This study experimentally analyzed the effect of L/B ratio of stone columns on the bearing capacity and settlement of sandy soil. Model tests were conducted with a square footing and single stone column with L/B ratios of 0.5, 1, 2, 2.5, and 3. The results showed that the minimum relative settlement corresponded to an L/B ratio of 2.5, which also had the highest bearing capacity of 318 kN/m2. Increasing the L/B ratio beyond 2.5 did not significantly improve the bearing capacity. Thus, the optimal L/B ratio for a single stone column was determined to be 2.5 based on minimizing settlement and maximizing capacity.

1. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online), Volume 6, Issue 1, January (2015), pp. 55-61 © IAEME
55
EFFECT OF L/B RATIO OF STONE COLUMN ON
BEARING CAPACITY AND RELATIVE SETTLEMENT OF
SANDY SOIL (AN EXPERIMENTAL STUDY)
Umar Rashid Lone1
, Mohd Hanief Dar2
, Mohd Younus Ahanger3
1
B tech, Department of Civil Engineering, NIT Srinagar, India
2
M tech, Department of Civil Engineering, NIT Srinagar, India
3
B tech, Department of Civil Engineering, NIT Srinagar, India
ABSTRACT
Stone columns are one method of ground improvement having a proven record of experience.
They are ideally suited for improving soft clays and silts and also for loose silty sands. In spite of the
wide use of stone columns and their development in construction methods, present design methods
are empirical, and only limited information about designing stone columns are available in technical
codes. This study is dedicated to observe practically the effect of various parameters of stone column
on the bearing capacity of sandy soils by model testing. In this study square footing has been used
and model tests were conducted with varying L/B ratio of stone columns. The test results followed
that relative settlement was minimum corresponding to L/B ratio (of stone column) of 2.5.
Key Words: Stone Column, Improvement of Soft Clays and Silts, Only Empirical Results
Available, Experimental Study, Best L/B Ratioobtained.
1. INTRODUCTION
The stone column technique was adopted in European countries in the early 1960s. Many
researchers have developed theoretical solutions for estimating the bearing capacity and settlement
of foundations reinforced with stone columns. Priebe, (1995) proposed a method for estimating the
settlement of foundations resting on an infinite grid of stone columns. The basic for this method is
the unit cell concept.
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2. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online), Volume 6, Issue 1, January (2015), pp. 55-61 © IAEME
56
In spite of the wide use of stone columns and their development in construction methods,
present design methods are empirical, and only limited information about designing stone columns
are available in technical codes.
This study is focused on the comparison of soil improvement by varying various parameters
of stone columns by conducting the miniature model tests on sandy bed with a single stone column.
Stone columns were installed using ramming technique.
2. MATERIAL USED (SAND) AND ITS PROPERTIES
Sand was used as the primary material on which various model tests were conducted to
enhance its bearing capacity by reinforcing it with stone columns. Normal aggregates of 10mm size
were used as stone column material. The various properties of sand used are tabulated in table1.
Table 1 various properties of sand
Property Value
Specific gravity 2.67
Effective grain size D10 (mm) 0.52 mm
D60 (mm) 0.90 mm
D30 (mm) 0.70mm
Co-efficient of Uniformity (Cc) 1.047
Co-efficient of Curvature (Cu) 1.731
Minimum dry unit weight(g/cc) 1.503
Maximum dry unit weight(g/cc) 1.74
Maximum void ratio 0.7764
Minimum void ratio 0.534
Bulking of sand (max.) 3.9% of water
Silt content 3.21 %
Friction angle 26◦
Cohesion 0.095 kN/m2
3. MODEL TESTS ON THE SOIL REINFORCED WITH SINGLE STONE COLUMN OF
DIFFERENT L/B RATIO
Model tests on the soil reinforced with single stone column (diameter 30mm) and the square
plate placed in the center of the model tank with stone column exactly in the center of square plate.
The sandy bed was prepared by compacting the sand in layer by layer into the steel tank of
dimension (40×37×49) cm at the 55% relative density. Details of proving ring, dial gauges and plate
used is as under:
1 division of proving ring =0.161 kg, Least count of dial gauge =0.01mm
Size of square plate (a) = 10cm, Area of square plate (A) =a2
= 0.01 m2
Density of sample in tank =1.638 g/cc. Weight of sand taken in tank = 118.787 kg
The test apparatus setup is shown in figure 1.

3. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online), Volume 6, Issue 1, January (2015), pp. 55-61 © IAEME
57
Figure 1 Test apparatus setup
3.1. L/B ratio equal to 0.5
The load settlement curve for Plate Load Test (PLT) is shown in Figure 2
Figure 2 Load settlement curve for PLT 1
Bearing capacity by double tangent method = 13.85 kN/m2
3.2. L/B ratio equal to 1
The load settlement curve for Plate Load Test (PLT) is shown in Figure 3.
0
5
10
15
20
25
0 10 20 30
Settlement(mm)
Load intensity (kN/m^2)
Load settlement curve
Load settlement
curve

4. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online), Volume 6, Issue 1, January (2015), pp. 55-61 © IAEME
58
Figure 3 Load settlement curve for PLT 2
Bearing capacity by double tangent method = 22.5 kN/m2
.
3.3. For L/B ratio equal to 2
The load settlement curve for Plate Load Test (PLT) is shown in Figure 4.
Figure 4 Load settlement for PLT 3
Bearing capacity by double tangent method = 238 kN/m2
3.4. For L/B ratio equal to 2.5
The load settlement curve for Plate Load Test (PLT) is shown in Figure 5.
0
5
10
15
20
25
0 10 20 30 40 50
Settlement(mm)
Load intensity (kN/m^2
Load settlement curve
load settlement curve
0
2
4
6
8
10
12
14
16
0 100 200 300
Settlement(mm)
Load intensity (kN/m^2)
Load settlement curve
Load settlement curve

5. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online), Volume 6, Issue 1, January (2015), pp. 55-61 © IAEME
59
Figure 5 Load settlement for PLT 4
Bearing capacity by double tangent method = 318 kN/m2
.
3.5. For L/B ratio equal to 3
The load settlement curve for Plate Load Test (PLT) is shown in Figure 6.
Figure 6 Load settlement curve for PLT 5
Bearing capacity by double tangent method = 320 kN/m2
.
4. RESULTS OF MODEL TESTS ON SOIL REINFORCED WITH SINGLE STONE
COLUMN
Model tests were conducted using square surface footing on soil reinforced with single stone
column in the center of the tank with different values of L/B.
0
5
10
15
20
25
0 100 200 300 400
Settlement(mm)
Load intensity (KN/m^2)
Load settlement curve
Load settlement curve
0
5
10
15
20
25
0 100 200 300 400
Settlement(mm)
Load intensity (kN/m^2)
Load settlement curve
Load settlement
curve

6. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online), Volume 6, Issue 1, January (2015), pp. 55-61 © IAEME
60
4.1 Comparison of bearing capacity of different model tests.
The bearing capacity of various models whose test data is presented above is compared in a
tabular form given in Table 2.
Table 2 Comparison of bearing capacity of different model tests
Test description qu of reinforced soil
(kN/m2
)
Footing type Stone column (L/B)
Square(10cm) 0.5 13.85
Square(10cm) 1.0 22.5
Square(10cm) 2.0 238
Square(10cm) 2.5 318
Square(10cm) 3.0 320
4.2 Analysis of results
Comparison between relative settlements of square footing on the soil reinforced with stone
column of different L/B ratio (L/B =0.5, 1, 2, 2.5, 3) is presented in graphical form as shown in
Figure 7.The curve shows that the soil reinforced with single stone column in the centre of L/B ratio
2.5 suffers a minimum settlement and its bearing capacity is more than others. On further increase of
L/B ratio there is no significant increase in the bearing capacity of the soil.
The effect on ultimate bearing capacity with the variation of L/B ratio is also presented in
Figure 8.
Figure 7 Relative settlement curve soil reinforced with stone column of different L/B.
0
2
4
6
8
10
12
14
16
18
20
22
0 50 100 150 200 250
%settlement
q/YB
Relative settlement curve
L/B =0.5
L/B =1
L/B =2
L/B =2.5
L/B =3

7. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online), Volume 6, Issue 1, January (2015), pp. 55-61 © IAEME
61
Figure 8 Effect of L/B on bearing capacity
5. CONCLUSION
From the model tests performed on the virgin soil and soil improved by the single stone
column it can be concluded that relative settlement studies show that the square footing on the soil
reinforced with single stone column with L/B = 2.5 in the center gives better bearing capacity.
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0
50
100
150
200
250
300
350
0 1 2 3 4
qu(kN/m2)
L/B Ratio
Effect of L/B on qu