Effects of Porosity on Mechanical Characteristics of Vesicular Basalts

Yang, Soonbo (Port and Airport Research Institute, National Institute of Maritime) | Sassa, Shinji (Port and Airport Research Institute, National Institute of Maritime)

OnePetro 

ABSTRACT

To investigate the effect of vesicular property on mechanical characteristics of basalts a series of uniaxial and triaxial compression tests were conducted for basaltic intact rocks sampled in the northeastern onshore and offshore, southeastern offshore and northwestern offshore of Jeju Island, South Korea. The uniaxial compressive strength and parameters used in the More-Coulomb failure criterion, namely cohesion and internal friction angle, estimated from the results of the uniaxial and triaxial compression tests were compared and analyzed with effective porosity, a parameter representing the vesicular property of basalts. The results demonstrate that the uniaxial compressive strength and cohesion with respect to the effective porosity can be classified clearly as two different non-linear regression curves in accordance with two different linear relationships between bulk specific gravity and effective porosity. As the effective porosity increases, the uniaxial compressive strength and cohesion decrease exponentially. On the other hand, the internal friction angle decreases gradually with the effective porosity, regardless of the relationships between bulk specific gravity and effective porosity.

INTRODUCTION

Basalt is one of the most common rock types of volcanic lava area, and has a fine-grained mineral texture. In addition, basalt has various shaped and sized vesicles formed by dissipation of gaseous phases in lava decompressed in the process of erupting onto the surface of the earth or flowing on the surface.

Vesicular structures of basalt have important effects on the physical and mechanical properties of the intact rock itself as well as the stability of rock mass which are crucial for the design of diverse foundation structures, tunnels, and other projects.

There are many studies of the effects of vesicular property on the physical and mechanical properties such as permeability, uniaxial compressive strength, elastic modulus, Poisson's ratio and ultrasonic velocities of vesicular basaltic intact rocks (Kelsall et al., 1986; Kim and Choi, 1991; Kwon et al., 1993; Al-Harthi et al., 1999; Saar and Manga, 1999; Eum, 2002; Kim, 2006; Gates, 2008; Cho et al., 2009; Moon et al., 2014; Yang, 2014; Yang, 2015a; Yang, 2015b; Yang, 2016; Yang and Sassa, 2016). Most studies on the basaltic intact rock revealed the relationship between physical parameters representing vesicular property and mechanical characteristics estimated from the results of uniaxial compression test. There are, however, very few studies about the strength parameters, such as cohesion and internal friction angle, which can be estimated directly from the results of three or more triaxial compression tests on basaltic intact rocks.