ESTUDO EXPERIMENTAL E NUMÉRICO DO EFEITO DA COMPENSAÇÃO NO COMPORTAMENTO DE UMA FUNDAÇÃO DE UM EDIFÍCIO ALTO

Abstract

This thesis investigates the effect of compensation on the behavior of piled raft foundations in residual soils of the Central-West region of Brazil, based on a case study of a 55-story building, 172.4 m high. Compensation refers to the balance between stress relief caused by excavation and stress increase induced by construction. The study combines geotechnical characterization, full-scale field instrumentation, and 2D and 3D numerical modeling to understand variations in the load–settlement behavior resulting from changes in soil stress conditions produced by basement excavation and raft construction. The experimental program included laboratory tests for physical and mechanical characterization of samples from different depths, as well as in-situ tests that highlighted the heterogeneity of the soil mass. Distinct subsoil profiles were identified beneath the raft, ranging from high-plasticity silt to silty sand, which directly influenced the geotechnical parameters adopted in the numerical models. The instrumentation program involved the design, calibration, and installation of 120 sensors to monitor column loads, raft contact stresses, and pile loads, allowing continuous monitoring throughout the construction stages. Analysis of the experimental data confirmed the compensation phenomenon, identifying the equilibrium point 677 days after the start of construction, when the applied load reached 219.6 MN, approximately 68 % of the total load at the end of monitoring. This point marked the transition from recompression to compression behavior, with a reduction in system stiffness by about 20 times. The instrumentation also revealed high contact stresses at the raft–soil interface and tensile loads at the pile heads during the early monitoring stages, indicating soil expansion due to stress relief caused by excavation. The 2D model established a progressive reduction in stiffness parameters and showed good agreement with the measured settlements. The 3D model captured the tridimensional interactions among the raft, piles, and surrounding soil, enabling analysis of settlement volumes and the evolution of the asymmetrical settlement basin throughout the construction stages. The combined 2D–3D modeling approach proved effective in representing the compensation phenomenon in deep foundations, provided that the stress history is properly considered and the constitutive model accounts for stiffness degradation. The results highlight the importance of integrating experimental observations, numerical modeling, and geotechnical characterization to improve design reliability and long-term performance assessment of piled raft foundations in tropical residual soils.