Bryant Andrew Robbins

• BS MS PhD
• Deputy Director at U.S. Army Corps of Engineers Risk Management Center

Backward erosion piping is a form of internal erosion that endangers the structural stability of levees and dams. Understanding the factors that influence this form of erosion can result in improved risk assessment and more appropriate modifications to new and existing structures. Historically, it has been assumed that the presence of silt size par...

Floodwalls are commonly used as part of flood risk reduction systems when constraints on right of way restrict the construction of embankments. For extreme events, floodwalls will overtop. The overtopping flow can cause scour behind the floodwall that may compromise the structural integrity of the system. To assess risks associated with floodwall o...

The state of the art in embankment dam design has changed substantially over the past century. In many instances, advancements to the state of the art have led to the realization that existing embankment dams may not be as safe as intended. This paper documents the historical evolution of embankment dam design by identifying key discoveries and eve...

The critical secant gradient function (CSGF) is a spatial function that defines the hydraulic conditions causing the progression of backward erosion piping, a significant internal erosion failure mode for dams and levees. While recent studies have defined the CSGF analytically and have also demonstrated how to measure it in the laboratory, uncertai...

Backward erosion piping (BEP), a form of erosion that occurs through a sandy foundation material beneath levees and dams, is a key risk driver for flood control systems worldwide. Current methods for predicting BEP progression predict that risks increase with decreasing particle size; however, these methods are based on experimental programs using...

Backward erosion piping (BEP) is a type of internal erosion that has caused the failure of many dams and levees and continues to threaten the safety of existing infrastructure. To manage this threat, failure risks are regularly evaluated to prioritize risk reduction measures. Unfortunately, current practice for assessing BEP is limited to simple ca...

Backward erosion piping poses a threat to levees and dams. Prediction of this phenomenon is generally conducted using models that are based on a two-dimensional pipe and flow pattern. However, the concentration of flow towards the pipe is essentially a three-dimensional phenomenon, causing model width and exit geometry to affect its progression. Th...

Backward erosion piping (BEP) is an internal erosion mechanism that erodes foundation sand from beneath levees and dams. Numerous failures have been attributed to BEP, and structural modifications are commonly made at great expense to reduce failure risks associated with BEP. In the event that structural modifications do not perform as anticipated,...

Backward erosion piping (BEP) is a type of internal erosion that describes the process by which shallow erosion channels progress upstream through sandy foundations beneath dams and levees. A substantial portion of historical dam and levee failures have been attributed to backwards erosion piping. Unfortunately, a rigorous predictive method for ass...

Backward erosion piping (BEP) is a form of internal erosion which can lead to failure of levees and dams. Most research focused on the critical head difference at which piping failure occurs. Two aspects have received less attention, namely (1) the temporal evolution of piping and (2) the local hydraulic conditions in the pipe and at the pipe tip....

Inundation modeling is often conducted for levee systems to understand current flood risks. The extent of inundation caused by a breach in the levee is highly influenced by the widening rate of the levee breach. This study presents an approach for calculating levee-breach widening rates based on average flow velocity through the breach, embankment...

Backward erosion piping (BEP) is a leading cause of failure in dams and levees, but uncertainties in erosion progression characteristics and soil properties provide significant challenges to a deterministic analysis approach. For this reason, a risk-based approach to BEP failure is of great interest to engineers. The probability of failure is most...

Backward erosion piping (BEP) is a type of internal erosion responsible for the failure of many dams and levees. BEP occurs when small, shallow erosion channels progress upstream through foundation sands beneath the structure. As analysis of BEP involves coupling two different sets of flow equations to describe the groundwater flow and erosion pipe...

This technical note documents the purpose, use, and preliminary results of a full-scale sand boil generator developed at the Geotechnical and Structures Laboratory of the U.S. Army Corps of Engineers.

The critical shear stress and erodibility of soil are fundamental parameters for modeling embankment breaching. Unfortunately, very few studies have examined the erosion characteristics of soils consisting predominantly of particles larger than sand. This report presents results of an experimental study in which the erosion characteristics of grave...

Most research on backward erosion piping (BEP) focuses on the critical conditions leading to failure. This paper studies the development of piping over time once the critical conditions are exceeded, which is useful to estimate time to failure. A commonly used small scale rectangular box setup is modified in order to monitor pore pressures and pipe...

