Complex Pier Research Articles

Subtraction Approach to Experimentally Assess the Contribution of the Complex Pier Components to the Local Scour Depth

AbstractIn the present study, a new physically sound approach to experimentally obtain the contribution of each complex pier component to the ensemble scour depth is presented and illustrated. The ...

Local scour prediction around piers with complex geometry

ABSTRACTA laboratory study of local scour at complex piers under steady clear-water conditions is presented. The term complex piers is used to define a bridge pier comprising of a column, pile cap, and pile group. Comprehensive data over the full range of possible pile cap elevations for complex piers with different geometries were obtained using five complex pier models, which were scaled down from existing bridges in Malaysia. The data are used to evaluate existing methodologies for characterizing the effective width of complex piers with varying pile cap location relative to the undisturbed streambed. The effect of pile cap location on scour depth is also addressed. To improve the predictions of local scour at complex piers, the new data and some previous data are used to propose a new method to predict local scour depth at complex piers.

Prediction of Equilibrium Local Scour Depth at Complex Bridge Piers

At present, bridges are frequently built with geometries that consist of a column founded on a pile cap and supported by an array of piles, referred to as common complex piers or most often (as also in this paper), briefly, as complex piers. This paper addresses prediction of local scour depth at those complex piers. An experimental campaign of 48 long-duration tests was performed with seven complex pier models under steady clear-water flow conditions to quantify the influence of the relative column width, Dc/Dpc (Dc = column width, Dpc = pile cap width), the relative pile cap thickness, T/h (T = pile cap thickness, h = approach flow depth), and the pile-group configuration on the equilibrium scour depth, dse. Several tests were carried out for the possible range of variations in the pile cap position relatively to the initial bed level. The values of dse were estimated by extrapolation of the experimental data series. The performance of three methods, i.e., Auckland, HEC-18, and Florida Department of Transportation (FDOT), to predict dse is analyzed and discussed. Based on the experimental results of the present study and on the conceptual approaches of Auckland and FDOT methods, an alternative formulation for a predictor of dse at (common) complex piers is suggested and validated.

Using field data to evaluate the complex bridge piers scour methods

Scour is a phenomenon that causes riverbed erosion. Many laboratory studies have been conducted to identify the complex geometry of the scour mechanism and to predict its depth, and various methods have been proposed. In this study, the performance of these methods in estimating scour depth was evaluated using field data. For this purpose, scour data on the Adinan Bridge, which was destroyed as a result of the scour phenomenon and consequently rebuilt, was collected. The bridge was built with complex piers. The flow and sediment characteristics for the bridge site were determined using field measurement. Then, the pier scour was calculated using the empirical formula and the calculated values were compared with the recorded data. The results showed the inefficiency of these methods in accurately estimating the scour depth. However, the role of the components of a composite pier has not been reflected properly in the determination of scour in these methods.

Characterization of the scour cavity evolution around a complex bridge pier

A study on the time development of local scour around a complex pier was developed using a small-scale model embedded in a sediment bed. A total of 15 laboratorial tests were performed at the Hydraulics Laboratory of the Faculty of Engineering of the University of Porto. The duration of each experiment was previously established to progressively characterize the scour cavity. After each experiment, the flume was gradually emptied to facilitate the application of close-range photogrammetry. The scour depth values resulting from the application of photogrammetry at the pile cap front agree well with the values obtained experimentally. The temporal development of the scour cavity is presented and discussed. Empirical formulas for the scour cavity time development and for the relation of scour depths to scour cavity volumes were obtained. The obtained three-dimensional models can also be used for calibration and validation of numerical models.

Effects of Relative Column Width and Pile-Cap Elevation on Local Scour Depth around Complex Piers

AbstractAn experimental campaign of 25 long-duration (13–47 days) laboratory tests was carried out with three complex pier models under steady clear-water flow conditions. Each model, characterized by a different relation between the column and the pile-cap widths, Dc/Dpc, was tested for a variety of pile-cap positions relatively to the initial bed, Hc. The experimental data were used to describe the temporal evolution of the scour depth as a function of Hc/h (h = approach flow depth). The common criterion to stop experimental tests on complex piers was analyzed, and a new criterion was introduced. The equilibrium scour depth, dse, was calculated by extrapolation of data series. The results are used to evaluate the effect of Dc/Dpc and Hc/h on dse when the pile cap is above the bed (Situation 1), partially buried in the bed (Situation 2), and completely buried in the bed (Situation 3). The analysis includes the definition of Hc at which the maximum dse occurs through an equation that takes into account th...

