Heather J Miller

Spring Thaw Predictor and Development of Real Time Spring Load Restrictions

In the fall of 2006, the State of New Hampshire Department of Transportation (NHDOT) began a two - year study to develop a Real Time Spring Load Restriction Methodology. The methodology is intended to guide the Maintenance Districts in their management of spring load restrictions by identifying the beginning and duration of spring thaw. Two methods will be used to determine how long load restrictions will be needed after the date of actual thaw: frost tube readings and computer model forecasting. A total of nine sites in the central part of the state were instrumented with frost tubes, water wells, subsurface temperature and moisture sensors, and weather stations. Falling Weight Deflectometer (FWD) tests were conducted at those sites from January 2008 through June 2008 with an additional test in August 2008 and another in October 2008. The U.S. Forest Service is continuing its work with the current developer of the Enhanced Integrated Climatic Model (EICM), which is embedded in the Mechanistic Pavement Design Procedure (MEPDG). It is proposed to use the EICM (isolated from the MEPDG) with the 7–10 day forecast temperatures to predict thaw. This paper describes the overall project, data collected to date, and preliminary results.

Keeping Springtime Low-Volume Road Damage to a Minimum: Toolkit of Practical Low-Cost Methods for Road Managers

There are approximately 3 million miles of low-volume roads (LVRs) in the United States, and approximately half of them are located in seasonal frost areas. Limiting or prohibiting loads during spring thaw can keep damage to a minimum. However, methods of determining when to place and remove spring load restrictions, particularly on LVRs, are often highly subjective—if restrictions are imposed at all. In partnership with several other agencies, the U.S. Department of Agriculture Forest Service has been compiling a toolkit of practical low-cost diagnostic techniques for determining conditions under which spring load restrictions should be placed and removed. This paper expands on techniques reported in a previous paper from a TRB low-volume roads conference and reports on further developments of additional methods. Techniques discussed include (a) subsurface instrumentation, (b) lightweight deflectometer, (c) thaw index, (d) climatic thaw predictor model, and (e) length of time. Requirements and equipment needed to use each of the techniques are described, strengths and weaknesses of each are outlined, and recommendations on various combinations of methods are provided to enable road managers to optimize placement of spring load restrictions.

Initial Analysis of the New Hampshire Spring Load Restriction Procedure

In late 2006, the New Hampshire Department of Transportation (NH DOT) initiated a study to develop a Real Time Spring Load Restriction (SLR) Methodology to guide the Maintenance Districts in their management of spring load restrictions by identifying the beginning and duration of the spring thaw period. The study includes selection of test areas, purchase and installation of instrumentation, collection and analysis of data from the instruments and development and implementation of the methodology, Eaton, et al (2009), discuss details of the project. In this paper the authors discuss the initial procedure, the installed instrumentation, observations from the instruments, and refinements indicated by the observations and initial analysis of the data.

Climate change: potential impacts on frost–thaw conditions and seasonal load restriction timing for low-volume roadways

Low-volume roads constitute a major percentage of roadways around the world. Many of these are located in seasonal frost areas where agencies increase and decrease the allowable weight limits based on seasonal fluctuations in the load carrying capacity of the roadway due to freeze–thaw conditions. As temperatures shift due to changing climate, the timing and duration of winter freeze and spring thaw periods are likely to change, potentially causing significant impacts to local industry and economies. In this study, an ensemble of 19 climate models were used to project future temperature changes and the impact of these changes on the frost depth and timing of seasonal load changes across five instrumented pavement sites in New England. The study shows that shifts of up to 2 weeks are projected at the end of the century and that moderate variability was observed across the study region, indicating that local conditions are important for future assessments depending on the desired level of accuracy. From 1970 to 1999, the average freezing season lasted between 9 and 13 weeks in the study region. By 2000–2029, the frozen period shortens by approximately 10 days over baseline duration (10–20% reduction). By the end of the century under RCP 4.5, frozen periods are typically shorter by 4 weeks or a 30–40% reduction. However, RCP 8.5 results indicate that four out of the five sites would have no frozen period during at least six winters from 2060 to 2089.

Progress and challenges in incorporating climate change information into transportation research and design

AbstractThe vulnerability of our nation’s transportation infrastructure to climate change and extreme weather is now well documented and the transportation community has identified numerous strateg...

Modification of the U.S. Army Corps of Engineers Model 158 for Prediction of Frost–Thaw Profiles in Northern New England

Knowledge concerning frost–thaw profiles is important in the design of pavements for low-volume roads located in seasonal frost areas. In addition, because these roads are highly susceptible to damage during the spring thaw–weakened period, this knowledge is helpful in making decisions about seasonal load restriction (SLR) policies. Direct measurement of frost depth is expensive and usually limited in scope. Therefore, several highway agencies have expressed the need for a prediction model to help them in estimating frost–thaw profiles beneath roadways. A report from the U.S. Army Corps of Engineers New England Division examined frost prediction models. One of the equations in that report was Model 158, which was similar to the modified Berggren equation. Model 158 uses air temperature indexes as well as pavement material properties to integrate heat flow into the calculation of maximum seasonal frost depth. That model has been modified slightly and programmed in an Excel spreadsheet to predict frost and thaw depths on a daily basis. This paper presents an overview of the modified Model 158 and compares predictions obtained from that model with measured frost–thaw profiles obtained at several test sites located in northern New England during a period of five freeze–thaw seasons. Results suggest that the model shows much promise although it generally tended to slightly underpredict maximum frost depths. In tracking the thaw process for SLR posting, the model tended to be conservative in estimating end-of-thaw dates (especially during rapid thawing events); in many instances, estimated end-of-thaw dates fell after measured dates.

