27 
© Adama Science & Technology University                                                                   https://ejssd.astu.edu.et 

Ethiopian Journal of Science and Sustainable Development (EJSSD) 

p-ISSN 1998-0531                                                                                                  Volume 5 (2), 2018 

Lime stabilization of highly plastic clayey soil for the 

impervious core of embankment dam: The case of Gidabo dam, 

Ethiopia 

Feysel Husein1 and Yadeta C. Chemeda2,* 

1
Dila University, College of Engineering and Technology, Civil Engineering Program  

2
Adama Science and Technology University, School of Applied Natural Science, 

Applied Geology Program, P. O. Box  1888, Adama, Ethiopia. 

* Corresponding author, e-mail: Yadeta.chemdesa@astu.edu.et 

 

Abstract 
The stability of different parts of zoned embankment dam including the core has to be 

guaranteed during design and construction to ensure the overall stability of the 

structure. Selection of appropriate material is a very crucial step. Important material 

properties of the core are low permeability, erosion resistance and cracking resistance. 

Impervious clayey soils are a widely available and used materials for the construction 

of core of zoned embankment dams in Ethiopia. However, such soil is characterized by 

high compressibility, poor shear strength when compacted and saturated, difficult in 

moisture control during construction (poor workability) and requires slow rate of 

construction to allow dissipation of excess pore water pressure. Despite their 

undesirable characteristics, the use of locally found material is becoming more 

necessary for sustainability reasons. The present study has been, thus, conducted with 

intention to alter some of the undesirable characteristics of clayey soil using chemical 

additives. Six soil samples from Gidabo dam area were collected and different 

laboratory tests were conducted (i.e. Atterberg limits, permeability, compaction, 1D-

consolidation, and undrained-unconsolidated (UU) triaxial) tests) on raw samples and 

after treatment with different percentage of hydrated lime. Seven days curing time and 

the lime addition ratios of 0 %, 2 %, 4 %, and 6 % by dry weight were considered. After 

lime treatment, the liquid limit, plasticity index and swelling potential decreased. The 

permeability also decreased by more than one order of magnitude from 4.47 * 10
-6

 to 

3.63 * 10
-7

. The stiffness and compressibility of the soil increased and reduced, 

respectively. Lime content of 6% has been found to be the minimum lime percentage 

required to make soils of the study area desirable core fill material.  

Keywords: Lime, stabilization, highly plastic clay, embankment, impervious core  

1. Introduction 

Dam, that is vital for the storage, 

requires a very detailed geotechnical 

investigation to ensure design of stable 

structure and also to select appropriate 

construction material at the vicinity of 

the construction site. There are two major 

types of dam: c o n c r e t e  d a m  a n d  

e mb a n k m e n t , depending on the type of 

mailto:Yadeta.chemdesa@astu.edu.et


Feysel Husse. & Chemeda Y.C.                                                                   EJSSD, V 5 (2), 2018 

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© Adama Science & Technology University                                                                   https://ejssd.astu.edu.et 

material used for construction (Fell et al., 

2005). For small scale irrigation and 

water supply, embankment dam is more 

economical as construction materials are 

to be principally supplied near the dam 

site.  

An embankment dam, which is 

sometimes called earth dam, is 

constructed from earth materials such as 

soil and rock excavated nearby. The 

zoned embankment dam has different 

part: shell, filter and impervious core. 

The materials used for different part of 

the dam vary based on the properties of 

the soil, such as grain size, permeability 

and density (Fell et al., 2005; Alonso & 

Cardoso, 2010). Rock fill materials (any 

type of rock) are commonly used for 

shells and granular materials are used for 

filters. Materials with low permeability, 

erosion resistant and intermediate to high 

plasticity to accommodate deformation 

without risk of cracking are more ideal to 

be used as a core fill (Fell et al., 2005). 

Asphalt, bituminous, concrete and clayey 

soils are among the different materials that 

meet the aforementioned properties to be 

used as impervious core. The major role 

of impervious core is to control seepage 

through the body of dame that can lead to 

failure. 

In most developing countries, clayey 

soils are widely used for core of 

embankment dam because they are very 

economical and can be easily found in 

large part of the earth surface as a 

weathering product of parent rocks. 

