Although riprap is the most commonly employed countermeasure against scouring around bridge piers, few studies exist of riprap performance under live-bed conditions. In this study, failure mechanis...

Riprap protection at bridge piers

Scour of sediments around bridge foundations by the stream is the most significant contributing factor for bridge failures. The scour failures tend to occur without prior warning and have led to fatalities and economic loss every year. A significant amount of work has been conducted on bridge scour. Such efforts can be broadly classified into two major categories, namely science driven and engineering driven. The science-driven research focuses on understanding the scour mechanism and aims to explain the cause of scour due to different factors. Meanwhile, engineering-driven research focuses on the estimation, monitoring and countermeasures of bridge scour. This paper presents a comprehensive and up-to-date literature review of bridge scour research and practice. Firstly, a brief introduction is given which includes recent cases of failures caused by bridge scour. Then, both scientific and technical research on bridge scour is reviewed, which are categorized into four aspects: macroscopic and microscopic mechanism, scour depth prediction carried out by experimental and field data, direct and remote monitoring methods and active and passive countermeasures. Finally, a summary is provided covering both experimental and computational methods for scour research. Discussion is also provided on emerging ideas to investigate bridge scour from both science and engineering perspectives.

A review of bridge scour: mechanism, estimation, monitoring and countermeasures

This report documents research on local scour at bridge piers resulting in the development and recommendation of a practical selection criteria for bridge-pier scour countermeasures, guidelines and specifications for design and construction of those countermeasures, and guidelines for their inspection, maintenance, and performance evaluation. Because of their critical role in ensuring bridge integrity and potentially high cost of these countermeasures, it is important that the most appropriate countermeasures be selected, designed, and constructed. The contents of this report are, therefore, of immediate interest to highway professionals responsible for planning, administrating, evaluating, designing, constructing, inspecting and maintaining bridges and other structures founded in erosive areas. The report is also of interest to those charged with specifying materials testing procedures and acceptable results, setting budget goals, and making policy.

Countermeasures to Protect Bridge Piers from Scour

Reduction of local scour around bridge pier groups using collars

This report presents the findings of a study to develop design guidelines, material specifications and test methods, construction specifications, and construction, inspection, and quality control guidelines for riprap at streams and riverbanks, bridge piers and abutments, and bridge scour countermeasures. Recommendations are provided on a design equation or design approach for each application. Filter requirements, material and testing specifications, construction and installation guidelines, and inspection and quality control procedures are also recommended for each riprap application. To guide the practitioner in developing appropriate designs for riprap armoring systems for these applications, the findings and recommendations are combined to provide design guideline appendixes for (1) Design and Specification of Rock Riprap Installations and (2) Construction, Inspection, and Maintenance of Rock Riprap Installations. This report will be particularly useful to bridge, hydraulic, and highway engineers, as well as bridge maintenance and inspection personnel responsible for design, construction, inspection, and maintenance of bridges and other highway structures.

Riprap Design Criteria, Recommended Specifications, and Quality Control

Experiments conducted under live-bed conditions show that a riprap layer at a cylindrical bridge pier will fail in either one of the following two modes: Total disintegration or embedment. The former refers to the break-up of the entire riprap layer where the stones are washed away by the flow field generated at the pier. The latter relates to the embedment of the riprap layer where it is buried in the sediment bed. The study proposes a criterion to demarcate the limiting condition between the two types of failure. It also identifies that embedment failure is a more common failure mode of riprap layer under live-bed conditions. The causes of embedment failure are twofold: (1) bed feature destabilization; and (2) differential mobility. Bed level fluctuations caused by the propagating bed features resulted in bed feature destabilization, whereas differential mobility is due to the different response of the riprap stones and bed sediments to the flow field. Experimental results also show that the riprap layer can degrade to an equilibrium level for a given flow condition. Finally, the study proposes a semiempirical equation to compute the maximum depth of riprap degradation, which occurs at the upper end of dune regime.

Failure behavior of riprap layer at bridge piers under live-bed conditions

This paper presents a parametric study on riprap protection around a cylindrical bridge pier with uniform bed sediments. Riprap layers with different characteristic parameters: thickness, cover width, and placement level of the riprap layer; median grain size and density of the riprap stone; and undisturbed approach flow depth were tested under a sequence formation of ripples, dunes and transition flat bed. Observations show that a riprap layer will eventually degrade to a maximum level which is the same as the maximum pier scour depth when the riprap layer is not present. This study proposed a criterion to determine the maximum embedment level and the embedment velocity, i.e., the flow velocity at which the riprap layer has embedded to its maximum level. The experimental results show that variations of the characteristic parameters have no influence on the embedment failure at the upper end of the dune regime. The study also proposes a maximum embedment velocity, which defines a critical flow velocity at...

Parametric study of riprap failure around bridge piers

Failure Behavior of Riprap Layer Around Bridge Piers

River hydraulic modelling is a vital component to perform preferable analysis. Mostly river hydraulic modelling was performed flood analysis and water resources analysis. The hydraulic engineer or modeller needs a better technical understanding on the simulated the model. However, river hydraulic modelling frequently encountered model stability or uncertainty problem during computation. The error for model stability was will notice by the modeller. Hence, the modeller needs to solve the error for the purpose to simulate the model without uncertainty interruption. In this paper an attempt has been made to review the research work done on the stability occurred in river hydraulic modelling. This research review shows that hydraulic geometry and hydraulic parameter input are the main role of occurrence model stability. 

Uncertainty in River Hydraulic Modelling: A Review for Fundamental Understanding

Rapid river basin urbanization inevitably results in drastic increase of water demand which necessitates the development of new water supply schemes to meet the sectorial water resource requirements. Various proposed water resources schemes will need to be evaluated and assessed and the optimum scheme selected for implementation. To prepare for capital budgeting, river basin managers need a set of comprehensive tools for objective decision-making to plan for the water works based on projected water demand due to population growth and water resources regime changes attributed to climate change. A multi-criteria analysis (MCA) approach has been developed for water resources planning with consideration of global changes to plan suitable schemes at various future years, using a set of technical evaluation tools, which comprise (i) water availability, (ii) system reserve capacity, (iii) climate resilience (iv) undeveloped (remaining) yield capacity and (iv) residual flow with respect to environmental flow. The indicators are based on a water resources index (WRI), defined as the ratio of the actual water resource availability (WRA) to the average water resources capacity (WRC) for a specified duration. The novel approach has been applied to Klang River basin in Malaysia, an example of a highly urbanized basin which is heavily dependent on inter-basin water resources. Water demand projection shows that the existing planned water works are inadequate beyond the medium time-horizon between the next five to ten years. There is thus an urgent need to attain water resource self-sufficiency for long-term sustainability. Proposed schemes are evaluated considering climate change up to year 2100. Analysis shows that Klang River basin can benefit from a coastal reservoir designed to intercept the basin river discharge for water resource development to reduce its dependence on inter-basin transfer from the adjacent Selangor River and Langat River basins which are under accelerated development and urbanization to avoid further water competition. The study is an outcome of the program entitled “National Water Balance System (NAWABS)” implemented by the Department of Irrigation and Drainage, Malaysia for basin-level water resource planning and operation towards drought preparedness. 

Foo-Hoat Lim

Papers

Failure behavior of riprap layer at bridge piers under live-bed conditions

Parametric study of riprap failure around bridge piers

Failure Behavior of Riprap Layer Around Bridge Piers

Uncertainty in River Hydraulic Modelling: A Review for Fundamental Understanding

Multicirteria evaluation for long-term water resources aumentation planing with considerations of global change