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The effect of compactive energy level on some soil properties
ELSEVIER
Applied Clay Science 12 (1997) 61-72
The effect of compactive energy level on some soil properties Mousa F. Attom
*
Civil Engineering Department, Jordan Uniuersir?, of Science and Technology, Zrbid 22110, Jordan
Received 22 February 1996; accepted 17 October 1996
Abstract This paper presents the effect of the applied compactive energy on the shear strength, permeability and swelling pressure of compacted cohesive soil at constant water content. Unconfined compression tests, permeability tests, and swelling pressure tests are performed on a selected soil to achieve the results of this study. The tests were conducted on the soil at optimum water content and at both the dry and the wet side of the optimum water content. It was found for a given water content on the dry side of the optimum water content the shear strength increases with increasing the compactive energy, increasing the compactive energy has a small or no effect on the unconfined compressive strength when the water content of the soil is above the optimum. Additionally, increasing the compactive energy at the dry side of the optimum will decrease the permeability and increase the swelling pressure of the compacted soil. Keywords: compaction;
compactive
effort; soil strength;
swelling
1. Introduction Compaction
is an engineering
technique
to densify
the soil by packing
the particles
closer together with the reduction in the volume of air, the soil fabric with increasing water content and compaction effort becomes more oriented or dispersed (see Fig. 1). This technique will result in increasing the shear strength of the soil and lower its compressibility (Craig, 1987). The compaction may also increase the bearing capacity of the soil, increase the factor of safety against possible failure and reduce the shrinking and swelling characteristics of the soils (Das, 1990). The properties of the compacted
* Tel.: + 962-2-295 111;fax: + 962-2-295 123. 0169-1317/97/$17.00
Copyright 0 1997 Elsevier Science B.V. All rights reserved.
PIZ SOl69-1317(96)00037-3
62
M.F. Attom/Applied
Clay Science 12 ~1997161-72
~
Low conlpactlve effort
A-.
--
Water content Fig.
I. Effect of compaction on soil structure (Lambe, 1958).
soil depend on the placement procedure. Loose placement does not give a satisfactory performance and the soil will be highly compressible. Because of this, engineers compact the soils to improve its engineering properties. The degree and mechanism of compaction, control the level of satisfaction of the reworked soil. Also, the degree of compaction depends on the purpose for which the soil is used. Airfield construction required 100% relative compaction based on standard AASHTO maximum dry unit weight, while the degree of compaction in pavement construction varies from 90% to 95% (Basma, 1993). This paper aims to study the effect of increasing the compactive energy of cohesive soil on unconfined compressive strength, permeability and swelling pressure of the soil at constant water content. For this reason, a soil is selected from a site in Irbid city in northern Jordan. Ten different compactive energy levels where applied on the selected soil at constant water content at the optimum and at both the dry and the wet side of the optimum (see Fig. 2). Then, the unconfined compression test, falling head test and zero swell test were conducted on the remolded samples at different energy levels to investigate the effect of increasing the compactive energy on the undrained unconfined compressive strength, permeability and the swelling pressure of the soil respectively.
2. Laboratory
testing program
To accomplish the objectives of this research, a natural disturbed clayey soil was used in this study. The soil is brought from Irbid city in northern Jordan and is known to have expansive properties in nature as indicated by earlier researchers (Salem and Kathuda, 1982; Tuncer et al., 1990). The soil was obtained from one meter below the ground surface. Then the soil was air dried and both the grain size distribution test and the Atterberg’s limits test were conducted in accordance with the American society for
M.F. Attom /Applied
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Clay Science 12 (1997) 61-72
63
\
El
1
ZAV
E3 E4 E5
O\O
.
E9 El0
12.5 12.0 J
10.0
20.0
Water Content Fig. 2. Water content-dry
30.0
40.0
(%)
density relationships
for the tested soil.
testing and materials (Head, 1992) standard procedure at the Jordan University of Science and Technology laboratory. The physical properties of the tested soil are shown in Table 1.
