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BEARING CAPACITY OF PARTIAL SKIRTED FOOTING ON CLAY
PUBLIKASI ILMIAH
Prepared as one of the requirement for achieving Bachelor Degree (Strata I) of Civil Engineering
Department of Engineering Faculty
Submitted by:
BASHAR MUSTAFA SMADI
D 100 122 011
CIVIL ENGINEERING DEPARTMENT
ENGINEERING FACULTY
UNIVERSITAS MUHAMMADIYAH SURAKARTA
2017
1
BEARING CAPACITY OF PARTIAL SKIRTED FOOTING ON CLAY
Abstract
In designing a foundation, bearing capaciy becomes the most important factor. In many case, it is so
necessary to maintan the improvement of the bearing capacity. Skirts that stick under the footing
can be an alternative. They are used to improve the shallower strength of the shallow footholds on
soft clay. The study performed nine laboratory experiments on a circular steel footing with different
diameters and partially different skirt lengths, on soft clay by maintaining the same water formation
and compaction method. From the laboratory tests performed, it was found that partial skirts were
very effective to increase the final bearing capacity, as it increased its length, the skirt also reduced
the settlement. Solutions generally decrease, when observed at the same load value, 1 kN. The
circular footing, whis is skirted with the longest skirt has the best settlement condition.
Keywords: bearing capacity, circular footing, foundation, soft clay, partial skirt.
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1.INTRODUCTION
Foundation is the base part of the structure on the bottom and its task of obtaining its
structure and removing it to the ground as well as no retaining it. Ordinary buried underground If
the foundation is made many things must be built type of structure, type of design and soil
specifications. Bearing capacity is the amount of land capacity to support applied to the soil. Land
carrying capacity is the average contact pressure between ponds and buildings that are not in the
ground. The maximum bearing capacity is theoretical maximum pressure that can be supported
without failure; The allowable carrying capacity is the final carrying capacity divided by the safety
factor. Sometimes, in soft soil locations, large settlements can occur under the foundations that are
loaded without actual failures occurring; In this case, the carrying capacity is allowed on. There are
three failure-resistant failure modes: general shear failure, and slide failure punching. Based on this,
the level of bearing capacity becomes the most important factor in making the foundation.
Therefore, it is necessary to make efforts to repair or investigation both on the ground and the
foundation itself. In this study, improvements or investigations will be made on the foundation, with
the addition of a skirt (vertical plate) on the surface of the foothold below the surface. This foothold
will then be referred to as a partial foothold.
2.METODE
The experimental tests and investigations were carried out on nine partial
laboratory experiments based on soft clay, nine partial pillars with 75 mm, 100 mm and
150 mm skirt lengths attached to three different diameter footholds (D) 75 mm, 100 mm
And 150. This experiment has been done with the same compacting method. The water
content test is investigated about 20% as a reference for all test models and this is always
maintained for all footing models. All footing models have smooth faces and notches in
the middle of the upper surface to mount a calibration proof that is calibrated through the
piston. Two open holes are drilled at the top surface of each modeling footing for the
above.
Figure 1 partial Skirted Footing Model
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Bin. It is made of a single steel cylinder as high as 500 mm and a diameter of 600 mm, with the top
side of the circle opened. Hydraulic loading machine. The loading frame machine has a maximum
load of 250 kN, the loading value is displayed on the digital device and a vertically mounted two-dial
gauge on the top surface of the footing to determine the displacement. The piston is used long and
conical at the end, laid just above the notching pad.
Figure 2 Sketch Setup of Testing Procedures
Some steps conducted for this research that will described as follow:
1. Prepare and organize clay materials and tools, which will be used in research. Clay must
be taken from the same location and condition. Clay in the dry air.
2. Investigation of dried clay soil (at room temperature) to obtain moisture content from
dried air.
3. The next step is time to conduct the experimental laboratory tests of covered
foundation.
First, the soil has been dried with dry clay with 1750 ml of water. The clay is pounded in
the soil test, because the first layer is clay with 50 strokes in each layer, and for one last
layer is Third, set the clay bin that has been compacted on the CBR machine. Fourth, for
the first test, place the wrapped foundation that has L / D = 0.5, right in the middle of the
test spot, and the press blanket to match the coated soil, observe the sand surface on the
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sheet through two Open the hole in the foundation. Fifth, set exactly two gauges on the
left and right of the foundation, to touch the urface above the foundation. This tool is
used to determine the decline that occurred. Then, set the piston right in the center of the
foundation. Sixth, the foundation is covered in the right position, then turn on the CBR
tool, observe and record all changes that occur on each test. The reduction of value will
be shown by two dial instruments associated with the foundation. Finally, stop the CBR
engine when the power has increased significantly, as an indication that the foundation
has been maximized. The next laboratory test, do the same test sequence above, but
replace the different foundations.
4. Because it is covered comparative data between the foundation and the foundation is not
covered, therefore conducted laboratory tests on the foundation is not covered. This step
has the same sequence as in Step III above, but only replace the foundation covered by
the foundation is not covered, with a diameter of 75, 100, and 150 mm.
5. Analyzing all data from laboratory test results from step I to stage IV, used for the
conclusion of all tests that have been done.
