of laboratory datasets, while it tends to overestimate field measurements. Guo's and Kim et al.'s relationships showed good agreements only for laboratory datasets with finer non-uniform sediments: deviations in predicting the maximum scour depth with non-uniform gravel beds were found to be significantly greater than those for non-uniform sand and fine gravel beds. Consequently, new K-factors for the Melville and Coleman's equation were proposed in this study for non-uniform gravel-bed streams using a curve-fitting method. The results revealed good agreements between observations and predictions, where this might be an attractive advancement in overcoming scale effects. Moreover, a sensitivity analysis was performed to identify the most sensitive K-factors.

Yes / Pier scour has been extensively studied in laboratory experiments. However, scour depth relationships based on data at the laboratory scale often yield unacceptable results when extended to field conditions. In this study, non-uniform gravel bed laboratory and field datasets with gravel of median size ranging from 2.7 to 14.25 mm were considered to predict the maximum equilibrium scour depth at cylindrical piers. Specifically, a total of 217 datasets were collected: 132 from literature sources and 85 in this study using new experiments at the laboratory scale, which constitute a novel contribution provided by this paper. From the analysis of data, it was observed that Melville and Coleman’s equation performs well in the case of laboratory datasets, while it tends to overestimate field measurements. Guo’s and Kim et al.’s relationships showed good agreements only for laboratory datasets with finer non-uniform sediments: deviations in predicting the maximum scour depth with non-uniform gravel beds were found to be significantly greater than those for non-uniform sand and fine gravel beds. Consequently, new K-factors for the Melville and Coleman’s equation were proposed in this study for non-uniform gravel-bed streams using a curve-fitting method. The results revealed good agreements between observations and predictions, where this might be an attractive advancement in overcoming scale effects. Moreover, a sensitivity analysis was performed to identify the most sensitive K-factors.