TECHNICAL | MECHANISED TUNNELLING


Table 4: Comparison between different rock type categorisations with the same RMR value and TBM FPI RMR input parameters


Rock mass properties


UCA (MPa) RQD (%)


Spacing of discontinuities (m) Condition of discontinuities (Jc) Groundwater general conditions


Basic RMR FPI (kN/cutter/mm/rev)


Table 5: Descriptive statistics of generated database based on different classes N


Class G & GN


FPI (kN/cutter/mm/rev) UCS (MPa) RQD (%) Jv


Class MV


FPI (kN/cutter/mm/rev) UCS (MPa) RQD (%) Class SLK


FPI (kN/cutter/mm/rev) UCS (MPa) RQD (%) Class C


FPI (kN/cutter/mm/rev) UCS (MPa) RQD (%)


143 143 143


139 139 139


126 126 126


5.9 16 10


9.52 20 30


1.43 6


10


70.68 227.4 100


45.44 176 100


19.91 105 90


22.2


96.36 70.37


19.42 78


70.87 11.15


40.34 49.58


14.37 50.33 18.46


6.44


38.23 17.93


4.57


23.94 21.58


258 258 258 258


14.01 38.3


18.31 0.2


161.25 267.9 100 29.3


49.71 151.13 85.5 8.5


30.36 57.65 13.62 4.47


Min Max Mean


Rock mass 1 (amphibolite) 170 95


0.8


Slightly rough and moderately to highly weathered, wall rock surface separation <1mm


Damp


Rock mass 2 (limestone) 170 95


0.8


Slightly rough and moderately to highly weathered, wall rock surface separation <1mm


Damp


Rating


Rock mass 1 Rock mass 2 12 20 15


12 20 15


20 10


77 46.81


20 10


77 38.48 Std. Deviation


Table 4 shows the basic RMR system calculated for


two rock masses in two different rock types. Overall, when comparing the most commonly used rock mass classification systems, the RMR classification is easiest to apply and shows better correlation with TBM performance, possibily due to the use of intact rock compressive strength as an input parameter. Moreover, RMR is frequently used in the tunnel design process and reported from the logging of cores as well as back mapping. As such, input parameters of RMR are often available from various projects.


As can be seen from Table 4, despite the similar


values found between two types of rocks (amphibolite, limestone), the boreability of rock masses are different. Several factors directly or indirectly can affect TBM performance, such as the angle between the tunnel axis and discontinuity planes  (alpha angle), crew experience, backup system, and so on, but from the geological points of view it can be expected that the differences are due to the rock texture and cementation. Therefore, boreability is impacted by rock texture and cementation (Salimi et al. (2019b). Similar results have been observed between other rock mass classifications, such as rock structure rating (RSR) by Wickham et al. (1972). In this study, given the available data, performance


Right, figure 2:


Percentage distribution of different rock type codes


prediction models are introduced based on similarities in rock textures categorised as G & GN, MV, SLK, and C. Descriptive statistical distribution of variables and input parameters for the generated model for each rock type are summarised in Table 5. The percentage distribution of different rock type categorisation is shown in Figure 2. Higher FPI values and associated parameters can be


G & GN MV 20 | July 2024 SLK C


found in hard rock (G, GN), whereas lower values are attributed to soft/weak and more fractured rock (C). This confirms the need to developing new models that include rock type categorisation to reflect similarities in texture. It is worth noting that in class G and GN


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87  |  Page 88  |  Page 89  |  Page 90  |  Page 91  |  Page 92  |  Page 93  |  Page 94  |  Page 95  |  Page 96  |  Page 97  |  Page 98  |  Page 99  |  Page 100  |  Page 101  |  Page 102  |  Page 103  |  Page 104  |  Page 105  |  Page 106  |  Page 107  |  Page 108  |  Page 109  |  Page 110  |  Page 111  |  Page 112  |  Page 113  |  Page 114  |  Page 115  |  Page 116  |  Page 117  |  Page 118  |  Page 119  |  Page 120  |  Page 121  |  Page 122  |  Page 123  |  Page 124  |  Page 125  |  Page 126  |  Page 127  |  Page 128  |  Page 129  |  Page 130  |  Page 131  |  Page 132  |  Page 133  |  Page 134  |  Page 135  |  Page 136  |  Page 137