Innovative Solutions for Slope Stability Reinforcement and Characterization: Vol. II, TR-489, 2005

Soil slope instability concerning highway infrastructure is an ongoing problem in Iowa, as slope failures endanger public safety and continue to result in costly repair work. While in the past extensive research has been conducted on slope stability investigations and analysis, this current research study consists of field investigations addressing both the characterization and reinforcement of such slope failures. While Volume I summarizes the research methods and findings of this study, Volume II provides procedural details for incorporating an infrequently-used testing technique, borehole shear tests, into practice. Fifteen slopes along Iowa highways were investigated, including thirteen slides (failed slopes), one unfailed slope, and one proposed embankment slope (the Sugar Creek Project). The slopes are mainly comprised of either clay shale or glacial till, and are generally gentle and of small scale, with slope angle ranging from 11 deg to 23 deg and height ranging from 6 to 23 m. Extensive field investigations and laboratory tests were performed for each slope. Field investigations included survey of slope geometry, borehole drilling, soil sampling, in-situ Borehole Shear Testing (BST) and ground water table measurement. Laboratory investigations mainly comprised of ring shear tests, soil basic property tests (grain size analysis and Atterberg limits test), mineralogy analyses, soil classifications, and natural water contents and density measurements on the representative soil samples from each slope. Extensive direct shear tests and a few triaxial compression tests and unconfined compression tests were also performed on undisturbed soil samples for the Sugar Creek Project. Based on the results of field and lab investigations, slope stability analysis was performed on each of the slopes to determine the possible factors resulting in the slope failures or to evaluate the potential slope instabilities using limit equilibrium methods. Deterministic slope analyses were performed for all the slopes. Probabilistic slope analysis and sensitivity study were also performed for the slope of the Sugar Creek Project. Results indicate that while the in-situ test rapidly provides effective shear strength parameters of soils, some training may be required for effective and appropriate use of the BST. Also, it is primarily intended to test cohesive soils and can produce erroneous results in gravelly soils. Additionally, the quality of boreholes affects test results, and disturbance to borehole walls should be minimized before test performance. A final limitation of widespread borehole shear testing may be its limited availability, as only about four to six test devices are currently being used in Iowa. Based on the data gathered in the field testing, reinforcement investigations are continued in Volume III.

Innovative Solutions for Slope Stability Reinforcement and Characterization: Vol. III, TR-489, 2005

Soil slope instability concerning highway infrastructure is an ongoing problem in Iowa, as slope failures endanger public safety and continue to result in costly repair work. Volume I of this current study summarizes research methods and findings, while Volume II provides procedural details for incorporating into practice an infrequently-used testing technique–borehole shear tests. Volume III of this study of field investigation of fifteen slopes in Iowa demonstrates through further experimental testing how lateral forces develop along stabilizing piles to resist slope movements. Results establish the feasibility of an alternative stabilization approach utilizing small-diameter pile elements. Also, a step-by-step procedure that can be used by both state and county transportation agencies to design slope reinforcement using slender piles is documented. Initial evidence of the efficiency and cost-effectiveness of stabilizing nuisance slope failures with grouted micropiles is presented. Employment of the remediation alternative is deemed more appropriate for stabilizing shallow slope failures. Overall, work accomplished in this research study included completing a comprehensive literature review on the state of the knowledge of slope stability and slope stabilization, the preparation and performance of fourteen full-scale pile load tests, the analysis of load test results, and the documentation of a design methodology for implementing the technology into current practices of slope stabilization. Recommendations for further research include monitoring pilot studies of slope reinforcement with grouted micropiles, supplementary experimental studies, and advanced numerical studies.

Thermoset Composite Concrete Reinforcement, HR-325, Part 1, 1992

The feasibility of substituting fibercomposite (FC) (thermoset) pavement dowels for steel pavement dowels was investigated in this research project. Load transfer capacity, flexural capacity, and material properties were examined. The objectives of Part 1 of this final report included the shear behavior and strength deformations of FC dowel bars without aging. Part 2 will contain the aging effects. This model included the effects of modulus of elasticity for the pavement dowel and concrete, dowel diameter, subgrade stiffness, and concrete compressive strength. An experimental investigation was carried out to establish the modulus of dowel support which is an important parameter for the analysis of dowels. The experimental investigation included measured deflections, observed behavioral characteristics, and failure mode observations. An extensive study was performed on various shear testing procedures. A modified Iosipescu shear method was selected for the test procedure. Also, a special test frame was designed and fabricated for this procedure. The experimental values of modulus of support for shear and FC dowels were used for arriving at the critical stresses and deflections for the theoretical model developed. Different theoretical methods based on analyses suggested by Timoshenko, Friberg, Bradbury, and Westergaard were studied and a comprehensive theoretical model was developed. The fibercomposite dowels were found to provide strengths and behavioral characteristics that appear promising as a potential substitute for steel dowels.

