Abstracts:This study presents the performance of a trial gravel road subjected to HVS (Heavy Vehicle Simulator) trafficking in a compressed time period. The road structure was constructed with 150mm-thick aggregate base course, and 125mm-thick sub-base course. The test road responses, such as surface deformation and rutting were recorded using laser profile measurement instrument while the unbound layers’ dynamic deflections and strains data were periodically recorded at different depths during the execution of the test by means of an array of micro strain gauges. The test road was also instrumented with Water Content Reflectometers to record the changes in moisture contents in the road layers caused by the raising of the water table level under HVS trafficking. A total number of 85,000 HVS passes were applied to the trial gravel road structure under near-optimum as well as partially submerged subgrade moisture conditions. The test results emphasize the fact that the partial soaking of the subgrade soil by raising the groundwater table level caused a serious damage to the tested gravel road, as further detailed in this paper.

Abstracts:Individual ballast particle movement significantly affects ballast performance. In order to improve ballast performance, geogrids are widely used to create interlocking of ballast particles to reduce particle movement. To better quantify the effect of geogrid on particle movement, two types of ballast box tests were conducted in this study: one without geogrid as a control and the other one with a layer of multiaxial geogrid placed at 25cm below the top of the ballast. The ballast box represents a half section of a railroad track structure consisting of a ballast layer, two crossties, and a rail (I-beam). A wireless device – “SmartRock” was embedded underneath the rail seat and the edge of a tie in the ballast layer to monitor particle translation and rotation under cyclic loading. The results indicate that (1) horizontal translation and rotation are important modes of movement for ballast particles under cyclic loading; (2) particle translational movement and rotation were higher beneath the edge of the tie than those beneath the rail seat; (3) the particle movement, such as translation and rotation, were significantly reduced with an inclusion of the geogrid under 500 load cycles. This investigation also demonstrates that the SmartRock is capable of recording and visualizing real-time particle movement including translation and rotation and, hence, can be used as a fundamental research and monitoring tool in railroad.

Abstracts:This keynote paper describes recent advances in chemical stabilization with a particular focus on applications related to transportation infrastructure. Chemical stabilization advances ranging from stabilization design guidelines with incorporation of fundamental soil chemistry principles to novel chemical additives for future stabilization are covered. This paper focuses on chemical treatments of shallow to moderate subgrade depths for supporting transportation pavement infrastructure. A background summary of stabilization methods along with modifications to the current design practices is presented. This section is followed by a comprehensive experimental program on chemical treatments of expansive subsoils. Both clay mineralogy influence and durability issues are fully addressed. Stabilization leachate studies and their implication in relation to real field performance are also addressed. The final outcome of this research is a more comprehensive stabilization methodology that addresses soil types and performance based testing methodologies. The last two sections cover a brief summary of new treatments of immense interest to addressing sustainable elements in ground improvement practices.

Abstracts:Test data from full-scale aircraft gear loading conducted at the National Airport Pavement Test Facility (NAPTF) by the US Federal Aviation Administration (FAA) were analyzed to investigate the effects of wander (offset loads) and channelized traffic loadings on the deformation behavior of unbound aggregate layers in asphalt pavement test sections. Insights were drawn on the complex rebound (recovered) and residual (unrecovered) deformation trends of granular materials due to passing of each of the 6-wheel Boeing 777 (B777) and the 4-wheel Boeing 747 (B747) gears for various combinations of loading (stress history effects), wander positions, and wander sequences. Measured field layer deformations and the accumulation rates could only be achieved when the magnitudes and variations of stress states in the granular layers, number of load applications, gear load wander patterns, previous loading stress history effects, trafficking speed or loading rate effects, and finally, principal stress rotation effects due to moving wheel loads were properly accounted for. Accordingly, measured transverse profiles and multi-depth deflectometer data were used to create individual pass residual deformation transverse profiles. The created transverse profiles were then combined with stress history effects to predict the residual transverse profiles for the test sections with P209/P154 granular base/subbase layers. The proposed method emphasizes the use of the previous load location and stress history of the pavement element to develop the residual deformation in that element. Calculation of the residual deformation in each element across the pavement surface results in the development of the complete permanent deformation transverse profile. This technique can be applied to estimate the transverse rutting profile of the pavement after trafficking based on any combination of applied wander and traffic direction.

Abstracts:This paper presents results from full-scale testing of six airfield matting systems of various materials and designs that were evaluated on subgrades constructed to a California bearing ratio (CBR) of 6 and subjected to simulated aircraft loads. Mat breakage, deformation, and subgrade earth pressure were monitored during each test to determine the effectiveness of the airfield mats in reducing cumulative subgrade deformation and decreasing subgrade stresses. Based on test results, a simplified expression was developed to predict subgrade deformation on a CBR of 6 as a function of aircraft passes and airfield mat properties. The values predicted showed reasonable correlation with the measured data. The empirical equation can be used as an expedient tool for characterizing airfield matting behavior.

