10th Asian Regional Conference of IAEG (2015)

Modification of Slope Mass Rating
for Stable Slope Design
Zufialdi ZAKARIA(1), Dicky MUSLIM(1), Luthfan H. JIHADI(2), Zahra Syahida SABILA(2)(1) Laboratoy of Engineering Geology, Faculty of Geology, Universitas Padjadjaran, Indonesia
Email: zufialdi_z@unpad.ac.id(2) Student at Faculty of Geology, Universitas Padjadjaran, Indonesia
Abstract
Slope Mass Rating (SMR) is a simple method to assess stable slope on cut-slope
design. Application of SMR is used to provide safe slope on open-pit mine planning, roadplanning, or highway planning. SMR value presupposes Rock Mass Rating (RMR)
according to geomechanics method from Bieniawski. Result of SMR gives different values
based on some researchers (i.e. Laubscher, Hall, and Orr). In order to get the optimum value,
SMR's modification of stable slope is required. SMR modification involved somesedimentary rocks of Halang Formation, tuff of the Young Volcanic Product, andesitic
igneous rock, and limestone of Rajamandala Formation. Result of the SMR modification
yielded an equation as follows: SMR = 8.2348 RMR0.4932 with correlation coefficient R=
0.99. Safe slope determination in stable-slope design can be specified as: (1) Very Poor
Quality Rock: Stable slope is designed only with slope < 36o; (2) Poor Quality Rock: Stableslope is designed with slope 37o – 51o ; (3) Fair Quality Rock: Stable slope is designed withslope 51o – 62o; (4) Good Quality Rock: Stable slope is designed with slope 63o – 71o; (5)Very Good Quality Rock: Stable slope is designed with slope 72o – 80o.

Keywords: SMR modification, RMR, stable-slope

1.

Introduction
As one of studies in slope stability, Slope Mass
Rating (SMR) is a method that can provide quick
suggestion for determining stable slope angle in bothmining engineering (open-pit mining) and civilengineering (planning). Some researchers proposed
different formulas of SMR, therefore to get optimum
value of SMR, an approach was carried out throughmodification. Research about SMR had been
conducted in Majalengka, West Java (Fig. 1), at
Halang Formation and Young Volcanic Product. In
the region of Majalengka, development is still
growing. Local Government will build KertajatiInternational Airport. Due to the construction of this
airport, it is required offices, public facilities, parks,
restaurants, hospitals, and others.
Other research was conducted on limestone hill ofRajamandala Formation in Pasir Pabeasan, Citatah,(Fig. 1), Padalarang, West Java (Zakaria, 2013). In
the Pasir Pabeasan, Citatah, limestone is mined by themining company. A part of the territory will beplanned for an alternative road.

Fig. 1. Location of research
2 Methods
2.1. Rock Mass Rating
Rock Mass Rating (RMR) is an assessment of1

10th Asian Regional Conference of IAEG (2015)

Table 1.

Rock Mass Rating System (Modified After Bieniawski,1989)

1A. CLASSIFICATION PARAMETERS AND THEIR RATING

1B. ROCK MASS CLASSES DETERMINED FROM TOTAL RATINGS

rock mass. Assessment of rating system can be seenin Table of Geomechanics Classification (Table 1A
and 1B). Result of the assessment is sum of allparameters rating in Table A. The parameters are: 1)
Strength of intact rock material, 2) RQD (RockQuality Designation), 3) Discontinuity spacing, 4)
Discontinuity condition, 5) Groundwater condition.
Table 1B shows the total amount put into groups
according to their rating, in order to get class number
and description of each RMR value. The purposes ofGeomechanics classification are to be acommunication tool within engineering problems bygeomechanics experts, to be a tool to estimate theproperties of rock mass, and also to assess thestability of tunnel, foundation, and slope.
Bieniawski's Geomechanics Classification Systemcreates classification of rock quality based on Rock
Mass Rating (RMR) to test quality with 0-100 scale(Table 1B). RQD (Rock Quality Designation) can be
determined by using scan-line measurement(Harisson & Hudson, 2000) and can be calculated

from outcrop in the field by equation: RQD = 100(0.1  + 1) e- 0.1 , where = scan-line (joint/meter).
2.2 Slope Mass Rating
Slope Mass Rating (SMR) is an application of
RMR to estimate angle of slope safety on cut-slope.
In mining, this method is often encountered indesigning open pit slope. In civil engineering, thismethod can be used to design stable slope for roaddesign, especially at hilly terrain. Some researchers
proposed SMR values based on Rock Mass Rating.
Laubscher (1975, in Djakamihardja & Soebowo,1996) discussed the relationship of RMR and SMR asin Table 2; Hall (1985), gave SMR value asfollows:
SMR = 0.65 RMR+25(1)

and Orr (1992) discussed the relationship as follows:
SMR = 35 ln RMR – 712(2)

10th Asian Regional Conference of IAEG (2015)

