West Chester, PA, United States
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Dabling M.R.,Utah State University | Tullis B.P.,Utah State University | Crookston B.M.,Schnabel Engineering
Journal of Irrigation and Drainage Engineering | Year: 2013

Labyrinth weirs with multiple crest elevations (i.e., staged labyrinth weirs) can be used in spillway design to confine base flows to a section of the crest and/or satisfy discharge hydrograph requirements. However, inadequate hydraulic design information is available specific to staged labyrinth weirs. In this study, the flow characteristics of various staged labyrinth weir configurations (laboratory-scale) were tested. Observations of staged labyrinth weir flow characteristics are presented. The influences of the lower stage length, depth, and location on discharge were studied and head-discharge relationships were experimentally determined. The accuracy of a head-discharge predictive technique on the basis of superposition and traditional labyrinth weir empirical data was also evaluated. Relative to the experimental results, the superposition technique estimations were generally within ±5% for all configurations tested except at lower headwater depths, where maximum estimation errors occurred (maximum of 15%). When discharge was limited to the lower stage weir segment, the predictive discharge errors were up to 20% for some notch configurations. This indicates the discharge of the lower stage segment is location-specific because of the complexity of the labyrinth weir geometry. © 2013 American Society of Civil Engineers.

Park C.H.,Schnabel Engineering | Bobet A.,Purdue University
Engineering Fracture Mechanics | Year: 2010

An extensive experimental program has been conducted on pre-cracked specimens of a rock-model material to investigate crack propagation and coalescence from frictional discontinuities. Prismatic gypsum specimens have been prepared with three pre-existing closed cracks (flaws). The flaws all have a constant length of 12.7. mm and are parallel to each other. Different geometries are obtained by changing the angle of the flaws with respect to the direction of loading, the spacing, and the continuity of the flaws. In the experiments, three different types of cracks have been observed: wing cracks, coplanar shear, and oblique shear cracks. These are the same types of cracks observed with open flaws. Crack initiation occurs simultaneously at all the tips of the flaws for wing and shear cracks. Mean crack initiation stress is higher for secondary cracks than for wing cracks. The differences however decrease as the flaws are oriented at smaller angles with the direction of loading. The types of coalescence (i.e. the type of cracks and crack pattern that link two flaws) from closed flaws are similar to those from open flaws. However, the type of coalescence observed in a specimen with open flaws is not necessarily produced when using the same geometry but with closed flaws. The most important conclusion reached in this research is that the fracturing processes in open and closed flaws are similar. Friction along the flaws increases the initiation and coalescence stress and favors linkage through shear cracks. © 2010 Elsevier Ltd.

McCann M.W.,Stanford University | Paxson G.,Schnabel Engineering
Association of State Dam Safety Officials, Dam Safety 2015 | Year: 2015

In water resources planning studies and dam safety risk analyses it is common to use best estimates of the probability of floods, best estimates of peak flood levels and best estimates of damage to estimate the "expected" value of economic consequences or fatalities from flood events or the uncontrolled release of a reservoir resulting from a dam breach. Typical practice does not consider the uncertainties (aleatory and epistemic) in various elements of the risk analysis, In risk analysis for dams, the failure to address uncertainties in the elements of the risk analysis can have important implications to; 1) understanding the distribution of consequences that can result from a dam breach, 2) level of confidence in the risk results, 3) potential area of inundation, the residences, infrastructure, and the population-at-risk, and 4) deriving a Bayesian estimate of the expected-value of losses from a dam breach. This paper looks at two aspects of risk analysis studies for dams; alternative approaches for calculating risk and the effect of uncertainties in the dam breach and inundation analysis and in the flood damage relationships on the estimate of flood damages. In the example presented, a seismic risk analysis for an earth embankment is presented in which the economic consequences of uncontrolled release of the reservoir is evaluated. The aleatory and epistemic uncertainties in the frequency of dam failure, the dam breach and inundation analysis and in the flood damage assessment are explicitly propagated through the estimates of the frequency distribution on economic consequences. © Copyright 2015 Association of State Dam Safety Officials, Inc. All Rights Reserved.

Hepler T.E.,Schnabel Engineering
Dam Protections against Overtopping and Accidental Leakage - Proceedings of the 1st International Seminar on Dam Protections Against Overtopping and Accidental Leakage | Year: 2015

This paper provides an overview of Technical Manual: Overtopping Protection for Dams, which was recently released by the Federal Emergency Management Agency (FEMA) of the United States, to be included in the Proceedings of International Seminar on Dam Protection against Overtopping and Accidental Leakage. U.S. customary units have been converted to S.I. metric units for purposes of this international seminar. © 2015 Taylor & Francis Group, London.

Cadden A.,Schnabel Engineering
Geotechnical Special Publication | Year: 2012

A Discussion Board was started on the professional networking site Linkedin. Its goal was to review the state of practice of Limited Mobility Grouting in karstic environments for foundation support. The discussion focused mostly on hole layout and grout depth relative to foundation stress or size, grouting procedures and refusal criteria, verification, quality control and quality assurance procedures. This paper summarizes the interesting ideas generated within the Discussion Board, and reviews recent publications on the subject. It also contains the author's experiences in the use of LMG for foundation applications in karst. © 2012 American Society of Civil Engineers.