Table 1 The physical
properties
of the tested soil
Consistency limits Liquid limit Plastic limit Plastic index Activity
81.8% 36.4% 45.4% 1.07%
Compaction Maximum dry unit weight (kN/m3) Optimum water content, wept (%) Specific gravity of solid, G,
13.78 28.2 2.7
Grain size Sand (2 mm-75 wrn) (%) Silt (75 pm-2 pm) (%o) Clay ( < 2 ym)
8 18 74
Mineralogy Percentage of total clay minerals Kaolinite Illite Montmorillonite Chlorite Vermiculite
56.32 14.63 8.3 1 20.74 -
M.F. Attom/Applied
64
Clay Science I2 (19971 61-72
2.1. Sample preparation Soil specimens were prepared in the standard compaction mold at ten different compactive levels. Table 2 shows the different compactive energies applied to the different samples. The compaction was conducted by using normal Standard Proctor and the AASHTO hammer. The unconfined compression test, permeability test and swelling test are then performed on samples extruded from the compaction mold by inserting an appropriate mold into the compacted soil to determine their shear strength, permeability and swelling pressure. Each test has a new sample with different compactive energy, and for each compactive energy effort three levels of water content are used (i.e., below the optimum, at the optimum, and above the optimum water content). 2.2. Test scheme To achieve the experimental program, enough numbers of samples were prepared for each test. The following describes the tests conducted in this research. 2.2.1. Unconfined compression tests Specimens were prepared at ten compactive energy at different water content for the unconfined compression test and subjected to a strain rate of 1.5 mm/min. The deformations due to the applied load were recorded at each level of loading. The peak stress in the stress strain relation is defined as undrained unconfined compressive strength of the soil. 2.2.2. Falling The falling performed on water content immersing the
Table 2 The compactive
head test head test is used to samples prepared below and equal samples inside the
measure the permeability of fine grain soil. This test is at four different compactive energies with different the optimum. The samples are then saturated by mold in the water for two weeks to obtain the required
energy applied on the tested sample
Sample No.
Hammer mass (kg)
Height of drop (cm)
No. of blows
No. of layers
Volume of mold (cm’)
Energy applied ’ (kJ/m3)
El E2 E3 E4 E5 E6 E7 E8 E9 El0
2.4947 2.4941 2.4947 2.4947 2.4947 2.4947 2.4941 4.5359 4.5359 4.5359
30.48 30.48 30.48 30.48 30.48 30.48 30.48 45.72 45.72 45.72
15 20 25 30 20 25 30 15 20 25
3 3 3 3 5 5 5 5 5 5
934.45 934.4s 934.45 934.4s 934.45 934.4s 934.45 934.45 934.45 934.45
355.6 474.2 592.7 711.3 790.3 987.8 I 185.4 1637.8 2155.1 2693.8
‘1 J=l
N.m
M.F. Attom/Applied
Clay Science 12 (1997) 61-72
65
saturation to conduct the test. The standard falling head test is repeated on each sample five times at different time intervals to ensure the accuracy of the test. 2.2.3. Zero swell test In this test the swelling pressure is defined as the pressure that prevents the soil sample from expansion. For this purpose samples were prepared at five compactive energy levels in the compacted mold at different water content (below the optimum, at the optimum and above the optimum) and placed in the standard consolidation cell after being extruded from the compaction mold. With initial seating load of 6.9 kPa, water is added to the cell. The expansion due to the addition of water will be ceased by applying small increments throughout the swelling process until no further swelling. The total load increments that ceased the expansion divided by the area of the sample is the swelling pressure of the soil.
3. Discussion of the experimental
result
As was mentioned earlier the different tests were conducted to investigate the effect of compactive energy on the undrained unconfined compressive strength, the permeability and the swelling pressure of the soil. The following subsections will present the experimental program results. 3.1. The effect of the cornpactive dry density of the soil
energy on the optimum
water content and maximum
The effect of compactive energy on the optimum water content and the maximum dry density are shown in Figs. 3 and 4, respectively. These two figures indicate that the
35
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E .E
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500
1000
Energy
1500
Effort
2000
2500
(kJ/rn3)
Fig. 3. The effect of energy effort on the optimum water content.
3000
M.F. Attom/Applied
66
1.500
1000
500
0
Clay Science 12 (1997161-72
Energy
Effort
2000
3000
2500
(kJ/rn3)
Fig. 4. The relation between the energy effort and the maximum dry unit weight.
increase in compactive energy will decrease the optimum water content and increase the maximum dry density of the soil. This can be explained as when the water content is added to the soil, the soil particles will be lubricated and due compaction it will slide to a denser state and thus, more compactive energy will need lower water content to reach the maximum dry density. 3.2. The effect of water content on unconfined
shear strength
qf the soil
The effect of the water content on the unconfined undrained shear strength of the compacted soil at different energy effort is shown in Fig. 5. For the same energy effort it
340
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320
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8Om 60
0
5
15
20
Water
25
Content
30
(%)
Fig. 5. The relation between the water content and the unconfined
compressive
strength
M.F. Attom/Applied
Clay Science 12 (1997) 61-72
67
was noticed from the curve that the unconfined shear strength increases with increasing the water content up to the optimum. Once the water content exceeds the optimum the unconfined shear strength decreases.
