Stability analysis of the cliffs of Ponta Pirambu, Northeastern Brazil

摘要

The coast of Rio Grande do Norte (RN) state, Northeastern Brazil, is characterized by the presence of dunes and cliffs. The latter consist of slopes with heights of up to 40 meters and inclination ranging from 30° to 90° above the horizon. Thus, the purpose of the present study was to assess the cliff stability of Ponta do Pirambu in Tibau do Sul town, in the State of Rio Grande do Norte (RN). The study at Ponta do Pirambu considered the possibility of colluvial cover varying from 0.50 to 5.00 meters thick. The studied area is described by identifying the natural dynamic processes of the site. The experimental program includes field and laboratory tests. Field activities such as technical visits, planialtimetric (field surveying), auger drilling, percussion (SPT) drilling and rotary percussion drilling were carried out in order to determine the profile of the cliff and to understand the natural processes occurring in the area. In the laboratory, physical, chemical, and mineralogical tests were carried out. In particular, CID triaxial tests were performed with effective confining stresses of 20 kPa, 100 kPa, and 300 kPa. Analyses were carried out using Bishop’s method and GE05 software. The results of geological and geotechnical characterization showed that the cliff consists of lateritic materials from Barreiras Formation, with an inclination of 37° from bottom to top and a height of twenty-one meters. It consists of four layers, top, middle, base and a strongly cemented layer between the middle and bottom layers. The cementing is due to the laterization process characteristic of tropical environments. The stability analysis showed that the Ponta do Pirambu cliff could be subject to surface landslides at points where there may be colluviums over two meters thick. However, the cliff remains stable, showing a Global Safety Factor (FS) of 2.30 or more in a saturated condition.