CHARACTERISTICS OF PEAT SOIL IN HOUSING AREA, TANJUNG API API, BANYUASIN, INDONESIA[1]

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CHARACTERISTICS OF PEAT SOIL IN HOUSING AREA, TANJUNG APIAPI, BANYUASIN – INDONESIA
Andriani1*, Eddy Ibrahim1, Dinar Da Putranto1, Azhar Choliq1
1

Department of Environmental Sciences, Sriwijaya University, Palembang, Indonesia

ABSTRACT
Peat soil is an accumulation of plant remnants with the condition of high natural
moisture content, so peat has marginal characteristics and strongly influenced by the
moisture content, the level of decomposition and organic matter content. Determination
of Tanjung Api-Api as a special economic area will trigger the growth of housing and
infrastructure in these locations. The development of infrastructure to support the
special economic zones in the area of Tanjung Api-Api is constrained by soil type in the
region. This study aimed to determine of the characteristics peat soil in Tanjung ApiApi area. Tests performed at the laboratory include physical and mechanical
characteristics of peat soil with condition disturbed and undisturbed. The results showed
that the development of infrastructure in the peat soil caused environmental problems,
particularly environmental degradation in the region. The low bearing capacity of peat
caused damage to several roads and housing floor of citizens. To overcome these
problems needs to be the choice of type material embankment and foundation

construction by the characteristics of peat soil.
Keywords: Bearing capacity; Characteristic of peat; Environmental degradation;
Housing area.
1. INTRODUCTION
High population growth resulting in limited availability of land that can be used as a
residential area. Limitations of land to agricultural, plantations, housing and industrial
may cause reclamation on wetlands. Development of the wetlands began in 1980
through the transmigration program outside Java, the island of Sumatra and Kalimantan.
Most areas in Sumatra and Kalimantan are consist of wetlands highly influenced by the
tidal conditions and mostly of soil types consist of peat. Based on research by using a
combination of analysis Landsat TM data and soil survey conducted by Wahyunto et al.
(2011), peatland area in Indonesia is about 14.9 million ha, scattered in Sumatra,
Kalimantan and Papua. Reclamation of wetlands conducted to obtain new land used as
housing areas, agriculture, plantation and industry. The Construction over peat soil will
cause various problems because the peat has a low shear strength, high deformation and
coefficient of consolidation (cv) is low (Munro, 2005; Haan & Kurse, 2006; Kazemian
et al., 2011; Al-Ani et al., 2013a). The high of organic content and moisture content
causes great compression index (cc) on peat soil (Huat, 2006; Kazemian et al., 2011;
Kalantari, 2013; Al -Ani, et al., 2013b).
The low of bearing capacity of peat could be seen from the characteristics of small bulk

density and capability of high water absorbed (Wahyunto et al., 2010). The important
*Corresponding author’s email: andriani.stmt@gmail.com

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factor to determination of peat mechanical characteristics is level of peat decomposition
and initial void ratio (eo) (Badv & Sayadian, 2011). The physical characteristics of peat
would affect mechanical characteristics of peat (Aminur et al., 2011). The high of
organic content caused by increasing the moisture content, porosity, compressibility and
cohesion conversely the density would be lower (Nie, 2012; Warburton, 2015; Kononen
et al., 2015). The decomposition level would determine the characteristics of peat soil.
According to Rahman and Ming (2015), there were three ways to be done to determine
the characteristics of peat namely: (1) classify of peat soil based weathering, (2)
determine of moisture content and particle size distribution and (3) determine of pH,
specific gravity and Loss on Ignition (LOI), while the testing of Atterberg's Limits is not
too important to do. The level of peat decomposition and moisture content will affect
the compression index (Huat, 2006; Duraisamy et al., 2007a; Kolay et al., 2012;
Kalantari, 2013). The shear strength of peat was different compared to the mineral soil,

