Abstract
Rock mass classification has played a crucial role in underground construction and mining projects in the past fifty years, especially the Rock Mass Rating (RMR) and Rock Tunneling Quality Index (Q) systems, which have been applied in many cases. The parameters of discontinuity conditions in the RMR system, along with the related ratings, were used to develop a new equation in order to introduce an intrinsic quality of a given rock mass, namely, rock bolt supporting factor (RSF). The RSF was used to develop a mathematical theory of the rock bolt supporting mechanism as a new principle in explaining rock bolting effects. Finally, using the parameters of the discontinuities in the Q-system, the QRSF is defined to present the capability of a given rock mass to be reinforced by rock bolting. The RSF leads to more reliable judgment of rock bolting capability of a given rock mass than the QRSF since it uses five parameters of discontinuity conditions while the QRSF uses only two parameters.
Highlights
Rock mass classifications form an integral part of the empirical design methods in mining and civil works which have provided the only systematic design aid in many cases of underground construction and mining projects (Bieniawsky 1989)
Rock mass classification has played a crucial role in underground construction and mining projects in the past fifty years, especially the Rock Mass Rating (RMR) and Rock Tunneling Quality Index (Q) systems, which have been applied in many cases
The QRSF value demonstrates an inability to generate an accurate assessment of the rock bolting capability of a rock mass. This is because the Q-system and, subsequently, the QRSF equation, use only two parameters of discontinuity conditions, which leads to a poorer assessment of the rock bolting capability of a rock mass
Summary
Rock mass classifications form an integral part of the empirical design methods in mining and civil works which have provided the only systematic design aid in many cases of underground construction and mining projects (Bieniawsky 1989). To classify a rock mass using the RMR system, six parameters, namely uniaxial compressive strength (UCS), rock quality designation (RQD), spacing of discontinuities, condition of discontinuities, groundwater conditions and orientation of discontinuities, are used (Bieniawsky 1989). This classification system will be thoroughly discussed since discontinuity conditions, as one of the input parameters in this classification system, are one of the main concerns in determining the rock bolt supporting factor (RSF) of a rock mass. Namely RQD, number of joint sets, roughness of the most unfavorable joint or discontinuity, degree of alteration or filling along the weakest joint, water inflow and stress condition, Barton et al (1974) defined the Rock Tunneling Quality Index (Q) as an equation two where the first quotient (RQD/Jn) represents the block size in the rock mass, the second quotient (Jr/Ja) represents the roughness and frictional characteristics of the joint walls or filling materials, and the third quotient (SRF/Jw) consists of two stress parameters
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