Análise da probabilidade de falha de uma fundação profunda na região centro-oeste do Brasil Failure probability analysis of a depth foundation in central-west region, Brazil
The Brazilian standard pertinent to the design and execution of foundations, NBR 6122/2019, establishes that the safety inspection of foundations of a given project must be conducted based on compliance with specified safety factors. Safety factor verification is imperative to meet regulatory requirements; however, it is not enough to guarantee the safety of a foundation. As there is variability in the resistance and solicitation of the piles that make up a foundation, each safety factor value reflects a failure probability. Therefore, it is fictitious that the use of an adequate safety factor value implies the absence of failure risk. Thus, a reliability analysis, applied to a real building with an access ramp whose foundations are composed of precast concrete piles, based on the probabilistic moments, mean, and coefficient of variation, associated with the variability of pile resistance and solicitation, is presented in this article. The values obtained for the safety factors (2.14 and 1.98 for the building and the ramp foundations, respectively) and failure probabilities (1:2,244 and 1:3,131 for the building and the ramp foundations, respectively) implies that the project in question has an acceptable safety level. This article allows us to conclude that a small variation in the reliability index results in a large variation in failure probability; that a greater global safety factor does not necessarily lead to a lower failure probability and it becomes evident that this reliability analysis is a practical way, to manage the uncertainties inherent in foundation design, allowing rational decision making regarding performance.
In this study, a ground anchored wall located in Belo Horizonte containing 295 anchorages in a sandy silt soil was analyzed. The load capacity of all the anchors was calculated by extrapolation of the receipt tests by the Van der Veen method through the CsAGeo web application. The shear strength in the soil-anchor interface was obtained from a semi-empirical method. Two criteria to analyze the extrapolated curves of Van der Veen were used. In the first criteria, the shear strengths of all the extrapolated curves were calculated. In the second criteria, only those curves from the extrapolations considered as reliable were used to calculate the shear strengths. The main objective of this work is to set up the value of shear strength at the soil-anchor interface through extrapolation of the mathematical and semi-empirical methods. The semi-empirical method was carried out in soil and executive methodology equal to the work analysed, which increases the accuracy of these values contributing to containments using anchors. The results were grouped according to the ranges of the penetration resistance (N SPT). An increasing tendency was identified in the shear strength as the value of the resistance to penetration increased. In addition, the linear tendency was observed for the reliable curves.
Forecasting bearing capacity performance with semiempirical and theoretical methods applied to precast concrete piles founded on sandy clay in the region of Uberlândia-MG, Brazil
A técnica de estruturas de contenção com ancoragens reinjetáveis e protendidas é muito utilizada no Brasil, mas há ainda muito o que se estudar sobre a determinação da carga de ruptura geotécnica e o dimensionamento do bulbo ancorado. Para o desenvolvimento deste trabalho utilizou-se um banco de dados de 40 tirantes executados em uma cortina atirantada do município de João Monlevade. Através da análise dos ensaios de recebimento, aplicou-se a extrapolação matemática de Van der Veen (1953), obtendo-se estimativas das cargas de ruptura para cada um dos tirantes executados na obra. Com esses valores de capacidade de carga e considerando o critério de exclusão de Aoki (2013) para cada uma das ancoragens, calculou-se, baseado na metodologia de Porto (2015), os comprimentos ancorados dos tirantes considerados “confiáveis”. Comparando os mesmos com o comprimento ancorado de projeto, os resultados encontrados se mostraram satisfatórios, já que os comprimentos ancorados provenientes da extrapolação foram menores que o comprimento ancorado de projeto, obtendo assim, relativamente, um dimensionamento mais econômico. Além disso, esse trabalho propôs um valor de “coeficiente de ancoragem” para o solo do tipo silte argilo arenoso, característico do local de construção da cortina atirantada, mostrando a relevância desse parâmetro na determinação de estimativas da capacidade de carga de ancoragens neste tipo de solo.
Análise de desempenho de métodos semiempíricos de previsão de capacidade de carga geotécnica aplicados a estacas pré-moldadas de concreto assentes em argila arenosa Performance analysis of semiempirical bearing capacity prediction methods applied to precast concrete piles based on sandy clay
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