Comparison of Test Sections of Low-Volume Roadways Reconstructed with Conventional Techniques and Full-Depth Reclamation

Three test sections were established in 2005 along a portion of the Kancamagus Highway in New Hampshire, where different reconstruction techniques were used: conventional (box-cut) reconstruction, full-depth reclamation (FDR), and FDR with cement-treated base. During the 2005–2006 winter and spring, elevation surveys were conducted to examine frost heave behavior. In 2006, those three test sections were folded into a larger research project sponsored by the New Hampshire Department of Transportation and the U.S. Department of Agricultures Forest Service. For that project, extensive falling weight deflectometer (FWD) testing was conducted during the 2008 spring-thaw period to investigate variations in pavement stiffness that result from seasonal changes in temperature and moisture. An additional elevation survey was conducted in July 2009 to check for rutting in the wheelpaths. Results of this research suggest that FDR provides an economical and environmentally friendly alternative for reconstruction of low-volume roads. The 2005–2006 data show that the two FDR test sections exhibited more frost heave than the box-cut section, presumably due to frost-susceptible subgrade soils that remained in place in those sections. However, the 2008 FWD data suggest that the overall stiffness of all three test sections was similar. Five years after initial reconstruction, survey data indicate that little to no rutting has occurred. Visual inspection revealed some cracking, with most of the observed distress attributed to thermal cracking on all three test sections.

Enhancements to a Simple Pavement Frost Model

The ability to predict the timing of thaw is important to the design and the maintenance of roads. Such knowledge allows highway agencies to reduce the damage caused by enacting seasonal load restrictions during thawing. Because measurement by observation or testing requires time and resources, one desirable solution is a predictive model. Simple models, such as the Cornell Pavement Frost Model (CPFM), require only daily temperature weather inputs. Possible improvements to the CPFM were tried with a primary goal of improving thaw timing while keeping the model simple and applicable across New York State and beyond. The proposed modifications included changing the thaw reference temperature, providing better tracking of thermal properties throughout seasonal changes, and driving thaw from underneath with a constant underground temperature. During the investigation, further changes were tested involving ways to treat latent heat during thaw, including decoupling. Changes were tested against frost tube data from Ithaca, New York. The model was evaluated and adjusted at other sites in Maine and New Hampshire. The additional inputs required by the resulting modified model were depth and value of constant temperature, moisture content, and estimated shade. The modified model greatly improved the depth and timing of the model for most sites. The final model used the original formulation with minor modifications for freezing and a latent heat formulation for thawing. With more than one freezing–thawing front, the formulas were decoupled. Further investigation should be done to improve frost depth and timing, and in particular, to find out why rapid thawing from underneath does not occur at some sites.

Solar Effects on Frost-Thaw Patterns at Two Adjacent Roadway Test Sections: Case Study

Many roads in seasonal frost areas experience costly damage as a result of freeze-thaw processes. In order to reduce damage, road management agencies apply Spring Load Restrictions (SLRs), which restrict the allowable load on a road during the critical time interval when the pavement is most vulnerable to damage. Methods of determining SLRs include use of set dates and/or visual inspection procedures, conducting falling weight deflectometer (FWD) testing, monitoring subsurface temperatures and/or moisture, and use of predictive models (based upon atmospheric weather data) to predict subsurface frost-thaw profiles. Regardless of which approach is used, a challenge in SLR posting is that many miles of roadway must be posted based on a very limited set of observations and data. This paper presents data from two closely spaced field test sections: one located in a very sunny area and the other located in a shaded area. Other than solar exposure, conditions at the two sites were considered the same. During the two-year study period, subsurface temperature monitoring showed substantial variation in frost-thaw patterns, particularly with regard to the end of thaw dates, which occurred 30 and 38 days later at the shaded site compared to the sunny site. FWD testing conducted at the sites also showed similar differences in thaw weakening and recovery patterns. Results of this study suggest that variability in solar radiation can have a significant impact upon appropriate SLR posting dates, particularly with regard to removing the SLR. Additionally, the project suggests a need for more cost-efficient monitoring systems, so that variability might be better quantified and accounted for by agencies charged with making SLR posting decisions.

Seamless data visualization for frost detection

Multimedia networking has been expanding its definition beyond communications of text, image, audio, and video as the Next Generation Internet evolves from social networks to cyber-physical networks. One application related to transportation infrastructure includes health monitoring of existing paved and un-surfaced roads. Embedding remote sensing and spatial information technology into roadways facilitates constant observation of road conditions and automatic detection of frost and thaw fronts during the spring thaw and recovery period. A system is being developed which provides critical quantitative data to eliminate or supplement components of current visual inspection procedures, and thus greatly assists transportation agencies in making spring load restriction (SLR) placement and removal decisions. This paper presents the data visualization module of a Decision Support System for Spring Load Restriction (DSS-SLR). After temperature data are collected by underground sensors and transferred by wireless/wired networks to a central database, a user can view the spatial and temporal temperature patterns via a Web browser. An embedded interpolation routine and a graphical user interface (GUI) enable the user to view a cross section showing frost and thaw depths over time. Our work pioneers this new frontier of multimedia networking, which will have significant applications with regard to health monitoring of existing paved roadway systems, as well as un-surfaced road evaluation and maintenance.