Ethiopia is one of the countries with 

extensive coverage of expansive soil as a 

result clayey soil is widely used as a core 

fill material. For instance, Tendaho, 

Kesem, Koga, Ribb, Megech, Maqa dam, 

etc are among the different embankment 

dam in Ethiopia where clayey soil were 

used as a core fill material. Although 

using such soils for core material is more 

economical as compared to asphalt, 

bituminous and concrete, their optimal 

use as a core fill has been limited due to 

their undesirable properties (Yilmaz & 

Erzin, 2004), such as potential for high 

swelling and cracking, poor workability, 

low resistance to deformation, etc. 

According to Yilmaz & Karacan (1996), 

to use for core of an embankment dam, 

the materials preferred to fullfill the 

following properties: Maximum dry 

density (MMD) > 1.6 g/cm3, optimum 

moisture content (OMC) = 15 – 20%, 

specific gravity (Gs) > 2.6, liquid limits 

(LL) = 40 – 50% and plasticity index = 

14 – 20%.                                                        

Due to the aforementioned reasons, 

the clayey soils in natural state are least 

preferred material for core of 

embankment dam (Wanger, 1957) and 

need to be avoided whenever possible. 

However, in some places, finding better 

alternative material may be difficult due 

to different reasons like shortage of 

budget. In addition, for both environmental 

and economic reasons and in a context of 

circular economy, it is necessary to use 

local material for construction works. 

Hence, there is a need to find a remedial 

measure or technique to improve the 

engineering properties of clayey soils, 

particularly highly plastic, to make them 

suitable materials for a core of 

embankment dam.  



Feysel Husse. & Chemeda Y.C.                                                                   EJSSD, V 5 (2), 2018 

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© Adama Science & Technology University                                                                   https://ejssd.astu.edu.et 

The most widely recognized form of 

soil stabilizations, in road construction, is 

lime treatment as it alters undesirable 

characteristics of clay minerals (Diamond 

& Kinter, 1965; Choquette et al., 1987; 

Verhasselt, 1990; He et al., 1995; Bell, 1996; 

Al-Rawas et al., 2005; Al-Mukhtar et al., 

2010; Eisazadeh et al., 2012; Pomakhina et 

al., 2012; Maubec et al., 2017; Guidobaldi et 

al., 2017; Vitale et al., 2017). However, the 

potential effectiveness of this technique 

for the embankment core material need to 

be checked before implementation in 

actual field projects. The minimum 

percentage of lime that need to be added 

to attain the optimum properties and meet 

the limits to be used as a core material is 

among issues that need to be addressed. 

For fulfillment of this goal, it is necessary 

to compare the relative desirability as a 

core material of raw and lime treated 

clayey soil samples under controlled 

condition. The present paper, thus, aimed 

to alter the undesirable characteristics of 

clayey soils using hydrated lime 

(Ca(OH)2) and to determine the optimum 

(minimum) lime percentage. The case of 

Gidabo dam is considered in this study 

and the necessary soil samples (red clay 

soil) have been collected from the dam 

site. 

2. Materials and methods 

2.1. Location of the project area 

The project area is located in the 

Southern Ethiopia, Abaya-Chamo sub-

basin of the Rift Valley about 17 km from 

Dilla town. The dam site is accessible via 

Addis Ababa – Dilla asphalt road, which 

is about 360 km and Dilla-Gidabo dam 

site weather road, which is about 17 km. 

It is geographically located between 

6°20' to 6° 25' N and 38° 05' to 38°10' E 

(Figure 1). 

2.2. Materials 

For Gidabo dam and irrigation 

project, two clay burrow sites (from 

upstream (site 1) and downstream (site 

2)) were selected as potential sources for 

the core material (Figure 1). A total of six 

disturbed soil samples were collected 

from the two clay burrow sites (three 

from each) for the present study. The 

hydrated lime used for the present 

experiment, with purity > 97%, was 

supplied by Derba Cement plc. 

2.3. Experimental approach 

A series of index and engineering 

property tests were carried on disturbed 

and remolded soil at optimum moisture 

content before and after lime treatment. 

