8 resultados para Unstable shoes
em Iowa Publications Online (IPO) - State Library, State of Iowa (Iowa), United States
Resumo:
Stability berms are commonly constructed where roadway embankments cross soft or unstable ground conditions. Under certain circumstances, the construction of stability berms cause unfavorable environmental impacts, either directly or indirectly, through their effect on wetlands, endangered species habitat, stream channelization, longer culvert lengths, larger right-of-way purchases, and construction access limits. Due to an ever more restrictive regulatory environment, these impacts are problematic. The result is the loss of valuable natural resources to the public, lengthy permitting review processes for the department of transportation and permitting agencies, and the additional expenditures of time and money for all parties. The purpose of this project was to review existing stability berm alternatives for potential use in environmentally sensitive areas. The project also evaluates how stabilization technologies are made feasible, desirable, and cost-effective for transportation projects and determines which alternatives afford practical solutions for avoiding and minimizing impacts to environmentally sensitive areas. An online survey of engineers at state departments of transportation was also conducted to assess the frequency and cost effectiveness of the various stabilization technologies. Geotechnical engineers that responded to the survey overwhelmingly use geosynthetic reinforcement as a suitable and cost-effective solution for stabilizing embankments and cut slopes. Alternatively, chemical stabilization and installation of lime/cement columns is rarely a remediation measure employed by state departments of transportation.
Resumo:
Highlights: * U.S. Labor Secretary Hilda Solis visited Iowa at the end of July....pg. 2 * The Shoes for Veterans campaign began following a visit to a homeless shelter in the Quad Cities....pg. 2 * Are You Prepared? An emergency – be it a flood, tornado, winter storm or power outage – can occur quickly and without warning...pg. 3 * The Southwest Iowa Employers’ Council & Iowa Workforce Development in conjunction with the Iowa Committee for ESGR will present two valuable training sessions for businesses.....pg. 3
Resumo:
According to prevailing ecological theory one would expect the most stable vegetation on sites which are least disturbed (Odum 1971). According to theory one would also expect the most diversity of species on undisturbed sites (Odum 1971). This stable and diverse community would be produced over a period of many years through a process of plant succession where annual herbs are replaced by perennial herbs and finally woody plants would come to dominate and perpetuate the community. Another ecological theory holds that the complexity (structure and species diversity) of a plant community is dependent upon the amount of disturbance to which it is subjected (Woodwell, 1970). According to this theory the normal succession of a plant community through its various stages may be arrested at some point depending upon the nature and severity of the disturbance. In applying these theories to roadside vegetation it becomes apparent that mass herbicide spraying and extensive mowing of roadsides has produced a relatively simple and unstable vegetation. It follows that if disturbances were reduced not only would the roadside plant community increase in stability but maintenance costs and energy usage would be reduced. In this study we have investigated several aspects of reduced disturbances on roadside vegetation. Research has centered on the effectiveness of spot spraying techniques on noxious weed control, establishment of native grass cover where ditch cleaning and other disturbance has left the bare soil exposed and the response of roadside vegetation when released from annual mass spraying.
Resumo:
This report summarizes research conducted at Iowa State University on behalf of the Iowa Department of Transportation, focusing on the volumetric state of hot-mix asphalt (HMA) mixtures as they transition from stable to unstable configurations. This has raditionally been addressed during mix design by meeting a minimum voids in the mineral aggregate (VMA) requirement, based solely upon the nominal maximum aggregate size without regard to other significant aggregate-related properties. The goal was to expand the current specification to include additional aggregate properties, e.g., fineness modulus, percent crushed fine and coarse aggregate, and their interactions. The work was accomplished in three phases: a literature review, extensive laboratory testing, and statistical analysis of test results. The literature review focused on the history and development of the current specification, laboratory methods of identifying critical mixtures, and the effects of other aggregate-related factors on critical mixtures. The laboratory testing involved three maximum aggregate sizes (19.0, 12.5, and 9.5 millimeters), three gradations (coarse, fine, and dense), and combinations of natural and manufactured coarse and fine aggregates. Specimens were compacted using the Superpave Gyratory Compactor (SGC), conventionally tested for bulk and maximum theoretical specific gravities and physically tested using the Nottingham Asphalt Tester (NAT) under a repeated load confined configuration to identify the transition state from sound to unsound. The statistical analysis involved using ANOVA and linear regression to examine the effects of identified aggregate factors on critical state transitions in asphalt paving mixtures and to develop predictive equations. The results clearly demonstrate that the volumetric conditions of an HMA mixture at the stable unstable threshold are influenced by a composite measure of the maximum aggregate size and gradation and by aggregate shape and texture. The currently defined VMA criterion, while significant, is seen to be insufficient by itself to correctly differentiate sound from unsound mixtures. Under current specifications, many otherwise sound mixtures are subject to rejection solely on the basis of failing to meet the VMA requirement. Based on the laboratory data and statistical analysis, a new paradigm to volumetric mix design is proposed that explicitly accounts for aggregate factors (gradation, shape, and texture).