because there are the fiber and organic content in the peat soil so it difficult to determine
the shear strength of peat. The shear strength of peat is low greatly could be landslides
(Long, 2005). Huat et al. (2014), shear strength of fibrous peat greater than amorphous
peat soil.
The rapid housing construction in the wetlands causes environmental degradation, for
the decreased bearing capacity of the environment due to rapid development.
Determination of Tanjung Api-Api as industrial zones and international port (special
economic zones) will cause to the development of housing in the wetland areas.
Geographically, the area of Tanjung Api-Api is in the wetlands. The soil type in the area
of Tanjung Api-Api mainly consists of peat and clay. Characteristics of the soil
significantly affect the bearing capacity and environmental capacity, investigation of the
properties of soil needs to be done to determine the suitability of land to avoid
environmental degradation. Environmental problems often occurs in peaty areas such as
forest fires, peat subsidence and rising carbon emissions as a result of the development
of wetlands (Soewandita 2008; Wahyunto et al, 2010; Suryadiputra, 2012; Khusyairi,
2014). Reclamation of wetlands as housing areas may cause a reduction in water
catchment areas, so that when the tidal of rapid rise and inundation the citizen housing
(Dahliani, 2012; Rijal & Aldy, 2012). Reclamation of peat land would cause changes in
the physical characteristics of peat. To achieve sustainability in peat lands required
different methods of land management in accordance with the characteristics of peat

(Kononen et al., 2015). Housing construction at peat lands should pay attention to
characteristics of peat so that it could be determined sustainability of method
construction to scheme housing, some of the methods that can be used in housing areas
of peat include: displacement and replacement, preloading and vertical drain,
lightweight foundation system, etc. (Duraisamy et al ., 2007b).
2. METHOD OF EXPERIMENT
Peat soils used in this study is derived from Tanjung Api-Api area, Banyuasin-South
Sumatera. The sampling of Peat soils conducted at 5 points. Tests carried out on
samples of peat soil disturbed and undisturbed using the ASTM standard. Figure 1
shows of peat soil on location at Tanjung Api-Api area. The physical properties test
performed on peat with disturbed conditions include the natural moisture content test,
organic matter content, ash content, the initial void ratio, dry volume weight, the limits
of Atterberg. From these data were then performed peat soil classification according to
ASTM Standard, Von Post and Mac Farlene. Furthermore, the relationship between the

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natural moisture content with the properties of peat founded, so could be revealed the

effect of the level of decomposition and the physical properties of peat.

(a)
(b)
Figure 1 Peat Soil at Tanjung Api-Api Area
(a) Condition of peat soil before sampling
(b) Condition of peat soil after sampling (disturbed condition)
Test of consolidation one dimension was performed by using Odometer on undisturbed
peat samples. All tests performed in accordance with ASTM D2435 standard. The
purpose of tests was to determine the time of consolidation (Tv) and settlement value
(Sc) on peat soil. Water content is maintained by use of plastic. Initial loading was
given on samples for 24 hours and record of changes in the deformation that occurs
after the initial loading after 24 hours then performed additional burden gradually with
load increment ratio (LIR) was 2 times, start of 25, 50, 100, 200, 400 kPa every
interval 24 hours . The sample was drained from top and bottom. From consolidation
tests will be obtained curve the relationship between the compression (%) and time
(minutes). From the curve can then is calculated coefficient of consolidation (cv) using
the formula below:
cv 

Tv H 2 dr
t

(1)

Besides the compression - time curve also obtained curve the relationship between the
void ratio (eo) and effective pressure (logarithmic scale). From this curve will be
obtained values of coefficient compression (cc) by using the slope of the straight section
of the curve of e versus log p'. Formula (2) below is used to find the value of
compression index (cc).
e1  e2

p '
(2)
log  2 ' 
p
1 

California Bearing Ratio (CBR) and Direct Shear test were performed to determine the
mechanical properties of peat so that it can be seen the relationship between the physical

cc 

e

 log p ,

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and mechanical properties of peat. Characteristics of peat gave influence toward
environment degradation on peat lands especially on housing area.
3. RESULTS AND DISCUSSION
The results of physical and mechanical properties of peat are shown in Table 1.
Table 1 the Result of Physical and Mechanical Properties of Peat
Tanjung Api-Api
Characteristics
Range Value
Natural moisture content
119 – 278

