Initial Research on Mechanical Response of Unbound Granular Material under Static Load with Various Moisture Content

In road engineering, the role of solid foundation is performed by base and sub-base layers which are often made of unbound materials. Cohesive and non-cohesive soils as well as unbound materials used in lower road pavement construction layers show a significant sensitivity to alterations of moisture content. Susceptibility to changing moisture conditions can be observed in variations of mechanical properties of cohesive or non-cohesive medium which describe material's behaviour under applied load. Observation of parameters such as internal friction angle (ϕ), cohesion (c) and modulus of elasticity (E) allows noticing clear connection between mechanical parameters of granular material and variable moisture content. In this article, authors presented the results of initial laboratory tests consisting of trial loadings of a non-cohesive granular medium with different graining and moisture content and a numerical analysis of the problem. Research program was divided into three parts: material testing, trial loadings of non-cohesive soils - medium sand and dolomite executed on a special laboratory test stand and a back calculation analysis using finite element method (FEM). Firstly, materials were identified by obtaining grain composition, optimum moisture content and dry density in Proctor apparatus and values of internal friction angles and cohesion. Trial loadings were performed in a small scale in test cylinder using static load transferred to a steel plate with a diameter of 10 cm. Diameter of the loading plate was chosen in accordance to model similarity principles. Attained vertical displacements were used to execute the back calculation analysis of granular layers for which parameters of Coulomb-Mohr model were obtained using finite element method (FEM). The results shown in this article are the part of a wider research program in which main aim is to evaluate the influence of variable moisture content of materials used in road pavement structures on their fatigue life and costs of maintenance in full life cycle of pavement structure (LCA – Life-cycle Assessment). (paper)