Abstract— Slope failures usually occur in Malaysia during the rainy season from the months of October to January annually causing damages to properties and fatalities. The common laboratory tests conducted to determine the soil characteristics include soil classification, moisture content, particle density, field bulk unit weight and Atterberg limit tests. In the case of Atterberg limit tests, only the silt and clay portions of the sandy soils were tested. Disturbed soil samples were collected from 10 slope failures in Baling and also from 19 slope failures in Penang. The slope failures in Penang are within the granitic residual soil while the slope failures in Baling are within the sedimentary residual soil. Field bulk density tests were carried out at all the locations where soil samples were taken. The objective of this research is to compare the characteristics of soils taken from slope failures within the granitic and sedimentary residual soils. The particle density and field bulk unit weight are very consistent at slope failures in both the sedimentary and granitic residual soils. In general, all the soil characteristics and properties found in this study are near or within the range that was found by earlier researchers for Malaysian residual soils.
Index Term— Granitic residual soil, Sedimentary residual soil, Slope failure, Soil characteristics.
I. INTRODUCTION
Slope failure is defined as a movement of a large volume of sediments and rocks down a slope under the influence of gravity as mentioned by [12]. This research is part of the overall study to determine the lower bound values of the
This work was supported by grants from Universiti Teknologi Mara (UiTM), Malaysia. Damanhuri Jamalludin is with Faculty of Civil Engineering, Universiti Teknologi Mara, Penang, Malaysia. Currently he is a postgraduate student at Universiti Sains Malaysia working on slope failures in residual soils. He is the correspondence author. (e-mail: daman466@ppinang.uitm.edu.my). Fauziah Ahmad is with School of Civil Engineering, Engineering Campus, Universiti Sains Malaysia, Malaysia (e-mail: cefahmad@yahoo.com). Roslan Zainal Abidin is with the Infrastructure University Kuala Lumpur (IUKL), Jalan Kajang-Serdang, Kajang, Selangor, Malaysia. Currently he is the Vice President of IUKL (e-mail: roslan@iukl.edu.my).
effective shear strength parameters to be used in design of new cut slopes in Malaysian residual soils. In Malaysia, many slopes designed by very experienced geotechnical design engineers, failed a few months after completion as described by [9]. Reference [2] conducted a study on the stability of the newly constructed road from Gap to Fraser Hill which is passing through a colluvium area. The hilly and winding road is only 9 km. During the rainy season in December 1997, a total of 33 slope failures were reported by [9] and [21]. A total of 50 boreholes were carried out along the new road alignment prior to the slope and road designs as stated by [16]. Although the road was designed by very experienced geotechnical engineers working with very experienced road consultant firm, 33 slopes failed during rainy season. Three major slope failures occurred, making the road impassable to all vehicles. Even though many boreholes and laboratory tests were conducted prior to the slopes and road designs, more than 30 slope failures occurred barely 4 months after its completion. The main reasons of the failures are due to the usage of higher values of shear strength parameters during the design stage as well as the road is passing through a treacherous instable geological setting area as explained by [14].The objective of this research is to compare the characteristics of soil taken from slope failures within the granitic and sedimentary residual soils in Northern Malaysia.
II. LITERATUREREVIEW
A study on the characterístics of soil taken from the hilly areas in Penang Island was conducted by [1]. They concluded that there will be higher risk of stable slope to fail when higher moisture content, higher value of liquid limit, higher % of clay portion and thicker layer of clayey soils existed in the stable soil slope. Reference [25] stressed that the higher the % of sand and silt, the higher is the risk of the stable slope to be eroded. Uncontrolled erosion occurring on a stable slope surface will later cause major slope failure if no immediate action is taken as mentioned by [7]. Reference [11] stated that most tropical residual soils are affected by drying where the index properties may change drastically even by partial drying. Efforts must be taken to ensure that moisture loss from the soil samples is prevented and laboratory tests to be carried out as fast as possible. Collivium deposits as explained by [19] and
Characteristics of Soil Taken from Slope
Failures in Sedimentary and Granitic Residual
Soils
Damanhuri Jamalludin
a*, Fauziah Ahmad
a, Roslan Zainal Abidin
baSchool of Civil Engineering, Engineering Campus, Universiti Sains Malaysia, 14300 Nibong Tebal, Penang,
Malaysia
[2] are transported materials formed from old major slope failure deposits that are now in stable condition covered with thick vegetations. Hence they are not easily detected. The previous major slope failures can occur thousands of years ago and they comprise of loose and weak materials of soil and rock admixtures. As such, colluviums deposits are highly susceptible to failures. Cutting of the presently stable slopes in order to get the road profiles will cause the loose materials to become unstable as the rainwater infiltrates and seeps through the loosely held materials.
