Análise R/S de sondagens conepenetrométricas CPTu em alguns depósitos argilosos do Estado do Rio de Janeiro

Abstract

This research aimed to study the vertical variability of several records of cone driving tests with CPTu pore pressure measurement in 3 (three) saturated soft clayey deposits, located in 2 (two) municipalities, Sarapuí in Duque de Caxias, Santa Cruz and Recreio dos Bandeirantes in the city of Rio de Janeiro. More specifically, the work sought to answer the question of possible randomness present in the signals of these tests, monitoring the variation in tip resistance and lateral friction, as well as pore pressure, with the depth of the sedimentary deposits. To this end, R/S analysis was used, one of the typical mathematical instruments for investigating self-similar temporal fractal signals, present in various phenomena (hydrological data, stock market, seismic data, acoustic emission data during the loading of different materials, electroencephalograms, electrocardiograms, etc.). The results definitively showed that the variation of the signals with the depth of the deposits is not random (Hurst exponents strongly different from 0.5), a situation in which the memory of these signals would be short-range, causing the correlation between them ceased to exist, to gradually increasing depths. In this sense, it is fair to state that all experimental data analyzed in this work are imbued with long-range memory, suggesting that the correlation between them remains strong, even for widely spaced spatial points, in each test investigated. The results clearly showed that the Hurst exponents of all tests were invariably in the range 0,5<H≤1, very close to unity, which suggests the presence, in the analyzed signals, of persistence, with the data being positively correlated, and therefore there is a greater probability of continuing an upward or downward trend with depth. Regarding correlation intensities, of the 39 (thirty-nine) R/S analyzes carried out, 37 (thirty-seven) analyzes which is equivalent to 94.87% presented a variation of values close to 100% and 2 (two) analysis, which is equivalent to 5.13%, presented a variation in values close to 50%, corroborating the trends suggested by Hurst's exponents, that is, that the experimental records are strongly correlated, regardless of the position of the points under study, whether whether they are more superficial or deeper, in the sedimentary deposit.