Análise das incertezas de ensaios CPTu na caracterização estatística de solos marinhos

Abstract

Structural integrity is an important premise in oil well design. In this context, soil characterization helps designers to assess its strength and design conductive casing columns, which support the well construction and operation loads. The Piezocone test (CPTu) is commonly used to obtain data on soil properties, as it is a simple but robust test capable of providing satisfactory data. However, the estimation of soil properties includes uncertainties arising from different sources, including spatial variability, measurement errors and the application of a transformation model. From the dataset of a CPTu test, it is possible to quantify soil resistance parameters using statistics presented in the literature. In order to choose a representative probability distribution of a soil sample, the quality of the data must be ensured, since compliant data enable a more accurate and reliable statistical characterization. It should be noted that the application of statistical procedures in the estimation of parameters must be done using samples that meet the criteria of weak stationarity. With a properly characterized soil property, the application of structural reliability concepts allows several analysis on the behavior of the casing of the well. The influence of the uncertainties in the parameters of the CPTu test in the statistical characterization of marine soils is evaluated through the analysis of the uncertainties linked to the transformation model. After that, a stationarity test of the sample is carried out using two main procedures: the removal of the trend function by linear regression and the modified Barlett Test. Once the stationarity is confirmed, the statistical characterization of the sample is carried out. The results show that the normal distribution was accepted with a 5% significance level for all analised layers, showing that the data closer to the mean have a greater probability of occurrence in the delimited stretches.