Relationships between unit weight, unconfined compressive strength, and deformation modulus of vesicular basalt

The presence of vesicles within basalt has a negative impact on both the unconfined compressive strength (UCS) and deformation modulus (axial stiffness) of basalt specimens. Vesicular basalt specimens (diameters of 44.45 mm) were cored from surface boulders obtained from southern Nevada. Each basalt boulder has its own unique pore sizes, pore spacing, and shape of pores. Sizes of these voids range from less than 1 mm to approximately 30 mm. To date, 26 specimens have been tested in unconfined compression to determine the engineering properties of peak strength and deformation modulus. The variation in these two parameters is assessed as a function of unit weight and total porosity. Results show the specimens fall within two distinct groups, one with relatively high unit weight (low total porosity) and one with relatively low unit weight (high total porosity). The high unit weight (low porosity) specimens had the greatest influence on developed relationships between peak strength or deformation modulus and unit weight or total porosity. Total porosity is a better predictor of peak strength and deformation modulus. Future work is presently underway to investigate potential size effects and characterize various macropore properties to augment the relationships developed through laboratory testing.