# Lessons Learned on Geosynthetics Applications in Road Structures in Silesia Mining Region in Poland
## 1 Introduction  
In Europe in late 80's, after the Iron Curtain collapsed, such countries as Poland started a new chapter in economical development. The infrastructure was one of the key areas where Poland was far behind Western Europe standards. Almost all the construction technologies were outdated, non-efficient, and in many cases unsafe for use [1; 2; 3]. Becoming open to new technologies and structural materials provided a strong impact for modernization of the entire construction industry, and until nowadays this trend is still being observed [4; 5; 6; 7; 8]. Lack of planning and poor economy management resulted in a huge production of waste, both municipal and industrial, which in many cases were deposited without any control [3; 4; 5]. The waste deposition became a serious issue, mainly in well-developed regions like Warsaw or Silesia, where the amount of by-products was rapidly increasing. A typical solution of the problem, back in the days was just enlarging the area used to deposit waste materials. In those days, the use of materials such as geosynthetics were barely noticeable [9; 10; 11; 12; 13]. Until 1990's only a few non-woven textiles manufacturers were operating, but the material quality and durability was insufficient for large scale road construction projects. Simultaneously, in Poland a boom in new geosynthetics applications has started. Now, after over two decades of gaining experience on a number of infrastructure projects, we are able to make scientifically based conclusions and comments on most of them. The present paper describes a case study on road construction works on post-mining areas. It concerns an underground mining coal extraction site where a new motorway was planned to be constructed. However, due to significant deformation of the ground surface, caused by former mining excavations, the sophisticated ground improvement methods were necessary to be applied. For the linear structures, like roads, or other geotechnical investments the mining activity is a major safety threat, thus the need of maintenance efforts increase significantly [14; 15; 16; 17]. Recently, a peculiar revolution in the field of understanding and describing the geogrid interaction with the unbound aggregate has been observed. It mainly concerns the road construction and ground mechanical condition improvement. An improved performance of the pavement due to the geosynthetic reinforcement and bearing capacity improvement [18; 19; 20; 21; 22; 23] depends on main mechanisms [24; 25; 26]:  
* Lateral confinement of the unbound aggregate in the base course;
* Increased bearing capacity;
* Tensioned membrane effect. The road pavement is made of layers, which distributes traffic generated loads, disabling excessive deformation of the subsoil. The major role of a road pavement is bearing high frequency loads. The pavement works provide a very small range of deformation, between \(10^{-6}\) and \(10^{-3}\) m, when considering the vehicles load and stiffness of pavement layers [3; 11]. The time gap between a road opening and the asphalt resurfacing is determined by the fatigue life. A depletion of the fatigue life of the pavement causes characteristic cracks and structural rutting. A significant issue when constructing a road is the location within mining areas where subsoil deformation occurs, including deformation of the surface. Mining deformations usually affect working conditions of the pavement layers, cause pavement stiffness reduction, and the decrease of fatigue life. The deformations of the ground surface can take the form of continuous [27] or discontinuous mechanisms [28; 29; 30; 31]. The cracks observed on the road pavement as a result of the subsoil deformations are presented in Figure 1.  
In the case of continuous deformation, there is a subsidence on the surface of the ground on which the continuity of the subsurface rock layer does not cease.