Transportation Research Record: Journal of the Transportation Research Board

Assessment of the conditions of current assets is a task of major relevance in a transportation agency asset management program. It not only provides information on the current condition of the asset but also helps the agency make decisions on future maintenance and rehabilitation activities. Although low-volume roadways represent a large proportion of the total road network in the United States, little research on the management of these assets has been done. Two major data collection techniques are used for roadway condition assessment: manual and automated. Although automated techniques have been found to be safer and quicker, manual condition surveys have been proven to offer preciseness and cost-effectiveness. In the case of low-volume roadway assessment, for which the funds available to asset managers are limited, manual condition surveys are often preferred. Nevertheless, manual condition surveys must address the potential subjectivity of the results. Therefore, agencies could benefit from a system for ensuring quality on manual condition surveys. This paper proposes a framework for assessment of data quality and presents a case study of its implementation in the Northern New Mexico Pavement Evaluation Program. The proposed framework is easily implementable and able to identify potential and actual data collection issues. The framework can be used as part of an asset management program and could be particularly beneficial in the case of low-volume roads.

This paper discusses the results of a field investigation of 19 fish passageways constructed by the Oregon Department of Transportation. The intent of these passageways is to avoid significant disruption to the habitats required for a healthy life cycle for fish and other aquatic organisms. The field investigation of physical factors that may correlate with successful passageways may provide insight into more reliable and sustainable solutions to the problem of constructing highway crossings over natural waterways. The investigation is part of a larger study of whether construction practices may be additional factors that result in success. The researchers collected measurement information, including slopes, channel configurations, crossing structure characteristics, and streambed soil characteristics. The sites were judged on the basis of their suitability as fish passageways; for analytical purposes, a success factor was created and used to rate each site on the basis of the field observations. The physical metrics of the sites were correlated against the success index and other important fish passageway factors, and the results are presented. Important findings include a relationship between downstream slope and scour as well as an assessment that subsurface flow may be related to factors—perhaps construction techniques—other than the configuration of the channel.

Life-cycle assessment (LCA) is a tool that can be used to identify the environmental impact of a product or process. This paper compares three replacement options for an aging portland cement concrete (PCC) pavement with the use of an LCA process-based protocol. The options are to remove and replace the aging pavement with PCC pavement; remove the aging pavement and replace it with hot-mix asphalt (HMA) pavement; and crack and seat the existing pavement and then place an HMA overlay. Each option investigated includes a detailed construction and rehabilitation schedule and is analyzed over 50 years. The results show that materials production (e.g., cement, asphalt, PCC, and HMA) dominates the energy use, emissions, and impacts for all three options. In general, HMA production tends to cause the HMA option to have the highest energy use, whereas cement production tends to cause the PCC option to have the highest global warming potential (GWP). The crack, seat, and overlay option was the lowest energy user, had the lowest GWP, and produced the least emissions in more categories measured than the other two options. This may become a strong argument for expansion of the crack, seat, and overlay method of rehabilitation.

Several accidents involving aircraft punching through airfield pavements prompted the U.S. Navy to develop a technology for void detection. Initially, a successful void detection survey was completed at a naval air station where several voids were generated by leakage of large underground drainpipes. Various methods were used, such as internal videotaping of the pipes, heavy weight deflectometer (HWD) testing, testing with a ground-penetrating radar, and testing with a dynamic cone penetrometer (DCP). A state-of-the-art review was also completed to assess all existing technology applicable to void detection under pavements. However, the optimum technology (visual inspection and testing with an HWD and a DCP) still presented limitations because of the availability and speed of data acquisition, requiring prioritization of the work. A risk analysis was then completed and established work prioritization within each airfield and providing a prioritization of all U.S. Navy and Marine Corps airfield pavements. An interim policy and technical guidance (IP&TG) was issued on March 23, 2000, to establish the void detection methodology developed. This IP&TG was recently updated and included as an appendix in U.S. Department of Defense Unified Facilities Criterion UFC 3-260-03 and routinely applied at all 70 major U.S. Navy and Marine Corps airfields. This paper summarizes the methodology used and presents some recent field cases.

