## 3 Materials and Methods
### Cement Stabilisation of Engineered Landfill  
To improve the surface soil layers, particularly when constructing embankment layers, mechanical and/or chemical stabilization is used. The latter includes stabilization with cement [21]. This type of stabilization has been in use in geotechnical engineering for almost a hundred years. Stabilization using this method involves properly fragmenting the layer to be stabilized, adding a suitable amount of cement, mixing it into a uniform phase, laying it in place, thickening and properly curing. For soils, there are clear guidelines concerning the use of cement for specific soil types. Soils subjected to such stabilization must meet specific requirements, for example those of standard PN-S-96012:1997 [21], which concerns their grain size, plasticity index (I\({}_{\text{p}}\) = 15%), liquid limit (w\({}_{\text{L}}\) = 40%), organic content (I\({}_{\text{om}}\) = 2%), reaction (5 \(<\) pH \(<\) 8) and sulfate content (SO\({}_{3}\) = 1%). The cement-soil load-bearing backbone forms as a result of the cement binding with the distributed sand and silt fraction. Soil particles not bound to cement form the filler and binder of the load-bearing backbone and, at the same time, serve as a dampener of external forces. When stabilizing soils, the amount of cement added is usually 3 to 10% (by weight) [21]. Of course, there are no such guidelines for using this type of stabilization with chemical plant waste. Before commencing the research, macroscopic waste mixing tests at different slag cement (CEM II/B-S-32.5 R) levels were conducted. They demonstrated that properties are significantly improved (very soft consistency turned into very stiff consistency) when about 10% slag cement (by weight) is added. Further laboratory tests to determine the angle of shearing resistance (\(\phi\)) and cohesion (c) were to demonstrate whether it was suitable for use in incorporation into an engineered landfill. The measure of this suitability will be obtaining an appropriate stability level (stability factor SF \(\geq\) 1.5) for the waste engineered landfill, determined on the basis of numeric calculations using the finite element method. When constructing the designed storage site, the waste was mixed at the solidification points with a capacity of 50 t/h, placed at the chemical plant grounds. The points were made up of cement silos and double-shaft continuous mixers with a feed functionality. First, the waste will be retrieved by excavators from the storage location, transported to the solidification points, processed, and subsequently transported by trucks and placed at the storage site. The strength parameters were determined by the tests conducted in a shearbox apparatus as per PN-B-04481:1988 [26]. In this test, the shearing strength is determined by applying a shearing force in a direction perpendicular to two opposite sides of a sample with a square cross-section (in projection), following the application of a force normal to the shearing plane. The shearing strength is considered to be the instantaneous strength achieved at a constant deformation speed within a range of up to 10%. The tests were performed on 60 \(\times\) 60 \(\times\) 18 mm cuboid samples cut from the blocks with the diameter of 200 mm and the height of 250 mm. The shearing plane was located at half sample height. Frame displacement in the horizontal and vertical directions was measured using dial gauges operating at the accuracy of 0.01 mm. The box was moved mechanically at a constant rate of 0.05 mm/min. The shearing force and the force normal to the shearing plane were measured at an accuracy of 1 kPa. The upper and lower surfaces of the sample were fitted with support plates with ribs and a right-angled triangular cross-section, positioned so that the hypotenuse surface of the rib was facing in the same direction as the shearing force when the frame moved in the direction in which the force was applied, and in the opposite direction when the frame was immobile.