An official website of the United States government
ABSTRACT Backward erosion piping (BEP) is a significant contributor to failures in global flood protection infrastructure, yet it remains among the least understood geotechnical phenomena, particularly concerning the fundamental mechanisms driving its initiation. This study focuses on the development of a novel stochastic framework for the prediction of critical hydraulic gradients causing BEP initiation. The novelty of the study lies in the following: (1) the development of a grain‐scale probabilistic model based on fundamental mechanisms by means of the theory of rate processes, (2) quantification of the influence of soil variability on BEP initiation probability by introducing an initiation probability function, and (3) an analytical framework reconciling grain kinetics of BEP initiation with the Weibull distribution. A particle‐scale BEP initiation probabilistic model is first established based on fundamental grain kinetics under seepage flow by using the theory of rate processes. To investigate how soil variability influences initiation, a stochastic dual random lattice modeling framework is exercised, complemented by direct x‐ray computed tomography measurements of soil variability conducted on sand samples. The analytical probabilistic model for BEP initiation closely aligns with the Weibull distribution, also demonstrating that soil variability influences both the scale and shape parameters of the distribution. This work establishes the linkage between probability of BEP initiation as described by the theory of rate processes and phenomenological Weibull statistics. Findings presented herein bring the potential to develop a multiscale probabilistic framework by means of Weibull statistics for evaluating the probability of BEP initiation at multiple scales.
more »
« less
Multiscale Stochastic Modeling of Backward Erosion Piping Initiation, From Grain Kinetics to Weibull Statistics. Part II: Model Validation and Applications
ABSTRACT Backward erosion piping (BEP) is a leading internal erosion mechanism for flood protection system failures. A model capable of predicting critical hydraulic conditions for BEP initiation at multiple scales while also incorporating soil variability is a pressing need. This study formulates and validates a novel multiscale probabilistic BEP initiation framework with incorporation of soil variability. The framework is based on a grain‐scale probabilistic model and the weakest link theory, and the theory of rate processes. The multiscale framework proposed herein is validated through a wide range of available experimental data from independent sources, encompassing tests performed at multiple scales. Following calibration with small‐scale experimental data, the model demonstrates accurate prediction of critical hydraulic gradients at larger scales (3–6 orders of magnitude difference), including the ability to capture the grain size dependence of BEP initiation and providing uncertainty estimates. A systematic analysis is performed to uncover the effects of different soil properties on multiscale critical hydraulic conditions.
more »
« less
- PAR ID:
- 10563604
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- International Journal for Numerical and Analytical Methods in Geomechanics
- Volume:
- 49
- Issue:
- 4
- ISSN:
- 0363-9061
- Format(s):
- Medium: X Size: p. 1247-1261
- Size(s):
- p. 1247-1261
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Backward erosion piping (BEP) has been recognised as a major cause of failures in water-retaining structures. However, the fundamental mechanisms controlling the phenomenon are not well understood. This research applies the theory of rate processes to develop a constitutive relationship between energy density of the seepage flow and the erosion rate of soils during the evolution of BEP. The resulting equation is used to analyse four datasets of previously reported experimental observations. The mechanical parameters estimated through the proposed model fall into the ranges of values that were reported in the literature. To validate the proposed approach, the constitutive model was incorporated into a multiphase numerical framework to simulate evolution of BEP in embankment soil and compared with reported experimental observations. The numerical framework with the proposed constitutive model is shown to be capable of reproducing both the observed evolution of local hydraulic gradients and pipe progression in the structure.more » « less
-
Backward erosion piping (BEP) is a major risk factor for both dams and levees. A significant amount of work has been performed to examine the likelihood of initiation of BEP through examination of critical gradients for sand boil formation and the development of semi-empirical approaches to assess the likelihood of erosion continuing and progressing to a breach. Recently, numerical analyses have been developed to model the BEP process and these tools offer a means to incorporate more complex geometries and soil conditions than can be assessed within the semi-empirical approaches. These simulation methods have been primarily applied to laboratory tests and physical models with uniform properties, but there is a need to validate these models using case histories and explore how variability in stratigraphy and properties influences the BEP process. This study will apply numerical approaches for simulating BEP to the case history of the Bois Brule levee breach that occurred during flooding in July 1993. This paper first describes the Bois Brule levee and observations during flooding. Numerical simulations of piping progression are used to explore the effect of reasonable variations in properties and stratigraphy on the likelihood of failure and the sensitivity of the results to the river level at the time of failure. The paper highlights challenges in modeling BEP and provides guidance on which factors have the largest impact of the results.more » « less
-
Rathje, Ellen; Montoya, Brina M.; Wayne, Mark H. (Ed.)Soil piping is the gradual and progressive erosion of soil grains, causing a void (open pipe) to form as water flows through the soil. In dam engineering, this type of internal erosion is often referred to as concentrated leak erosion and has been a cause of failure at multiple dams. Soil piping has also been observed in many landslides and contributes significantly to soil degradation in hillslopes and agricultural areas. Despite these many important impacts, there is still limited understanding of how soil pipes develop and progress and what factors control pipe stability. One of the significant challenges with analyzing soil piping, or concentrated leak erosion, is that it typically occurs in the vadose zone, where unsaturated conditions are present. However, most studies examining internal erosion have focused on saturated conditions, and few studies have examined the role unsaturated hydraulic properties (i.e., air entry value, matric suction, etc.) may play in the likelihood of internal erosion. Consequently, this study aims to explore the mechanisms controlling the erosion rate within soil pipes from the perspective of unsaturated soil mechanics. Bench-scale experiments were performed to examine the formation and progression of an eroded pipe in a small slope constructed at different water contents. Soil samples were also tested to measure its unsaturated hydraulic properties. The results show that the likelihood of pipe formation varies with the moisture content and, therefore, suction in the soil, as does the potential for pipe collapse. This demonstrates that unsaturated soil properties are key to understanding the formation and progression of piping in slopes.more » « less
-
Abstract Water inside plants forms a continuous chain from water in soils to the water evaporating from leaf surfaces. Failures in this chain result in reduced transpiration and photosynthesis and are caused by soil drying and/or cavitation‐induced xylem embolism. Xylem embolism and plant hydraulic failure share several analogies to ‘catastrophe theory’ in dynamical systems. These catastrophes are often represented in the physiological and ecological literature as tipping points when control variables exogenous (e.g., soil water potential) or endogenous (e.g., leaf water potential) to the plant are allowed to vary on time scales much longer than time scales associated with cavitation events. Here, plant hydraulics viewed from the perspective of catastrophes at multiple spatial scales is considered with attention to bubble expansion within a xylem conduit, organ‐scale vulnerability to embolism, and whole‐plant biomass as a proxy for transpiration and hydraulic function. The hydraulic safety‐efficiency tradeoff, hydraulic segmentation and maximum plant transpiration are examined using this framework. Underlying mechanisms for hydraulic failure at fine scales such as pit membranes and cell‐wall mechanics, intermediate scales such as xylem network properties and at larger scales such as soil–tree hydraulic pathways are discussed. Understudied areas in plant hydraulics are also flagged where progress is urgently needed.more » « less