The present study deals with the revision of the current model in the Mechanistic–Empirical Pavement Design Guide (MEPDG) used to predict the environmental factor for unfrozen unbound materials (F_U), which is used to adjust the resilient response of soils resulting from seasonal changes. A large database with data from the existing literature and studies at Arizona State University was developed to evaluate the model. The results suggest that the environmental factor is underestimated for fine-grained materials with high plasticity under dry (arid) conditions. However, insufficient data were available to enhance the F_U models for wetter conditions. Three fundamental factors that may have impacts on the F_U values were evaluated in this study: stress state, compaction energy (soil density), and soil type. The stress state was found to have little to no impact on the predictions of F_U. But density changes and soil type were found to be important. The potential for soil index properties to be predictive variables was assessed. Models dependent on enhanced moisture content accounting for the effect of soil type are proposed for nonplastic and plastic materials. The range of predicted F_U values is in close agreement with the actual measured F_U values found from laboratory studies. It is recommended that the new models be adopted in the revision of the MEPDG model for the drier conditions described in this report and that research be conducted to enhance the F_U approach in the current MEPDG for wetter conditions brought on for a variety of reasons (e.g., groundwater table change, increased rainfall, and frost effects).

Climatic and environmental conditions have significant effects on pavement performance but have been inadequately considered in previous design methods. The Mechanistic–Empirical Pavement Design Guide (MEPDG) accounts for these effects through the use of the enhanced integrated climatic model. The present study examined the effects of climate on pavement performance predictions and the effects of climatic file generation by using MEPDG. The paper details the effort required to compare performance predictions for composite pavement consisting of asphalt cement over portland cement concrete (PCC) for 610 locations across the United States, with the use of MEPDG, Version 1.0. Analysis of the results was performed at the national, regional, and local levels. Although in general the results agree with the anticipated trends of environmental effects on pavement performance, the prediction of performance according to the predicted transverse cracking in the PCC layer was found to contain inconsistencies. These inconsistencies are attributed to the quality of the climatic data. The paper concludes that the MEPDG climatic database should be cleansed of incomplete or questionable climatic data files to ensure reliable performance prediction.

Significant amounts of money are spent annually on the rehabilitation of damaged pavements and approach slabs near bridge ends. Investigation of such failures often reveals that saturated base and subgrade materials or the loss of soil material from underneath the approach slab, pavement, or rip-rap slabs have contributed to failure. This paper reports findings from a research study entitled Water Intrusion in Base–Subgrade Materials at Bridge Ends. The objectives of this research project were to identify potential sources of water intrusion at bridge ends and develop maintenance strategies that can be economically implemented in the field to minimize future occurrences of the problem. The study focused on existing, in-service bridges and remedial strategies that have been successfully implemented. A survey questionnaire was developed and sent to all 25 Texas Department of Transportation administrative districts to collect information about the major factors contributing to water intrusion and bridge-end settlement problems. Field evaluations of selected bridges in four Texas DOT districts were conducted, and one bridge site was selected for detailed field study. On the basis of the information collected, the researchers developed a site assessment protocol to evaluate the potential of a particular site to incur water intrusion and methods to develop optimum repair strategies. The paper reports on the commonly observed sources of water intrusion at the bridge sites investigated. It also lists the preventive maintenance steps that must be taken to ensure that bridge approach pavements have adequate service lives.

This paper demonstrates the applicability of the genetic algorithm and curve-shifting methodology to the estimation of the resilient modulus at various stress states for subgrade soils by using the results of triaxial resilient modulus tests. This innovative methodology is proposed as an alternative to conventional nonlinear constitutive relationships. With the genetic algorithm, laboratory curves for different deviator stress levels at different confining pressures are horizontally shifted to form a final gamma distribution curve that can represent the stress–strain behavior of subgrade soils with the corresponding predicted shift factors. Resilient modulus values for a given stress state can be estimated on the basis of this curve and another gamma function that represents the variation of the shift values for different confining stresses. To compare the effectiveness of these two approaches, coefficients for the Uzan constitutive model were also determined for each laboratory test and compared with those determined by the approach described in this paper. Predicted resilient modulus values from each approach are separately compared with artificial neural network (ANN) model predictions to evaluate their efficiency and reliability for resilient response prediction. The results of the analysis indicated that the curve-shifting methodology gave superior estimates and a coefficient of determination 14% higher than the Uzan model predictions when the results were evaluated with the ANN model outputs. Thus, although it is not a constitutive model, use of the genetic algorithm and curve-shifting methodology is proposed as a promising technique for the evaluation of the stress–strain dependency of subgrade soils.

This paper details an official testing program developed by researchers at the Texas Transportation Institute (TTI) to classify sediment retention devices on the basis of their sediment removal performance. The testing facility designed as part of this study was constructed at the Texas Department of Transportation–TTI Hydraulics, Sedimentation, and Erosion Control Laboratory (HSECL) located at the Texas A&M University Riverside Campus. The facility consists of a parabola-shaped testing channel 4.6 m (15 ft) wide and 5.5 m (18 ft) long with a maximum depth of 0.8 m (2.5 ft) at the center and a slope of 3%. Two commercially available artificial sediments were mixed in equal proportions to create the artificial storm water for testing. The flow rate and turbidity of the water entering and leaving the channel were monitored for the duration of the test. The turbidity measurements were converted to suspended solid concentration by using a relationship developed in the HSECL laboratory. A simple mass balance calculation was used to determine the amount of sediment trapped in the channel.

