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Project Highlights (continued)
Interdisciplinary Team at SDSU Studies New Method for Predicting Bridge Scour
Francis Ting, a hydraulic engineer, and Allen Jones, a geotechnical engineer, from South Dakota State University are working together to evaluate a new method for predicting bridge scour in cohesive sediments.
The new method, called SRICOS (Scour Rate In COhesive Soils), was originally developed at Texas A&M University by an interdisciplinary team of researchers including Ting. Unlike conventional methods, which only predict the equilibrium depth of scour, SRICOS can predict the scour history over the lifetime of a structure. Many bridges in South Dakota are founded on cohesive soils consisting of silts and clays. The new method could lead to substantial saving in bridge construction costs if the expected scour is significantly less than the equilibrium scour.
Subsurface exploration was completed at three bridge sites (Big Sioux River near Flandreau, Split Rock Creek near Brandon, and White River near Presho) in South Dakota in the summer and fall of 2007 to determine the soil stratigraphy and to obtain soil samples for erosion rate and laboratory testing.
The SDSU researchers measured soil erosion rates using an erosion function apparatus at the Minnesota Department of Transportation Materials Laboratory. The results of the soil tests are presented combined with computed flow conditions at the bridge sites to predict their scour histories for comparison with measured scour data collected by the United States Geological Survey (USGS) during the floods in 1993.
In addition to evaluating the SRICOS method for South Dakota bridges, the researchers will also conduct a sensitivity analysis to identify the critical input parameters and to develop guidelines on the use of the method for small watersheds and ungaged streams. This project is co-sponsored by the Mountain-Plains Consortium (MPC) and South Dakota Department of Transportation (SDDOT). Ryan Larsen, a native from Elk Point, SD, is a student research assistant on the project.
CSU Studies Shredded, Used Tires as Roadbed Filler
A Colorado State University professor is researching whether some of Colorado's 40 million stockpiled rubber tires – the largest batch in the nation – can be reused to bolster residential foundations and road bases to mitigate the effects of expansive soils.
Antonio Carraro, assistant professor of civil and environmental engineering, is leading an experiment with the city of Loveland to test a mixture of expansive soil and scrap tire rubber just below the pavement on a 200-foot, low-volume stretch of road near I-25. Lime and fly ash are the traditional materials typically used to mitigate the shrink-swell potential of roadbed soils.
"We're always looking for opportunities to improve our roads and do a better job with making our products more environmentally friendly," said Keith Reester, director of Public Works for the city of Loveland. "Hopefully we have a product that works and that will allow us to take some of those tires out of the waste stream."
Carraro also recently received a $128,913 grant from the Colorado Commission on Higher Education to test his expansive soil-rubber mixtures in residential foundations.
The road test section in Loveland will use only about 20 percent rubber by weight when combined with soil. But there are lots of scrap tires stockpiled in the state – With 40 million tires, Colorado leads the seven states that host 84 percent of all stockpiled tires in the United States, according to 2005 figures from the Rubber Manufacturers Association. New York ranks second with 37 million tires. Carraro has worked with Front Range Tire Recycle in Sedalia and Jai Tire Industries in Denver for tire samples.
"Only about 2 percent of scrap tire rubber products are reused in civil engineering applications in EPA Region VIII (which includes Colorado and five other western states) while other regions, such as the midwestern United States, reuse more than 25 percent," Carraro said. "It's a major solid waste problem, particularly in the West where the population is spread out and there is less demand and no established civil engineering markets for reusing the tires."
"We are trying to come up with a sustainable way of mitigating the expansive soils problem in Colorado that takes into account the beneficial use of a waste material that has great recycling potential," Carraro said. "Soil-rubber mixtures have been studied and used since the late 1980s, but the transfer of this technology to civil engineering applications that involve expansive soil mitigation is innovative. This is a new technology for expansive soils. These projects will allow us to understand in a more fundamental way the many interesting technical aspects associated with the design, construction and performance of expansive soil-rubber mixtures."
Carraro and his students will monitor the effects of the expansive soil-rubber mixture on the road in Loveland. They will assess cracks, ruts, permanent deformation, potholes and overall quality of the pavement.
In Colorado, shredded tires are largely in demand for landfill construction, said Rick Welle, general manager of Front Range Tire Recycle in Sedalia. The tire "shreds" are also used as floor material for horse arenas and children's playgrounds, but tire recyclers are always looking for other markets. The Loveland project is using about 25 tons of shredded tires equal to 2,225 passenger vehicle and light truck tires, Welle said.
"What we're hoping with this study is to show that tire shreds are beneficial for road base and that over time it will be a cost-effective product," Welle said. "It would be a huge market to really help Colorado get back with the rest of the country as far as managing scrap tires."
Carraro is also experimenting with the amount and size of scrap tire rubber products in his projects. Larger ones, called tire chips (containing particles up to 2 inches in diameter) can cost roughly $30 per ton, while smaller rubber products, called granulated rubber (containing particles less than 0.5 inches in diameter) can cost up to $450 per ton.
(by Emily Wilmsen, Senior Media and Community Relations Coordinator, Colorado State University)
Utah Traffic Lab Models Traffic to Aid in Express Lane Pricing
Innovative lane management offers the opportunity to levy fees for premium road space. One option being used in Salt Lake City, express lanes, offers road users reduced journey time for a fee.
The Utah Department of Transportation recently converted the high occupancy vehicle (HOV) lanes on Interstate 15 (I-15) from 600 North Street in Salt Lake City, Salt Lake County, to University Parkway (SR-265) in Orem, Utah County to express lanes. Subscribers (single occupant vehicles) who pay a monthly fee and high occupancy vehicles now share the express lane. This concept will be further advanced through the application of an electronic toll-collecting system.
Consequently, UDOT management would like to learn how to best implement future High Occupancy Toll (HOT) pricing. The Utah Traffic Lab at the University of Utah will use an I-15 VISSIM (transportation modeling software) model for that purpose. The Utah Traffic Lab has already built and calibrated a microsimulation model of I-15 from 600 N in Salt Lake City to University Parkway in Provo, UT. The Traffic Lab has extended the original UDOT model and constructed two sub models for a.m. and p.m. traffic conditions.
The models have been calibrated and validated based on field data collected through numerous GPS travel time runs and other data collection methods. However, current HOT operations in the model, which were inherited from the original UDOT model, do not reflect the fact that HOT users can access HOT lanes only at certain points along the freeway. The VISSIM model has no access restrictions in the VISSIM model.
The existing model will be modified to properly model HOT operations. Once those modifications are made the model will be able to simulate current HOT operations and integrate a future dynamic toll pricing to enable real-time variable congestion pricing.
