Chapter 16 - Rock mass classification for the assessment of blastability in tropically weathered igneous rocks

Abstract

Tropical climate and posttectonic impact on the rock mass cause severe and deep weathering in complex rock formations. The uniqueness of tropical influence on the geoengineering properties of rock mass leads to significant effects on blast performance especially in the developmental stage. Rock mass classification systems have been implemented for last century for various applications to simplify complexity of rock mass. The objectives of this study are to determine the significant factors of tropically weathered igneous rock mass properties that influence blast performance and to develop a rock mass classification system for blastability in tropically weathered rocks. Several research studies have been carried out on rock mass and material properties for five classes of weathered rocks—fresh, slightly, moderately, highly, and completely weathered rock. Initially, weathering profiles at each site from Thailand, Cambodia, Malaysia, and Indonesia are studied. Various rock mass properties of igneous weathered rocks for each site are evaluated. Rock density and blastability index (BI) can be correlated with degree of weathering. Porosity, water absorption, and point load index strength have drastic change in properties for highly and completely weathered igneous rocks as compared to fresh to moderately weathered igneous rocks based on moisture content. Rock quality designation (RQD) and geological strength index (GSI) values are lowest for highly and completely weathered igneous rocks. On the other hand, RQD and GSI values increase from moderately weathered to fresh igneous rocks. Assessment of rock mass classification system for blastability is useful for mining sustainability. Rock mass classification system for blastability is proposed for tropically weathered igneous rocks based on rock density, degree of weathering, RQD, GSI, porosity, water absorption, point load strength index, and BI.