ABSTRACT:
This paper introduces a new in-situ technique for characterizing rock mass mechanical strength and the associated spatial distribution in the ground. The technique involves automatic drilling process monitoring (DPM). Case examples are given to show the original DPM data and analyzed results in a weathered rock mass. The drilling machines in the examples are pneumatic rotary-percussive drilling machines with down-the-hole hammers. The DPM data can directly show the in-situ rock mass drilling resistance strengths and their spatial distribution along the drillhole in the ground. The DPM is a simple, reliable and practical tool for furthering the practice and knowledge of rock mechanics and engineering in the underground environments comprising weathered soils and rocks.
1 INTRODUCTION
Characterization of rock mass quality has been an important area of research and development in rock mechanics since Ritter (1879) attempted to formalize an empirical approach to tunnel design. For more than 100 years, a number of rock mass classification methods have been developed and adopted to quantify rock mass quality in rock engineering design (for example, tunnel and cavern support design). They include the Rock Quality Designation Index (Deere et al. 1967), the Rock Structure Rating (Wickham et al. 1972), the Rock Mass Rating (Bieniawski 1973, 1976, 1989), the Rock Tunnelling Quality Index (Barton et al. 1974, Barton 2006), the Basic Quality and the Host Rock Rating (Lee et al. 1996). 1996). An examination of these methods indicates that similar parameters are used in all the methods in describing rock mass quality. These parameters include the rock quality designation (RQD), uniaxial compressive strength of intact rock (UCS), rock structural conditions (block size, frequency of joints), conditions of joints (spacing, size, aperture, infilling, roughness), orientation of the joints relative to opening axis, groundwater conditions and insitu stresses
