Rockmass classification of tropically weathered karst limestone of Cambodia for blastability

Abstract

In civil and mining projects, blasting may be necessary for breaking rocks prior to excavation. Due to tectonic activities faulting and folding in rockmass takes place resulting change in physical and mechanical properties of rock. Rocks are further exposed to weathering which affect geomechanical properties of rockmass. Thus, rockmass has different geomechanical and varied physical properties in the same rockmass. Practicing civil and mining engineers should be able to visualize rockmass in the field to get desired blasting results. Rockmass is heterogeneous material having varied geo-mechanical properties which affect blast fragmentation. Due to geological discontinuities such as faults, folds there can be environmental effect such as fly rock and ground vibration which need to be controlled as there may be local community. This research study is for developing rockmass assessment system for karst limestone in Cambodia which will be useful for design of blast with commons known parameters used by field engineers so that desired result of fragmentation can be obtained. Further this rockmass assessment system will be practical to minimize the effect of fly rock hazard and ground vibration due to blasting. Limestone in Cambodia is explored and initial stage of development. Blastability index (BI) will be compared to recent approaches and these parameters will be considered for rockmass assessment. During initial stage of mining project, detailed information on limestone deposit may not be available. The proposed methodology of rockmass assessment is based on review and will be useful for blast design and prediction of blast performance in Cambodian limestone deposit. Karst limestone in Cambodia is classified into five classes based on exploration data consisting of RQD, degree of weathering, degree of hardness and percentage cavities based on exploration data. Major cavities observed are in cherty limestone and argillaceous limestone. 65% cavities are filled with clay and 35% cavities are not filled with any material. Further exploration data is classified based on block model based on structures identified, hardness of rock and will be useful for co-relating with blastability index. 99% of cavities in karst limestone are found with argillaceous and upper cherty limestone. Based on cavity classification, 74% drilling area has average cavities of 0.37% which is least. 9% of drilling area has >20% of cavities or 2% of total area which is highest and concern for blast performance from fly rock, fragmentation and back break point of view.