For lime treatment, desired amount of 

lime (2%, 4% and 6% by weight of dry 

soil) was mixed with the air dried soil in 

the dry state until an even distribution of 

lime in mixture was obtained. Then, 

mixed by adding water to reach the 

optimum moisture content. Then, the 

mixture is stored in airtight plastic bag at 

room temperature for 7 days before and 

after compaction depending on the type 

of test. The quantity of lime to be added 

is calculated according to the following 

expression:

 



Feysel Husse. & Chemeda Y.C.                                                                   EJSSD, V 5 (2), 2018 

30 
© Adama Science & Technology University                                                                   https://ejssd.astu.edu.et 

A
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Fig. 6.1 Construction material sites (soil & rock) of Gidabo Irrigation project

Q-2

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Swampy are a

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0 1 2

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1200 m

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 m

𝐿𝑖𝑚𝑒 % =
Mass of lime

Mass of lime + Mass of Soil
∗ 100% 

 

 

 

 

 

 

 

 

 

 

 

Figure 1. Map showing the material source sites. Burrow site 1 and 2 are a source for 

clayey core material. 

 

All the tests (i.e. grain size 

distribution, liquid limit, plastic limit, 

compaction, permeability, strength, and 

consolidation) were conducted according 

to ASTM standards. Both liquid limit 

(based on Casagrande method) and 

plastic limit tests have been performed on 

soil fraction passing 0.425 mm sieve, 

after adding a considerable amount of 

water to moist the soil grain and left for 

hours.  

The swelling characteristics of the 

soil is assessed by determining the free 

swelling index. The test is performed by 

slowly pouring 10 cm3 of dry soil which 

has passed the No. 40 (0.425mm) sieve 

in to 100 cm3 graduated cylinder filled 

with distilled water. After 24 hours, final 

volume of the suspension is recorded. 

Hence, free swell index is calculated 

using the following expression:

𝐹𝑟𝑒𝑒 𝑆𝑤𝑒𝑙𝑙 𝐼𝑛𝑑𝑒𝑥 % =
Final volume −  Initial volume

Initial volume
∗ 100% 

The standard proctor compaction tests 

were done on the investigated soil 

according to ASTM D698-98 method A 

to determine optimum moisture content 

at which maximum compacted dry 

density achieved. For the test, soil 

fraction passing the No. 4.75 mm sieve 

was soaked overnight. Then, they were 

compacted in a cylindrical mold of 944 

cm3 volume (10 cm diameter and 12 cm 

height) standard proctor mold by 

repeated blows from the mass of a 



Feysel Husse. & Chemeda Y.C.                                                                   EJSSD, V 5 (2), 2018 

31 
© Adama Science & Technology University                                                                   https://ejssd.astu.edu.et 

hammer 2.5 kg falling freely from a 

height of 30.5 cm. The soils were 

compacted in three layers, each layer 

being subjected to 25 blows. 

Permeability and mechanical tests 

(consolidation and triaxial compression tests) 

were conducted on one selected soil 

sample after compaction at optimum 

moisture content. After compaction, 

specimens were taken out from the molds 

and cured at 20°C for 7 days. 

Permeability of the studied samples were 

determined from the falling head 

permeability tests following ASTM D-

2434 standard. Before the 

commencement of the test, the soil was 

saturated by allowing water to flow 

continuously through it from the 

standpipe. One-dimensional (1-D) 

consolidation tests were performed in 

accordance with ASTM D2435, on 

specimens trimmed from remolded 

samples. The test specimens were loaded 

at twenty-four hour intervals using a 

load-increment ratio of two, and they 

were unloaded at twenty-four hour. The 

triaxial test is the most commonly used 

method for determining the shear 

strength of soils in the laboratory. The 

test was conducted on 38 mm diameter 

cylindrical sample. The test specimen 

were prepared from remolded soil which 

is extruded hydraulically by pushing the 

soil in to 38 mm diameter tubes and 76 

mm in height. 

3. Result and discussion 

3.1. Result 

3.1.1. Initial soil sample characterization 

The basic physical properties of the 

studied soil samples are outlined in Table 

1. All the soil samples under the study are 

fine grained soil with > 80% of the grains 

passed through sieve # 200 and liquid 

limit and plasticity index greater than 

50% and 30%, respectively. According 

to unified soil classification plasticity 

chart, the studied soils lies above A-line 

(Figure 6) which means the soils are 

clayey soil with high plasticity (CH). The 

free swell index ranges from 70% to 

90%, which is a typical characteristics of 

expansive soil. The amount of swelling is 

known to be dependent on the clay 

mineral types. Soil which contain 

sufficient amount of montimorillonite 

tends to swell when they absorb moisture 

and shrink when they lose moisture.  