Retaining Wall - Modular Unit Reinforced Earth Tensar Geogrid Reinforcement, HR-549, 1998

This research, initiated in October 1992, was located at the intersection of Blairs Ferry Road and Lindale Drive in the City of Marion. The wall is located on the southeast corner of the intersection. Reinforced retaining wall construction started with a five inch base of roadstone with one inch of sand for leveling purposes. One and one-half to two feet of one inch clean stone was placed behind the blocks. A four inch perforated plastic pipe was placed approximately nine inches from the bottom of the one inch clean stone. The Tenswal, tensar geogrid was placed at every third layer. Openings in the Tenswal are hooked over plastic dowels in the blocks. The tenswal reaches from the face of the wall back 5' to 8'. The cost for constructing this wall was $124,400. The wall has performed well for the past five years. The wall improves the aesthetics of a high traffic volume intersection of an urban area. Many positive comments have been received by the city regarding its appearance. The City of Marion has been pleased with the wall and has used this type of wall on subsequent projects.

A Ten Year Performance Summary of Fibrous PC Concrete Overlay Research in Greene County, Iowa, HR-165, 1984

The Greene County, Iowa, overlay project, completed in October, 1973, was evaluated in October, 1978, after five years of service and most recently in October, 1983, after ten years of service. The 33 fibrous concrete sections, four CRCP sections, two mesh reinforced and two plain concrete sections with doweled reinforcement were rated relative to each other on a scale of 0 to 100. The rating was conducted by original members of the Project Planning Committee, Iowa DOT, Iowa County, Federal Highway Administration, University of Illinois and industry representatives. In all, there were 23 and 24 representatives who rated the project in 1978 and 1983 respectively. The 23 or 24 values were then averaged to provide a final rating number for each section or variable. All experimental overlay sections had performed quite well in the period from five through 10 years, experiencing only limited additional deterioration. Based upon this relatively good performance through 10 years, the sections will be maintained for further research with another evaluation at 15 years. The 4" thick nonfibrous mesh reinforced continuous reinforced concrete pavement overlay sections provided the best performance in this research project. Another nonfibrous 5" thick bar reinforced overlay section performed almost as well. The best performance of a fibrous reinforced concrete section was obtained with 160 pounds of fiber per cubic yard.

Performance of Reinforcement Fabric Used Under Asphaltic Concrete Overlays, MLR-83-03, 1983

The 1982 cost of a two-inch asphaltic concrete overlay, with fabric, was an average of 85% of the cost of a three-inch overlay (see attached calculations). A structural number can be assigned to the extra inch of overlay, whereas it is doubtful that any number can be assigned to the fabric. The observations made on the projects in this report leave little reason to be optimistic on the use of fabrics under asphalt overlays. This is especially true of the Floyd, Dallas and Clarke county projects. A great amount of fabric is being used nationwide for this purpose, probably more from sales promotion than from actual documented performance. Full scale field testing is continuing each time a project is let utilizing fabric reinforcement under asphaltic concrete overlays. It has already become apparent that the use of fabrics in AC overlays is not always cost effective.

Investigation of Glass Fiber Composite Dowel Bars for Highway Pavement Slabs, TR-408, 2001

Contractors, engineers, owners and manufacturers want to be certain that a new product or procedure will yield beneficial results when compared to the current method of construction. The following research was conducted in order to compare the performance of epoxy coated dowel bars to dowel bars of alternative shapes and materials such as stainless steel and glass fiber reinforced polymer (GFRP). Research was also done on the effect that dowel bar spacing has on the performance of concrete pavements. Four phases of this research are described in this report.

Evaluation of Corrosion Resistance of Different Steel Reinforcement Types, 2006

The corrosion of steel reinforcement in an aging highway infrastructure is a major problem currently facing the transportation engineering community. In the United States alone, maintenance and replacement costs for deficient bridges are measured in billions of dollars. The application of corrosion-resistant steel reinforcement as an alternative reinforcement to existing mild steel reinforced concrete bridge decks has potential to mitigate corrosion problems, due to the fundamental properties associated with the materials. To investigate corrosion prevention through the use of corrosion-resistant alloys, the performance of corrosion resistance of MMFX microcomposite steel reinforcement, a high-strength, high-chromium steel reinforcement, was evaluated. The study consisted of both field and laboratory components conducted at the Iowa State University Bridge Engineering Center to determine whether MMFX reinforcement provides superior corrosion resistance to epoxy-coated mild steel reinforcement in bridge decks. Because definitive field evidence of the corrosion resistance of MMFX reinforcement may require several years of monitoring, strict attention was given to investigating reinforcement under accelerated conditions in the laboratory, based on typical ASTM and Rapid Macrocell accelerated corrosion tests. After 40 weeks of laboratory testing, the ASTM ACT corrosion potentials indicate that corrosion had not initiated for either MMFX or the as-delivered epoxy-coated reinforcement. Conversely, uncoated mild steel specimens underwent corrosion within the fifth week, while epoxy-coated reinforcement specimens with induced holidays underwent corrosion between 15 and 30 weeks. Within the fifth week of testing, the Rapid Macrocell ACT produced corrosion risk potentials that indicate active corrosion for all reinforcement types tested. While the limited results from the 40 weeks of laboratory testing may not constitute a prediction of life expectancy and life-cycle cost, a procedure is presented herein to determine life expectancy and associated life-cycle costs.