Use of SPT tests for the analysis of load capacity of foundations in deterministic and probabilistic terms

Abstract

The present work aims to elaborate a deterministic and probabilistic analysis of three adopted elements of deep foundation: Strauss pile, continuous helix and precast (centrifuged), through the use of SPT type test data. For the deterministic analysis, the Aoki-Velloso method (1975) was used to determine the load capacity of the foundation element, which uses the index of resistance to soil penetration. For the probabilistic analysis, the FOSM methodology was used to calculate the probability of failure for the three cuttings chosen according to the diameter values, mean values of the penetration resistance and correction factor indexes presented in the literature. Both the deterministic approach and the probabilistic approach were performed through computational implementation, through programming language using Matlab software. The compilation of data obtained from SPT tests was established in spreadsheets in Excel software with the following parameters: soil classification, water level, soil penetration resistance indexes, coefficient in relation to soil type (K), soil friction coefficient (?) and variation of layer thickness. Then, it was verified average load capacity and the probability of failure for three loads adopted and three diameters according to the literature for each pile adopted. After obtained results, acceptable values of rupture probability were found for all the piles analyzed, with the Strauss pile, with its higher workload of 600 kN and smaller diameter of 0.27m, presenting the highest probability of failure and the Continuous Helix pile,with its lower workload of 500 kN and smaller diameter of 0.275m, presenting the lowest probability of failure. The precast pile (centrifuged), therefore, presented the highest last loads calculated. The results were satisfactory and the calculations should serve as a basis for possible geotechnical studies involving SPT tests.