Sri Lanka is situated in a tropical climate where rainfall takes place throughout the year. As limestones in Sri Lanka are frequently exposed to rain water, limestone absorbs water and forms carbonic acid. With various geological discontinuities such as faults, folds, joints, water flows through these cavities. The weathering process along these cracks or cavities takes place at a faster rate. This further enhances the process of dissolution resulting in change in geomechanical properties of limestone. Limestone deposit at Aruwakkalu based on rock structure is classified as (i) Heavily cracked, frequent weak joints, weakly cemented layers (ii) Thin, well-cemented layers with tight joints (iii) Massive intact rock. This limestone deposit is also classified as a bedding plane dipping into the slope face, bedding plane dipping into a cut slope face and other cases. Existing system of rockmass classification at Sri Lanka is described in this paper. Thus for Aruwakkalu limestone deposit, rockmass can be classified based on type of rock structure, Blastability Index (BI), RQD%, degree of weathering and degree of hardness. Average powder factor of 0.15 kg/t can be correlated with BI
