The unbound granular layers (UGM's) and the subgrade of a pavement structure provide a significant support for the structure as a whole. Hence the mechanical properties of these materials are important for the overall performance of the structure. These materials exhibit both non-linear stress dependency and their mechanical properties are highly affected by their moisture content. This paper describes two of the most important material properties of the unbound layers of the pavements, i.e. the resilient and the permanent deformation properties. The stress dependency of UGMs can be captured by the universal model or the enhanced model by Cary and Zapata (2011) for materials with high fine content. The Bishop's effective stress approach can be used for high fine content materials for estimating the effect of suction. UGMs and subgrade materials are further highly dependent on moisture content. Either the AASHTO sigmoidal model can be used to describe the moisture dependency or the simple exponential model described in this paper. The paper further discusses four models to characterize the accumulation of permanent deformation with the number of load repetitions in repeated load triaxial (RLT) testing. The models are all developed to fit single stage (SS) RLT test results but have been extended to fit multi-stage (MS) RLT test results with the aid of the time hardening scheme. The advantage of the MS RLT tests over the SS RLT tests is that it applies a range of stress paths on a single specimen, thus taking into account the effect of stress history and reducing the time and effort required to test a separate specimen for each stress path.

Excess moisture presence in pavement unbound layers can result in lower structural stiffness and reduce the service life of road systems. A field study was conducted along the county road 126 near Torpsbruk to investigate the effect of the moisture content on the bearing capacity of a flexible pavement structure and its unbound layers stiffness. The subsurface drainage system of the test road was clogged during a three-month period in summer 2010, raising the groundwater level under pavement structure and therefore increasing the moisture content of the pavement unbound layers. During this period, the groundwater level and the volumetric moisture content of the pavement was continuously monitored using the instrumentations at test site and the structural response of the pavement was evaluated by conducting frequent Falling Weight Deflectometer (FWD) tests with multilevel loads. Using the FWD data, the unbound layers stiffness were back-calculated and their sensitivity to the moisture content and load level were studied. The field measurements showed that the groundwater level can significantly affect the moisture condition of the unbound layers and therefore their stiffness. Both the unbound granular layer and the subgrade showed stress dependent behavior to multilevel FWD loads.

Ökad fuktkvot i vägars obundna lager kan inverka på vägkonstruktionens strukturella styvhet och minska dess livslängd. En fältstudie gjordes längs riksväg 126 nära Torpsbruk för att undersöka de obundna lagrens fuktkvoter på vägkonstruktionens strukturella respons och styvhet. Vägkonstruktionens dräneringssystem täpptes till under tre månader under sommaren 2010. Tilltäppningen av dräneringssystemet resulterade i en snabb höjning av grundvattennivån, samtidigt ökade de obundna lagrens fuktkvot. Under studieförloppet har grundvattennivåns läge och fuktkvoten i vägkonstruktionens obundna lager mätts kontinuerligt med hjälp av fältinstrumenteringar. Dessutom gjordes frekventa fallviktsmätningar med tre lastnivåer för att mäta konstruktionens strukturella respons. På så sätt kunde lastnivåns och fuktkvotens inverkan på de obundna lagrens beteende studeras med målsättningen att bestämma egenskaperna hos de obundna materialen genom bakberäkning av fallviktmätningsdata. Enligt bakberäkningarna resulterade konstruktionens fuktökning till en betydande reducering av de obundna lagrens styvhet. Det observerades dessutom att de obundna lagren visade ett spänningsberoende beteende under de olika lastnivåerna vid fallviktsmättningarna.