Geotechnical characterization of an amphibolite from Baixada Santista-SP, Brazil

Abstract

Abstract This work presents the results of the characterization of a sound to slightly weathered amphibolite, sampled at Baixada Santista, on the coast of the state of São Paulo, in the southeastern region of Brazil. Initially, petrographic analysis of material sheets were performed. Characterization tests were carried out to determine the physical indexes and to determine p-wave propagation velocity. For the mechanical characterization of these materials, uniaxial compression and point load tests were carried out in two different loading directions. The results of the micro petrographic analysis indicate that an average of 66% of the analysed minerals did not present weathering and 34% percent of the minerals are the result of weathering. The physical characterization results indicate (average values) of apparent porosity equal to 2.77%, apparent absorption capacity of 0.92% and apparent specific dry mass of 2.69 g/cm3. The results of p-wave propagation velocity measurements indicate a 2.63% reduction in the wave velocity of the ones measured on parallel direction to the ones on perpendicular direction. As for the mechanical characterization tests, there was an average value of uniaxial compressive strength equal to 77.40 MPa for samples loaded on the parallel direction and 92.96 MPa for samples loaded on the perpendicular direction (differences of about 20%). For the point load compression tests, an Is50 value of 2.44 MPa was obtained for the samples loaded on the direction parallel to the foliation and of 5.41 MPa for the samples loaded on the perpendicular direction (increase of about 121%). The UCS/Is50 ratio was determined for both loading directions, being equal to 17.2 and 31.7 for samples loaded on the parallel and perpendicular directions to the foliation, respectively.