The maximum dry density (MDD) for 

the soils under the investigation achieved 

at relatively higher moisture content (24 

– 35%), suggesting poor compaction 

characteristic of the soil. The 

permeability coefficients of the tested 

samples ranges from 2.51 * 10-6 to 9.45 * 

10-6. The soils are categorized as low to 

very low permeable soil (Head, 1985). 

The consolidation characteristic of the 

soil was assessed in terms of the 

consolidation index (Cc). The obtained 

value of 0.24 for the tested soil is 

generally a characteristic of medium to 

high compressible clay soils. 

 

 



Feysel Husse. & Chemeda Y.C.                                                                   EJSSD, V 5 (2), 2018 

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© Adama Science & Technology University                                                                   https://ejssd.astu.edu.et 

Table 1: Basic properties of soil samples from the six burrow sites 

 

Property 

Soil samples 

TP-1 TP-2 TP-3 TP-4 TP-5 TP-6 

Specific Gravity 2.7 2.69 2.75 2.65 2.76 2.69 

Liquid limit (%) 62.4 68 71.5 65 56 66 

Plastic limit (%) 28.9 32.4 26.7 24.2 24 19 

Plasticity index (%) 33.5 35.6 44.8 40.8 32 47 

Maximum Dry Density (g/cm3) 1.59 1.55 1.52 1.57 1.37 1.49 

Optimum Moisture Content (%) 27.8 26 26.8 24.5 35 35 

Free swelling index (%) 80 75 90 70 80 70 

Sand (%) 8 5 5 7 9 8 

Silt (%) 32 38 40 36 39 38 

Clay (%) 60 57 55 57 52 54 

3.1.2. Lime treated soil 

a) Effect of lime on soil plasticity 

and swelling 

The effect of lime on the consistency 

limits (i.e. liquid limit, plastic limit and 

plasticity index) of the soil is shown in 

Figure 2. With increasing lime content 

from 0% to 6%, the liquid limit decreased 

markedly compared to plastic limit, 

which shows slight increasing trend. The 

overall effect leads to decrease in 

plasticity index value. Similarly the free 

swelling index decreased after lime 

treatment (Figure 3). The results of both 

tests clearly reveal that lime treatment is 

effective in decreasing water retaining 

capacity of clayey soil. 

 

 

 

 

 

 

 

 

Figure 2. Influence of lime on atterberg limits (the values are an average of the six soil 

samples). LL = liquid limit, PL = plastic limit and PI = plasticity index 



Feysel Husse. & Chemeda Y.C.                                                                   EJSSD, V 5 (2), 2018 

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© Adama Science & Technology University                                                                   https://ejssd.astu.edu.et 

. 

 

 

 

 

 

 

Figure 3. Influence of lime on free swelling index (the values are an average of the six 

soil samples)  

b) Compressibility characteristics 

The comparison of 1-D consolidation 

curves of untreated and lime treated (4 

and 6% dry weight) soils are presented in 

Figure 4.  The initial void ratio of 

untreated soil sample is higher than the 

lime treated soil sample and it decreases 

with increasing the percentage of 

stabilizer. The compression index (i.e. 

the slope of the linear portion of void 

ratio – log stress curve) also decreased 

from 0.24 to 0.175 with increasing lime 

percentage to 6%, implying the 

compressibility property of the soil 

improved after lime treatment.

 

 

 

 

 

  

 

  Figure 4. Influence of lime on the compressibility characteristics of soil (TP-1) 

c) Shear resistance 

The aim of the UU triaxial shear 

resistance measurements is to assess the 

improvement of mechanical stability of 

core material as a result of lime 

treatment. The results obtained after 

treatment with different percentage of 

lime at seven days curing period and 

compacted at OMC are reported on the 

Figure 5. With increasing the lime 



Feysel Husse. & Chemeda Y.C.                                                                   EJSSD, V 5 (2), 2018 

34 
© Adama Science & Technology University                                                                   https://ejssd.astu.edu.et 

percentage, the strain-stress curve shifted 

upward indicating the maximum stress 

that the specimen can sustain improved 

after lime treatment. In addition, the 

treated soil become stiffer or less 

deformed as indicated by increase of the 

slope of pre-peak curve. 

d) Hydraulic conductivity 

The coefficient of permeability, k 

(determined from falling head test) is 

used to study the permeability 

characteristics of treated soil samples. 

