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2019 University of Kansas Transportation Projects

Internal Reinforcement of Backfill behind Bridge Abutments to Mitigate Approach Slab Distresses

Principal Investigator: Jie Han

Co-Principal Investigator: Robert L. Parsons

When embankments are constructed to approach bridge abutments, an uneven approach slab condition often occurs. This uneven approach slab condition is caused by the differential settlement between the embankment soil and the abutment, and the resulting deformation or fracture of the bridge approach slab. Embankment soil settlement is often induced by thermal expansion/shrinkage of the bridge deck, resulting in the movement of the abutment and the embankment soil. Traffic loading on the approach slab also induces settlement of embankment soil. Embankment soil settlement causes the approach slab of the bridge to lose its support from the soil. When the soil support is lost, the slab will bend and even break under the worst case. The loads on the deformed slab will redistribute to its ends, which may result in faulting and bump formation across the roadway at the ends of the approach slab. Such problems have repeatedly occurred in KDOT projects, posed risks to the safety of vehicles and drivers, and required repeated maintenance, repair, and even re-construction. To mitigate the above problems, internal reinforcement is proposed in this research to minimize embankment soil movement behind abutments and under approach slabs. The geosynthetic reinforcement is expected to minimize embankment soil settlement behind the abutment and under the approach slab. The objective of this research is to evaluate the performance of internal reinforcement to mitigate approach slab distresses using large scale model testing in the laboratory. It is expected that KDOT bridge and geotechnical engineers will implement the findings and recommendations from this research into the design of bridge abutments and approach slabs.

Field Monitoring of Wicking Geotextile for Moisture Reduction in Pavements

Principal Investigator: Jie Han

Co-Principal Investigator: Robert L. Parsons

Water is often detrimental to the performance of pavements since it reduces soil strength and modulus and provides sources for erosion and freeze-thaw of base courses and subgrade. Removal of water from pavements can improve the performance of pavements and make them last longer. A common approach to remove water within pavements is to provide a drainage system, which is effective only when the soil beneath the pavement is saturated and water drains out under a hydraulic gradient. However, a majority of pavement soils and aggregate base beneath pavements are mostly unsaturated during their service life. Therefore, the conventional drainage method is not effective in removing moisture in pavements. A newly developed geosynthetic product (also called a wicking geotextile) has been recently introduced into practice. It has been used in Alaska, Wisconsin, and Missouri to effectively solve freeze-thaw problems in subgrade soils and aggregate bases beneath the pavement structure. The research team at the University of Kansas has conducted a series of laboratory tests to evaluate the effectiveness of the wicking geotextile fabric to reduce moisture in Kansas aggregate bases (Guo et al., 2017; Wang et al., 2017). The test results verified the effectiveness of wicking geotextile in reducing moisture in aggregate bases. The aggregate bases with moisture reduction performed much better than those without moisture reduction in terms of base course deformation under cyclic plate loading. Before this product can be widely used in actual subgrade soil and aggregate base moisture reduction applications, a field trial with test sections is necessary to verify its field performance. KDOT has a plan to use this wicking geotextile in a project on US-169 in Allen County as a field trial, which includes two 1000-foot long test sections with a wicking geotextile with each section having different aggregate base type materials. There is a need for field monitoring of the wicking geotextile for moisture reduction in pavements. The purpose of this preproposal is to address this need. The field monitoring includes the installation and measurement of moisture and temperature sensors, sampling and dynamic cone penetration testing, and visual observation of pavement distresses for these two test sections during pavement service. The data collected will be used to evaluate the performance of wicking geotextile in moisture reduction in pavements.

Development of Risk-Based Protocol for KDOT Construction Inspection

Principal Investigator: Daniel Tran

Material quality assurance (QA) for highway construction has been fundamental to meeting the missions of State Departments of Transportation (DOT) and the Federal Highway Administration (FHWA). Traditionally, DOTs specified materials quality standards based on detailed instructions describing the required materials and construction methods. Acceptance was determined based on pass/fail standards or engineering experience and judgment. Although these standards appeared to work well, a grand challenge that DOTs are facing is the ever-growing gap between the demand for inspection and available resources. Many state DOTs including KDOT have lost experienced construction inspection staff while the number of projects are increased with a high level of inspection required. To address this issue, DOTs often rely on a contractor’s quality control (QC) and outsource to the third party for testing and inspection. This strategy, however, is not always a cost-effective approach.

This study will develop a risk-based protocol for KDOT to optimize the allocation of available resources to critical inspection items. The proposed protocol will be developed based on the probability (likelihood) and consequence (severity) of a failure of material testing or construction activities associated with a core list of inspection items. The risk-based protocol will focus on interpreting the risks in a comprehensive but practical manner.

