Ayres Associates Inc.

Fort Collins, CO, United States

Ayres Associates Inc.

Fort Collins, CO, United States
Time filter
Source Type

Yeh G.-T.,University of Central Florida | Fang Y.,Pacific Northwest National Laboratory | Zhang F.,Oak Ridge National Laboratory | Sun J.,Applied Sciences, Inc. | And 3 more authors.
Computational Geosciences | Year: 2010

Subsurface contamination problems of metals and radionuclides are ubiquitous. Metals and radionuclides may exist in the solute phase or may be bound to soil particles and interstitial portions of the geologic matrix. Accurate tools to reliably predict the migration and transformation of these metals and radionuclides in the subsurface environment enhance the ability of environmental scientists, engineers, and decision makers to analyze their impact and to evaluate the efficacy of alternative remediation techniques prior to incurring expense in the field. A mechanistic-based numerical model could provide such a tool. This paper communicates the development and verification of a mechanistically coupled fluid-flow thermal-reactive biogeochemical-transport model where both fast and slow reactions occur in porous and fractured media. Theoretical bases, numerical implementations, and numerical experiments using the model are described. A definition of the "rates" of fast/equilibrium reactions is presented to come up with a consistent set of governing equations. Two example problems are presented. The first one is a reactive transport problem which elucidates the non-isothermal effects on heterogeneous reactions. It also demonstrates that the rates of fast/equilibrium reactions are not necessarily greater than that of slow/kinetic reactions in the context of reactive transport. The second example focuses on a complicated but realistic advective-dispersive-reactive transport problem. This example exemplifies the need for innovative numerical algorithms to solve problems involving stiff geochemical reactions. It also demonstrates that rates of all fast/equilibrium reactions are finite and definite. Furthermore, it is noted that a species-versus-time curve cannot be used to characterize the rate of homogeneous fast/equilibrium reaction in a reactive transport system even if one and only one such reaction is responsible for the production of this species. © Springer Science + Business Media B.V. 2009.

Sayed S.M.,GCI Inc. | Sunna H.N.,Ayres Associates Inc. | Moore P.R.,GCI Inc.
Journal of Bridge Engineering | Year: 2012

Bridges with unknown foundations have been a burden on the transportation agencies across the United States because of the lack of funding and availability of rational methods to determine the risk of failure of these bridges from scour. The embedment of unknown foundation bridges is a key to proceed further with any risk-based management approach and/or the widely used Federal Highway Administration (FHWA) guidelines on the methods of evaluation of unknown foundations. The need for a practical, cost-effective, and rational approach to positive discovery of bridge foundations and to reclassify bridges with unknown foundations is greater than ever. This technical note presents an assessment of the predictive capability of various methods currently in use to determine the embedment of unknown foundation bridges. The methods discussed in this paper include sonic echo method (or pile integrity tester) as non-destructive testing (NDT), inference (IM) and/or back calculation (BC) [i.e., reverse engineering (RE)], and static/back calculation (S/B-C). The well-documented case histories presented in the paper illustrate the usefulness of using the S/B-C method in determining the embedment of unknown foundations. The S/B-C also can be used to assess/validate NDT results and embedment estimates made by IM and/or BC (RE) approaches. For high priority unknown foundation bridges, the S/B-C reasonable minimum embedment and the embedment required for stability considering the scour can be used to plan and efficiently implement any future NDT for these bridges. It can significantly reduce the cost of treating unknown foundation bridges by optimizing the use of NDT, if warranted. The three case histories presented in the paper also suggest that, in general, the sonic echo (i.e., pile integrity tester)/NDT tends to be conservative whereas the IM and/or BC (RE) methods tend to be unconservative. This would lead to high cost or high risk, respectively, if such estimates are used to assess the stability of unknown foundation bridges impacted by scour. © 2012 American Society of Civil Engineers.

Sayed S.M.,GCI Inc. | Sunna H.,Ayres Associates Inc. | Moore P.R.,GCI Inc.
Geotechnical Special Publication | Year: 2010

A practical, cost-effective and rational approach to re-classify bridges with unknown foundations is presented in this paper. The method is based on satisfying static equilibrium under appropriate loads for the existing bridge pier/bent conditions using three-dimensional, non-linear finite element analysis. The method is applicable to partially and fully-embedded piled-foundation sub-structures where physical measurements of the super-structure and top of the foundation elements (layout, type, and size) can be made. The computed pile embedment using the proposed method is remarkably in close agreement with the actual embedment for bridges referenced in this paper. The approach presented in this practice-oriented paper can provide confidence in assessing the "unknown foundation" bridges and will expedite the screening of these bridges to protect the public. The methodology can also be used to validate embedment determinations done by Non-Destructive Testing (NDT) methods in previous or current projects and to guide any future NDT. © 2010 American Society of Civil Engineers.