3.3. The effect of compactiue the optimum
energy on the unconfined
shear strength at the dry side of
Fig. 6 depicts the relation between the different levels of the compactive energy and the unconfined undrained shear strength of the remolded samples at constant water contents at the dry side of the optimum. This figure indicates that there is a significant increase in the unconfined shear strength with the increase in the compactive effort. This behavior can be explained by Lambe’s edge-to-face theory. When the water content at the dry side of the optimum increases, the higher compactive energy causes the flocculated particles to come closer to each other in a denser position resulting in increasing the shear strength.
3.4. The effect of the compactiue water content
energy on the unconfined
shear strength at optimum
Fig. 7 shows the effect of the compactive energy on the unconfined compression strength at the optimum water content. It is obvious from the curve that increasing the compactive energy at the optimum water content will substantially increase the unconfined shear strength.
-
A-A e-0 A-A
25% 22%
)I-*
15%
*
18%
J
50
0
500
1000
Energy Fig. 6. The effect of energy effort on the unconfined optimum.
1500
Effort
2000
2500
3000
(kJ/rn3)
compressive
strength
of the soil at the dry side of the
M.F. Attom/Applied
68
1000
Energy Fig. 7. The effect of compactive water content.
The effect of the optimum
3.5.
Clay Science 12 (1997) 61-72
1500
Effort
energy on the unconfined
2000
(kJ/rn3) compressive
strength of the soil at the optimum
of the compactive energy on the unconfined shear strength at the wet side
As shown in Fig. 8, increasing the compactive energy in the wet side of the optimum, results in a slight increase or decrease in the unconfined compression strength of the soil. This can be explained, when the compactive energy increases this will cause the
I
A-A e-0 A-A .-A
35% 31% 28% 25%
=---==a=--===+ A 1000
Energy Fig. 8. The effect optimum.
of compactive
energy
1500
Effort
on the unconfined
2000
2500
.xJOO
(kJ/m3) compressive
strength
at the wet side of the
M.F. Attom/Applied lE-6
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-
zi
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-
lE-9
-
.T n
z
Clay Science 12 (1997) 61-72
69
. lE-10
.
\
a lE-11
-
.
/
lE-12 5
10
25
20
15
Water
Content
Fig. 9. The effect of water content on permeability
35
30
40
(%)
at different compactive
energies.
clay particles which are in dispersive condition to slide over each other causing, in general, reduction of the shear strength. This result indicates that increasing the compactive energy for any water content higher than the optimum (on the wet side of the optimum) does not influence the unconfined compressive strength very much. 3.6. The effect of compactiue
energy on the permeability
of the soil
Figs. 9-l 1 show the effect of the compaction level on the permeability of the soil. The tested samples were remolded at the dry side and at the optimum at four different
lE-6 A-A lE-7
-
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E 2.2 x .e
lE-8
-
lE-9
-
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W=15%
0-e
W=18%
A-A
W=22%
A---A
W=25%
.z D al
E b a
lE-12
\
0
1000
Compactive Fig. 10. The effect of compactive
1500
Energy
energy on the permeability
2000
(kJ/m3) of the soil at the dry of the optimum.
70
M.F. Attom/Applied
Clay Science 12 (1997) 61-72
1E-6 r---lE-7 ‘;; 2 \
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s Z-, .e .Z cl ::
^_l^
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lE-12
L 0
500
1000
Compactive Fig.
1500
Energy
2000
2500
3000
(kJ/m3)
Il. The effect of compactive energy on the permeability at the optimum water content.
energy levels (El, E6, ES, ElO). It is clear from Fig. 9 that the increase in the water content for all compaction levels will decrease the permeability of the soil if the water content of the soil is below the optimum water content where it reaches its lowest value, then the permeability starts increasing once the water content exceeds the optimum. Figs. 10 and 11 show the effect of the compactive level on the permeability of the soil at the optimum water content and at the dry side of the optimum, respectively. It is obvious from the two curves that increasing the compactive level at any water content below the optimum will significantly decrease the permeability of the soil. This can be explained
4.5
N^ 5 .g.