III. GEOLOGYANDSOILSSAMPLING
A. Geology
Residual soils (RS) are formed from the decomposition and weathering of parent materials and they remain at their formation place as explained by [17]. The properties of residual soils depend strongly on the decomposition conditions and features of the parent materials. The distribution of tropical residual soils is closely related to the distribution of the various parent rock types in Malaysia. Reference [10] produced a simplified geological map for Peninsular Malaysia as shown in Figure 1 which also shows the distribution of the three major classes of soils widely found in Peninsular Malaysia. As described by [15], the three types of soils commonly found in Peninsular Malaysia are granitic residual soil, sedimentary which includes meta-sedimentary residual soil and coastal or river alluvium soil. As explained by [20], granite rock which is part of igneous rocks is mostly and widely found in Malaysia while sedimentary and meta-sedimentary rocks widely found in Malaysia are sandstone, schist, mudstone and shale. Figure 1 also shows the study areas of slope failures in Northern Malaysia. Figures 2 and 3 show the location of slope failures selected in Baling which is situated within the sedimentary residual soil and in Penang which is located within the granitic residual soil respectively.
B. Soil sampling and field tests
Soil sampling points taken at the slope failures are shown in Figure 4. Slope failure zone includes the failed section, the
un-failed section next to the un-failed one as well as the slope crest and slope toe. Disturbed soil samples were taken at a depth of 100mm below the existing soil surface. They were placed immediately into two layers of plastic bags to prevent moisture loss after retrieving from the ground. Field bulk density tests were carried out at all locations where soil samples were taken.
C. Testing program
Soil characteristics tests such as classification (sieve & hydrometer), moisture content, particle density and Atterberg limittests were conducted based on procedures as stated by
0 30km Graniti c rocks Sedime ntary rocks Alluviu m soils Slope failure location
Gerik
PERAK KEDAH THAILAND
N Granitic rocks
Sedimentary rocks
Alluvium soils
Slope failure
Fig. 2. Slope failures in Baling within the simplified geology map. Baling
Penang Island
0 30 km
0 5km
Teluk Kumbar Gertak
Sanggul
Alluvium soil Teluk Bahang
N
Fig. 3. Slope failures in Penang Island within the simplified geology map.
Slope failure
Granitic rocks Relau
Balik Pulau
A B
B
Disturbed soil sampling points
G
C
F E
A B
Slope failure
Un-failed slope Un-failed
slope
A
A
D
Slope crest
Slope toe
A
Section A - A
Soil sampling at 100mm depth
Un-failed slope Fig. 1. Simplified geology map of study areas (Simplified geology map
of Malaysia after [10]
N 0 50 km THAILAND
Study area
N
Kuala Lumpur Penang
Island
Baling
Fraser Hill
Alluvium soils
Granitic rocks
[8], [3], [24] and [4] as well as [5]. The soil classifications were based on [6].
IV. RESULTS AND DISCUSSION
A. Coefficient of variation (COV)
Reference [18] explained that when comparing the distributions of different means and standard deviations, a useful measurement is the COV. The COV is the ratio of the standard deviation to the mean as in (1).
cov = Standard deviationMean (1)
COV is independent of units used and for this reasons, it is useful when comparing the distribution of variation where the units may be different. References [23] and [18] explained that when the value of COV < 1, the distributions are considered as low-variance with smaller relative variations. This implies that the data are more consistent. Those with value of COV > 1, the distributions are considered as high-variance. The larger the values of COV, the greater are the relative variations.
