Correlation of TBM and drilling machine performances with rock brittleness
Introduction
Rotary and percussion drilling equipment is widely used in rock excavation. Tunnel boring machines (TBMs) are ubiquitous in civil engineering applications. Having some prior knowledge of the potential performance of the selected rock drilling equipment or boring machines is very important in rock excavation projects for the planning and the cost estimation purposes. Drillability and borability can be predicted from a combination of machine characteristics and rock properties. Uniaxial compressive strength is the most widely used parameter for predicting the performance of tunnelling machines and drilling rigs Paone and Madson, 1966, Paone et al., 1969a, Paone et al., 1969b, Barendsen, 1970, Fowel and McFeat-Smith, 1976, Brown and Phillips, 1977, Poole and Farmer, 1978, Aleman, 1981, Hughes, 1986, Karpuz et al., 1990, Bilgin et al., 1996, Kahraman, 1999. In addition, a wide range of empirical tests has been used to predict the performance of drilling or boring machines. Among these are: Schmidt hammer, Taber abrasion, point load, cone indenter, Shore hardness, drilling rate index (DRI) and coefficient of rock strength (CRS) McFeat-Smith and Fowel, 1977, Howarth, 1986, Nilsen and Ozdemir, 1993, Li et al., 2000. Recently, rock mass classification systems, such as Q-system and RMR-system, have been used for the estimation of TBM performance Alber, 1996, Barton, 1999.
Evans and Pomeroy (1966) theoretically showed that impact energy of a cutter pick is inversely proportional to brittleness. Singh (1986) indicated that cuttability, penetrability and Protodyakonov strength index of coal strongly depended on the brittleness of coal. Singh (1987) showed that a directly proportional relationship existed between in situ specific energy and brittleness of three Utah coals. Göktan (1991) stated that the brittleness concept might not be a representative measure of rock cutting-specific energy consumption.
Brittleness is one of the most important mechanical properties of rocks. However, there is no available published material on the relationship between brittleness and both drillability and borability. In this study, the correlations between brittleness and both drillability and borability were analyzed using the raw data obtained from the experimental works of different researchers. Rock properties and performance data obtained from the different researchers were listed in the respective tables. The calculation of brittleness values and generation of the plots were performed by the author.
Section snippets
Brittleness
Morley (1944) and Hetényi (1966) defined brittleness as the lack of ductility. Materials such as cast iron and many rocks usually terminating by fracture at or only slightly beyond the yield stress have been defined as brittle by Obert and Duvall (1967). Ramsay (1967) defines brittleness as follows: when the internal cohesion of rocks is broken, the rocks are said to be brittle. The definition of brittleness as a mechanical property varies from author to author. However, it may be stated that
Tunnel boring
Howarth et al. (1986) reported the performance characteristics of a model TBM in six sedimentary rock types. The model TBM had an overall diameter of 106 mm and was fitted with six tungsten carbide-tipped square-faced drag bits of dimensions 9.5×9.5 mm and a spacing between adjacent cutters of 7.5 mm. Penetration rates, rock properties and calculated brittleness values are given in Table 1.
The performance characteristics of the model TBM were analysed using the method of least squares
Correlations among the three different methods of measuring brittleness
To see whether a method of measuring brittleness differs from the other methods, the data in Table 1, Table 2, Table 3, Table 4, Table 5, Table 6, Table 7, Table 8, Table 9 were analysed using the least square regression method. It was seen that there is a strong logarithmic relationship between the brittleness of B1 and B2. Fig. 10 was given as an example. As seen in the examples of Fig. 11, Fig. 12, there is no correlation between the brittleness of B3 and the brittleness of both B1 and B2.
Conclusions
Brittleness, defined differently by different authors, is an important mechanical property of rocks, but the correlations between the brittleness and both drillability and borability have not been clearly explained yet. The relationships between three different methods of brittleness and both drillability and borability were statistically examined using the raw data obtained from the experimental works of different researchers.
There are strong exponential relationships between the penetration
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