Effectiveness of Entertaining Non-Traffic Related Messages on Dynamic Message Signs

Principal Investigator: Alexandra Kondyli

Co-Principal Investigator: Steven D. Schrock

A large number of transportation agencies across the US use Dynamic Message Signs (DMS) to display traffic-related information to motorists, such as travel times, lane closures, incidents, inclement weather, etc. Recently, several agencies have gone even further and started using entertaining messages in an effort to grab motorists’ attention and change their behavior. These messages focus on seat belt use, distracted driving, aggressiveness, or reinforcing driving rules. There are several examples that have been used by state departments of transportation (DOTs). For example, Massachusetts exploited the regional dialect to display “Use yah blinkah” and “Make yah ma proud, wear yah seatbelt.” Utah displayed “That seat belt looks good on you” and one of Tennessee’s popular messages is “Texting and driving, oh cell no.” The Iowa and Missouri DOTs are also displaying messages such as “Exit to text it”, or “Get your head out of your apps.” In an effort to raise awareness, some DOTs have contests and ask the public to contribute to the pool of entertaining messages. Following the steps of these DOTs, the Kansas DOT (KDOT) is considering displaying these messages along major freeways in the state. Although these messages seem to gain approval from the public, no study has been done to evaluate how effective these are in actually changing behavior and promoting safety. As such, the goal of this project is to investigate how entertaining non-traffic related messages influence driver behavior.


Synthesis of Value Engineering (VE) Study on Mechanically Stabilized Earth (MSE) Walls for KDOT (Phase I)

Principal Investigator: Daniel Tran

State departments of transportation (DOTs) across the nation are continually facing technical complexities, regulatory restrictions, and pressures to deliver quality projects on time and within budget. To successfully deliver transportation projects, DOTs often apply Value Engineering (VE) to balance project needs (safety, quality, and operations) and resources (cost, schedule, and materials). VE has been used to improve transportation projects for more than two decades and is required for federal-aid projects. Currently, the Federal Highway Administration (FHWA) requires that state DOTs perform VE studies for all applicable federal-aid highway projects with an estimated total cost of $50 million or more and $40 million or more for bridge projects.

VE is often applied to a wide range of project elements and activities to provide recommendations for improving project functionality, shortening project schedule, and lowering overall project cost. One of the most common VE recommendations is related to the use of Mechanically Stabilized Earth (MSE) walls. While MSE walls offer a number of advantages over conventional cast-in-place retaining structures, several issues surrounding the use of MSE walls in Kansas remain unclear. These issues include cost-effectiveness, cost savings, the overall stability with long-term performance, the site condition where MSE walls should or should not be used, or materials and construction methods to construct the walls. There is a need for investigating and analyzing the use of MSE walls in Kansas to provide valuable information for decision making within KDOT when reviewing and approving VE recommendations.

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2018 University of Kansas Transportation Projects

Analytical Investigation of Saddle Connections for Overhead Sign Trusses with Respect to strength and fatigue performance

Principal Investigator: William Collins

Co-Principal Investigators: Jian Li, Matthew Fadden

The Kansas DOT is currently using a new saddle-type connection for use in highway overhead sign trusses between the truss and end support columns. Compared with the coupler connections introduced in the early 1970s, the saddle connections are easier to inspect and appear to offer better strength and fatigue performance. However, no quantitative understanding of these saddle connections exists regarding their mechanical performance, including ultimate strength and fatigue susceptibility, compared to the coupler connections. As a result, KDOT does not have a procedure to verify the ultimate and fatigue strengths of these details in the design process. This project aims to investigate the ultimate and fatigue strength of the saddle connections through finite element (FE) analysis.

Promoting the Transportation Systems Management and Operations Program in Kansas

Principal Investigator: Alexandra Kondyli

As congestion continues to increase and funding for new infrastructure and agency personnel is ever more constrained, transportation agencies are seeking efficient strategies to better manage existing capacity. Apart from recurring congestion, our transportation system has become sensitive to crashes, construction/work zones, and adverse weather, which contribute to unreliability and to excessive delays. To tackle the adverse effects of congestion and unreliability, transportation agencies at the local and state level are encouraged to develop a Transportation Systems Management & Operations (TSM&O) program. TSM&O is an integrated program to optimize the performance of existing infrastructure through the implementation of strategies, methods, services, and projects to preserve capacity and improve the safety, security, and reliability of our transportation system.

Currently, the Wichita area (District 5) appears to have a TSM&O program in place. Kansas City’s Scout also offers a good example of advanced transportation systems management in real-time. With the exception of these two areas, no such program exists at the state level. The proposed research will investigate implementations of TSM&O within the state (Wichita and Kansas City) as well as successful implementations at other states (such as CO, FL, IA, and WA), and identify the critical elements for developing a statewide TSM&O program.