B. Bulk unit weight (γb)
Figure 5 illustrates the distributions of bulk unit weight at slope failures along sample locations in both the sedimentary and granitic residual soils. There are very slight variations of bulk unit weight at slope failures in the sedimentary and granitic residual soils. Table 1 shows the distribution properties of bulk unit weight at slope failures in the sedimentary and granitic residual soils. The values of COV are very small and less than 1 indicating that the data are very consistent. The mean and the range of bulk unit weight at slope failures are slightly smaller in the sedimentary residual soil than in granitic residual soil as shown in Table 1. The range of bulk unit weight for Malaysian residual soils is between 15.0 – 23.0 kN/m3 based on [22], while [11] explained that that the range of bulk unit weight for Malaysian residual soils is between 13.0 – 20.0 kN/m3. The range of bulk unit weight found in this study is between 12.2 – 20.4 kN/m3. The range of bulk unit weight found in this study is close with the range that was found by [11] and [22].
TABLE 1
DISTRIBUTION PROPERTIES OF FIELD BULK UNIT WEIGHT AT SLOPE FAILURES
Distribution properties Sedimentary RS Granitic RS
No of data 114 136
Min (kN/m3) 12.2 12.2
Max (kN/m3) 19.2 20.4
Mean (kN/m3) 16.5 17.7
Standard deviation 1.2 1.2
COV 0.07 0.07
Range (kN/m3) 12.2-19.2 12.2-20.4
Range from publications 13.0-23.0 kN/m3
C. Moisture content (m)
Figure 6 shows the distributions of natural (Nat m) and submerged (Sub m) moisture contents along sample locations at slope failures in sedimentary and granitic residual soils. Natural moisture contents tests were done on samples taken from the 2 layers of plastic bags before the shear box tests were conducted while submerged moisture content tests were done after the completion of shear box tests were carried out in soaked condition. Both the natural and submerged moisture contents are slightly higher in sedimentary residual soil than in granitic residual soil probably due to the higher clay/silt contents in the sedimentary residual soil than in granitic residual soil which readily absorbed water. As expected from Table 2, the means of the submerged moisture contents are higher than the means of the natural moisture contents. All the values of COV are less than 1 indicating that the data are consistent. Based on [22] the range of natural moisture content for Malaysian residual soils is between 1.0 – 59.0 % while [11] mentioned that the range
0 5 10 15 20 25
0 50 100 150
γb
AT
SL
O
PE
FAI
LUR
ES
(kN/m
3)
SAMPLE LOCATIONS
GRANITIC RS
SEDIMENTARY RS
Fig. 5. Distributions of field bulk unit weight at slope failures in sedimentary and granitic residual soils
0 10 20 30 40 50
0 30 60 90 120 150 180
N
AT
m
(%
)
SAMPLE LOCATION
GRANITIC RS
SEDIMENTARY RS
Fig. 6. Distributions of (a) natural moisture contents (b) submerged moisture contents along sample locations at slope failures in sedimentary
and granitic residual soils
(a)
0 10 20 30 40 50 60
0 30 60 90 120 150 180
SUB
m
(%
)
SAMPLE LOCATIONS
GRANITIC RS
SEDIMENATRY RS
TABLE II
DISTRIBUTION PROPERTIES OF NATURAL (Nat m) AND SUBMERGED MOISTURE CONTENT (Sub m) TESTS AT SLOPE
FAILURES Distribution
property
Sedimentary RS Granitic RS
Nat m Sub m Nat m Sub m
No of data 94 94 105 105
Min (%) 7.2 19.0 1.1 9.2
Max (%) 41.3 55.8 27.1 42.1
Mean (%) 22.3 33.8 13.0 23.8
Standard deviation
7.3 6.5 5.8 5.6
COV 0.3 0.2 0.4 0.2
Range (%) 7.2 – 41.3 19.0 – 55.8 1.1 – 27.1 9.2 – 42.1
Range from publications (%)
1.0-76.0 - 1.0-76.0 -
of natural moisture content for Malaysian residual soils is between 7.0 – 76.0 %. There is no range of submerged moisture contents since they were not commonly done. The range of natural moisture content found in this study is between 1.1 – 41.3% while the submerged moisture content found this study is between 9.2 – 55.8 %. The range of natural moisture content in this study is within the range of natural moisture content found by [22] and [11].