4.0
3.5
A-A
W=15%
O-0
W=18%
A-A
W=22%
.-.
W=25%
.
A
5 p
3.0
2 8
2.5
a’ F .= g (fJ
2.0
.
1.5
I A
1.0 0
500
1000
Compactive Fig. 12. The effect of compactive
1500
Energy
2000
2500
3000
(kJ/m3)
energy on the swelling pressure of the soil at the dry side of the optimum.
M. F. Attom /Applied
Clay Science 12 (I 997) 61- 72
71
J 0
500
1000
Compactive Fig. 13. The effect of compactive
1500
Energy
The effect of compactive
2500
3000
(kJ/m3)
energy on the swelling pressure at the optimum water content.
by the fact that the dry density of the soil increases and this will decrease the volume of voids available reducing the permeability. 3.7.
2000
by increasing the compaction effort, for the flow of the water resulting in
energy on the swelling pressure
of the soil
Figs. 12-14 depict the effect of compactive energy level on the swelling pressure of the soil. From these figures and at five different compactive energies (El, E3, E6, E8,
3.0
c;
2.5
-
< Y
m
2.0
-
1.5
^
1.0
-
0.5
-
A-A
W=35%
a-0
W=31%
A-A
W=ZB%
A-A
W=25%
L?! ii I a” m .g :
A
0
500
1000
Compactive Fig. 14. The effect of compactive
1500
Energy
2000
2500
3000
(kJ/m3)
energy on the swelling pressure of the soil at the wet side of the optimum.
12
M.F. Attom/Applied
Clay Science 12 (1997) 61-72
ElO), it can be stated that the increase in the compactive energy at any water content at the dry side of the optimum will increase the swelling pressure of the soil. This is because the increase in the compactive energy in the dry side of the optimum will increase the dry density of the soil as mentioned earlier in Section 3.1. The increase in the dry density of the soil will result in increasing the swelling pressure of the soil, where it reaches its maximum value at the optimum water content. At the same time increasing the compactive energy of the soil above the optimum water content has a slight or no effect on the swelling pressure. This can be explained by the fact that the increase in the water content above the optimum will decrease the dry density and the soil will have a high water content in which the soil does not show a high swelling pressure due to a high initial water content.
4. Conclusions Based on the test data the following conclusion may be drawn: (1) The unconfined shear strength of the clay is significantly increased by increasing the compactive energy effort when the water content of the soil is below the optimum water content. Increasing the compactive effort has a small or no effect on the unconfined shear strength of the soil when the water content of the soil is above the optimum. (2) At any compaction level, the permeability decreases by increasing the water content at the dry side of the optimum and then increases at the wet side of the optimum and reaches its lowest value at the optimum water content. The increase in the compactive energy at any water content below or equal to the optimum will result in tremendous decrease in the permeability of the soil. (3) The swelling pressure of the soil is increased by increasing the compactive energy when the water content of the soil is below or equal the optimum. The swelling pressure will not be affected by the increase in the compactive energy when the water content is above the optimum.
References Basma, A.A.,
1993. Prediction of expansion degree for natural compacted clays. Geotechn. Test. .I., 16(4): 542-549. Craig, R.F., 1987. Soil Mechanics. Van Nostrand Reinhold, 4th ed., 410 pp. Das, B.M., 1990. Principles of Foundation Engineering. PWS-KENT, 2nd ed., 731 pp. Head, K.H., 1992. Manual of Soil Laboratory Testing, 1. ASTM D-698, D-1557, D2166, London. Lambe, J.W., 1958. The structure of compacted clay. J. Soil Mech. Found. Div. ASCE, 84(5M2): 1654-l1654-34. Salem, A. and Kathuda, I.D., 1982. Laboratory investigation of geotechnical properties of clays. location No. 2, Smeissani. R. Sci. Sot., Amman, 47 pp. Tuncer, E.R., Basma, A.A. and Taqieddin, S., 1990. Geotechnical properties of some selected Irbid lays. Report 14/87, JUST, It-bid, 91 pp.
