Annual freeze–thaw cycles reduce the overall performance and ride quality of granular-surfaced roadways by causing significant damage in the roadbed system during spring thaw periods. The severity of the damage depends on the subgrade properties and external environmental factors. Field monitoring can play an important role in quantifying these factors as well as the roadbed subgrade responses to further our understanding of the resulting moisture transport and freeze–thaw mechanisms. Field monitoring can also be used to assess the effectiveness of computational models that use measurements of the environmental factors to predict the subgrade response. In this study, an extensive sensor network was installed up to a depth of 213 cm (7 ft) under a granular-surfaced roadway in Hamilton County, Iowa, for continuous measurement of soil temperature and water content. Soil index properties and hydraulic properties of the subgrade soils were determined by laboratory testing of disturbed and intact soil samples. This paper presents and compares the collected data on in-situ soil temperature and soil moisture distributions with those of preliminary computational modeling of the soil response using the SHAW Model. Laboratory-assessed soil properties and weather station measurements were used as inputs for the computational predictive models. The computational models give promising results, particularly for prediction of the subgrade temperature profiles.

Approximately 110,000 km (68,400 mi) of granular roadways exist in the 183,500-km (114,000-mi) road network in the state of Iowa, and operation and maintenance of these roadways costs roughly US$270 million annually. The major maintenance costs of these roads are aggregate cost and hauling costs from the quarry to the site. Accordingly, acquiring a costeffective and high-performance surface material to be utilized in granular roadways can be a challenge. In this study, three conventional granular roadway materials and four coarser aggregate materials from different quarries were used to construct seven test sections to assess their relative performance and costs. The first three test sections were constructed with conventional materials, and the other four sections used optimum mixtures of the four coarse aggregate materials with the local conventional aggregate. The long-term performance and mechanistic behaviors of the different surface materials, including stiffness, changes in ride roughness, and dust production were evaluated for a period of 2 years. Using the resulting data, a mechanistic life-cycle benefit–cost analysis approach was developed to evaluate the use of coarse aggregate materials on granular roadways. The stochastic benefit–cost analysis results for different aggregate materials are presented in the form of probability density functions. Two different scenarios are presented based on the field test results, and the benefits in terms of dust production and surface ride quality are evaluated for each section.

Aggregate durability is crucially important for performance of granular roadways. Therefore, proper laboratory durability evaluations of aggregates that will be used during construction and maintenance of granular roadways are very critical. Los-Angeles (LA) abrasion and Micro-Deval tests were two conventional methods that are used for laboratory during tests. However, it is very well known that these tests are not adequate to simulate the durability of aggregates under vehicle and compactor loads. The current study proposes to use the gyratory compaction method to evaluate the durability of aggregate materials. During gyratory tests, gradations, shear resistances, void ratios, and maximum dry unit weights of each material were monitored before and after tests. The results of this study showed that the fines content of the materials did not change significantly, while the gravel and sand contents of all materials changed considerably. It was also observed that the energy required to gain the optimum void ratio and dry unit weight were always higher than those required for the modified and standard Proctor tests energy levels. However, two out of three materials achieved 90% of the maximum shear strength at lower energy levels that were required for the modified Proctor test.

Granular-surfaced roads in seasonally cold regions regularly experience damage and degradation due to freeze–thaw cycles and steadily increasing traffic loads. Repair and maintenance of such roads can consume significant portions of budgets from counties and secondary roads departments.

Granular-surfaced roads comprise 73% of Iowa’s county road network. The surfaces of these gravel roads undergo mechanical and chemical deterioration over time due to extreme weather conditions and traffic loads. The goal of the present study is to improve our understanding of the mechanical deterioration that affects the performance of different geological types of coarse aggregates used in granular roads and shoulders. Samples of coarse aggregates were collected from four different quarries in Iowa. Laboratory gyratory compaction tests (GCT) were performed on specimens of the quarry samples to simulate their degradation under traffic loading conditions over time. From the results of GCTs, breakage parameters are evaluated, and relationships between dry unit weight, shear strength, and compaction energy are established for the different aggregate types examined. From these relationships, an efficient field-compaction energy criterion is determined to maximize density and shear strength while minimizing over-compaction and breakage of the aggregates.

Preliminary results are presented for full-scale vibration tests of piles using random vibration methods and a new servo-hydraulic inertial shaker testing system. Separate tests of vertical and coupled horizontal-rocking modes as well as hybrid multi-mode tests were performed on two steel HP 10x42 piles installed to a depth of 20 ft at a site containing soft clays. One pile was tested in the natural soil profile while the other had a cement deep soil mixed (CDSM) improved zone near the surface. Three excitation techniques were examined using a range of forcing intensities to determine the optimal testing configuration. The multi-modal vertical-eccentric test format was investigated as an efficient alternative to traditionally separate tests having vertical or horizontal forcing. Design of the experimental testing system is described, followed by a preliminary comparison of results from the various test configurations. Measurements indicate that the new excitation and instrumentation systems were successful in stimulating and capturing the broadband dynamic response of the soil-pile system for use in validating and calibrating advanced 3D computational continuum models.