Abstracts:The stabilisation of road subgrade soil may improve its mechanical properties considerably, however under the combined effect of cumulative traffic load and weathering these materials deteriorate over time and lose performance. However, current road design procedures neglect such deterioration of stabilised soils and consequently their use may result in the under-design of road pavements and as a result unplanned maintenance and/or premature road failure. To address this, this research presents the results of a research programme marrying experimental, analytical and numerical work which was used to develop a methodology which can be used for the first time to design accurately road pavements incorporating stabilised subgrade soils. An extensive experimental programme was carried out consisting of laboratory durability tests to determine the mechanical behaviour of stabilised subgrade soils, in terms of resilient modulus and permanent deformation, under cycles of wetting and drying. Results of the durability tests were used to validate an analytical predictive equation which considers the changes that take place to the material after cycles of wetting and drying. The experimental results show a decrease in the resilient modulus after 25 cycles of wetting and drying cycles for three types of fine grained subgrade soils stabilised with varying amounts of lime-cement. In order to adequately replicate the stress dependency of the performance of the stabilised subgrades for analytical pavement design, two equations were developed that relate the resilient modulus of a stabilised soil with unconfined compressive strength (UCS). The developed equations were utilised with a numerical finite element model of a road pavement to determine the most appropriate road pavement designs, on an engineering basis, for a variety of stabilised soils.

Abstracts:Unbound aggregate base and subbase layers distribute wheel load induced stresses to protect subgrade. Standards such as AASHTO and individual states specifications have set several quality control limits for a variety of properties of aggregates used in the pavement base and subbase courses. Most standards and DOT specifications suggest that the ratio of percent passing No. 200 sieve to percent passing No. 40 sieve should not be greater than two thirds, and plasticity index of the material passing No. 40 sieve should be less than 6%. The ratio of percent passing No. 200 to percent passing No. 40 sieves is called the dust ratio (DR). There are many states that have either waived the standard limits or adopted their own quality control method. In this study the effect of dust ratio, percent passing No. 200 sieve and plasticity index (PI) affecting moisture-density and strength characteristics of crushed limestone aggregates are investigated. The prepared samples represented one of the most commonly utilized dense-graded standard aggregate gradation in Illinois, i.e. CA6. Standard Proctor compaction and soaked California Bearing Ratio (CBR) tests were conducted on specimens to determine the moisture-density and strength characteristics of the material with moisture content, respectively. In addition, two staged triaxial tests using three confining pressures were performed to study the effect of confining pressure and fine quantity on strength of aggregates. According to the results, the effect of percent passing No. 200 sieve on strength variation is significant in unbound aggregates. The sensitivity of aggregate strength to moisture content variation is also discussed.

Abstracts:Conventional test methods for roadway compaction cover less than one percent of roadway; whereas, intelligent compaction (IC) offers a method to measure 100 percent of a roadway. IC offers the ability to increase compaction uniformity of soils and asphalt pavements, which leads to decreased maintenance costs and an extended service life. This paper examines IC technology, how IC quality control and assurance specifications can encourage IC adoption, knowledge and use of IC through survey responses, and benefits and costs of IC. The surveys reveal that a majority of respondents from state departments of transportation have conducted IC demonstration projects, but questions about cost and willingness of policymakers to adopt IC remain a barrier to implementation. The benefit-cost analysis demonstrates that use of IC reduces compaction costs by as much as 54 percent and results in a US$15,385 annual savings per 1.6km throughout the roadway’s life. The framework of the benefit-cost analysis can be readily adopted by transportation agencies to facilitate the implementation of intelligent compaction in future roadway construction.

Abstracts:This paper presents a thorough analysis of an experimental method for measuring aggregate friction properties. The second-generation Aggregate Image Measurement System (AIMS) is used to measure coarse aggregate surface texture before and after polishing in a modified Micro-Deval (MD) test procedure, in addition to Variable Speed Friction Test (VST) samples. Investigating the relationships between AIMS-MD angularity and texture, a weak relationship was found between VST friction values and AIMS angularity after MD polishing for 105min (AMD-105). Furthermore, the strong correlation between AIMS AMD-105 texture and the surface texture of VST friction samples indicated that MD is a viable option for replacing VST as a polishing mechanism. Finally, cluster analysis was conducted to obtain threshold for classifying aggregate angularity and texture into acceptable and non-acceptable zones (i.e., defining the criteria for qualifying aggregates for friction purposes).

Abstracts:This paper uses a numerical model to investigate the influence of tree root water uptake and tree removal on pore water pressures and the vertical movement of a clay fill railway embankment. Simulated results of soil wetting and drying are compared with field measurements from an instrumented railway embankment before and after tree removal. A parametric study compares the influence of vegetation on the seasonal movement of the embankment slope. The simulations and field measurements show that while trees cause significant seasonal variations in pore water pressure and water content near the soil surface, they can maintain persistent soil suctions at depth within the tree rooting zone. Demonstration of this result using a numerical model requires a root water uptake function that separates spatially the processes of water infiltration, evaporation and transpiration. When all of the trees are removed, the persistent soil suctions established by the trees are lost as water infiltrates from the soil surface. Leaving the trees in place over the bottom third of the slope can maintain persistent suctions at the slope toe, while potentially also reducing seasonal ground movements at the crest that may adversely affect railway track geometry.