Applied Clay Science 12 (1997) 61-72
The effect of compactive energy level on some soil properties Mousa F. Attom
*
Civil Engineering Department, Jordan Uniuersir?, of Science and Technology, Zrbid 22110, Jordan
Received 22 February 1996; accepted 17 October 1996
Abstract This paper presents the effect of the applied compactive energy on the shear strength, permeability and swelling pressure of compacted cohesive soil at constant water content. Unconfined compression tests, permeability tests, and swelling pressure tests are performed on a selected soil to achieve the results of this study. The tests were conducted on the soil at optimum water content and at both the dry and the wet side of the optimum water content. It was found for a given water content on the dry side of the optimum water content the shear strength increases with increasing the compactive energy, increasing the compactive energy has a small or no effect on the unconfined compressive strength when the water content of the soil is above the optimum. Additionally, increasing the compactive energy at the dry side of the optimum will decrease the permeability and increase the swelling pressure of the compacted soil. Keywords: compaction;
compactive
effort; soil strength;
swelling
1. Introduction Compaction
is an engineering
technique
to densify
the soil by packing
the particles
closer together with the reduction in the volume of air, the soil fabric with increasing water content and compaction effort becomes more oriented or dispersed (see Fig. 1). This technique will result in increasing the shear strength of the soil and lower its compressibility (Craig, 1987). The compaction may also increase the bearing capacity of the soil, increase the factor of safety against possible failure and reduce the shrinking and swelling characteristics of the soils (Das, 1990). The properties of the compacted
* Tel.: + 962-2-295 111;fax: + 962-2-295 123. 0169-1317/97/$17.00
Copyright 0 1997 Elsevier Science B.V. All rights reserved.
PIZ SOl69-1317(96)00037-3
62
M.F. Attom/Applied
Clay Science 12 ~1997161-72
~
Low conlpactlve effort
A-.
--
Water content Fig.
I. Effect of compaction on soil structure (Lambe, 1958).
soil depend on the placement procedure. Loose placement does not give a satisfactory performance and the soil will be highly compressible. Because of this, engineers compact the soils to improve its engineering properties. The degree and mechanism of compaction, control the level of satisfaction of the reworked soil. Also, the degree of compaction depends on the purpose for which the soil is used. Airfield construction required 100% relative compaction based on standard AASHTO maximum dry unit weight, while the degree of compaction in pavement construction varies from 90% to 95% (Basma, 1993). This paper aims to study the effect of increasing the compactive energy of cohesive soil on unconfined compressive strength, permeability and swelling pressure of the soil at constant water content. For this reason, a soil is selected from a site in Irbid city in northern Jordan. Ten different compactive energy levels where applied on the selected soil at constant water content at the optimum and at both the dry and the wet side of the optimum (see Fig. 2). Then, the unconfined compression test, falling head test and zero swell test were conducted on the remolded samples at different energy levels to investigate the effect of increasing the compactive energy on the undrained unconfined compressive strength, permeability and the swelling pressure of the soil respectively.
2. Laboratory
testing program
To accomplish the objectives of this research, a natural disturbed clayey soil was used in this study. The soil is brought from Irbid city in northern Jordan and is known to have expansive properties in nature as indicated by earlier researchers (Salem and Kathuda, 1982; Tuncer et al., 1990). The soil was obtained from one meter below the ground surface. Then the soil was air dried and both the grain size distribution test and the Atterberg’s limits test were conducted in accordance with the American society for
M.F. Attom /Applied
o-o ?? --•E2 A-A ~--)l o--o m-=E6 o---vE7 r--rE8 o--o ??-+
16.0 15.5 rn;
15.0
zy
14.5
2
14.0
CT '5 3
13.5
.$
13.0
3
Clay Science 12 (1997) 61-72
63
\
El
1
ZAV
E3 E4 E5
O\O
.
E9 El0
12.5 12.0 J
10.0
20.0
Water Content Fig. 2. Water content-dry
30.0
40.0
(%)
density relationships
for the tested soil.
testing and materials (Head, 1992) standard procedure at the Jordan University of Science and Technology laboratory. The physical properties of the tested soil are shown in Table 1.
