# Lessons Learned on Geosynthetics Applications in Road Structures in Silesia Mining Region in Poland
## 2 Materials and Methods
### Evaluation of Mining Waste Mechanical Parameters  
Part of the complex preparation of the motorway design was the determination of the strength parameters of the mining waste materials that were to be used for the construction of an embankment body. In this case a full scale in-situ test, based on the method of trial loading was performed [29; 30; 31; 32]. The applied methodology guaranteed a comprehensive distribution of the stress paths that were crucial for the proper identification of the design parameters. With reference to the trial loading of slopes, the in-situ tests enabled appropriate simulation of the failure process, incomparable to any laboratory tests or numerical analyses. The technical issues here referred to difficulties in achieving boundary equilibrium, corresponding with the most realistic estimations of the strength parameters: the internal friction angle (\(\varphi\)) and the cohesion (\(c\)) [33]. The tests performed on an experimental embankment allowed the measurement of the \"load-settlement\" relationship. It was necessary for further analyses by means of an elastic--ideally the plastic soil model. The model was used to measure the slope geometry before and after the failure, taking into account a destructive load. The loading of the top surface of the slope with a pile of pavement slabs with a measurement of the settlements after each incremental step was considered to be the optimum solution. To be capable of considering the problem as linear (planar strain), a load was assumed to be applied on the length of a minimum of three pavement slabs, used as a surcharge. The model is presented in Figure 5.  
The computations included estimations of the \(\varphi\) and \(c\) values, as parameters of an elastic (ideally plastic) Coulomb-Mohr model, based on back analyses applying the finite element method (FEM)  
Figure 4: Installation of the geomattress, made of two layers of monolithic geogrids and anthropogenic aggregates. method and the Janbu method, respectively. The results obtained for the mechanical parameters, using the modeling, and also the physical parameters are listed in Table 1.  
The modeling part refers directly to the reliability assessment of waste strength parameters results, obtained on the basis of trial loading of the road embankment slope in the natural scale. The full-scale trial loading test was carried out using 18,000 tons of material on the 100 m long, 20 m wide, and 5 m high road embankment, presented in Figure 6.  
The results of the strength parameters evaluation, with relatively low values of standard deviation, were used to design a motorway embankment in a section located near the mine. In 1990, the Polish government decided to construct a new section of a motorway passing through the Silesia region with over 50 active deep coal mines. The length of the Silesian part of the motorway is 45 km and the majority of it runs over the mining areas. The only material used for the embankment construction was anthropogenic soil. At this stage a decision was made that the impact of the mining influences on the motorway should be reduced and protective layers with geogrids should be designed [31]. Based on observed reduction in the pavement durability by 20% and more (higher designed deformations), it was necessary to apply solutions that minimize the impact of mining deformations. Due to a small range of the deformations, it was also necessary to mobilize the geosynthetics at the initial stage of the deformation.