We would like to express our appreciation to Drs Irfan and Cheung for their interest in our publication and for providing additional published or unpublished data on the conversion factor (K) between the uniaxial compressive strength (Co) and the point load stength index (L(50~) corrected to a specimen diameter of 50 mm for some Hong Kong rocks. We are happy that the discussion here provides us further opportunity to bring into focus some points concerning our study on the conversion factor x between the uniaxial compressive strength and the point load strength index.
Drs Irfan and Cheung state in their summary of discussion that a substantial amount of test data is available to support the use of a constant tc (about 24) recommended by ISRM [1] or by Broch and Franklin [2] for isotropic rocks found in Hong Kong. In addition, they also question the validity of our experimental data for estimating x for fresh to moderately decomposed granite and fresh tuff. They also seem to misinterpret our theoretical model for the prediction of x. We will, however, explain that their claim for "substantial amount of test data available" is not substantiated by enough evidence, assure that our experiments have been done properly and reliably, and reinforce that our theoretical prediction for ~c should provide a plausible explanation for why tc obtained by us and others [3][4][5][6][7][8] differs from the Broch-Franklin constant of 24. Indeed, the main contribution of [9] is to open up an opportunity for debate that ~: can be a function of rock type, grain-size, degree of weathering, as well as the mineral composition. We, of course, welcome further studies, both experimental and theoretical, that examine the validity of our preliminary finding in ref [9]. Since the discussion by Drs Irfan and Cheung is divided into seven sections, we answer their queries here section by section.