Table 2. Laubscher’s SMR methods

Value of RMR
81
61
41
21
0

Description RMR value forthe quality of rock

Recommended slope angle

Very good rock
Good Rock
Fairly rock
Poorly rock
Very poorly rock

75o
65 o
55 o
45 o
35 o

- 100
- 80
- 60
- 40
- 20

Table 3. Results of the calculation of the SMR, Majalengka

Material and location

RMR

Class

Tuff rock. Location at Babakan Jawa

50

Sandstone. Location at Majalengka

Slope Mass Rating ( o )Laubcher

Hall

Orr

III

55

58

66

53

III

55

59

68

Polymictic breccia. Location at Majalengka

64

II

65

67

75

Andesitic igneous rock. Intrusion of igneous rock. Location:
Cibodas-1,

65

II

65

67

75

Sedimentary rock. Sandstone, intercalated sandstone & clay.
Location: Cibodas-2,

60

III

65

64

73

Source: BPREC-FTG (2009), Zakaria & Muslim (2014)
Note:
Based on SMR, the value of slope angle suggested is the smallest slope angle on each methods

3 Result and Discussion
3.1 Halang Formation, Lava, and Andesite
RMR in Majalengka observations (Table 3) wereobtained from several locations as follows: Location at Babakan Jawa. Including the resultsof the Young Volcanic Product. Tuff rock in theform of a yellowish brown, very fine grain size.
Rock strength UCS = 1.33 MPa (rating = 0);
scan-line,  = 3.5, the value of RQD = 95.13(rating = 20), spacing of discontuinity is <60 mm(rating = 5), the condition of the fielddiscontinuity has a very rough surface, weathered,
there is a gouge <5 mm, strain gouge constantly-5 mm (rating = 10). Dry soil water conditions(rating = 15). RMR = 50.
 Location in Majalengka, around the base of thebridge. Sedimentary rock in the form of sandstone,
medium hardness, easily destroyed if hit byhammer, the estimated strength of the rocks(based on Deere, 1969, and Party, 1975, in Hunt,
2007) around 9.81 MPa (rating = 1); scan-line, = 7, the value of RQD = 84.42 (rating = 17),
spacing of discontuinity is 20-60 cM (rating = 10),rough surface, the majority a little weathered,
there is a gouge <1mm (rating = 10). Rock Mass
Rating = 53.

3

10th Asian Regional Conference of IAEG (2015)

 Location in Majalengka, Polymictic breccia formof weathered rock breccia with chunks ofandesitic. The strength of rocks (based on Deere,
1969, and Party, 1975, in Hunt, 2007) is 25 MPa(rating = 4). Scan-line,  = 3.44, the value of
RQD = 96.31 (rating = 20), spacing of
discontuinity is between 40 to 70 cM (rating = 15),
a rough surface on muscular surfaces, weathering
being, there is a gouge on average 3 mm (rating =10). Dry soil conditions (rating = 15). RMR = 64.
 Location Cibodas-1. Intrusion of Igneous Rock.
Andesitic, in the form of light gray, porphyritic,
containing minerals pyroxene and feldspar. Rockstrength UCS = 1.76 MPa (rating = 0), thescan-line,  = 1.3, the value of RQD = 95.13(rating = 99.23), spacing of discontuinity is <6mm, discontinuity field conditions showed a very
rough surface , slightly weathered, stretch <5 mm,
no gouge. (rating = 25), groundwater conditions
no flow (rating = 150). RMR = 65.
 Location Cibodas-2, Lower member Halang
Formations. Intercalated sandstone and claystone.
Sedimentary rock. Rock strength = 1.26 MPa(rating = 0), the scan-line, = 3.95, RQD = 93.89(rating = 20), spacing of discontuinity is <60 mm(rating = 5), very rough surface discontinuities
field , slightly weathered, strain <1 mm, no gouge,
Soft-wall (rating 20), groundwater conditions
there is no flow of water / dry (rating = 15). RMR= 60.

3.2 Rajamandala Formation at Padalarang
Calculations had been made for the value of RMR(Zakaria et al., 2012) with some additional field data.
There are 3 groups of limestone with different wallconditions.
 Eastern Wall: Limestone, hard to very hard,need a lot of hammer blows to take sample.
Estimated value according to rock strength 196.13
MPa, scan-line = 4 joint/M, RQD = 93.84 %(based on Harisson & Hudson, 2000). Spacingof discontinuity is < 60 mM. Condition of
discontinuities: rough fracture surface, slickenside
wall, gouge 1-5 mm thick. Groundwater conditionis dry.
 Middle Wall: Limestone, medium hardness, easy
broken. Estimated value according to rockstrength. Estimated value according to rockstrength 9.81 MPa, scan-line = 23 to 24 joint/M,
RQD = 33.09 to 30.84 % (based on Harisson &Hudson, 2000), Spacing of discontinuities 60-200
cM. Condition of discontinuities:
Slightlyrough fracture surface, slightly weathered, gouge> 5 mm thick. Groundwater condition is moist.
 Western Wall: Limestone, hard to very hard, needa lot of hammer blows to take sample. Estimatedvalue according to rock strength 217.75 MPa to >250 MPa, scan-line = 1.125 to 1. 4 joint/M, RQD= 99.11 – 99.41 % (based on Harisson & Hudson,
2000). Spacing of discontinuities, 60-200 cM.
Condition of discontinuities: Very rough fracturesurface, slightly weathered, no gouge, hard walls.
Groundwater condition is dry

