A building of high complexity was constructed in the south of Sweden, comprising a 35 m high warehouse. In order to hose the maximum acceptable inclination difference for loaded flooring ground improvement and steel fibres reinforcement of the concrete slab in the high-rising warehouse was used. The soil in the area contained filling, sand, till and peat with a variety of properties. Advanced numerical analyses were made and the Observational Method (OM) was used for jet grouting and cement surface stabilisation. The jet-grouted columns had a minimum diameter of 0.8 m and a minimum mean compressive strength of 4 MPa. The cement-stabilised layers were installed with a minimum compressive strength of 2 MPa and with a total thickness of 1.0 m. The concrete slab was 0.2 m thick, reinforced with 35 kg steel fibres/m3. OM was applied by quality control of material properties in order to verify the conditions and construction work. Field and laboratory tests were performed in the controlling process. The test results were compared to FEM calculated deflection curves based on verified material properties. Threshold limits on material properties were identified and taken into account for work and monitoring plans as well as an action plan of corrective measures.