Rio Blanco County is located in the rural northwestern corner of the State of Colorado. Recently, there has been a significant increase in the truck traffic on the county roads, due to increased oil and gas exploration activities. The presence of such heavy trucks has raised concerns about the impact of additional truckloads on the pavement conditions of the county roads, particularly due to the seasonal variation in the subgrade soil conditions as a result of temperature variation. A study was initiated to develop short term Spring Load Restrictions (SLR) guidelines for Rio Blanco County for the spring 2007. This study was based on deflection testing and was successfully completed by late spring 2007. The results from this studywere further validated using data collected from sub-surface instrumentation used as part of the on-going Phase 2 of the study to develop long termSLR guidelines for the County. In spring 2007, the start of the SLR was estimated using a combination of deflection testing and Thawing Index (TI) model. In this approach, the TI model from Minnesota DOT was adopted to define the expected time frame of the start of the spring thawing. Deflection testing was then performed during this time to examine the actual decrease in strength of the pavement structure and thus define the appropriate start of the SLR on the County roads. The end of the SLR was estimated again based on deflection testing to monitor the pavement condition. The deflection data collected during this project showed that the subgrade soils inthe study are susceptible to a reduction in structural strength during the spring thaw season. Additional deflection testing cycles were completed to determine when the pavement regained its strength. Validation data fromthe sub-surface instrumentation showed that the TI model might be acceptable to define the start of the SLR based on the forecasted weather conditions, while monitoring moisture content exclusively might not be adequate for determining when SLR can be lifted unless more historical data exists for comparison. In this paper, the development of the short term SLR policies for spring 2007 for Rio Blanco County is presented, together with the validation of the results of this study using data collected during spring 2008.
Samenvatting