Based on Geomechanics Classification System(Bieniawski, 1989), the results are divided into twoclasses as follows:
1) Tuff rock, at Babakan Jawa, RMR = 50, RMR =class III. Fair quality rock2) Sandstone, at Majalengka, RMR = 53, RMR =class III. Fair quality rock.
3) Polymictic breccia, at Majalengka, RMR = 64,
RMR = class II. Good quality rock.
4) Andesitic igneous rock, at Cibodas-1, RMR = 65,
RMR = class II. Good quality rock.
5) Sandstone, at Cibodas-2, RMR = 60, RMR = class
III. Fair quality rock.

Based on Geomechanics Classification System(Bieniawski, 1989), the limestone are divided into
three classes (in Table 4) as follows:
1) Eastern Wall, RMR = 72, class of RMR = II, fairrock2) Middle Wall, RMR = 24, class of RMR = IV,poor rock3) Western Wall, RMR = 82 to 85, clas of RMR = I,very good rock

Table 4. SMR Calculation results of limestone Rajamandala Formation

Location

RMR

Class

Eastern Wall
Middle Wall
Middle Wall
Western Wall
Western Wall

72
24
24
82
85

II
IV
IV
I
I

Slope Mass Rating ( o )(Laubscher)(Hall)

(Orr)

65
45
45

72
41
41
78
80

79

75
75

4

40
40
83
84

10th Asian Regional Conference of IAEG (2015)

To obtain the optimum slope, modification of
SMR was made involving RMR. For the modification,
this paper involves Rajamandala Formation at Citatah.
Rock formation studied in Rajamandala Formation is
limestone. In Majalengka, the rock formation is
Halang Formation, Old Volcanic Deposit, and Young
Volcanic Deposit. SMR method does not determine
type of rock; it only assesses the RMR value.
In another method by Romana et al. (2003), SMR
is calculated by considering the type of excavation,
whether with heavy equipment, with blasting, without
blasting, and so on. This method is usually used inopen-pit mining that use dynamite to blow up the rock.
In this study, modification of SMR should involve
RMR value with complete class of RMR (class I to V).
However, RMR class is not always complete;therefore it is combined with rock groups in otherplaces. Then, in each location, the smallest values arecollected to analyze the relationship between RMR
and smallest value of SMR, so we get a new equation
comprising the smallest values. Fig. 2 shows theresults of relationship between RMR and SMR withthe equation written as follows:
SMR = 8.2348 RMR0.4932 (R = 0.99)

Fig. 3. Relationship between RMR with therecommended slope angle on modification SMR

4 Conclusion
This modification of SMR is an approach toprovide optimum slope by considering three methods
from Laubscher, Orr, and Hall. From two research
location, the result of SMR modification is shown by
Equation of Power Regression as SMR = 8.2348
RMR0.4932, with correlation coefficient R = 0.99,
according to the result of all method from researchers
above. Safe slope determination in stable-slope
design can be specified as:(1) Very Poor Quality Rock: Stable slope is designed
only with slope < 36o;
(2) Poor Quality Rock: Stable slope is designed withslope 37o – 51o ;(3) Fair Quality Rock: Stable slope is designed withslope 51o – 62o;(4) Good Quality Rock: Stable slope is designed withslope 63o – 71o;(5) Very Good Quality Rock: Stable slope is designedwith slope 72o – 80o.

(3)

Fig. 2. Relationship of Slope Mass Rating and Rock
Mass RatingWith this equati0n, the nodification of Slope
Mass Raing value can be seen in Fig. 3. Based on Fig.
3, for RMR class and the description of rock quality,
suggestion of the safe slope is:Class IClass IIClass IIIClass IVClass VAcknowledgements
The authors would like to show gratitude to the
Rector of Universitas Padjadjaran (Unpad) and theDean of Faculty of Geology, Universitas Padjadjaran(Unpad), who giving the opportunity to present thispaper in 10th Asian Regional Conference of IAEG.
The authors are grateful to the Chairman of theInstitute for Research and Community Service,
Universitas Padjadjaran (Unpad) for the opportunity
given to implement this research.

= very good 81-100, SMR is 72o to 80 o
= good 61-80 64.1, SMR is 63o to 71o= moderate 41-60, SMR is 51o to 62o= poor 21-40, SMR is 37o to 51o= very poor < 20, SMR is < 36 o510th Asian Regional Conference of IAEG (2015)

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