Crookston B.M.,Schnabel Engineering | Welle P.I.,Schnabel Engineering
Association of State Dam Safety Officials Annual Conference 2014, Dam Safety 2014 | Year: 2014

The American Society of Civil Engineers estimates that there are approximately 4,000 deficient dams in the United States. Dams provide many benefits to society, but dam failures can have severe consequences such as fatalities, environmental impacts, infrastructure damage, and lost revenue. Dam breach inundation studies are performed in an effort to manage these potential consequences. There are a variety of model approaches and modeling software available for these studies, including one-dimensional models such as HEC-RAS; and computational fluid dynamic (CFD) models using the two-dimensional shallow water approach or three-dimensional simulations based upon the complete set of Navier-Stokes equations. Inundation modeling of several existing embankment dams was performed using 1-D, 2-D, and 3-D models using HECRAS (1-D) and Flow-3D (2-D and 3-D). The results of this study include observed differences between each model approach, including flow depths, velocities, and flood wave arrival. Information regarding model development and simulation times is also included. Finally, observations concerning numerical model limitations are discussed, with several generalized conclusions regarding the suitability and efficiency of each model for inundation studies.

Hansen K.D.,Denver | Fitzgerald T.J.,Schnabel Engineering
Association of State Dam Safety Officials Annual Conference 2014, Dam Safety 2014 | Year: 2014

The use of Roller-Compacted Concrete (RCC) placed on the downstream slope of embankment dams to provide erosion resistance during overtopping was started 30 years ago. Since that time, about 120 such projects have been completed in the United States to increase spillway capacity for infrequent overtopping flows. Because most of these improvements were designed to accommodate rare flooding events, little information is available on the performance of such spillways when overtopped. However, recent extreme rainfall events caused several RCC spillways to be activated. Also, there have been some spillways designed for fairly routine storm events that have been subjected to full scale testing. This paper will focus on the lessons learned and/or re-learned in the past ten years regarding the performance of RCC overtopping protection and spillways when subjected to flows from extreme flooding events, including flows carrying large amounts of gravel and rock. In addition, the paper will evaluate the performance of several RCC mixtures due to weathering effects-mainly freeze-thaw (F/T) cycles in variable climates around the country. Some of the new topics covered include: • The performance of two dams with RCC overtopping protection that were subjected to the 2013 flooding in Colorado. • The performance of an RCC faced inlet structure in Las Vegas that was subjected to an extreme rainfall event on August 25, 2013. The six hour storm event was nearly twice the annual average rainfall in Las Vegas and the resulting flows included large amounts of erosive debris. • The effect of aggregate gradation on the compressive strength of the RCC and the associated durability of the exposed RCC. • Various covers for RCC to limit F/T damage and a discussion on the use of air-entrained RCC. Based on these and other case studies, Conclusions and Recommendations are presented to improve the state of the practice for RCC overtopping protection and spillway design.

Lazarte C.A.,Schnabel Engineering
Geotechnical Special Publication | Year: 2013

This paper presents the results of the calibration of resistance factors for the pullout capacity of soil nails in three types of soil. The data and statistical parameters used in this calibration were obtained in a recent research program. The calibration was conducted using reliability methods, where the target reliability index was selected to be representative of structures with a relatively high degree of redundancy. The calibration used a Monte Carlo simulation with up to 10,000 random simulations for each variable. Calibrated resistance factors used in LRFD design were found to provide results that, on average, are comparable to those obtained using safety factors currently used in practice. © 2013 American Society of Civil Engineers.

Shearin-Feimster L.E.,Schnabel Engineering
6th International Symposium on Hydraulic Structures: Hydraulic Structures and Water System Management, ISHS 2016 | Year: 2016

The dissipation of excess energy from flows exiting a spillway is often needed to prevent or reduce to acceptable levels conceivable negative impacts to the downstream channel, spillway, and dam (e.g., erosion, undermining). The optimization of a hydraulic jump type stilling basin using general-purpose, published design methodologies (i.e., USBR, SAF, etc.) for a project can be challenging, as these methodologies may not account for all site specific conditions and structure formulations by designers. Also, it is not often clear to a designer as to which flow rates (and corresponding flood events) will have the greatest influence on the basin geometry and features (i.e., jump formation location and stability). This can be further obscured for projects where a high tailwater condition is predicted during flood events. This paper presents several recent dam rehabilitation projects where a high tailwater impacted the designs of the stilling basins. Each project features a different spillway, chute, and basin configuration. An overview of each site and summary of key challenges encountered during the design of the spillways and stilling basins is included. In addition, a discussion of which design methods were selected, why they were selected, and additional measures that were taken to address the uncertainties at the site is included. This documentation of unique site conditions and design methodologies for stilling basins is intended to show the importance of collaboration between the designer and the owner in selecting a design approach for a specific situation.

Brown W.K.,Schnabel Engineering | Crookston B.M.,Schnabel Engineering
6th International Symposium on Hydraulic Structures: Hydraulic Structures and Water System Management, ISHS 2016 | Year: 2016

The flow patterns observed in supercritical flows at bends in open channels are encountered in spillways, canals, and drainage works - this complex flow condition has been investigated more than 80 years ago, first with hydraulic models and more recently using numerical models. This paper presents a numerical investigation using a selection of experimental data from Dr. A. T. Ippen and a commercially available 3-dimensional CFD solver. A comparison of the numerical results to the physical data is presented, highlighting the ability of the numerical models to reproduce these complex water surface profiles, including the magnitude and location of standing waves. Modeling efforts were of a single fluid and used RNG and LES turbulence models. Furthermore, the observations, findings, and conclusions of this paper are discussed as they relate to open channel design.

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