Specific gravity
1.54 – 1.67
Plasticity Index (%)
Non plastic
Organic content (%)
64.8 – 76. 5
Natural unit weigth (kN/m3)
3.82 – 7. 11
Fiber content (%)
6.78 – 19. 17
Ash Content (%)
23.5 – 35. 2
Initial void ratio (eo)
3.4 – 8. 5
pH
4.7 – 5. 6
Coefficient Compression (cc )
1.18 – 3.17
Coefficient
of

Consolidation,
cv
3,623 – 5,147
(m2/year)
8. 7 – 13.5
Cohesion (c)
8-22
o
Friction angle(θ )
0.56 – 1.30
Depth of Peat (m)
1.81 – 2.47
CBR undisturbed (%)
2.35- 4.68
CBR remoulded (%)
3.1. Peat classification
Peat soil in Tanjung Api-Api area has a thickness of between 80 cm up to 130 cm so
that it can be classified as peat with shallow depth and partly of peat as medium depth.
Meanwhile, according to Macfarlene and Radforth (1965), peat soil at Tanjung Api-Api
is amorphous peat (because the fiber content of less than 20%). According to Von Post

scale (1926), including the H8 - H10 and according ASTM D - 4427, peat soil in
Tanjung Api-Api area classified as organic soil because average of organic content < 75
%, the decomposition level is sapric because fiber content of 6.78% - 19.17%; the ash
content is high (> 15%); formed of ferns and ability of absorb water is small.
3.2. The physical and mechanical properties of peat soil
Figure 2 shows physical characteristic of peat soil. From figure 2 we can see that there
are relationship between natural moisture content with specific gravity, organic content,
fiber content and initial void ratio (eo).

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Specific

Organic content (%)

gravity

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Gs = 1.633864-0.00051*Wn

R2 = 0.961827

OC = 57.94532+0.061717 *Wn
R2 = 0.917991

Natural moisture content, Wn (%)

Natural moisture content, Wn (%)

(a) Relationship between Wn and Specific Gravity

(b) Relationship between Wn and Organic Content

Fiber content (%)

20
15
10

FC = -1.69457 +0.075402*Wn

5

R2 =0.979565

0
0

100

200

Initial void ratio (eo)

25

Eo = 0.410621+0.030438*Wn
R2 =0.955445

300

Natural moisture content, Wn (%)
Natural moisture content, Wn (%)

(c) Relationship between Wn and Fiber Content

(d) Relationship between Wn and Initial Void Ratio

Figure 2 The Physical Properties of Peat Soils.
The moisture content would affect to physical properties of peat soils. Organic matter
content, fiber content and initial void ratio (eo) increase with increasing moisture
content but the specific gravity decreasing with increasing moisture content of peat
soils. The fiber content in peat soils save more water in macrospores or microspores,
the higher of fiber content in the peat soil so cause natural moisture content increased.
The high of moisture content and fiber content affect to initial void ratio (eo). Initial
void ratio of peat is increasing along with the increasing of natural moisture content and
fiber content, because of the large void that is formed in a layer of peat. Meanwhile, due
to high natural moisture content caused specific gravity decrease because of the unit
weight solid (γs) is smaller with increasing water content in the peat, since most of the
volume of the void is filled with water and air.

