Characterization and correlation of engineering properties of basalts

Basalts are a common lithology found beneath Lisbon and are the predominant rocks of the Volcanic Complex of Lisbon (CVL) (72 Myr). These basalts exhibit variable texture and composition. Given the vast extent of the CVL, which encompasses Lisbon and its surroundings, and the establishment of several present and future engineering works upon this rock mass, the geotechnical study of the CVL is relevant. This type of information is scarce in comparison to petrographic and geochemical studies already available. From this perspective, a study of the intact rock was carried out, involving a total of 349 specimens of seven samples of basalts collected at five distinct locations and displaying different grades of weathering and fracture spacing. Non-destructive and destructive tests were conducted to characterize the physical, mechanical, and dynamic properties of the intact rock. The test results are in agreement with those established for basalts around the world. However, the correlations for basalts presented in the literature cannot be applied to the CVL materials due to several variations in its texture and structure and therefore on the mechanical, physical, and dynamic properties. Consequently, some new correlations of index, strength, and deformational properties of intact rocks are presented. These are intended to be applied in future studies involving basalts of this complex or similar rocks.