<p>Pile and raft foundations are widely used to meet the requirements of prevailing standards for maximum permissible deformations. During construction of multistorey and high-rise buildings with significant loads on the foundation, especially in formations overlain by weak water-saturated soils at the top. The applicability of raft foundations in this case must be is confirmed by calculations with scientific and technical justifications of the adopted model of the soil base and its parameters. The purpose of the paper is to justify an improved model of the soil base in the form of a continuous “stepped” layer of finite distribution capability and its parameters, based on the comparison of the results of numerical calculations and observations of the settlements of two adjacent multistorey buildings on raft foundations during construction and operation. Simulation and calculation were performed for adjacent raft foundations of a two-section multistory building with reference to the different number of floors of the sections during construction in the base—foundation—building system, which interacts with an improved model of the soil base, represented as a continuous “stepped” layer of finite distribution capability with different laws of soil deformation. The research results confirmed the applicability of the improved soil base model for estimating the deformations of different-storey sectional buildings on large-sized raft foundations, where weak water-saturated sandy soils occur close to the surface. Numerical studies indicate that considering different compressible layer, thicknesses under differently loaded foundations in the base model in combination with the “Hardening Soil” deformation law allows for the most accurate simulation of the horizontal movements (tilts) of each section of a two-section building.</p>