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CBR undistrubed = 2.646445-0.0031*Wn
R2= 0.744781
CBRremoulded =5.981169-0.013*Wn
R2= 0.96712

Result of consolidation test

CBR (%)

6

cv

5

cc
4

3
2

Cc= -0.04705+0.011999*wn
R2= 0.901864
Cv= 6.05984-0.00906*wn
R2= 0.935394

1
0

0

100
200
300
Natural moisture content, Wn (%)

Natural moisture content, Wn (%)

(b) Relationship between natural moisture content
with cc and cv value

(a) Relationship between natural moisture
content with CBR value

Friction angle, θo

Cohesion, c (kPa)

25

Cohesion = 15.04298-0.3358*FC
R2 = 0.827352

20
15
10

Θ = 5.404605 + 0.958975 * FC
R2 = 0.780929

5
0
0

5

10

15

20

25

Fiber content, FC (%)
Fiber content, FC (%)

(c) Relationship between fiber content with
cohesion

(d) Relation between fiber content with friction
angle

Figure 3 The Mechanical Properties of Peat Soil.
CBR value of peat soil at Tanjung Api-Api ranged from 1.81 % to 4.68 %, the low of
CBR value cause a reduction in the ability to bear loads of traffic so roads suffered
damage, crack and settlement the road (figure 4). CBR value decreases with increasing
natural moisture content, it was due to the reduced density of the soil. The value of CBR
undisturbed was smaller than value of CBR remolded because CBR Remolded have
compacted. Compression index (cc) of peat soil is an essential factor to determine value
of settlement on peat soil. Figure 3 (b) indicates that the value of compression index (cc)
increased but the value of coefficients consolidation (cv) decreased, increasing of
moisture content on peat caused the water was difficult to out of the pores of the peat so
it takes a long time to complete the consolidation settlement the value of compression
index (cc), coefficients of consolidation (cv) was down. The big value of compression
index (cc) caused a big settlement on construction (Figure 4), but coefficients of
consolidation (cv) decreased so time of settlement will be long term. Fiber content affect
the value of cohesion and friction angle, cohesion value decreased with increasing fiber
content but the value of friction angle increases. The value of cohesion and friction
angle affected the bearing capacity of peat soils.

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Peat soil has the ability to absorbed high of water, drainage of excess on peat soil as a
result of settlements can lead to degradation of the environment by reducing the ability
of peat to store water so the peat will dry quickly, to reduced water in the peat land, can
trigger a peat fire and increasing emissions of greenhouse gases that resulting from the
release of methane. The natural moisture content and fiber content of peat would
determine the physical and mechanical properties of peat. The higher of natural
moisture content and fiber content because physical and mechanical properties of peat is
less favorable to building infrastructure and housing. The low of bearing capacity on
peat causes the reduction to carrying the large loads. The building of housing and
infrastructure on peat is potential to cause damage on the floor of the house, road
damage and settlement of foundation (figure 4).
Peat soil characteristics are greatly influences the type of environmental degradation.
The natural moisture content and fiber content would determine the physical and
mechanical properties of peat soils. The high of natural moisture content cause the rate
of degradation is also high, the low level of peat decomposition will be make of the
physical and mechanical characteristics of peat soil is less favorable for the
development of housing and infrastructure that will require improvement and specific of
construction on peat soil, so cause the high cost of building settlements and
infrastructure.

(b)
(a)
Figure 4 Damage to the floor of the house (a) and the road (b).
4. CONCLUSION
Peat soil at Tanjung Api -Api was classified as amorphous pein soil with a level of
sapric decomposition. The natural moisture content and fiber content of peat soil affect
the physical and mechanical properties of peat soils. The high of natural moisture
content affect density value, the initial void ratio (eo), the value of CBR, cohesion and
friction angle, compression index (cc) and coefficient of consolidation (cv). The high of
compression index (cc) on peat cause a large settlement so that it would cause damage to
residential buildings and infrastructure. The low of CBR value and shear strength of
peat soil cause damage to the road construction and settlement on construction. To
overcome these problems was done by improving the bearing capacity and accelerate
time factor consolidation in peat soil. Selection of the type of embankment material is
essential to avoid damage, as well as the selection of construction type and soil
improvement methods used in order to prevent damage to construction on peat land.
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