Table 1 The physical
properties
of the tested soil
Consistency limits Liquid limit Plastic limit Plastic index Activity
81.8% 36.4% 45.4% 1.07%
Compaction Maximum dry unit weight (kN/m3) Optimum water content, wept (%) Specific gravity of solid, G,
13.78 28.2 2.7
Grain size Sand (2 mm-75 wrn) (%) Silt (75 pm-2 pm) (%o) Clay ( < 2 ym)
8 18 74
Mineralogy Percentage of total clay minerals Kaolinite Illite Montmorillonite Chlorite Vermiculite
56.32 14.63 8.3 1 20.74 -
M.F. Attom/Applied
64
Clay Science I2 (19971 61-72
2.1. Sample preparation Soil specimens were prepared in the standard compaction mold at ten different compactive levels. Table 2 shows the different compactive energies applied to the different samples. The compaction was conducted by using normal Standard Proctor and the AASHTO hammer. The unconfined compression test, permeability test and swelling test are then performed on samples extruded from the compaction mold by inserting an appropriate mold into the compacted soil to determine their shear strength, permeability and swelling pressure. Each test has a new sample with different compactive energy, and for each compactive energy effort three levels of water content are used (i.e., below the optimum, at the optimum, and above the optimum water content). 2.2. Test scheme To achieve the experimental program, enough numbers of samples were prepared for each test. The following describes the tests conducted in this research. 2.2.1. Unconfined compression tests Specimens were prepared at ten compactive energy at different water content for the unconfined compression test and subjected to a strain rate of 1.5 mm/min. The deformations due to the applied load were recorded at each level of loading. The peak stress in the stress strain relation is defined as undrained unconfined compressive strength of the soil. 2.2.2. Falling The falling performed on water content immersing the
Table 2 The compactive
head test head test is used to samples prepared below and equal samples inside the
measure the permeability of fine grain soil. This test is at four different compactive energies with different the optimum. The samples are then saturated by mold in the water for two weeks to obtain the required
energy applied on the tested sample
Sample No.
Hammer mass (kg)
Height of drop (cm)
No. of blows
No. of layers
Volume of mold (cm’)
Energy applied ’ (kJ/m3)
El E2 E3 E4 E5 E6 E7 E8 E9 El0
2.4947 2.4941 2.4947 2.4947 2.4947 2.4947 2.4941 4.5359 4.5359 4.5359
30.48 30.48 30.48 30.48 30.48 30.48 30.48 45.72 45.72 45.72
15 20 25 30 20 25 30 15 20 25
3 3 3 3 5 5 5 5 5 5
934.45 934.4s 934.45 934.4s 934.45 934.4s 934.45 934.45 934.45 934.45
355.6 474.2 592.7 711.3 790.3 987.8 I 185.4 1637.8 2155.1 2693.8
‘1 J=l
N.m
M.F. Attom/Applied
Clay Science 12 (1997) 61-72
65
saturation to conduct the test. The standard falling head test is repeated on each sample five times at different time intervals to ensure the accuracy of the test. 2.2.3. Zero swell test In this test the swelling pressure is defined as the pressure that prevents the soil sample from expansion. For this purpose samples were prepared at five compactive energy levels in the compacted mold at different water content (below the optimum, at the optimum and above the optimum) and placed in the standard consolidation cell after being extruded from the compaction mold. With initial seating load of 6.9 kPa, water is added to the cell. The expansion due to the addition of water will be ceased by applying small increments throughout the swelling process until no further swelling. The total load increments that ceased the expansion divided by the area of the sample is the swelling pressure of the soil.
3. Discussion of the experimental
result
As was mentioned earlier the different tests were conducted to investigate the effect of compactive energy on the undrained unconfined compressive strength, the permeability and the swelling pressure of the soil. The following subsections will present the experimental program results. 3.1. The effect of the cornpactive dry density of the soil
energy on the optimum
water content and maximum
The effect of compactive energy on the optimum water content and the maximum dry density are shown in Figs. 3 and 4, respectively. These two figures indicate that the
35
;
-
30
A
\ “\
-E 5
Ab’A.A \
0 2
25
-
20
-
4
E .E
A
-G_ 0
15 0
500
1000
Energy
1500
Effort
2000
2500
(kJ/rn3)
Fig. 3. The effect of energy effort on the optimum water content.
3000
M.F. Attom/Applied
66
1.500
1000
500
0
Clay Science 12 (1997161-72
Energy
Effort
2000
3000
2500
(kJ/rn3)
Fig. 4. The relation between the energy effort and the maximum dry unit weight.
increase in compactive energy will decrease the optimum water content and increase the maximum dry density of the soil. This can be explained as when the water content is added to the soil, the soil particles will be lubricated and due compaction it will slide to a denser state and thus, more compactive energy will need lower water content to reach the maximum dry density. 3.2. The effect of water content on unconfined
shear strength
qf the soil
The effect of the water content on the unconfined undrained shear strength of the compacted soil at different energy effort is shown in Fig. 5. For the same energy effort it
340
-
320
-
I
o-o
El E2
G 4
300
-
0-e
‘;
260
-
A-A
E3
Fh G 2
260
-
.-.