D. Soil classifications
Figure 7 shows the typicalparticle size distribution curves at slope failures in sedimentary and granitic residual soils. Figure 8 shows the distributions of the percentages of gravel, sand, silt and clay along sample locations at slope failures in sedimentary and granitic residual soils. The composition of silt is consistently the highest along the sample locations in sedimentary residual soil as shown in Figure 8 (a). In granitic residual soils, the highest composition varies initially from gravel followed by silt and finally sand along the sample locations as shown in Figure 8(b). In both cases, the clay portion is the smallest throughout the sample locations. The distribution properties of the % of gravel, sand, silt and clay at slope failures are shown in Table 3and 4for the sedimentary and granitic residual soils respectively. The values of COV in both tables are generally less than 1 indicating that the data are consistent except for the variation of the clay portion at slope failures both in sedimentary and granitic residual soils where the values of COV are greater than 1. This is probably due to the values of the means being affected by outlier data. Based on [22] the ranges of percentage of gravel, sand, silt and clay for Malaysian residual soils are between 0.0 – 92.0 %, 0.0 – 94.0 %, 0.0 – 90.0 % and 0.0 – 58.0% respectively while [11] mentioned that the range of percentage of sand, silt and clay for Malaysian residual soils are between 4.0 – 49.0 %, 2.0 – 43.0 % and 5.0 – 67.0 %. The ranges of percentage of gravel, sand, silt and clay found in this study are between 0.1 - 76.9 %, 5.7 – 67.8 %, 15.5 - 90.1 % and 0 - 8.8 % respectively and these ranges are within the ranges found by [22] and [11]. Table 5 shows the types of soils found at the slope failuresin sedimentary and granitic residual soils. The soil types found in this research are mainly silt, sandy silt, gravelly silt, silty sand, very silty sand, and very silty gravel. Table 5 shows the
percentages of soil types found at slope failures both in sedimentary and granitic residual soils. Silt is the most
TABLE III
DISTRIBUTION PROPERTIES OF THE % OF GRAVEL, SAND, SILT AND CLAY AT SLOPE FAILURES IN SEDIMENTARY RS Distribution
property
Sedimentary RS
Gravel Sand Silt Clay
No of data 114 114 114 114
Min (%) 0.3 8.0 24.7 0.0
Max (%) 36.1 53.2 90.1 8.8
Mean (%) 7.4 23.9 68.0 0.7
Standard deviation
6.50 10.97 14.83 1.30
COV 0.88 0.46 0.22 1.89
Range (%) 0.3-36.1 8.0-53.2 24.7-90.1 0.0-8.8 Range from
publications (%)
0.0-92.0 0.0-94.0 0.0-90.0 0.0-67.0
0 20 40 60 80 100
0 30 60 90 120 150
% O F GR AV EL , S AN D , SI LT & C LAY SAMPLE LOCATIONS % GRAVEL % SAND % SILT % CLAY
Fig. 8. Distributions of the % of gravel, sand, silt & clay along sample locations at slope failures in (a) sedimentary residual soil (b) granitic
residual soil (a) 0 20 40 60 80 100
0 30 60 90 120 150
% GR AV EL , S AN D , S IL T & C LAY SAMPLE LOCATIONS % GRAVEL % SAND % SILT % CLAY (b) 0 20 40 60 80 100
0.001 0.01 0.1 1 10 100
%
PAS
SI
N
G
PARTICLE SIZE (mm)
