O A RIGINAL

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Journal of Applied Sciences Research, 9(3): 2378-2385, 2013
ISSN 1819-544X
This is a refereed journal and all articles are professionally screened and reviewed
ORIGINAL ARTICLES
Experimental Study of Bearing Capacity for Egyptian Soils Reinforced by Geotextiles
1
M.H. Elshakankery, 1Alsaid Ahmed Almetwally and 2K.A. Tawfik
1
2
Textile Eng. Dept., National Research Center, Dokki, Cairo, Egypt
Faculty of Engineering, Cairo University, Cairo, Egypt
ABSTRACT
Nonwoven geotextiles have been successfully used for reinforcement of soil to improve bearing capacity.
The purpose of this study was to quantify the benefit of using geotextile materials as reinforcement of different
Egyptian soils. Laboratory California bearing ratio (CBR) tests were performed to investigate the load –
penetration behavior for different three soils types with different weights of geotextiles. Soil samples are tested
for CBR with and without reinforcement .i.e. geotextile materials. The result of these tests shows that hard soil
with high weight of geotextile samples increases the CBR slightly. Furthermore, bearing ratio of reinforced
other soil samples with geotextile increases. The relation between the apparent opening sizes of a geotextiles
and particles size of soil is taken into consideration.
Key words: Nonwoven geotextiles, CBR Tests, Soil, and Reinforced ratio
Introduction
In Egypt, there are many hard solid, changeable sand and poor soils in many areas as a result of which the
subgrades will shrink and swell with variations in water and moisture content in the soil. This shrinking and
swelling movement causes irregular road surface and road deterioration, resulting in a need for premature
rehabilitation of the pavement road. In recent years, there are many available technologies to improve the
mechanical properties and performance of soil by using geotextiles material.
Conventional road structure:
The road is usually built up in several layers, each have some special functions. As shown in fig.1 a typical
road cross-section consists of:
Fig. 1: Road structure
a) A graded and compacted subgrade.
b) Aggregate base course to cover the subgrade.
c) Road base layer to cover the sub-base course layer.
d) Tope wearing surface or surfacing layer.
Over weak subgrades, a sub-base between the aggregate layer and the soil subgrade is commonly found to be
economical.
Corresponding Author: M.H. Elshakankery, Textile Eng. Dept., National Research Center, Dokki, Cairo, Egypt
E-mail: [email protected]
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J. Appl. Sci. Res., 9(3): 2378-2385, 2013
The subgrade strength used in road construction does not stay the same during its life; the change in the
subgrade strength may be due to the following causes:
- Regression of the crushed stone aggregate to the subgrade layer.
- Variation in soil moisture content.
Regression is the main cause of road structure failure; for that to obtain soil stabilization and extended
life of road structure there are three important factors play a role in the design of such a system:
1- Suitability of subgrade soil as identified by its CBR (California Bearing Ratio)
2- Thickness of aggregate layer is determined by the subgrade layer and the type and volume of traffic to
be cared on the road.
3- Type of wearing surface as determined by the type and volume of traffic as well as environment
conditions.
Geotextiles:
The uses of geotextiles in many engineering applications have become more apparent and have proven to be
an effective means of soil improvement. The history of geotextiles is relatively short. The South Carolina (USA)
Highway Department placed a heavy woven cotton fabric in several rural roads in 1926. With data from at least
eight separate field tests, they reported in 1935 that the fabric reduced cracking and failures in the road. Giroud
and Noiray (1981) first introduced an analytical approach to the design of geotextile-reinforced unpaved roads.
