Can Protracted Drought Undermine the Structural Integrity of California’s Earthen Levees?

Vahedifard, Farshid; Robinson, Joe D.; AghaKouchak, Amir

doi:10.1061/(asce)gt.1943-5606.0001465

Cited by 51 publications

(19 citation statements)

References 26 publications

(36 reference statements)

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“…Among others, the effective degree of saturation (S e ) and suction stress (σ s ) are two parameters of interest that influence the strength of unsaturated soils (Lu et al 2010;Robinson and Vahedifard 2016;Vahedifard et al 2016a). Soil strength is the primary factor contributing to the stability of any earthen structure (e.g., Fredlund and Rahardjo 1993;Vanapalli et al 1996;Vahedifard et al 2015aVahedifard et al , 2016b. The interactive thermodynamic free energy collectively represented by the suction stress in unsaturated soils can exist in the form of van der Waals forces, electric double-layer forces, surface tension, and soil-fluid air-interface forces resulting D r a f t 10 from matric suction (e.g., Lu et al 2010).…”

Section: R a F T 9 Fully Coupled Numerical Modeling Of Transient Unmentioning

confidence: 99%

Rainfall-triggered slope instabilities under a changing climate: comparative study using historical and projected precipitation extremes

2017

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This study aims to quantitatively assess the impact of extreme precipitation events under current and future climate scenarios on landslides. Rainfall-triggered landslides are analyzed primarily using extreme precipitation estimates, derived using the so-called stationary assumption (i.e., statistics of extreme events will not vary significantly over a long period of time). However, extreme precipitation patterns have shown to vary substantially due to climate change, leading to unprecedented changes in the statistics of extremes. In this study, a nonstationary approach, applied to climate model simulations, is adopted to project the upper bound of future precipitation extremes. Future precipitation estimates are obtained from the coupled model intercomparison project phase 5 (CMIP5) simulations. Baseline (historical) and projected (future) precipitation extremes are obtained for a study area near Seattle, Washington. The precipitation patterns are integrated into a series of fully coupled two-dimensional stress – unsaturated flow finite element simulations. The responses of the baseline and projected models at a 7 day rainfall duration obtained for a 50 year recurrence interval are compared in terms of the local strength reduction factor, displacements, matric suctions, and suction stresses. The results indicate that the usage of historical rainfall data can lead to underestimations in the hydromechanical behavior of natural slopes where locally increased transient seepage rates occur from the upper bound of future extreme precipitation estimates.

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Section: R a F T 9 Fully Coupled Numerical Modeling Of Transient Unmentioning

confidence: 99%

Rainfall-triggered slope instabilities under a changing climate: comparative study using historical and projected precipitation extremes

2017

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“…It is noted that much larger suctions can possibly be developed in marginal fills under certain circumstances (e.g., prolonged droughts). A heavy rain after or in the middle of a prolonged drought has been reported in several cases and can impose a more critical scenario to earthen structures including MSE walls (e.g., Vahedifard et al 2015aVahedifard et al , 2016dRobinson and Vahedifard 2016). Such a case involves a multihazard analysis including consecutive extreme events (i.e., drought followed by a heavy rain).…”

Section: Modeling Stagesmentioning

confidence: 99%

“…Even concurrent and compounding extreme events have increased substantially in recent decades (Hao et al 2013;Mazdiyasni and AghaKouchak 2015;Wahl et al 2015). These climate trends unfavorably influence existing natural and artificial geotechnical structures by exposing them to drying, soil desiccation, shrinkage, fluctuation in the groundwater table, significant erosion, and highly dynamic pore pressure changes (e.g., CACC 2015; Vardon 2015;Vahedifard et al 2015aVahedifard et al , 2016dRobinson and Vahedifard 2016;Robinson et al 2017). The imposed impacts can threaten the integrity of geotechnical structures and lead to various modes of failure such as uplift, subsidence, piping, internal erosion, and slope instability (e.g., NRC 2008;Crozier 2010;Taylor et al 2013;Vardon 2015).…”

Section: Introductionmentioning

confidence: 99%

“…Such quantitative studies can help to properly evaluate the failure risk and resilience of current earth structures and to safely design future earth structures for a changing climate. For this purpose, the geotechnical engineering community needs to closely collaborate with other related disciplines, including climate change scientists, to specifically address the following questions (e.g., CACC 2015; Vahedifard et al 2016d): (1) How does climate change and variability affect recurrence intervals of climatic extremes? (2) How does soil behavior vary under thermohydromechanical processes imposed by changes in extremes?…”