BG1A SILT BG3A SANDY SILT BG4A SILT BG7A SANDY SILT BG10A SANDY SILT
Fig. 7. Typical particle size distribution curves at slope failures in (a) sedimentary residual soil (b) granitic residual soil (a) 0 20 40 60 80 100
0.001 0.01 0.1 1 10 100
%
PAS
SI
N
G
PARTICLE SIZE (mm)
BP3A SANDY SILT
BP4A V SILTY GRAVEL
BP5A V SILTY SAND
BP7A V SILTY GRAVEL
BP10A V SILTY GRAVEL
TABLE IV
DISTRIBUTION PROPERTIES OF THE % OF GRAVEL, SAND, SILT AND CLAY AT SLOPE FAILURES IN GRANITIC RS Distribution
property
Granitic RS
Gravel Sand Silt Clay
No of data 136 136 136 136
Min (%) 0.1 7.5 15.5 0.0
Max (%) 76.9 67.8 81.9 1.8
Mean (%) 20.6 36.7 42.4 0.4
Standard deviation
15.62 15.69 19.33 0.48
COV 0.76 0.43 0.46 1.35
Range (%) 0.1-76.9 5.7-67.8 15.5-81.9 0.0-1.8 Range from
publications (%)
0.0-92.0 0.0-94.0 0.0-90.0 0.0-67.0
common soil type in sedimentary residual soil while coarse-grained soils dominate the granitic residual soil.
E. Atterberg limit tests
Figure 9 shows the distributions of liquid limit (LL) and plastic limit (PL) along sample locations at slope failures in sedimentary and granitic residual soils. Generally, there are slight variations between the distributions for liquid limit at slope failures in both sedimentary and granitic residual soils. However, there are wider variations in the distributions of
TABLE V
PERCENTAGES OF SOIL TYPES AT SLOPE FAILURES
Soil type Sedimentary RS Granitic RS
% %
Silt 64 18
Sandy silt 30 25
Gravelly silt 0 11
Silty sand 1 1
Very silty sand 4 26
Very silty gravel 1 19
Total (%) 100 100
plastic limit along sample locations at slope failures in sedimentary residual soil than in granitic residual soils. Figure 10 refers to the liquid limit versus plastic limit at slope failures
in sedimentary and granitic residual soils. It seems that the results are consistent and all the points are concentrated within a range of liquid limit between 30 – 70 % and range of plastic limit between 15 – 50 % with wider variation of plastic limit occurring in sedimentary residual soil. Tables 6 and 7 refer to the distribution properties at slope failures for the Atterberg limit tests in sedimentary and granitic residual soils respectively. From Tables 6 and 7, the values of COV are generally less than 1 indicating that the data are consistent. It is observed from Tables 6 and 7 that the means of the liquid limit, plastic limit and plasticity index are slightly higher in sedimentary residual soil than in granitic residual soil. This is probably due to sedimentary residual soil consisting mainly of fines particles as compared to granitic residual soil. According to [22], the ranges of liquid limit and plasticity index for Malaysian residual soils are between 20.0 – 95.0 % and 0.0 – 32.0 % respectively while [11] described that the ranges of liquid limit and plasticity index for Malaysian residual soils are between 25.0 – 107.0 % and 15.0 – 59.0 % respectively. The ranges of liquid limit and plasticity index found in this study are between 28.8 – 69.8 % and 0.2 –46.5 % respectively. Both ranges are within the ranges found by [22] and [11].
