Mechanical Characterization of Granitic Rocks of Hong Kong by Improved Index Testing Procedures with Reference to Weathering Induced Microstructural Changes

This dissertation, "Mechanical Characterization of Granitic Rocks of Hong Kong by Improved Index Testing Procedures With Reference to Weathering Induced Microstructural Changes" by Arindam, Basu, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled MECHANICAL CHARACTERIZATION OF GRANITIC ROCKS OF HONG KONG BY IMPROVED INDEX TESTING PROCEDURES WITH REFERENCE TO WEATHERING INDUCED MICROSTRUCTURAL CHANGES Submitted by Arindam Basu for the degree of Doctor of Philosophy at The University of Hong Kong in December 2005 This study aimed to improve various aspects of the most common mechanical index tests (Brazilian, point load, Schmidt hammer and ultrasonic) based on theoretical and practical considerations for better prediction of mechanical properties and degree of weathering of rock materials. The validity and success rates of the proposed improvements were investigated by a comprehensive experimental study of granitic rocks of various weathering grades from Hong Kong. Test results were correlated with microstructural, physical and mechanical properties and plotted against a refined weathering classification (up to Grade IV). The most significant achievements and relevant conclusions are summarized below. The initial response of the diametral stress-strain behavioral patterns in Brazilian test exhibited by the granitic rocks, named as Brazilian deformation index, was found to be sensitive enough to detect even minor variations brought about by weathering. This new index also proved very efficient in predicting microstructural, physical and mechanical properties. Continuous measurement of cone penetration for the first time in point load testing revealed that penetration is deeper in fresh rocks than in weathered rocks, and reduced data scatter leading to a better regression coefficient and lower conversion factor between the point load strength index and uniaxial compressive strength. The index with this measurement also proved to be better interrelated to the other properties and weathering grades. A new analytical formulation for normalization of the Schmidt hammer rebound values to nullify the gravity effect was proposed. This normalization method can be used for any type of Schmidt hammer fired in any direction on a wide range of rock materials, and was proven to be more accurate than empirical methods. A critical methodology adopted for the Schmidt hammer investigation showed that both L and N hammers are fairly sensitive to microstructural and physical properties of the granitic rocks. The N hammer proved to be more efficient than the L hammer in predicting mechanical properties. The nature of these correlation curves highlighted different weathering responses of mechanical properties under uniaxial compression and rebound values. Rebound value after multiple impacts at a given point produced a better indication of the weathering grade than a single impact value. A theoretical relationship was derived to guide transducer selection for the use of ultrasonic velocity in characterizing rock materials. The validity of this relation was verified experimentally. The study revealed that the existing standards do not provide sufficient and/or practical guidelines on a number of issues, and called for consideration of the proposed modifications. Point load test proved to be the most competent means among all the improved index tests of predicting mechanical properties. On the other hand, of the improved test results obtained in this st