The bearing capacity of the soft subgrade is considered to increase from πcu to (π+ 2)cu with the inclusion of a
geotextile; where c is the inexpert shear strength of the soil and u is recommended coefficient for the soilconfining effect with stabilization fabrics. The value of u can adjust slightly (1.95-2.05) for different acceptable
rut depth. Additional improvement due to membrane action is considered to be a function of the geotextile
strength and allowable rut depth. Another technique proposed by Milligan et al. (1984) is based on a small rut
depth concept and does not consider membrane action. Using the Milligan et al. technique, the bearing capacity
of the subgrade is improved and increases from (π/2 + 1) cu to (π/2+ 2) cu by placing a geotextile layer at the
subgrade-granular fill interface. Resl and Werner (1986) carried out the laboratory tests under an axisymmetric
loading condition using nonwoven, needle-punched geotextiles. The results showed that the nonwoven layers
placed between subsoil and subgrade can significantly increase the bearing capacity of soft subgrades. Houlsby
and Jewell (1990) extended the Milligan et al. (1984) technique to circular loadings by increasing the subgrade
bearing capacity from 3.07cu for an unreinforced soil layer to 5.69 cu for a reinforced soil layer. Fannin and
Sigurdsson (1996) carried out a full-scale field trial to study the performance of different geosynthetics in
unpaved road construction over soft ground. Several papers have examined the reinforcement of soil (Bergado
et al., 2001; Raymonda and Ismail, 2003; Park and Tan, 2005; Yetimoglu et al., 2005; Patra et al., 2005; Varuso
et al., 2005); current research work mainly emphasize on the strength, mechanism and bearing capacity at the
reinforced soil (Haeri et al., 2000; Michalowski, 2004; Zhang et al., 2006; Latha and Murthy, 2007; and Senthil
Kumar et al., 2012;). CBR tests are also conducted by introducing geotextiles and geogrid in hard soil (Naeini
and Mirzakhanlari, 2008; Duncan et al., 2008; Naeini and Moayed, 2009; and Dhule et al., 2011). Further, based
on CBR test, the influence of geotextile, geogrid and geonet are investigated in clay with low or medium
compressibility (Love et al, 1987; Srivastava et al., 1995; Giroud et al., part I and Part II, 2004; Naeini and
Moayed, 2009; Nair and Latha, 2010; Moayed and Nazari, 2011; and Nair and Latha 2011) as soft subgrade in
an unpaved road system.
Hence, in this study the effect of non-woven geotextiles placed between two different layers (subsoil &
aggregate) on the CBR strength by the comparison between three types of soil bearing capacity in dry condition,
under axisymmetric loading were investigated.
Experimental Work:
The materials used, experimental set-up, tests conducted and the experimental procedures have been
presented as follows.
Material:
Soil:
Three different Egyptian compressible soil samples obtained are used for the present experimental
investigations. The required properties of them were determined and are presented in Table 1. The particles
Distributions are showed in Figure 2.
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Geotextiles Properties:
Five different needle-punched polyester geotextiles were tested: G1, G2, G3, G4, and G5, respectively.
Table 2 gives the geotextiles physical and mechanical properties. All of the samples from the geotextiles listed
in Table 2 were tested with the length direction (parallel machine direction) and crosswise.
Table 1: Soils Properties
Particulars Soil
Specific Gravity Tons/m3
Maximum Dry Density Tons/m3
Optimum Moisture Content %
Porosity %
Particles D90 mm
Soil Class
CBR ratio % at 0.1
CBR ratio % at 0.2
Table 2: Geotextiles Properties
Physical property
Fiber Dinner
Fiber Length (mm)
Mass per unit area (g/m2)
ASTM D 5261
Thickness (mm)
ASTM D 5199
Wide Width Strength (kN/m)
ASTM D 4595 (200 mm)
Machine direction/ Crosswise
Grab strength (N)
ASTM D 4632
Machine direction/ Crosswise
Elongation at break (%)
ASTM D 4632
Machine direction/ Crosswise
Puncture resistance (N)
ASTM D 4833
Equivalent opening size (μm)
ASTM D 4751
Soil I
1.91
1.42
12.6
47
0.096
Solid or hard
66.71
84.0
Soil II
2.03
1.82
18.3
32.2
0.154
Medium
54.8
54.54
Soil III
2.88
1.74
32.2
38
0.25
Very soft
27.5
25.2
G1
G2
G3
G4
G5
6
128
6
128
9
128
9
128
9
128
250
300
400
500
600
2.12
2.56
3.78
4.22
4.82
10.5/17.3
13.3/20.4
15/24.5
18.8/31.3
20.334.2
508/610
635/756
882/964
996/1330
1236/1840
92/82
85/81
75/62
65/60
62/54
420
688
866
950
1200
125:177
105:125
74:88
74:88
>74
Aggregate:
Aggregate is a broad category of coarse particulate material used in construction, including sand, gravel,
crushed stone, slag and recycled concrete. Aggregates are used as base material under foundations, roads, and
railroads. The grain size distribution of the aggregate shown in Figure 2 indicated that it was somewhat finer
than the allowable gradation specifications, the aggregate used in the CBR test is classified as well graded
gravel.