The permeability decreased significantly by 

one order of magnitude, from 4.47 * 10-

06 (low permeable) to 3.63 * 10-07 (very 

low permeable), after lime treatment 

(Figure 6). The effect is more 

pronounced at lower percentage of lime 

(2%) and the effect become less with 

increasing lime content.

 

 

 

 

 

 

 

 

Figure 5. Influence of different lime content on the compressive strength of soil (TP-1) 

 

 

 

 

 

 

 

 

 

Figure 6. Influence of lime content on the hydraulic conductivity of soil (TP-1) 



Feysel Husse. & Chemeda Y.C.                                                                   EJSSD, V 5 (2), 2018 

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© Adama Science & Technology University                                                                   https://ejssd.astu.edu.et 

3.2. Discussion 

The studied soils are characterized by 

high plasticity, high compressibility and 

medium to high swelling potential. These 

properties make such kind of clayey soil 

less suitable for construction of road, 

building, dams and other engineering 

structures. However, the low 

permeability and self-sealing stability 

makes it cost effective alternative 

material for engineering barrier and for 

the core of embankment dam. Apart from 

permeability, factors like Maximum dry 

density (MMD), optimum moisture content 

(OMC), specific gravity (Gs), liquid 

limits (LL) and plasticity index (PI) 

governess the suitability of clayey soil 

for embankment core material (Yilmaz & 

Karacan, 1996). Except the specific 

gravity, the other properties of the 

studied soil do not meet the specified 

engineering requirement to be used as 

core fill material. It suggests compaction 

alone is not sufficient in improving the 

property of clayey materials since it does 

not alter the chemistry of clay minerals.  

After lime treatment with different 

lime content, the engineering and index 

properties of the studied soils are 

improved. The classification after 

treatment is summarized in Figure 7. The 

untreated soil and 2% and 4% lime 

treated soils grouped as CH (high 

plasticity inorganic clay), while the soil 

is grouped to CL (Low plastic inorganic 

clay) after 6% lime treatment. The CL soil 

is characterized by medium compressibility, 

has fair shear strength and good workability 

as compared to CH soils. According to 

engineering use chart of Wanger (1957) 

for core of embankment dam, CH soils 

rated 7 (very low level of desirability), 

while CL soil rated 3 (Good level of 

desirability). Blending with granular 

material such as sand is an alternative 

method to improve the property of clayey 

soil. However, it increases the 

permeability of the soil.

 

 

 

  

  

 

 

 

Figure 7. USCS classification of raw soil sample and after treatment with lime 



Feysel Husse. & Chemeda Y.C.                                                                   EJSSD, V 5 (2), 2018 

36 
© Adama Science & Technology University                                                                   https://ejssd.astu.edu.et 

The liquid limit and plasticity index 

are compared with the limit suggested by 

Yilmaz & Karacan (1996) in Table 2. 

Similar to untreated sample, 2% and 4% 

lime treated soils are also failed to satisfy 

the limits as the values of liquid limit and 

plasticity indexes are over the suggested 

limits. In the case of 6% lime treated soil, 

however, the parameters meet the limits. 

Therefore, 6% lime has been found to be 

the minimum lime content required to 

stabilize the soils of the study area for the 

desired purpose. The presence of lime 

nodules in the 7 days cured sample 

reveals the water content near the 

optimum moisture content is not enough 

to dissolve all the lime to keep the pore 

water pH higher enough to initiate 

pozzolanic reaction during the curing 

period.  

Table 2. Comparison of the average index properties value with the limit values for core 

material suggested by Yilmaz & Karacan (1996) 

Test type Limit for core material Lime % 

0% 2% 4% 6% 

Specific gravity ≥ 2.6 2.71 - - - 

MMD (g/cm3) ≥ 1.6 1.52 - - - 

OMC (%) 15 - 20 29 - - - 

LL (%) 40 - 50 65 58 52 44 

PI (%) 14 - 20 39 35 26 18 

 

As the results of this work clearly 

shows, lime treatment is efficient 

technique in altering undesirable 

characteristics of high plastic clay soils. 