TABLE VI
DISTRIBUTION PROPERTIES OF ATTERBERG LIMIT TESTS AT SLOPE FAILURES IN SEDIMENTARY RS
Distribution property Sedimentary RS
LL PL PI
No of data 86 86 86
Min (%) 31.6 5.6 0.2
Max (%) 69.8 55.6 46.5
Mean (%) 49.5 31.6 17.9
Standard deviation 7.1 7.6 8.4
COV 0.14 0.24 0.47
Range (%) 31.6-69.8
5.6-55.6
0.2-46.5
Range from publications (%) 20.0-107.0 - 0.0-59.0
. 0 10 20 30 40 50 60
0 20 40 60 80
PL
(%
)
LL (%)
GRANITIC RS
SEDIMENTARY RS
Fig. 10. Liquid limit versus plastic limit at slope failures both in sedimentary and granitic residual soils
0 20 40 60 80
0 30 60 90 120 150 180
LL
(%
)
SAMPLE LOCATIONS
GRANITIC RS
SEDIMENTARY RS
Fig. 9. Distributions of (a) liquid limit (b) plastic limit along sample locations in both sedimentary & granitic residual soils
(a)
0 10 20 30 40 50 60
0 30 60 90 120 150 180
PL
(
%
)
SAMPLE LOCATIONS
GRANITIC RS
SEDIMENTARY RS
TABLE VII
DISTRIBUTION PROPERTIES OF ATTERBERG LIMIT TESTS AT SLOPE FAILURES IN GRANITIC RS
Distribution property Granitic RS
LL PL PI
No of data 128 128 128
Min (%) 28.8 16.4 2.5
Max (%) 65.2 37.6 38.2
Mean (%) 41.5 27.3 14.2
Standard deviation 7.3 4.5 7.0
COV 0.18 0.16 0.49
Range (%) 28.8-65.2 16.4-37.6 2.5-38.2
Range from publications (%)
20.0-107.0 - 0.0-59.0
Particle density (ρS)
Figure 11 shows the results of particle density tests at slope failures along sample locations in sedimentary and granitic residual soils. From Figure 11, the values of particle density are very consistent throughout the sample locations both in sedimentary and granitic residual soils. Table 8 shows the distribution properties of particle density tests at slope failures in the sedimentary and granitic residual soils. Slightly larger range of particle density is observed in sedimentary residual soils as compare to granitic residual soil. However, all the values of COV are less than 1 indicating that the data are consistent. Reference [22] explained that the range of particle density for Malaysian residual soils is between 2.59 – 2.72 Mg/m3 while [11] mentioned that the range of particle density for Malaysian residual soils is between 2.60 – 3.40 Mg/m3. Reference [13] mentioned that particle density found along Malaysian North - South highway is between 0.49 – 2.73 Mg/m3. Therefore the overall range of particle density found by earlier researchers is between 0.49 – 3.40 Mg/m3. The range of particle densityfound in this study is between 2.02 – 2.85 Mg/m3. The range of particle density found in this study is within that was found by earlier researchers.
TABLE VIII
DISTRIBUTION PROPERTIES OF PARTICLE DENSITY (ρS) AT SLOPE FAILURES
Distribution properties Sedimentary RS Granitic RS
No of data 114 136
Min (Mg/m3 ) 2.02 2.21
Max (Mg/m3) 2.85 2.69
Mean (Mg/m3 ) 2.47 2.47
Standard deviation 0.17 0.12
COV 0.07 0.05
Range (Mg/m3 ) 2.02-2.85 2.21-2.69
Range from publications (Mg/m3 ) 0.49-3.40
V. CONCLUSIONS
The particle density and field bulk unit weight are very consistent in both the sedimentary and granitic residual soils. Silt is the most common soil type at slope failures in the sedimentary residual soil while coarse-grained soils dominate in the granitic residual soil. Both the natural and submerged moisture contents are slightly higher in sedimentary residual soil than in granitic residual soil probably due to the higher clay/silt contents in the sedimentary residual soil than in granitic residual soil which readily absorbs water. The means of the liquid limit, plastic limit and plasticity index are slightly higher in sedimentary residual soil than in granitic residual soil. In general, all the soil characteristics and properties found in this study are near or within the range that was found by earlier researchers for Malaysian residual soils.
ACKNOWLEDGMENT
Many thanks are due to Mohd Mustaqim Md Nordin who have assisted the authors to publish this paper.
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(
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![Fig. 1. Simplified geology map of study areas (Simplified geology map of Malaysia after [10]](https://thumb-us.123doks.com/thumbv2/123dok_us/1363038.1645644/2.612.78.269.469.641/fig-simplified-geology-study-areas-simplified-geology-malaysia.webp)