Local scour at piled bridge piers including an examination of the superposition method

An experimental investigation of clear water scour at complex piers is presented. Five complex piers, comprising different configurations of piles, pile cap, and column, were tested in a laboratory flume using uniform bed material. The piers were tested for a range of possible elevations relative to the streambed elevation. Experiments were undertaken using the complex piers and also using the individual components of each complex pier. A comparison of the results for the intact piers and for their components enabled an evaluation of the prediction methods involving superposition of scour depths at piles, pile cap, and pier column. The superposition method is found to give inadequate estimates of total scour depth in many cases.

Local scour around complex pier groups and combined piles at semi-integral bridge

Abstract This research presents an experimental study on the scouring mechanism at semi-integral bridge piers. Based on laboratory experiments, this study focuses on the relationship between scour depth in complex pier groups and combined piles bridge and various parameters including the variation of inflow velocity, distance, and time. 1 200 data were collected for flow velocity and scour. The flow pattern and scour were analyzed for different flow discharges and flow depths. The results showed that the scour development with respect to time was greater for higher flow depth and bigger flow discharge at semi-integral bridges. In addition, the equilibrium scour depth increased with the approach flow depth around piers at semi-integral bridges. Velocity distribution also affected the scour development. It decreased when approaching the bridge but increased from upstream to downstream of the flume.

Effects of Pile Cap Thickness on the Maximum Scour Depth at a Complex Pier

An experimental campaign of 21 long-duration tests on scouring at complex piers of different configurations was performed to investigate the effect of pile cap thickness on the temporal evolution of the maximum scour depth and the development of equilibrium conditions. Two test series were performed with two significantly different pile cap thicknesses over a wide range of pile cap elevations with respect to the expected scour hole and the approach flow depth. In addition, the accuracy of existing methods to calculate the maximum scour depth was evaluated and discussed. The results show that, in general, the thicker the pile cap, the deeper the corresponding scour hole. The increase in scour depth that is attributable to the pile cap thickness depends on the distance between the pile cap and the original bed level. The observed maximum scour depth was greater with the thicker pile cap (with respect to the thinner pile cap) when it was entirely immerged into the flow, partially buried, or totally buried at a small depth from the initial bed level. Depending on the distance between the pile cap and initial bed level, the pile cap thickness may also influence the temporal evolution of the maximum scour depth by increasing or reducing the scouring rate.

Design Procedure and Considerations for Piers in Expansive Soils

The design of pier foundations in expansive soils is an important and challenging aspect of geotechnical engineering. Established methods for pier analysis include rigid and elastic methods. These methods have certain limitations that restrict their applicability to evaluate certain complex aspects of pier heave, including variable soil profiles, complex wetting profiles, large length-to-diameter ratios, and complex pier configurations and materials. To address those limitations, a method of analysis was developed providing a versatile and robust tool to predict both pier heave and axial forces developed by expansive soils. This method utilizes a standard finite-element code to solve for pier heave and force in the pier for the given boundary conditions. This paper contains both a discussion of the general design procedure and the finite-element formulation. This design procedure, including the finite-element code, accurately determines pier heave and force in a pier compared with field-measured data. The design procedure and the finite-element code in particular, address the limitations of the established rigid and elastic pier analysis methods with the flexibility to evaluate complex design situations. A comparison with field-measured pier heave and tensile force in the pier demonstrates that the design procedure accurately models both the magnitude of pier heave and force in the pier. The results obtained using this design procedure have been compared with those obtained using the established pier analysis methods for simplified drilled pier examples. The comparison of the various methods of analysis demonstrates that the finite-element design procedure predicts pier heave values that are generally less than the existing elastic and rigid pier analysis methods. It is believed that the proposed design method is more realistic and provides a design tool with improved accuracy compared with existing methods.