E4
240
-
In 220 Y ‘Z 200 I b& 180
-
E
160
-
8
140
-
Pc
120
-
‘$
100
-
: 3
-
O--n
E5
w-u
E6
V-V
E7
O-O
ES
??-+
El0
8Om 60
0
5
15
20
Water
25
Content
30
(%)
Fig. 5. The relation between the water content and the unconfined
compressive
strength
M.F. Attom/Applied
Clay Science 12 (1997) 61-72
67
was noticed from the curve that the unconfined shear strength increases with increasing the water content up to the optimum. Once the water content exceeds the optimum the unconfined shear strength decreases.
3.3. The effect of compactiue the optimum
energy on the unconfined
shear strength at the dry side of
Fig. 6 depicts the relation between the different levels of the compactive energy and the unconfined undrained shear strength of the remolded samples at constant water contents at the dry side of the optimum. This figure indicates that there is a significant increase in the unconfined shear strength with the increase in the compactive effort. This behavior can be explained by Lambe’s edge-to-face theory. When the water content at the dry side of the optimum increases, the higher compactive energy causes the flocculated particles to come closer to each other in a denser position resulting in increasing the shear strength.
3.4. The effect of the compactiue water content
energy on the unconfined
shear strength at optimum
Fig. 7 shows the effect of the compactive energy on the unconfined compression strength at the optimum water content. It is obvious from the curve that increasing the compactive energy at the optimum water content will substantially increase the unconfined shear strength.
-
A-A e-0 A-A
25% 22%
)I-*
15%
*
18%
J
50
0
500
1000
Energy Fig. 6. The effect of energy effort on the unconfined optimum.
1500
Effort
2000
2500
3000
(kJ/rn3)
compressive
strength
of the soil at the dry side of the
M.F. Attom/Applied
68
1000
Energy Fig. 7. The effect of compactive water content.
The effect of the optimum
3.5.
Clay Science 12 (1997) 61-72
1500
Effort
energy on the unconfined
2000
(kJ/rn3) compressive
strength of the soil at the optimum
of the compactive energy on the unconfined shear strength at the wet side
As shown in Fig. 8, increasing the compactive energy in the wet side of the optimum, results in a slight increase or decrease in the unconfined compression strength of the soil. This can be explained, when the compactive energy increases this will cause the
I
A-A e-0 A-A .-A
35% 31% 28% 25%
=---==a=--===+ A 1000
Energy Fig. 8. The effect optimum.
of compactive
energy
1500
Effort
on the unconfined
2000
2500
.xJOO
(kJ/m3) compressive
strength
at the wet side of the
M.F. Attom/Applied lE-6
-
lE-7
-
zi
E 23 x .e
El
??---•
E6 E8 El0
A-A A-A
‘;; \
A-A
lE-8
-
lE-9
-
.T n
z
Clay Science 12 (1997) 61-72
69
. lE-10
.
\
a lE-11
-
.
/
lE-12 5
10
25
20
15
Water
Content
Fig. 9. The effect of water content on permeability
35
30
40
(%)
at different compactive
energies.
clay particles which are in dispersive condition to slide over each other causing, in general, reduction of the shear strength. This result indicates that increasing the compactive energy for any water content higher than the optimum (on the wet side of the optimum) does not influence the unconfined compressive strength very much. 3.6. The effect of compactiue
energy on the permeability
of the soil
Figs. 9-l 1 show the effect of the compaction level on the permeability of the soil. The tested samples were remolded at the dry side and at the optimum at four different
lE-6 A-A lE-7
-
‘;‘ : \
E 2.2 x .e
lE-8
-
lE-9
-
lE-10
-
lE-11
-
W=15%
0-e
W=18%
A-A
W=22%
A---A
W=25%
.z D al
E b a
lE-12
\
0
1000
Compactive Fig. 10. The effect of compactive
1500
Energy
energy on the permeability
2000
(kJ/m3) of the soil at the dry of the optimum.
70
M.F. Attom/Applied
Clay Science 12 (1997) 61-72
1E-6 r---lE-7 ‘;; 2 \
lE-8 E
s Z-, .e .Z cl ::
^_l^
lE-9
lE-10
E a lE-11
lE-12
L 0
500
1000
Compactive Fig.
