The mechanical performance of pavement systems depends on the stiffness of subsurface soil and aggregate materials. The moduli of base course, subbase, and subgrade soils included in pavement systems need to be characterized for their use in the new empirical-mechanistic design procedure (NCHRP 1-37A). Typically, the resilient modulus test is used in the design of base and subbase layers under repetitive loads. Unfortunately, resilient modulus tests are expensive and cannot be applied to materials that contain particles larger than 25 mm (for 125-mm diameter specimens) without scalping the large grains. This paper examines a new methodology for estimating resilient modulus based on the propagation of elastic waves. The method is based on using a mechanistic approach that relates the P -wave velocity-based modulus to the resilient modulus through corrections for stress, void ratio, strain, and Poisson’s ratio effects. Results of this study indicate that resilient moduli are approximately 30% of Young’s mod...

The paper presents the results of an experimental investigation of fine particle migration from pore body to the pore throat and toward the contact between particles and its effect on skeleton stiffness of granular materials. We hypothesize that the suspended colloids in the pore fluid migrate and deposit on the contact surface between the skeleton-forming particles and change the magnitude of the soil stiffness. Three specimens were prepared using uniform spherical glass particles that were saturated with deionized water and kaolinite or silt-base slurries. The specimens were drained by evaporation which retained the fines in the soil while increasing the matric suction. Changes in soil dynamic stiffness were evaluated using piezoelectric transducers while the migration of fines and the changes of the properties of the pore fluid were monitored using synchrotron X-ray microcomputed tomography (SMCT) on identical specimens. The wave propagation experiments show that the stiffness of the tested specimens i...

Estimation de la saturation irréductible en eau à partir de la pression capillaire et des mesures de la résistivité électrique-Cet article présente les résultats de mesures de la pression capillaire et de la résistance électrique de trois types de roches : le sable argileux (Berea), le quartz et le calcaire. Nous rapportons également des données expérimentales pour l'indice de résistivité, le facteur de formation, la tortuosité, la pression capillaire et les exposants de saturation en eau de ces roches dans le système air/saumure. Les données de résistivité électrique sont évaluées par la loi d'Archie modifiée. Les résultats des mesures de la pression capillaire et de la résistivité électrique en fonction de la saturation en saumure montrent l'existence de deux saturations irréductibles en eau correspondant à deux phénomènes physiques différents. Les deux valeurs des saturations irréductibles forment des limites hautes et basses qui peuvent être utilisées pour estimer la capacité de la production d'un milieu poreux. L'analyse détaillée des données a aussi montré un changement de valeur de l'exposant de saturation. Ce changement pourrait également être observé à la saturation irréductible en saumure obtenu lors des mesures de pression capillaire.

Most earthwork construction specifications recommend a lift thickness of 0.2 m for subgrade soils during road construction. These limits were originally implemented to ensure uniform compaction across the entire depth of the soil lifts. However, it has also been argued that the larger footprints and weight available in modern compaction equipment could potentially compact thicker layers without sacrificing the mechanical performance of subbases. This paper describes a field study on the effects of the lift thickness and compactors on the quality of compacted subbases. The effectiveness of two compactors was evaluated on coarse-grained soils. Different types of geotechnical instruments were used to determine variations in the mechanical properties of soils under applied compaction energy. The main goal was to combine the information of different testing types to determine whether it is possible to use a thicker lift of coarse-grained subgrade soils during compaction. The field test results show that compaction energy propagates up to the 0.3-m depth into the soil lift. Therefore, the conventional 0.2-m lift thickness specification for road construction may be updated to potentially save construction costs without compromising mechanical performance.

Between 1980 and 2008, traffic on Class 1 railroads has increased 93% and total track length has decreased 42%, leading to a substantial increase in traffic density and maintenance requirements. To improve maintenance techniques for problematic rail infrastructure elements (e.g., bolted rail joints, intersections, bridge approaches, etc.), a method of reinforcing ballast layers using rigid polyurethane has been developed. Laboratory tests on polyurethane-stabilized ballast (PSB) shows that strength and resistance to permanent deformation is higher than untreated ballast; however, the elastic (resilient) modulus is lower. Consequently, the introduction of this stabilization material into the track substructure needs to be addressed, including the functionality of the rail infrastructure. A finite element model was developed to simulate the rail, tie, ballast, polyurethane-treated ballast, subballast, and subgrade system. The numerical model was used to determine the impacts that location, thickness, and properties of polyurethane reinforcement in the ballast layer have on track resilient behavior. Simulations on polyurethane-reinforced track substructure reveal that there is minimal change in strain of each substructure layer (i.e., ballast, subballast, and subgrade) and no negative effect on overall track elastic response under loading due to change in stiffness of the polyurethane reinforced areas.