## 1 Introduction  
Ground deformations have a major impact on the distribution of forces in a structure. In order to properly design a built structure, it is extremely important to reliably represent the behaviour of the subsoil underneath. Recent years have seen a very intensive development of analysis using the Finite Element Method (FEM). Due to the availability of more efficient machines, it is possible to make calculations for every larger model in much less time. Today's design practically does not exist without using FEM, so it is important to share experiences and the results of such calculations in order to better calibrate models and obtain more reliable results. The interaction between built structures and the subsoil is often analysed as a two-dimensional issue, e.g., for a selected cross-section of the structure [1, 2, 3]. For axially symmetrical problems, a section of the structure can be used [4]. Three-dimensional models of buildings are the most reliable. However, many analyses are often limited to foundations and based on the assumption that there is a rigid subsoil underneath, or described with one-parameter stiffness [5; 6; 7]. Sometimes subsoil mass is modelled with a small fragment of the structure [8; 9]. Three-dimensional analysis of a building with subsoil is a complicated and laborious issue, but it is the most reliable one [10; 11; 12]. Sometimes analyses are performed over a larger area, e.g., for a development concept [13] or a larger site stability analysis [14]. The present work describes the process of conducting a three-dimensional analysis of cooperation between a real building located in Lublin in eastern Poland and loess soil it is founded on. Research included studying the soil and the structure, numerical modelling and geodetic measurements. The final results are the product of subsequent iterations adapting model parameters to the actual behaviour of the objects. Figure 1 shows a graphical representation of the overall analysis. The paper presents a broad analysis of the cooperation between the building and the subsoil. Such full-scale analyses are performed very rarely, as they require the collection of a large database (soil parameters, settlement measurements, control of subsequent construction phases), are labor-intensive and time-consuming (e.g., construction and calibration of FEM models, soil tests and geodetic measurements in a wide range). The implementation takes several years, because we need data obtained both before the start of construction (soil investigation), during the process (verification of dynamic response of construction), and during geodetic measurements carried out for several years after the completion (building settlement). Despite the time-consuming nature of the work, the results of such works are very valuable in the context of designing new buildings in similar ground conditions. Figure 1: A scheme of the analysis process. Loess is a specific type of soil, associated mainly with collapse settlement, but a proper analysis in the design process related to subsoil stiffness is extremely important. The available literature includes publications covering the analysis of foundation settlement on loess; however, these are works of a much smaller scope, including single foundations [15; 16], or without FEM analyses covering entire buildings [17]. Additionally, apart from the author's publication [18], there are no publications at all about FEM analysis in the loess of the Naleczow Plateau. Despite a similar genesis (aeolian), soils may behave in different ways in different parts of the world. To describe the behaviour of the subsoil, parameters that are derived in various types of subsoil studies are needed. Soil parameters determined by different methods can differ significantly [19; 20; 21]. One of the most important features of soil is its deformability, which shows a strong non-linearity and is variable depending on the range of deformations considered.