Backward erosion piping (BEP) is a type of internal erosion that threatens the integrity of dams and levees. BEP has been shown to be highly sensitive to spatial variations in soil properties; however, there are presently no assessment methods that permit incorporating spatial variation in soil properties into BEP analysis. The Random Finite Elemen...

The orientation of constructed levee embankments relative to alluvial swales is a useful measure for identifying regions susceptible to backward erosion piping (BEP). This research was conducted to create an automated, efficient process to classify patterns and orientations of swales within the Lower Mississippi Valley (LMV) to support levee risk a...

It is often of great interest in geomechanical analysis to model localized phenomena, such as strain concentrations along failure planes or hydraulic gradient concentrations near discontinuities and exit points. Focus in recent years on massively parallel finite element codes with adaptive meshing algorithms, have left many previously developed lib...

Backward erosion piping (BEP) is a common hazard along artificial levees in the Lower Mississippi Valley (LMV). This study applies an empirical assessment of overbank deposit thickness, also referred to as blanket thickness, and the probability of BEP initiation within the LMV. A dataset composed of 800 boreholes, 500 piezometers, and 2,691 sand bo...

The state of the art in embankment dam design has changed substantially over the past century. In many instances, advancements to the state of the art have led to the realization that existing embankment dams may not be as safe as intended. Following the failure of Teton Dam in 1978, Congress passed legislation that permitted the U.S. Bureau of Rec...

Backward erosion piping (BEP) is a type of internal erosion that significantly contributes to internal erosion being a leading cause of levee and dam failures, second only to overtopping. Despite its significance, very few numerical or analytical tools exist for assessing the progression of backward erosion pipes. Further, existing tools do not aut...

Sand boils are formed when seepage carries foundation soils to the ground surface near the toe of an embankment through cracks or defects. Sand boils can be an indicator of backward erosion piping, which is a type of internal erosion that gradually degrades the foundation of the structure, potentially leading to failure. The technique used for cont...

Backward erosion piping is a leading cause of levee failures, second only to overtopping, and is therefore of great concern to engineers involved in flood control. Backward erosion piping refers to a process by which shallow erosion channels propagate upstream through foundation sands beneath water-retaining structures. If the erosion channels reac...

This article describes the field of geotechnical engineering and provides an overview of the geotechnical engineer's activities, responsibilities, and interfaces. Most geotechnical work starts with site characterization, which usually involves some subsurface investigation and laboratory testing. Analysis of these results leads to design properties...

Backward erosion piping (BEP) is a failure mechanism of serious concern for both dams and levees. Finite element models have been developed for analysis of BEP; however, these models often assume foundation soils are entirely homogenous. Recent laboratory investigations have demonstrated that spatial variability in soil substantially affects the BE...

Backward erosion piping is a threat for relatively impermeable dikes that are founded on a sandy, more permeable subsoil. Groundwater flow concentrates on the boundary between the impermeable layer and the sand and may cause erosion of the sand grains. The driving force is the head difference over the dike. If the sand on which the dike is founded...

The presence of sand boils near the toe of a levee indicates that backward erosion piping, an internal erosion process, has initiated at a given location. As a primary failure mechanism for levees, backward erosion piping is commonly evaluated as part of levee risk analysis. Currently, sand boil observations are subjectively incorporated into risk...

Backward erosion piping is a failure mechanism which involves the formation of shallow pipes in a sandy foundation layer and is considered to be a major risk for levees. For understanding this mechanism and the development of prediction models, laboratory experiments are essential. In addition, due to scale effects and heterogeneity in field condit...

Backward erosion piping is a highly three-dimensional process responsible for the failure of many embankment dams and levees. Unfortunately, the majority of numerical models developed for predicting piping are two-dimensional. This study presents finite element models for backward erosion piping computations in both two- and three-dimensional domai...

Backward erosion piping involves the gradual removal of granular material under the action of water flow from the foundation of a dam or levee, whereby shallow pipes are formed that grow in the direction opposite to the flow. This pipe-forming process can ultimately lead to failure of a water-retaining structure and is considered one of the most im...