Sedimentary rock fragments are used to build embankments. The fragments are made of durable and nondurable rocks. Durable rocks are defined as those that do not slake in the presence of water. In embankments, nondurable rock fragments are subjected to (a) compressive contact forces induced by other fragments and (b) slaking when they come into contact with water. These two processes convert the nondurable rock fragments into soil that moves into the space between the durable rock fragments, causing the settlement of the embankment. The goal of the present study was to calculate the amount of settlement experienced by a mixture of nondurable shale and durable limestone fragments when it is subjected to embankment loads. To this end, mixtures of the shale and limestone were placed in a metallic cylinder and subjected to three constant pressures. The settlement of the mixtures was measured at pressures equal to 345, 690, and 1,380 kPa. The settlements were measured first when the mixtures were dry. Then the mixtures were flooded with water, and the new settlements were recorded. The amount of settlement varied with the percentage by weight of the shale in the mixtures. The greatest settlements were recorded in the mixtures made of 100% shale. Small settlements were recorded when the mixtures were dry. Settlement was the result of the crushing and slaking of the shale fragments.

In July 2006, a large embankment failure occurred during construction of a four-lane divided highway leading to the Canada–U.S. border crossing in St. Stephen, New Brunswick, Canada. The highway embankment was approximately 12.3 m in height, just short of the design height of 14 m, when it failed. The cause of the failure was attributed to the rapid rate of construction and the intensity of loading on low-strength foundation soils, consisting of up to 15 m of soft marine clay. The reconstruction effort used 1.4 million scrap tires to create the tire-derived aggregate (TDA) as lightweight fill. TDA was placed within the new embankment, constructed over the site of the original failure. An important element to the design was the installation of geotechnical instrumentation, which allowed an observational approach to be taken during the construction process. This approach resulted in modifications to the original design throughout the process of reconstructing the TDA embankment. This paper presents the results of the TDA embankment and foundation performance over 25 months, with an emphasis on the design and behavior of the TDA during construction. The predicted values versus the values measured in the field for geotechnical parameters and the performance characteristics of TDA are presented, including unit weight, temperature, immediate compression, and time-dependent compression. The values for these measured parameters are compared with those from similar case histories and published values available from the literature. The TDA embankment reconstruction project began in the summer of 2007 and was successfully completed in the late fall of 2008.

This paper presents the framework for the interim design guideline for the use of expanded polystyrene (EPS) block geofoam for slope stabilization and repair, based on the findings of the NCHRP Project 24-11(02) Phase I study. The overall objective of this research is to develop a design guideline as well as an appropriate material and construction standard for the use of EPS block geofoam for the function of lightweight fill in slope stability applications. The recommended design methodology included in the framework is based on an assessment of the existing technology and literature. The Phase II work will refine the interim design guideline framework and address some uncertainties in the current state of the practice of analyzing various failure mechanisms included in the design procedure. The completed research will consist of the following five primary research products: (a) a summary of the relevant engineering properties, (b) a comprehensive design guideline, (c) a material and construction standard, (d) economic data, and (e) a detailed numerical example. No formal design guidelines on the use of any type of lightweight fill for slope stabilization by reducing the driving forces are available. Therefore, the proposed interim design guideline for EPS block geofoam can serve as a blueprint for the use of other types of lightweight fills in slope stability applications. The NCHRP Project 24-11(01) and the Project 24-11(02) Phase I research confirmed that EPS block geofoam is a unique lightweight fill material and can provide a safe and economical solution for slope stabilization and repair.

This paper presents a unified testing approach for measuring drying and wetting diffusion coefficients for unsaturated soil in the laboratory. Transient moisture flow in an unsaturated soil in response to suction changes is controlled by the unsaturated moisture diffusion coefficient. The moisture diffusion coefficient can be determined by measuring suction profiles over time. The laboratory testing approach involves measurement of the total suction changes with time with thermocouple psychrometers in cylindrical soil specimens with predetermined boundary conditions. The determination of the diffusion coefficient by this method is simple and relatively rapid and can be carried out on a routine basis in a geotechnical engineering laboratory. It is well-known that soils exhibit hysteresis with drying and wetting cycles. A similar hysteresis has been observed between the drying and wetting diffusion parameters for a number of undisturbed soil samples obtained from field borings across Oklahoma. The wetting diffusion coefficients are generally greater than the drying diffusion coefficients by a factor of up to 2.