Section: Introductionmentioning

confidence: 99%

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Resilience of MSE Walls with Marginal Backfill under a Changing Climate: Quantitative Assessment for Extreme Precipitation Events

Vahedifard

Tehrani

Galavi

et al. 2017

J. Geotech. Geoenviron. Eng.

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Climate change is expected to alter statistics of extreme events in the future. Adapting geotechnical infrastructure to a changing climate necessitates quantitative assessment of the potential climate change impacts on the performance of infrastructure. This study numerically investigates the hydromechanical response of a mechanically stabilized earth (MSE) wall constructed with marginal backfill to extreme rainfall events under a changing climate. The need for investigating the effects of extreme precipitation on marginal backfill is more pronounced because larger matric suction can be developed in such backfills. To address this need, this paper compares the performance of an MSE wall using two sets of rainfall intensity-duration-frequency (IDF) curves, denoted as baseline and projected, for the Seattle area. The baseline IDF curves are provided by the National Oceanic and Atmospheric Administration (NOAA) and currently used for design purposes, and the projected IDF curves are obtained using 20 climate model simulations of the future. The results show that use of the baseline IDFs can lead to underestimation of the wall deformation and loads carried by reinforcements. The results highlight the importance of site-specific assessments to quantify the potential impacts of climate change on the performance of current and future MSE walls. Such consideration gains even more importance considering the increasing interest in using marginal backfills in earth retaining structures due to economic and environmental considerations.

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“…Allegedly anticipated effects of global warming suggest that structures will be subjected more often to extreme hydrologic events, which are characterized by intermittent droughts and torrential rains of ever-increasing amplitudes (Vahedifard et al, [14], Vano et al [15]). For example, Lake Oroville (behind the Oroville dam) was in the center of public attention for several years during the most recent drought in California.…”

Section: Introductionmentioning

confidence: 99%

Phreatic seepage flow through an earth dam with an impeding strip

2019

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New mathematical models are developed and corresponding boundary value problems are analytically and numerically solved for Darcian flows in earth (rock)-filled dams, which have a vertical impermeable barrier on the downstream slope. For saturated flow, a 2-D potential model considers a free boundary problem to Laplace's equation with a traveling-wave phreatic line generated by a linear drawup of a water level in the dam reservoir. The barrier re-directs seepage from purely horizontal (a seepage face outlet) to purely vertical (a no-flow boundary). An alternative model is also used for a hydraulic approximation of a 3-D steady flow when the barrier is only a partial obstruction to seepage. The Poisson equation is solved with respect to Strack's potential, which predicts the position of the phreatic surface and hydraulic gradient in the dam body. Simulations with HYDRUS, a FEM-code for solving Richards' PDE, i.e., saturated-unsaturated flows without free boundaries, are carried out for both 2-D and 3-D regimes in rectangular and hexagonal domains. The Barenblatt and Kalashnikov closed-form analytical solutions in non-capillarity soils are compared with the HYDRUS results. Analytical and numerical solutions match well when soil capillarity is minor. The found distributions of the Darcian velocity, the pore pressure, and total hydraulic heads in the vicinity of the barrier corroborate serious concerns about a high risk to the structural stability of the dam due to seepage. The modeling results are related to a "forensic" review of the recent collapse of the spillway of the Oroville Dam, CA, USA. Keywords 2-,3-D transient seepage with a phreatic surface . earth dams . analytical models . Richards' equation . fields of pore pressure head . water content and velocity . heaving and suffusion 2010 Mathematics Subject Classification • 76S05Flows in porous media; filtration; seepage • 30E25Boundary value problems • 35K61Nonlinear initial-boundary value problems for nonlinear parabolic equations • 65M60Finite elements, Rayleigh-Ritz and Galerkin methods, finite methods Electronic supplementary material The online version of this article (https://doi.

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Can Protracted Drought Undermine the Structural Integrity of California’s Earthen Levees?

Cited by 51 publications

References 26 publications

Rainfall-triggered slope instabilities under a changing climate: comparative study using historical and projected precipitation extremes

Rainfall-triggered slope instabilities under a changing climate: comparative study using historical and projected precipitation extremes

Resilience of MSE Walls with Marginal Backfill under a Changing Climate: Quantitative Assessment for Extreme Precipitation Events

Phreatic seepage flow through an earth dam with an impeding strip

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