A sand boil is a cone of granular material deposited on the ground surface around concentrated points of vertical seepage. Sand boils often form downstream of embankments during flood events, creating unfiltered seepage exits that may lead to initiation of backward erosion piping (BEP) in the foundation materials. Further progression of the backwar...

Internal erosion (IE) refers to any process by which soil particles are eroded from within or beneath a water retaining structure. As half of embankment dam failures are caused by IE, it is an issue of major concern. Approaches for designing against IE have been well established for over 50 years; however, a large fraction of existing embankments a...

The critical shear stress and erodibility of soil are fundamental parameters for modeling embankment breaching. Unfortunately, very few studies have examined the erosion characteristics of soils consisting predominantly of particles larger than sand. This paper presents results of an experimental study in which the erosion characteristics of gravel...

This discussion presents over 300 measurements of soil critical shear stress obtained from jet erosion test (JET) and erosion function apparatus (EFA) type measurements to supplement the measurements presented in the original article. The data compilation illustrates that soil classification alone is insufficient information to predict the critical...

A new fragment type is developed using finite elements, with results presented in the form of charts for the estimation of seepage beneath levees and other water-retaining structures. The chart solutions are then compared with existing approximate solutions based on blanket theory. The charts are shown to agree well with existing methods, while inc...

Results of an experimental study are presented in which the horizontal, critical gradient required for backward erosion piping of fine gravel was measured. A horizontal flume was constructed that allowed samples to be subjected to a vertical confining stress and unidirectional flow. The seepage gradient was increased gradually during each test, whi...

The soil water characteristic curve (SWCC) is an integral part of transient seepage analyses. Typically, empirical correlations or sample SWCCs based on soil type are used to predict the SWCC. This study examines the performance of five SWCC prediction methods through comparisons with measured SWCCs for four randomly chosen soils from the literatur...

A new type of laboratory test has been developed for measuring the local hydraulic conditions required for the progression of backward erosion piping, an internal erosion mechanism for water-retaining structures. The device consists of clear acrylic cylinders in which soil samples can be subjected to unidirectional, horizontal flow. The cylindrical...

The U.S. Army Corps of Engineers (USACE) has gradually implemented risk assessment into its dam and levee safety programs over the last 10 years. This has resulted in a focused effort to better understand potential failure modes. A common assessment by engineers is that the presence of sand boils indicates a high risk condition. It is often assumed...

Internal erosion refers to mechanisms by which soil particles are eroded from beneath or within embankments due to the forces of moving water. The initiation of internal erosion can be readily prevented through the use of properly designed filters and drainage features in embankments; however, many existing embankments do not include these features...

Backward erosion piping (BEP) is a type of internal erosion that typically involves the erosion of foundation materials beneath an embankment. BEP has been shown, historically, to be the cause of approximately one third of all internal erosion related failures. As such, the probability of BEP is commonly evaluated as part of routine risk assessment...

To evaluate the potential influence of a tree on embankment stability, it is necessary to estimate the void that will occur in the embankment if the root system were to fail from storm loads. Currently, there is no published scientific literature focusing solely on this issue from an engineering perspective. This study reviewed existing research re...

The Jet Erosion Test (JET) has been used extensively throughout the United States as both a field and laboratory test for the quantification of erosion characteristics of soils. While the primary advantage of the JET is that it can be used in the field, situations often arise where a laboratory JET is more convenient. This paper documents one such...

The mechanical behavior of geomaterials is highly dependent on the particle microstructure. The term microstructure in this context includes the shape, distribution, and arrangement of particles and void space. Because of the inherent difficulties in measuring soil and rock properties on a microscale, geo-professionals use macro properties to estim...

Reduced flood control capacity of levees due to consolidation, weathering, sedimentation, and poor maintenance combined with updated hydrological data have led to increased risks of embankment failure due to overtopping. Prolonged overtopping during extreme flood events may erode the embankment and lead to breaching and/or catastrophic failure as s...

X-ray computed tomography (CT scanning) was used to determine the vesicular porosity, average vesicle size, and average vesicle perimeter of fourteen specimens taken from five boulders. Band Pass Filtering was determined to be the best image processing technique to determine vesicular porosity. Porosity values determined using density values were 1...