Samorodov O. Development of scientific basis for the selection of rational parameters of combined pile and raft foundations for multi-storey buildings

The thesis deals with the creation of the computational and theoretical apparatus to design cost-effective large-sized combined pile and raft foundations for multi-storey and high-rise buildings. Within the scope of the thesis, extensive full-scale and laboratory studies have been carried out of the interaction with the soil mass of both separate elements in the form of piles (including multi-section piles) and plates, and large-sized raft and pile and raft foundations of buildings, which makes it possible to reveal experimental and theoretical dependences and regularities, propose new designs and develop or improve means, methods and techniques of testing and calculation to design efficient combined pile and raft foundations for multi-storey and high-rise buildings. A method has been developed for determining the rational parameters of large-sized combined pile and raft foundations by the maximum permissible settlements of structures without considering the load-bearing capacity of single piles to soil, and a method has been developed for determining the tilts of pile and raft foundations by testing soils using piles, including outside their stabilized settlements under load. A new method has been developed and methods have been proposed for calculating the load-bearing capacity of bored piles based on the newly discovered forces of the soil strength along their lateral surface under the action of a torsional momental load (conditionally at rest), with account of additional обжатия forces under the action of both pressing in and pull out loads; new regulatory techniques have been developed and known regulatory techniques have been improved to identify additional load friction forces in structurally unstable soils. Based on the analysis of a significant amount of experimental data and theoretical justification, the methods have been improved for determining the design strength of the base soil R, its compressible thickness H and the stress-strain modulus E depending on the size of the foundation. A method has been proposed for assigning the parameters Е0 and Н0 of the elastic finite layer model for soil bases of large-sized foundations, which makes it possible to adequately model the stress-strain condition of the base-foundation-structure system as shown by the numerical analysis of the object on the pile and raft foundation under the influence of various models of a linearly elastic medium. A universal method has been developed for evaluating the effectiveness of any design solutions for large-sized combined pile and raft foundations, where, apart from the cost, the utilization factor for the mechanical properties of the base and foundation is taken into consideration. When tested on real-life objects, the method confirmed the high effectiveness of the proposed foundation designs with rational parameters. The results of the doctoral thesis use in the development of a project of normative document: DBN V.2.1-10-201X "Basics and foundations of buildings and structures. Key provisions", and the economic effect of implementing the results of the dissertation amounted to more than 1,9 million UAH.