Keaton J.R.,Amec Foster Wheeler | Mishra S.K.,HDR | Clopper P.E.,Ayres Associates Inc.
43rd Symposium on Engineering Geology and Geotechnical Engineering 2011: Water, Soils and Sustainability in the Intermountain West | Year: 2011

The essence of National Cooperative Highway Research Program Project 24-29 is geotechnical site characterization in scour-relevant terms for use by hydraulic engineers. The project goal is to develop guidelines that can be integrated with the procedures of Federal Highway Administration Hydraulic Engineering Circular No. 18 (HEC-18) for evaluating scour at bridge foundations on rock. Scour in rock channels appears to be related to five processes: 1) physical and chemical weathering of rock surfaces exposed to scour, 2) dissolution of soluble rocks, 3) cavitation, 4) quarrying and plucking of jointed durable rocks, and 5) abrasion of degradable rocks. Defining 'rock' for scour purposes is just as problematic as it is for other engineering applications because physical properties range from strong soil to better than concrete. Bridge sites in Florida, Oregon, New York, Utah, and California visited in 2008, provided a range of conditions, data, and samples for the guidelines. Stream power is useful for characterizing hydraulic loading conditions because it is the product of hydraulic shear stress and velocity and it can be accumulated over a desired time period. Probability weighted flood frequency can be expressed in stream power as well as peak or mean discharge; mean discharge and flow duration must be used to calculate stream power. Repeated cross sections that document scour can be correlated directly with cumulative stream power for the time interval between the cross sections to provide a basis for estimating average annual scour per unit of stream power. Design scour depth is the product of average annual scour and the life of the bridge. Geotechnical evaluations are needed to verify uniformity of conditions. Laboratory test results provide a basis for comparing locations with and without repeated cross sections. Checklist guidance is provided for determining which scour processes can be dismissed and which deserve specific evaluation.

Voigt K.H.,Ayres Associates Inc.
Society of Petroleum Engineers - Carbon Management Technology Conference 2012 | Year: 2012

Knowing that today's transportation system accounts for 28% of our Nation's greenhouse gases, second only to electrical energy production requires the transportation profession to take very seriously operational management policies and construction techniques to reduce our carbon footprint. This means using transportation techniques to minimize greenhouse gas emissions by reducing travel delays and congestion as well as promoting non-single occupant vehicle travel such as transit and carpools or the use of non-motorized transportation such as bicycles and walking. Roadway construction techniques are available to further reduce greenhouse gas emissions to construct sustainable roadway infrastructure. The transportation industry needs to develop policies that rate and/or provide incentives for a sustainable transportation system. This paper provides a summary of the state of the practice to reduce fuel consumption and greenhouse gas emissions related to today's transportation systems and a recommendation on national policy for transportation sustainability. Copyright 2012, Carbon Management Technology Conference.

Clopper P.E.,Ayres Associates Inc. | Lagasse P.F.,Ayres Associates Inc.
Transportation Research Record | Year: 2011

Load and resistance factor design (LRFD) incorporates state-of-the-art analysis and design methodologies with load and resistance factors that are based on the known variability of applied loads and material properties. These load and resistance factors are calibrated from actual bridge statistics to ensure a uniform level of reliability. LRFD allows a bridge designer to focus on a design objective or limit state; doing so can lead to a similar probability of failure in each component of the bridge. Bridges designed with the LRFD specifications should have relatively uniform reliability levels; such uniformity should ensure superior serviceability and long-term maintainability. Bridge hydraulics engineers should have the option of and ability to perform scour calculations that incorporate similar probabilistic methods. With this objective in mind, NCHRP Project 24-34 was initiated in April 2010 to develop a risk-reliability-based methodology that was based on risk and reliability and that could be used in calculating bridge pier, abutment, and contraction scour at waterway crossings so that scour estimates could be linked to a probability. The developed probabilistic procedures will be consistent with LRFD approaches used by structural and geotechnical engineers. This paper discusses sources of uncertainty in hydrologic estimates as those sources relate to bridge scour computations and summarizes a conceptual approach to the problem.

Richardson E.V.,Ayres Associates Inc. | Lagasse P.F.,Ayres Associates Inc.
Geotechnical Special Publication | Year: 2010

In the 1960's Frank Johnson, Chief of the Hydraulics Branch of the Federal Highway Administration, and Regional FHWA Hydraulic Engineers were concerned that State, Federal and Consulting Engineers were not cognizant of the interaction between highway crossings and encroachments and the river environment. As a result, FHWA funded the development of a manual and training course in 1975, which was revised in 1990. In 2001 the manual was revised and issued as FHWA HDS-6. HDS-6 has chapters giving the fundamentals of open channel flow; alluvial channel flow; sediment transport; geomorphology and river morphology; river stabilization and bank protection; scour at bridges; data needs and sources; design considerations; and examples of real design and evaluation problems. There are 646 pages, 231 figures, and 425 references in HDS-6. The course has been given 45 times to over 1,100 highway engineers. This paper summarizes the chapters in HDS-6 and the history of the manual and training course. © 2010 American Society of Civil Engineers.