The modification of the properties of the 

lime treated soil is due to two-stage 

reaction mechanism initiated by lime 

addition: short-term and long-term 

reactions (Diamond and Kinter, 1965; 

Choquette et al., 1987; Verhasselt, 1990; 

He et al., 1995; Bell, 1996). Immediately 

as the lime mixed with soil and water, 

cation exchange begins to take place 

between the metallic ions associated with 

the surfaces of the clay particles and the 

free calcium ions of the lime, which 

reduces the double layer thickness (film 

of water) around the clay particles. The 

compression of diffused electrical double 

layer in turn leads to the decrease of 

repulsive potential between clay 

particles, thus the particles being 

attracted closer to each other to form 

flocks. The overall effects are 

flocculation and particle aggregation, 

decrease reactivity with water and 

plasticity, improved workability and 

reduced volume change characteristics. 

The long term reaction, unlike to the 

immediate effect, is initiated by alkaline 

environment (pH > 12.4) produced by the 

addition of lime. The high pH facilitates 

dissolution of clay particles that releases 

Si and Al, which together with Ca 



Feysel Husse. & Chemeda Y.C.                                                                   EJSSD, V 5 (2), 2018 

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© Adama Science & Technology University                                                                   https://ejssd.astu.edu.et 

precipitated as hydrated cementious 

phases (like calcium silicate hydrates (C-

S-H) and calcium silicate aluminate 

hydrate (C-S-A-H). The cementation 

process bounds individual grains 

together and significantly increases the 

mechanical strength (increase in stiffness 

and decrease in compressibility 

characteristics) of the lime treated soil. 

The decrease in hydraulic conductivity 

(k) is also a result of change in the soil 

texture or decrease of pore size due to 

cementious gel that formed by 

pozzolanic reaction. The decrease in 

permeability has advantage in reducing 

the risk of internal erosion and ensuring 

dam stability. 

4. Conclusion 

This paper presents the effect of lime 

treatment on the engineering properties 

of clayey soils that are selected to be used 

for the construction of core of Gidabo 

embankment dam. All the soil samples 

taken from the six identified burrow sites 

are classified as fine grained high plastic 

soil (CH) according to USCS 

classification system. CH soils are 

characterized by high swelling-shrinkage 

potential, high compressibility, poor 

workability and low shear strength when 

compacted and saturated with water. 

These properties make CH soil 

undesirable for construction of core of 

embankment dam. After lime treatment, 

however, the engineering properties of 

the soil improved (i.e. water holding 

capacity and plasticity reduced, the 

compressibility reduced, the strength, 

stiffness and compaction characteristics 

improved). The minimum lime content 

required to make the soil of the study area 

desirable core fill material has found to 

be 6%. Generally, the relative 

desirability of the soil for the impervious 

core of embankment dam is improved to 

rank 3 (Good level of desirability) after 

6% lime treatment from rank 7 (very low 

level of desirability). This improvement 

in engineering properties is due to 

alteration of the surface chemistry of the 

clay particles in short-term and 

cementation of soil particles by calcium 

silicate and aluminate hydrates in the 

long-term.  

The main conclusion of this work is, 

although the red clayey soil found nearby 

Gidabo dam site and other similar soil 

types (CH) have some undesirable 

characteristics, it can be used for the core 

fill material after mixing with lime (≥ 

6%) and compaction at controlled water 

content (i.e. near to optimum moisture 

content). In terms of water content, it is 

recommended to treat the soil at water 

content higher than optimum moisture 

content to dissolve the lime nodules. 

Acknowledgment  

The authors wish to thank Adama 

Science and Technology University, 

postgraduate program for providing 

financial support (Mr. Fayisal) and 

laboratory services. The authors also 

would like to thank Gidabo dam project 

and Ethiopian Water Works Enterprise 

for providing the necessary information 

about the dam project, laboratory 

facilities and transportation.



Feysel Husse. & Chemeda Y.C.                                                                   EJSSD, V 5 (2), 2018 

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© Adama Science & Technology University                                                                   https://ejssd.astu.edu.et 

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Feysel Husse. & Chemeda Y.C.                                                                   EJSSD, V 5 (2), 2018 

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