Fig. 2: Particle size distribution of the aggregate and deferent soils
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Cbr Test Procedure:
The California bearing ratio (CBR) is a penetration test for mechanical strength evaluation of road
subgrades and base courses with standard circular piston at the rate of 1.25 mm/min. The CBR test is made
according to ASTM Standards D1883-07 (for laboratory-prepared samples). Samples for the CBR were
compacted according to ASTM Standards D 698 (Methods B and D). The samples were placed in three layers at
the standard mould. First layer was a soil which compacted for 5 inches height by 56 a rammer dropped blows
from 12 inches. Second layer was a geotextile sample which was placed between first layer and aggregate final
layer which was compacted for 2 inches as shown in figure 3.
Fig. 3: Schematic arrangement of the Soil-Aggregate in the CBR mould with geotextiles
Results And Discussion
Different soils with different geotextile weight materials are tested and results are obtained. The results
obtained by taking the average of three trails for each penetration levels are plotted as stress with geotextiles
weight. The variation of penetration stress curves for different soil samples and aggregate without geotextiles
material are shown in figure 4. The variation of penetration stress curves for different soil samples and
aggregate with geotextiles material are shown in figures 5, 6 and 7.
Soil I
Soil II
Soil III
Penetration stress psi
1400
1200
1000
800
600
400
200
0
0
0.025 0.05 0.075
0.1
0.125 0.15 0.175
0.2
0.3
Penetration depth In
Fig. 4: Penetration stress of different soil samples-Aggregate without geotextiles material
Soil I:
0.4
0.5
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J. Appl. Sci. Res., 9(3): 2378-2385, 2013
Fig. 5: Penetration stress of soil I -Aggregate with different geotextiles weight
Table 4: Multiple regression analysis of soil I for penetration stress
R= .74039580 R²= .5481859 Adjusted R²= .53116798
F(2,57)=81.234 p<.00000 Std. Error of estimate: 5.11
St. Err.
Soil I
BETA
of BETA
Intercept
Penetration depth
0.85976
0.06750
Geotextile weight
0.03306
0.07563
B
287.290
2838.620
0.12545
St. Err.
of B
116.739
222.866
0.25616
t(57)
2.461
12.737
0.48973
p-level
0.01691
0.00000
0.62620
Fig. 6: Deformation and cause penetration failure in the geotextiles 250 g/m2 through CBR testing
From the penetration stress curve of figure 5 and table 4, geotextiles weight in final strand has a p-level of
0.6262 which is not statistically significant effective in penetration stress. This is due to the fact that soil I is very
hard and the light weight of geotextiles (250 and 300 g/m2) are deformed and cause penetration failure in the
material through CBR testing as shown in figure 6. Furthermore, increasing geotextile weight (at high weight
levels of 500 and 600 g/m2) has slightly increasing on penetration stress but these have not significant effective. In
this case, the geotextiles material is used as a separation between sub-soil and aggregate but the soil particles and
geotextiles equivalent opening size is taken into consideration. Soil particles must be bigger than geotextiles
material opening size.
Soil II:
Table 5 shows the regression analysis for penetration stress. It is clear from table 4 that the multiple
correlation factors are about 0.862 at a high significant level which is a good correlation.
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J. Appl. Sci. Res., 9(3): 2378-2385, 2013
Fig. 7: Penetration stress of soil II -Aggregate with different geotextiles weight
Table 5: Multiple regression analysis of soil II for penetration stress
R= .86234543 R²= .74363959 Adjusted R²= .73489242
F(2,57)=59.531 p<.00000 Std. Error of estimate: 4.36
St. Err.
