This article presents the results of the study of changes in mineral and chemical composition of artificial aggregates consisting of coal shale (a hard coal mining waste) and fluidized ashes. Such an aggregate was used for road construction. After completion of the construction works but before making the road available for public use, significant deformation of the surface in the form of irregular buckling of the asphalt layer occurred. It was excluded that this resulted from mining damage, design errors or performance mistakes, among others. A study of the materials that had been incorporated in the construction layers was undertaken in order to find the component and the mechanism responsible for the buckling of the road surface. A comparison of the mineral and chemical composition of aggregate samples collected from the embankment where the road buckled with the reference sample and samples from places without deformations showed that the bumps in the road embankment consisted of minerals that were not initially present in the aggregate. Wastes produced as a result of high temperatures (slag and power plants ashes, metallurgical wastes) are not as stable in terms of chemical and phase composition in the hypergenic environment. As a result of the processes occurring in the road embankment, anhydrite, which is the primary component of fluidized ashes, was transformed into gypsum and ettringite. As a result of contact with water CaO (present in fluidized ashes) easily changed into calcium hydroxide. As the crystallization of these minerals is expansive, it resulted in the filling of pores and, in extreme cases, in a substantial increase in the volume of the aggregate and, consequently, in the deformation of the road surface.

In this article, the issue of mining impact on road pavements and subgrade is presented, taking into account the interaction between geosynthetic reinforcement and unbound aggregate layers. Underground mining extraction causes continuous and discontinuous deformations of the pavement subgrade. Structural deformations in the form of ruts are associated with the compaction of granular layers under cyclic loading induced by heavy vehicles. Horizontal tensile strains cause the loosening of the subgrade and base layers. The granular layers under cyclic loading are additionally compacted and the depth of ruts increases. Moreover, tensile strains can cause discontinuous deformations that affect the pavement in the form of cracks and crevices. Discontinuous deformations also affect the pavement in the fault zones during the impact of mining extraction. The use of geosynthetic reinforcement enables the mitigation of the adverse effects of horizontal tensile strains. Horizontal compressive strains can cause surface wrinkling and bumps. Subsidence causes significant changes in the longitudinal and transverse inclination of road surface. Both examples of the laboratory test results of the impact of subgrade horizontal strains on reinforced aggregate layers and the selected example of the impact of mining deformation on road subgrade are presented in this article. The examples show the beneficial impact of the use of geosynthetic reinforcement to stabilize unbound aggregate layers in mining areas.