1500
Energy
2000
2500
3000
(kJ/m3)
Il. The effect of compactive energy on the permeability at the optimum water content.
energy levels (El, E6, ES, ElO). It is clear from Fig. 9 that the increase in the water content for all compaction levels will decrease the permeability of the soil if the water content of the soil is below the optimum water content where it reaches its lowest value, then the permeability starts increasing once the water content exceeds the optimum. Figs. 10 and 11 show the effect of the compactive level on the permeability of the soil at the optimum water content and at the dry side of the optimum, respectively. It is obvious from the two curves that increasing the compactive level at any water content below the optimum will significantly decrease the permeability of the soil. This can be explained
4.5
N^ 5 .g.
4.0
3.5
A-A
W=15%
O-0
W=18%
A-A
W=22%
.-.
W=25%
.
A
5 p
3.0
2 8
2.5
a’ F .= g (fJ
2.0
.
1.5
I A
1.0 0
500
1000
Compactive Fig. 12. The effect of compactive
1500
Energy
2000
2500
3000
(kJ/m3)
energy on the swelling pressure of the soil at the dry side of the optimum.
M. F. Attom /Applied
Clay Science 12 (I 997) 61- 72
71
J 0
500
1000
Compactive Fig. 13. The effect of compactive
1500
Energy
The effect of compactive
2500
3000
(kJ/m3)
energy on the swelling pressure at the optimum water content.
by the fact that the dry density of the soil increases and this will decrease the volume of voids available reducing the permeability. 3.7.
2000
by increasing the compaction effort, for the flow of the water resulting in
energy on the swelling pressure
of the soil
Figs. 12-14 depict the effect of compactive energy level on the swelling pressure of the soil. From these figures and at five different compactive energies (El, E3, E6, E8,
3.0
c;
2.5
-
< Y
m
2.0
-
1.5
^
1.0
-
0.5
-
A-A
W=35%
a-0
W=31%
A-A
W=ZB%
A-A
W=25%
L?! ii I a” m .g :
A
0
500
1000
Compactive Fig. 14. The effect of compactive
1500
Energy
2000
2500
3000
(kJ/m3)
energy on the swelling pressure of the soil at the wet side of the optimum.
12
M.F. Attom/Applied
Clay Science 12 (1997) 61-72
ElO), it can be stated that the increase in the compactive energy at any water content at the dry side of the optimum will increase the swelling pressure of the soil. This is because the increase in the compactive energy in the dry side of the optimum will increase the dry density of the soil as mentioned earlier in Section 3.1. The increase in the dry density of the soil will result in increasing the swelling pressure of the soil, where it reaches its maximum value at the optimum water content. At the same time increasing the compactive energy of the soil above the optimum water content has a slight or no effect on the swelling pressure. This can be explained by the fact that the increase in the water content above the optimum will decrease the dry density and the soil will have a high water content in which the soil does not show a high swelling pressure due to a high initial water content.
4. Conclusions Based on the test data the following conclusion may be drawn: (1) The unconfined shear strength of the clay is significantly increased by increasing the compactive energy effort when the water content of the soil is below the optimum water content. Increasing the compactive effort has a small or no effect on the unconfined shear strength of the soil when the water content of the soil is above the optimum. (2) At any compaction level, the permeability decreases by increasing the water content at the dry side of the optimum and then increases at the wet side of the optimum and reaches its lowest value at the optimum water content. The increase in the compactive energy at any water content below or equal to the optimum will result in tremendous decrease in the permeability of the soil. (3) The swelling pressure of the soil is increased by increasing the compactive energy when the water content of the soil is below or equal the optimum. The swelling pressure will not be affected by the increase in the compactive energy when the water content is above the optimum.
References Basma, A.A.,
1993. Prediction of expansion degree for natural compacted clays. Geotechn. Test. .I., 16(4): 542-549. Craig, R.F., 1987. Soil Mechanics. Van Nostrand Reinhold, 4th ed., 410 pp. Das, B.M., 1990. Principles of Foundation Engineering. PWS-KENT, 2nd ed., 731 pp. Head, K.H., 1992. Manual of Soil Laboratory Testing, 1. ASTM D-698, D-1557, D2166, London. Lambe, J.W., 1958. The structure of compacted clay. J. Soil Mech. Found. Div. ASCE, 84(5M2): 1654-l1654-34. Salem, A. and Kathuda, I.D., 1982. Laboratory investigation of geotechnical properties of clays. location No. 2, Smeissani. R. Sci. Sot., Amman, 47 pp. Tuncer, E.R., Basma, A.A. and Taqieddin, S., 1990. Geotechnical properties of some selected Irbid lays. Report 14/87, JUST, It-bid, 91 pp.