National Geoscience Conference 2011 - Department Of Geology ...

NATIONAL GEOSCIENCE CONFERENCE 2011
11 – 12 June 2011 • The Puteri Pacific Johor Bahru, Johor, Malaysia
Paper A5
Rock Mass Quality of the Crocker Formation from Tamparuli, Sabah, Malaysia
Ismail Abd Rahim*, Sanudin Tahir, Baba Musta, Rodeano Roslee & Mohd Muzhafar Mohd Zaki
Geology Program, Universiti Malaysia Sabah, Jalan UMS, 88400 Kota Kinabalu, Sabah, Malaysia
*Email address: arismail@ums.edu.my
The quality of a rock mass can be represented by the rock mass classification system. Methods of classifying hard
rock masses based on simple field and drill core observations have been extensively used as an aid for excavation
design of tunnels, mines, slope and foundation (Bieniawski, 1993). RMR (Rock Mass Rating) geomechanics
classification was introduced and developed by Bieniawski (1973, 1984, 1989). In Bieniawski (1976), the ‘rating
adjustment for discontinuity orientation’ for slope are very favourable (0), favourable (-5), fair (-25), unfavourable
(-50) and very unfavourable (-60). No guidelines have been publishing for the definition of each class. Romana
(1985, 1993) proposed a new definition for the RMR concept, especially suited to slopes and called it Slope Mass
Rating (SMR) system, which has been endorsed by Bieniawski (1989). Ismail Abd Rahim et al. (2009a) adjusted
the calculation and determination of some parameters in SMR system to produced the Modified Slope Mass Rating
(M-SMR) system for interbedded Crocker Formation in Kota Kinabalu, Sabah.
This paper highlights the application of M-SMR system in cut rock slopes (slope B1, B2, B3 and B4) (Figure
1) of the Crocker Formation in CPSB Stone Quarry, Tamparuli (Figure 2) to assess the value of rock mass quality.
The aims are to measure the value of M-SMR, to determine the controlling factor for M-SMR value and nature of
rock slope failure for this rock formation. In the M-SMR system, the rock mass quality is representing by the risk
to slope instability. The M-SMR is obtained from basic Rock Mass Rating (RMR b
) by adding a new adjustment
factor (discontinuity orientation parameter, Ismail Abd Rahim et al., 2011) which is dependant on the relative
orientation of discontinuity and slope (parallelism between discontinuities and slope, discontinuities dip angle in
failure modes, relationship between slope, and discontinuity dip) as well as another adjustment factors depending on
the method of excavation. The RMR b
consists of unconfined compressive strength (UCS), rock quality designation
(RQD), discontinuity spacing, discontinuity condition and water flow, which is determined by lithological unit
thickness (LUT) approach (Ismail Abd Rahim et al., 2009b) and Deere et al. (1967) method, weighted average of
discontinuity set spacing, weighted average of discontinuity condition and normal water flow. Kinematic analysis
(Markland, 1972) has been used in determining the mode of slope failure.
The intact rock strength for rock slope material is classified as very strong, ‘good’ quality of RQD and wide to
very wide discontinuity spacing. The discontinuity condition is smooth surface, separation between the wall is less
than 1 mm and containing soft infilling material (illite and montmorillonite), continuous and moderately weathered.
The water flow condition is dry and the discontinuity orientation is fair to very unfavourable. The RMR b
value is
good for the rock mass in the study area. The result of analysis shows that the rock mass quality or values of M-SMR
are 19.45, 7.20, 42.60 and 21.50 for slope B1, B2, B3 and B4, respectively (Table 1). Slope B1 and B2 are predicted
to have very high risk, slope B4 is high risk and slope B3 is moderate risk rock mass. The rock mass quality or
M-SMR value is control by discontinuity orientation parameters (adjustment factor). The mode of slope failure in
slope B1, B2 and B3 and B4 are classified as wedge and planar failures.
References
Bieniawski, Z. T. 1973. Engineering classification of jointed rock masses. Trans. S. Afr. Inst. Civ. Eng. 15, pp. 355-344.
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interbedded Crocker Formation in Kota Kinabalu, Sabah, Malaysia. Proceeding of the 8 th Seminar on Science and Technology
2009 (S&T2009), 18-19 December 2009, Shangri-La’s Rasa Ria Resort, Pantai Dalit, Tuaran.
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Ismail Abd Rahim, Sanudin Tahir, Baba Musta & Shariff A. K. Omang. 2011. New approach of adjustment factor (NAF) calculation
for Slope Mass Rating (SMR) system. Sains Malaysiana. Universiti Kebangsaan Malaysia, Bangi, Selangor (Accepted).
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