A local scour prediction method for pile caps in complex piers

The outcomes of an experimental study on local scour at a pile cap are presented. Experiments were conducted with the approaching flow having an undisturbed flow depth and a threshold flow velocity. The main variables investigated were pile cap dimensions and location relative to the streambed. According to the rate of change in scour depth, the scour at a pile cap for different cap levels was divided into four cases. Equations for a correction factor for these four cases are derived. The correction factor Kc has the effect of reducing the scour depth from a corresponding full-depth pier of the same width as the pile cap. A new methodology is presented to estimate local scour depth at a pile cap as a component of a complex pier. The proposed method was evaluated with the results from this experimental study and historical measurements. The proposed method, which corresponds closely to the observations, can be used to predict local scour at a pile cap as a component of a complex pier in the superposition method. It is also applicable to the prediction of local scour due to a caisson being sunk onto a mobile bed in a current.

Experimental Investigation of Clear-Water Local Scour of Compound Piers

Local scour around complex piers under steady clear-water condition was studied experimentally for a variety of configuration, including different sizes and shapes of complex piers. A total of 70 experiments were carried out. Three sets of experiments were performed over the entire range of possible pile cap elevations for complex piers with different geometrical characteristics. The collected data are used to quantify the pile cap elevations that maximize or minimize the local scour depth. Some of the available methodologies to estimate the maximum local scour depth around such complex piers are evaluated. The predictions of the scour depths improved by using the revised methods of Hydraulic Engineering Circular Number 18 and Coleman.

Experimental Investigation of Clear‐Water Local Scour of Compound Piers

Local scour around complex piers under steady clear-water condition was studied experimentally for a variety of configuration, including different sizes and shapes of complex piers. A total of 70 experiments were carried out. Three sets of experiments were performed over the entire range of possible pile cap elevations for complex piers with different geometrical characteristics. The collected data are used to quantify the pile cap elevations that maximize or minimize the local scour depth. Some of the available methodologies to estimate the maximum local scour depth around such complex piers are evaluated. The predictions of the scour depths improved by using the revised methods of Hydraulic Engineering Circular Number 18 and Coleman.

Experimental Study of Three-Dimensional Flow Field around a Complex Bridge Pier

In this paper, three-dimensional turbulent flow field around a complex bridge pier placed on a rough fixed bed is experimentally investigated. The complex pier foundation consists of a column, a pile cap, and a 2×4 pile group. All of the elements are exposed to the approaching flow. An acoustic-Doppler velocimeter was used to measure instantaneously the three components of the velocities at different horizontal and vertical planes. Profiles and contours of time-averaged velocity components, turbulent intensity components, turbulent kinetic energy, and Reynolds stresses, as well as velocity vectors are presented and discussed at different vertical and horizontal planes. The approaching boundary layer at the upstream of the pile cap separated in two vertical directions and induced an upward flow toward the column and a contracted downward flow below the pile cap and toward the piles. The contracted upward flow on the pile cap interacts with downflow in the front of the column and deflects toward the side of...

3D Unsteady RANS Modeling of Complex Hydraulic Engineering Flows. II: Model Validation and Flow Physics

A chimera overset grid flow solver is developed for solving the unsteady Reynolds-averaged Navier-Stokes (RANS) equations in arbitrarily complex, multiconnected domains. The details of the numerical method were presented in Part I of this paper. In this work, the method is validated and applied to investigate the physics of flow past a real-life bridge foundation mounted on a fixed flat bed. It is shown that the numerical model can reproduce large-scale unsteady vortices that contain a significant portion of the total turbulence kinetic energy. These coherent motions cannot be captured in previous steady three-dimensional (3D) models. To validate the importance of the unsteady motions, experiments are conducted in the Georgia Institute of Technology scour flume facility. The measured mean velocity and turbulence kinetic energy profiles are compared with the numerical simulation results and are shown to be in good agreement with the numerical simulations. A series of numerical tests is carried out to examine the sensitivity of the solutions to grid refinement and investigate the effect of inflow and far-field boundary conditions. As further validation of the numerical results, the sensitivity of the turbulence kinetic energy profiles on either side of the complex pier bent to a slight asymmetry of the approach flow observed in the experiments is reproduced by the numerical model. In addition, the computed flat-bed flow characteristics are analyzed in comparison with the scour patterns observed in the laboratory to identify key flow features responsible for the initiation of scour. Regions of maximum shear velocity are shown to correspond to maximum scour depths in the shear zone to either side of the upstream pier, but numerical values of vertical velocity are found to be very important in explaining scour and deposition patterns immediately upstream and downstream of the pier bent.

