Adjustment Factor Of Slope Mass Rating (SMR) System: Revisited
Writers : Ismail Abd Rahim, Sanudin Hj. Tahir, Baba Musta & Shariff A.K. Omang
Date : 23-24 June 2012
Publisher : National Geoscience Conference 2012 (NGC 2012)
Location : Pullman Hotel, Kuching
The SMR (Romana, 1985) is obtained from RMRb (basic RMR) by adding an adjustment factor (F). The adjustment factor of SMR is the product of four factors from Romana (1985) and Anbalagan et al. (1992).
F = (F1xF2xF3) + F4 (1)
F1 depends on parallelism between direction of discontinuity intersection line or discontinuities and slope dip direction. F2 refers to discontinuity dip and plunge angles of intersection line in the planar and wedge mode of failures, respectively. F3 reflects the relationship between slope and discontinuity dips. F4 is an adjustment factor for method of excavation which considers natural slope and methods of blasting and excavation (presplitting, smooth blasting, blasting and mechanical and normal blasting).
This SMR system was applied to four slopes in rock quarry at Tamparuli and found a problem in calculating adjustment factor parameters. The result is quite reasonable and consistence for sub-parameters F2, F3 and F4 but not for F1. Some of the results do not fulfill the parallelism concept (0o<parallelism,q<90o) and ranges of rating values (0 to 1) especially for toppling mode of failure.
This study also found that, there is a strange in the calculation of F1 rating value for toppling failure by Romana (1985) and Anbalagan et al. (1992). They are using B in calculating parallelism value but A in Equation 2 for F1 rating value. This is quite different with the calculation of parallelism and F1 rating value for planar and wedge failures. Both failures are calculated by using A in Equation 2.
F1 = (1 – sin A)2 (2)
Due to that situation, this study was trying an alternative to calculate the rating value for toppling failure by using B in the original F1 of Romana (1985) and Anbalagan et al. (1992). The result is better but some F1 rating values are still over estimated.
In order to fulfill the parallisme concept and ranges of rating values in F1 sub-parameter, the new approach of adjustment factor (NAAF) for SMR is introduced (Equation 3).
F1 = (1 – sin Z)2 (3)
The parallelism and rating values of F1 by NAAF for the study area are shown in Table 3. The result shows that the NAAF are more accurate, consistence, without assumption and user friendly to calculate parallelism sub-parameter (F1) of adjustment factor for Slope Mass Rating (SMR) system.
Key words: Discontinuity orientation, Crocker Formation, Slope Mass Rating (SMR), New approach of adjustment factor (NAAF).