Análise de suscetibilidade à liquefação dinâmica de areias com diferentes teores carbonáticos do litoral cearense mediante ensaios triaxiais cíclicos

Abstract

This study aims to investigate and evaluate the dynamic behavior and liquefaction susceptibility of soil samples with varying carbonate contents. This research is part of a larger project funded by Petrobras in partnership with the Federal University of Ceará. For this purpose, sandy samples were collected from different locations along the coastal zone of Ceará, exhibiting distinct carbonate contents in their compositions. These samples were obtained both from beach zones and from the offshore continental shelf. The selected sampling sites were Barra do Ceará Beach in Fortaleza, Moitas Beach in the county of Amontada, and Icapuí Beach in the county of same name. The samples were submitted characterization and calcimetric tests for classification purposes. Subsequently, a series of cyclic triaxial tests under strain-controlled conditions was performed. For the cyclic tests, the samples were sieved through a 2.38 mm mesh, in accordance with standard requirements and to ensure compatibility of results with the ongoing research. The samples were designated as follows: Barra do Ceará (BC 4), Moitas (MT 3), Icapuí (ICAP 5), and Offshore Platform (PCO 3). Based on their measured carbonate contents, they were classified respectively as lithoclastic (9.17%), lithobioclastic (40.70%), bioclastic (85.98%), and bioclastic (92.03%). The cyclic loading frequency adopted for all tests was 1.0 Hz, with strain amplitudes of 0.1%, 0.3%, 0.5%, and 0.7%. The confining pressure applied in all tests was 50 kPa, and all specimens were prepared at a relative density corresponding to a loose condition. The analyses considered the following parameters and plots: deviator stress, stress–strain behavior, pore pressure ratio, stress path, cyclic resistance, and stiffness degradation. The results indicated that samples with higher carbonate contents – particularly ICAP 5 – exhibited plots, behaviors, and cyclic resistance relatively superior to those of the predominantly quartzose sample (BC 4). In conclusion, it was observed that samples with higher carbonate contents tend to present greater cyclic resistance and lower stiffness degradation, likely associated with their carbonate composition. Furthermore, it was verified that bioclastic samples are capable of developing cyclic resistance exceeding 100% in certain cases, as evidenced by the mobilized deviator stress and the number of cycles required for liquefaction to occur.