Resumo:
General principles • Everyone at the construction site, particularly foremen and supervisors, is responsible for recognizing and troubleshooting potential problems as they arise. • Batches of concrete should be consistent and uniformly mixed. • A major cause of pavement failure is unstable subgrade. The subgrade should consist of uniform material, and the subgrade system must drain well. • Dowel bars are important for load transfer at transverse joints on pavements with high truck volumes. Dowels must be carefully aligned, horizontally and vertically, to prevent pavement damage at the joints. • Stringlines control the slipform paver’s horizontal and vertical movement and ensure a smooth pavement profile. Once stringlines are set, they should be checked often and not disturbed. • Overfinishing the new pavement and/or adding water to the surface can lead to pavement surface problems. If the concrete isn’t sufficiently workable, crews should contact the project manager. Changes to the mixture or to paver equipment may reduce the problem. • Proper curing is critical to preventing pavement damage from rapid moisture loss at the pavement surface. • A well spaced and constructed system of joints is critical to prevent random cracking. • Joints are simply controlled cracks. They must be sawed during the brief time after the pavement has gained enough strength to prevent raveling but before it begins to crack randomly (the “sawing window”). • Seasonal and daily weather variations affect setting time and other variables in new concrete. Construction operations should be adjusted appropriately.
Resumo:
Since the turn of the century, tributaries to the Missouri River in western Iowa have entrenched their channels to as much as six times their original depth. This channel degradation is accompanied by widening as the channel side slopes become unstable and landslides occur. The deepening and widening of these streams have endangered about 25% of the highway bridges in 13 counties [Lohnes et al. 1980]. Grade stabilization structures have been recommended as the most effective remedial measure for stream degradation [Brice et al., 1978]. In western Iowa, within the last seven years, reinforced concrete grade stabilization structures have cost between $300,000 and $1,200,000. Recognizing that the high cost of these structures may be prohibitive in many situations, the Iowa Department of Transportation (Iowa DOT) sponsored a study at Iowa State University (ISU) to find low-cost alternative structures. This was Phase I of the stream degradation study. Analytical and laboratory work led to the conclusion that alternative construction materials such as gabions and soil-cement might result in more economical structures [Lohnes et al. 1980]. The ISU study also recommended that six experimental structures be built and their performance evaluated. Phase II involved the design of the demonstration structures, and Phase III included monitoring and evaluating their performance.
Resumo:
Reinforced Earth is a French development that has been used in the United States for approximately ten years. Virbro-Replacement, more commonly referred to as stone columns, is an outgrowth of deep densification of cohesionless soils originally developed in Germany. Reinforced Earth has applicability when wall height is greater than about twelve feet and deep seated foundation failure is not a concern. Stone columns are applicable when soft, cohesive subsoil conditions are encountered and bearing capacity and shearing resistance must be increased. The conditions in Sioux City on Wesley Way can be summarized as: (1) restricted right of way, (2) fill height in excess of 25 feet creating unstable conditions, (3) adjacent structures that could not be removed. After analyzing alternatives, it was decided that Reinforced Earth walls constructed on top of stone columns were the most practical approach.
Resumo:
With this application, the College Creek sub-watershed in Ames represents both regional collaboration and locally directed action to improve an Iowa watershed. Already completed watershed assessment identified more than 4000 tons/yr of sediment delivered from within the Ames city limits due to degraded stream conditions. The water quality enhancement goal of this project is reducing sediment delivery specifically from unstable streambanks and degrading stream channels on College Creek, one of 4 Ames tributaries to Squaw Creek. The project will also redirect urban storm water runoff into engineered infiltration systems, intercepting it from storm drains entering College Creek. This application builds on storm water runoff demonstration projects and research already funded in the College Creek sub-watershed by EPA Region 7 and Iowa DNR. Public outreach, one of the key elements of this project, is built into every phase from engineering design feedback to construction. Innovative neighborhood learning circles are utilized to educate residents and share public feedback with project engineers to ensure that project elements are both technically appropriate and socially acceptable. All practices proposed in this project -stream stabilization, storm water infiltration, and neighborhood learning circle techniques-have already been successfully demonstrated in the College Creek sub-watershed by the City of Ames in partnership with Iowa State University.