Clearwater Local Scour at Complex Piers

A new methodology to predict local scour depth at a complex pier is presented herein that combines existing expressions for scouring respectively at uniform piers, caisson-founded piers, pile groups with debris rafts, and pile groups alone. The method recognises the relative scouring potentials of the components of complex piers and the transition of scouring processes occurring for varying pile-cap elevation. The validity of the method is confirmed herein using the present and also historical measurements of local scour at complex piers. The proposed methodology has the advantages of being conceptually consistent with observed scour behaviours, relatively simple to apply, applicable to wide ranges of flow and sediment conditions (through incorporation into a more general analysis framework), and applicable over the entire range of possible pile-cap elevations. For design purposes, the present method highlights respective pile-cap elevations that maximize (i.e., to be avoided over the pier life) and minimize local scour at complex piers. The present method reinforces that where the pile-cap elevation relative to the bed can vary with time at a bridge site, potential local-scour depths need to be assessed over the range of possible pile-cap elevations for the pier.

SRICOS-EFA Method for Complex Piers in Fine-Grained Soils

The SRICOS-EFA method was developed by Briaud, Chen, and their students starting in the early 1990s to predict the scour depth versus time curve for a cylindrical pier in deep water subjected to a multiflood hydrograph and founded in a layered soil. Here, the SRICOS-EFA method is extended on the basis of flume tests and numerical simulations to the case of multiple rectangular piers lined perpendicularly to the flow, in any water depth, with a certain flow attack angle. The results show that the scour depth in shallow water can be much smaller than in deep water but does develop faster than in deep water, that there is a magnifying effect on the scour depth for piers that are spaced less than 3 pier diameters apart, that the scour depth for rectangular piers is about 10% larger than the one for a cylindrical pier except in the case of a wide and thin pier obstructing the flow where the scour depth can be significantly larger than for the cylindrical pier, and that the effect of the flow attack angle can be satisfactorily handled by using the projected width of the pier perpendicularly to the flow. The SRICOS-EFA computer program which automates these and other scour depth calculations can be downloaded free of charge from a website: http://ceprofs.tamu.edu/briaud/sricos-efa.htm. The SRICOS-EFA method recommended in HEC-18 offers a significant number of refinements compared to the method recommended for coarse-grain soils in HEC-18. It is site specific because it uses site specific samples that are not limited to coarse-grain soils, it includes the time effect through the use of a hydrograph, and it can handle layered soil systems. The coarse-grain soil approach presented in HEC-18 is typically conservative and sometimes very conservative when used for fine-grain soils.

Bridge pier scour assessment for the Confederation Bridge

The Northumberland Strait Crossing Project has presented many engineering challenges, one of which has been the assessment of scour protection requirements for the 65 bridge piers. The direct application of standard scour design techniques was not possible for this project because of the combination of complex flow conditions (waves and currents), complex pier geometry (conical pier bases, with some piers located in dredged pits), and complex seabed conditions (highly weathered and fractured bedrock). A multi-faceted coastal engineering investigation was undertaken by Baird & Associates to assess the scour protection requirements. Key activities included geotechnical investigations to define the seabed characteristics, numerical modelling to define the wave, current, and water level conditions at the crossing site, physical modelling of wave-current interaction with the bridge piers, and the development of a new methodology to estimate the erosion potential of the seabed around the bridge piers under extreme wave and current conditions. This technical note provides a brief overview of the investigations completed and a description of the new scour design methodology.

The History and Architecture of the Church of St. Fortunatus at Charlieu in Burgundy

At the beginning of the eleventh century there existed throughout much of western Europe a type of ecclesiastical architecture which Puig y Cadafalch has named the First Romanesque style.2 Its representative monuments varied in different regions, but certain distinguishing characteristics were common to most of them. Conspicuous among these were the small size and simple plan of the churches, the plain round or square supports between the nave and the aisles (though cruciform and even more complex piers elaborated by additional pilasters were not infrequent), the almost complete lack of sculpture, and the use of arched corbel tables and pilaster strips for exterior decoration. In addition, vaulted churches were to be found in certain regions notably Catalonia and Burgundy.