Zevenbergen L.W.,Ayres Associates Inc.
Geotechnical Special Publication | Year: 2010

Three frequently cited pier scour equations are the HEC-18 (also known as the CSU equation), Melville and Sheppard equations. Direct comparisons of these three equations were conducted for a wide range of realistic hydraulic, pier size and sediment size conditions. Each equation was applied following the procedure prescribed in the applicable manuals. The range of conditions was intended to cover the vast majority of pier scour calculations that would be encountered during scour evaluations. More than 2500 scour calculations were performed for each equation. This exercise was not meant to determine which equation is "right," "wrong," "better," or "worse." It was meant to give insight into the similarities and differences between the results of the equations and to address the topic of the perceived degree of conservativeness in pier scour calculations. Each of the equations predicts much greater or less scour than the other two depending on the specific input data. The Melville equation tends to produce the greatest scour and the Sheppard equation tends to produce the least. On average, the Melville equation computes scour over 30 percent more than the Sheppard equation and the HEC-18 equation computes scour approximately 15 percent more than the Sheppard equation. The majority of results were within +/- 30 percent for HEC-18 compared with Sheppard. One difference between the equations is that Sheppard includes a threshold velocity condition for pier scour, so it can predict zero scour for some conditions. Neither the HEC-18 nor Melville equations include this threshold velocity, so some amount of pier scour is always computed for these equations. © 2010 American Society of Civil Engineers.

Johnson P.A.,Pennsylvania State University | Clopper P.E.,Ayres Associates Inc. | Zevenbergen L.W.,Tetra Tech Inc. | Lagasse P.F.,Tetra Tech Inc.
Journal of Hydraulic Engineering | Year: 2015

The majority of the bridges in the U.S. National Bridge Inventory (NBI) are built over waterways. Many will experience problems with scour, bank erosion, and channel instability during their design life. A number of studies in the recent past have attempted to quantify the uncertainty in predicting these erosional processes, particularly in pier scour, and developing probabilistic estimates of scour as a means of incorporating uncertainty. However, none of these studies have examined the overall uncertainty in local pier or abutment scour in combination with contraction scour. This study quantifies the model uncertainty in commonly used scour equations as well as parameter uncertainty. The overall reliability of the scour equations is then assessed for the individual components of scour and combined scour. The results lead to a set of scour design factors that are based on the reliability of the design estimate. © 2015 American Society of Civil Engineers.

Lesak A.A.,University of Wisconsin - Madison | Radeloff V.C.,University of Wisconsin - Madison | Hawbaker T.J.,University of Wisconsin - Madison | Pidgeon A.M.,University of Wisconsin - Madison | And 2 more authors.
Remote Sensing of Environment | Year: 2011

Conservation of biodiversity requires information at many spatial scales in order to detect and preserve habitat for many species, often simultaneously. Vegetation structure information is particularly important for avian habitat models and has largely been unavailable for large areas at the desired resolution. Airborne LiDAR, with its combination of relatively broad coverage and fine resolution provides existing new opportunities to map vegetation structure and hence avian habitat. Our goal was to model the richness of forest songbirds using forest structure information obtained from LiDAR data. In deciduous forests of southern Wisconsin, USA, we used discrete-return airborne LiDAR to derive forest structure metrics related to the height and density of vegetation returns, as well as composite variables that captured major forest structural elements. We conducted point counts to determine total forest songbird richness and the richness of foraging, nesting, and forest edge-related habitat guilds. A suite of 35 LiDAR variables were used to model bird species richness using best-subsets regression and we used hierarchical partitioning analysis to quantify the explanatory power of each variable in the multivariate models. Songbird species richness was correlated most strongly with LiDAR variables related to canopy and midstory height and midstory density (R2=0.204, p<0.001). Richness of species that nest in the midstory was best explained by canopy height variables (R2=0.197, p<0.001). Species that forage on the ground responded to mean canopy height and the height of the lower canopy (R2=0.149, p<0.005) while aerial foragers had higher richness where the canopy was tall and dense and the midstory more sparse (R2=0.216, p<0.001). Richness of edge-preferring species was greater where there were fewer vegetation returns but higher density in the understory (R2=0.153, p<0.005). Forest interior specialists responded positively to a tall canopy, developed midstory, and a higher proportion of vegetation returns (R2=0.195, p<0.001). LiDAR forest structure metrics explained between 15 and 20% of the variability in richness within deciduous forest songbird communities. This variability was associated with vertical structure alone and shows how LiDAR can provide a source of complementary predictive data that can be incorporated in models of wildlife habitat associations across broad geographical extents. © 2011 Elsevier Inc.

Loading Ayres Associates Inc. collaborators
Loading Ayres Associates Inc. collaborators