Dynamic Performance of Cantilevered Sign Trusses for Fatigue

Principal Investigator: Matthew Fadden

Co-Principal Investigators: William Collins, Jian Li, Mark Ewing

Cantilevered sign truss structures are susceptible to fatigue issues at the connection between the pole and mast arm due to vibrations caused by galloping, vortex shedding, natural wind gusts, and truck-induced wind gusts. Calculations carried out by engineers at KDOT indicate that box connection details should be susceptible to fatigue; however, no fatigue cracks have been observed. Recently, it has been proposed to remove walkways on cantilevered sign trusses to prevent vandalism. It is not evident what impact walkway removal will have on the aerodynamic/aeroelastic properties of cantilevered sign trusses and how this will influence fatigue performance. To understand the risk of potential failures, there is a need to evaluate these sign structures and develop strategies that result in lower levels of vibrations to mitigate fatigue problems. Research has considered wind loads in sign structures [1,2], but the impact of walkway removal remains unclear. The proposed work is an important step in ensuring safe cantilevered sign trusses.


DSR-based test procedures and specification guidelines for grading PG58-XX and PG64S-XX asphalt binders in the state of Kansas

Principal Investigator: Matthew Fadden

Co-Principal Investigators: William Collins, Jian Li, Mark Ewing

Application of the MSCR test in grading and grade adjustment of modified asphalt binders has gained popularity in recent years. Two separate parameters are determined from the MSCR test, namely: non-recoverable creep compliance (Jnr) and percentage of recovery (MSCR %R). The Jnr value indicates the rutting resistance of asphalt binders while MSCR %R represents the capability of binders to relax stresses and recover strains. While there is a consensus among the pavement community that the MSCR test parameters can be used effectively for the specification of modified binders, it disregards asphalt binders that have relatively high non-recoverable compliance, Jnr, and states that those binders must be used without modification and the MSCR %R criteria must be waived. Interestingly, a wide variety of modified and current asphalt binders used in the state of Kansas (e.g., PG64S-XX and PG58-XX binders) does not satisfy the Jnr criteria and therefore are disregarded and not included in the specification system. There is a clear need to investigate how the MSCR and other DSR-based test parameters should be applied for grading and grade adjustment of these binders. This research proposal aims at the development of clear guidelines on how to test and characterize modified PG64S-XX and current PG58-XX binders used in the state of Kansas.


Investigation of Corrosion Potential Variations in Mechanically Stabilized Earth Backfill due to Migration of Fines

Principal Investigator: Robert L. Parsons

Co-Principal Investigators: Jie Han

Identification of aggregates that present minimal corrosion risk, even if the fines become concentrated, or, as an alternative, identifying favorable gradations that prevent migration of fines, could extend the life of new MSE structures and limit repair and rehabilitation costs. KDOT currently has a 5000/3000 ohm-cm minimum standard for the resistivity of aggregate backfill used for mechanically stabilized earth (MSE) walls. During a recent study on the applicability of the AASHTO T 288 resistivity test, KU found that resistivity of aggregate is not a fixed value, but that it may change as precipitation filters through the aggregate. For many cases this can be good as the “washing” of the aggregate can result in a cleaner backfill and increased resistivity (less corrosion potential). However, if the reduction in resistivity is caused by the “washing” of fines, those fines have to go somewhere and may be deposited and concentrated at the base of the fill. There is a need to confirm that aggregates are being specified that will not present a corrosion concern even if the fines become concentrated. It would also be beneficial to identify gradations that prevent the internal migration and concentration of fines.


Evaluation of Cement Modified Soil (CMS) with Micro-cracking

Principal Investigator: Jie Han

Co-Principal Investigators: Robert L. Parsons, Chi Zhang

Fly ash has been commonly used by KDOT to modify subgrade. Recently, fly ash has become less available and therefore the price has gone up significantly. In addition, a much higher percentage of fly ash needs be used to achieve the same subgrade strength and stiffness than that of cement. Therefore, cement has become more economical for modifying subgrade. However, cement has a major issue of shrinkage cracking, which may result in reflective cracking in asphalt pavements after construction. A high percentage of cement is often needed for some subgrade soils to meet the unconfined compressive strength requirement without jeopardizing durability and stiffness. Higher percentages of cement can result in more shrinkage cracking. To overcome this problem, micro-cracking technology has been adopted in the field. This technology involves compaction of cement-modified soil (CMS) and re-compaction of CMS by a roller 24 to 48 hours later to induce micro-cracks in the CMS and minimize shrinkage cracking. However, micro-cracking of CMS is expected to reduce its strength and stiffness but increase its permeability. To verify the performance of CMS with micro-cracking, an experimental study is proposed which involves field and laboratory tests. During these tests, strength, stiffness, percent of shrinkage, and permeability of CMS before and after micro-cracking will be evaluated. In addition to conventional laboratory and field test methods, the resistivity method will be adopted to evaluate the physical properties of CMS with micro-cracking.


Bridge Deck Drainage: Evaluation and Updating of Current Design Guidance

Principal Investigator: Bruce McEnroe

Proper drainage of bridge decks is essential for safe travel and for the longevity of the bridge. Poor drainage can cause water to spread onto the driving lanes, which increases the risk of hydroplaning and ice formation. It might be possible to reduce the likelihood of future deck-drainage problems on new bridges by making certain changes to KDOT’s design guidelines. It might also be possible to improve and simplify KDOT’s current procedures for design of bridge-deck drainage.