Leonnie Kavanagh

Impacts of Reduced Tire Pressure on Strain Response of Thaw-Weakened, Low-Volume Roads in Manitoba, Canada

The spring thaw period significantly reduces the bearing capacity of low-volume asphalt roads. To compensate for the reduced bearing capacity, highway agencies apply spring load restrictions (SLR) to limit the damage caused by heavy loads during the period when the road is weakened by thaw. Although the imposition of SLR may reduce road damage, it has a major impact on truck productivity. An alternative to reducing truck loads during the spring is the reduction of truck tire pressure. The reduced tire pressure lowers the tire–pavement contact pressure and the associated damage during the spring period. In 2008, asphalt strain gauges were installed in a section of a low-volume haul road in Manitoba, Canada. Field testing was conducted in the spring and fall of 2009 with a double semitrailer or B-Train equipped with a semiautomated tire pressure control system. The tests were conducted at various loads and speeds and at normal and reduced tire pressures. The results of the field testing showed that when the tire pressure was reduced by 50%, the measured maximum tensile strain at the bottom of the asphalt layer decreased by an average of 15% to 20%. The effects of gauge orientation, truck speed, and tire offset from the strain gauge were analyzed and are presented.

Comparison of Pavement Texture Measurements from a Three-Dimensional Profiler and a Circular Track Meter at MnROAD Test Facilities

This paper compares pavement texture measurements from a three-dimensional (3-D) line-laser scanner and from a two-dimensional (2-D) spot-laser circular track (CT) meter to determine whether correlations exist between their texture parameters. Measurements with the two devices were taken simultaneously on pavements at the Minnesota Department of Transportation MnROAD test facilities. The 3-D texture heights were decomposed by using a discrete wavelet transform to separate microtexture from macrotexture. Macrotexture parameters from the two devices were analyzed. A linear relationship, with an R2 value of .94, was found between the 2-D mean profile depth and the 3-D digitally simulated mean texture depth. Similarly, the R2 value was .98 between the 2-D root mean square roughness and the 3-D root mean square deviation. These correlations are essential and can be used by road agencies to predict texture indexes between 2-D and 3-D measurements for data comparison or quality assurance when equipment is of different dimensions.

Implementation of a Strain-Based Policy for Managing Weight Restrictions During the Spring: Low-Volume Roads in Manitoba, Canada

A strain-based concept for managing spring weight restrictions (SWRs) on load levels and duration for low-volume roads was developed and applied to a low-volume road in Manitoba, Canada. Local fatigue and rutting damage models were used to predict limiting failure strains during the spring. The limiting failure strains were compared with predicted strains at SWR loads during the spring. On the basis of the results, the strain-based concept can be used to manage SWR load levels and the duration of SWR during the spring. Analysis of limiting failure strain should be applied to other pavements to verify the findings. For the strain-based concept to be practical, use of the Minnesota thawing index procedure based on climatic data is recommended for estimating the start of the SWR period.

Validating Spring Weight Restriction Limits with Mechanistic–Empirical Failure Prediction Models: Low-Volume Roads in Manitoba, Canada

This study developed local mechanistic–empirical failure models to predict fatigue and rutting damage on spring-weight-restricted (SWR) roads in Manitoba, Canada. The local models were used to assess the SWR load limits and to validate the current SWR deflection levels that regulate commercial vehicle weights during the spring period. The local model predictions were compared with the damage models of the Asphalt Institute (AI) and the Mechanistic–Empirical Design Guide (MEPDG). The results indicated that the predicted equivalent single-axle load repetitions to fatigue failure from the local model were higher than those of the MEPDG and the AI models by an average of 37% and 20%, respectively. On the basis of the local model equivalent single-axle load predictions, the current SWR deflection limits used in Manitoba appear to be a reasonable method for regulating B-Train operations during the spring period.