Soil II
BETA
of BETA
Intercept
Penetration depth
0.78987
0.07536
Geotextile weight
0.22882
0.05344
B
100.741
1850.919
0.61631
St. Err.
of B
92.506
176.603
0.20299
t(57)
1.089
10.481
3.036
p-level
0.28073
0.00000
0.00361
From the penetration stress curve of figure 7 and table 5, geotextiles weight in final strand has a p-level of
0.00361 which is statistically significant effective in penetration resistance. It is clear that increasing geotextiles
weight leads to increase penetration resistance. Maximum penetration stress is obtained at higher geotextiles
weight.
3. 3. Soil III:
Table 6 shows the regression analysis for penetration stress. It is clear from table 6 that the multiple
correlation factors are about 0.884 at a high significant level which is a good correlation. It is clearly observed
that there is a significance effect for geotextiles weight in resistance of penetration stress at different levels of
penetration depth as shown in figure 8. Geotextiles weight in final strand has a p-level of 0.00008 which is
statistically significant effective in penetration resistance.
Fig. 8: Penetration stress of soil III -Aggregate with different geotextiles weight
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Table 6: Multiple regression analysis of soil III for penetration stress
R= .88466840 R²= .782638177 Adjusted R²= .77222045
F(2,57)=45.662 p<.00000 Std. Error of estimate: 4.68
St. Err.
Soil III
BETA
of BETA
Intercept
Penetration depth
0.70255
0.09843
Geotextile weight
0.34947
0.08211
St. Err.
of B
49.158
93.848
0.10787
B
39.824
802.983
0.45910
t(57)
0.81011
8.556
4.256
p-level
0.42124
0.00000
0.00008
Further, in order to quantify the amount of increase in the penetration resistance, the reinforcement ratio is
taken into consideration. The reinforcement ratio at a particular penetration is:
Reinforcem ent ratio  (1 - (
reinforcem ent withou t geotextile s
)) x100
reinforcem ent with geotextile s
Table 7: Reinforcement ratio for different Geotextiles weight and soil samples
Geotextiles weight g/m2
Soil I
250
0.43
300
0.51
400
1.01
500
1.35
600
2.87
Soil II
2.55
4.92
9.61
15.99
26.92
Soil III
1.07
8.55
14.80
25.61
33.38
Table 7 shows the reinforcement ratio for different geotextiles material weight and soil samples at the high
levels of penetration depth. It is clear that increasing geotextiles weight leads to an increase of reinforcement
ratio for all soil samples expect soil I (hard soil). It is clear for soft soil III sample; there is a more effective for
geotextiles material weight in CBR strength in general. This is evident from Table 7.
The small size of the test samples creates concerns about the difference of dimensions of the aggregate
particles, mould diameter, and plunger (loading head). Although the smaller load head allows for the
development of a non-constant stress profile in the bounds of the mould, but it is given some indication about
the relation between laboratory scale and full-scale pavement. For example, soil I did not need reinforcement
geotextiles, but needed only separation layer between aggregate and sub-soil. Furthermore, contact area of the
truck tire has a nominal radius of 6 inch approximately, and the stress profile is distributed over a much greater
side level for the full-scale pavement. These are considered limitations of the study along with the rigid
boundary; calibration against full scale testing is required to determine the actual behavior.
Conclusion:
A series of CBR tests have been conducted to investigate the effect of geotextile weight on the bearing ratio
of soils. The conclusions from this study are summarized as follows:
 The improvement of bearing ratio of soils with geotextile materials depends on the soil type.
 It implies that geotextile reinforced soils in unpaved or paved roads will perform better than
unreinforced ones and increase load carrying capacity of soils.
 As compared with penetration stress of soil II and soil III without geotextile the maximum is 914.58
and 438.1psi respectively, when with geotextile materials (600g/m2) the increase in reinforcement is 1251.48
and 657.61 psi respectively.
 Large scale test is also needed to determine the levels effective influence on test results.
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