6. The next test experiment, do the same test sequence above, but just replace the
foundation with different sizes.
7. The final step, analyzing all data from laboratory test results from Step I to Step III, it is
used to derive conclusions from all the tests that have been performed.
3.RESULT AND DISCUSSION
The investigation of " bearing capacity of partial skirted footing on clay " was carried out
with a circular footing model based on clay, nine partial skirted footing with a diameter of (D) of 75
mm, 100 mm, 150 mm with length (L) 100 mm and 150 mm, This experiment has already been done
with the same compacting method. The water content test was investigated about 20% for layered
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soils as a reference for all test models and this was always kept for all 9 footing models.
Figure 1Load-Settlemnet Relationship for Footing Diameter 75 mm
Figure 2Load-Settlement Relationship for Footing Diameter 100 mm
-30.00
-25.00
-20.00
-15.00
-10.00
-5.00
0.00
0.00 5.00 10.00 15.00 20.00 25.00 30.00
Set
tlem
ent,
mm
Load, kN
75 mm 100 mm 150 mm
-30.00
-25.00
-20.00
-15.00
-10.00
-5.00
0.00
0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00
Set
tlem
ent,
mm
Load, kN
75 mm 100 mm 150 mm
6
Figure 3Load-Settlement Relationship for Footing Diameter 150 mm
This can be seen from the Figures above which corresponds between the same thing for all
nonlinear loads for the small payload range, and this relationship is not linear for large ranges and
does not indicate. It has been described by Hary Christady Hadiyatmo (2010) in Vesic's theory
(1963) regarding the phase of foundation failure. When initial loading, the ground below the
foothold descends the deformation, So the settlement is comparable to the moderate, soil conditions
are still controlled elastic. Then the subsequent loading of soil plastic deformation becomes more
apparent, with the higher the plastic zone growing.
3.1.Settlement in Similar Load as Reference
To know the magnitude of the settlement due to the effect of additional skirts on a partial
footing, it should be checked on the same charge (P, kN). It was taken 1 kN. There are no special
requirements in determining the value, simply because one partial partial skirt type is through 1 kN.
The analysis of completion with the same value of (1 kN) is shown in Figure V.4, V.5, V.6.
-30.00
-25.00
-20.00
-15.00
-10.00
-5.00
0.00
0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00
Set
tlem
ent,
mm
Load, kN
75 mm 100 mm 150 mm
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Figure 4Settlement Analysis on Footing Diameter 75 mm
Figure 5Settlement Analysis on Footing Diameter 100 mm
-20.00
-18.00
-16.00
-14.00
-12.00
-10.00
-8.00
-6.00
-4.00
-2.00
0.00
0.00 0.50 1.00 1.50 2.00 2.50 3.00
Set
tlem
ent,
mm
Load, kN
L= 75 mm L = 100 mm L = 150 mm
-0.8 -1.3
-7.2
-10.00
-9.00
-8.00
-7.00
-6.00
-5.00
-4.00
-3.00
-2.00
-1.00
0.00
0.00 0.50 1.00 1.50 2.00
Set
tlem
ent,
mm
Load, kN
L= 75 mm L= 100 mm L = 150 mm
-1.1 -0.6
-2.2
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Figure 6 Settlement Analysis on Footing Diameter 150 mm
The analysis of settlement on the same value of load (1 kN) is shown on Figure V.4, V.5, and
V.6. Then, Table V.1. shows the result information of the settlement magnitude that caused by
different skirt length on the same diameter of partially footing.
Table 1 Settlement magnitude on load is 1.5 kN
Footing diameter
D (mm)
Skirt
length, L
(mm)
L/D Settlement (S)
on 1 kN, (mm)
75 0 0.00 12.63
75 75 1.00 7.2
75 100 1.33 1.3
75 150 2.00 0.8
100 0 0.00 8.90
100 75 0.75 2.2
100 100 1.00 1.1
100 150 1.50 0.6
150 0 0.00 1.72
150 75 0.50 0.19
150 100 0.67 0.1
150 150 1.00 0.03
The magnitude of the settlement which is according to the difference in long skirts, the
settlements generally declined. It can be seen in diameter (D) 150 mm with length (L) 75 mm =
0.19 mm, (L) 100 mm = 0.1 and (L) 150 mm = 0.03 mm. However, different data on a similar
circular footing (L) = 150 with different diameters (D) 75 mm = 0.8 mm, (D) 100 mm = 1.3 mm,
-1.00
-0.90
-0.80
-0.70
-0.60
-0.50
-0.40
-0.30
-0.20
-0.10
0.00
0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 4.00S
ettl
emen
t, m
m
Load, kN
L= 75 mm L= 100 mm L = 150 mm
-0.1 -0.19
-0.03
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and (D) 150 = 7.2. This shows the diameter of 100 mm increases. This may be due to the pressure
imposed by an unstable hydraulic machine which may differ in settlements and is also very strong
between the two sample test steps. Can be different on the value of water content or compaction
method.
Table V.1 also shows different conditions at L / D ratio, observed from the same diameter and
different skirt length, when the L / D ratio increases the decrease, the bigger diameter the smaller
settlement, that proof is shown in Figure V. 7 presented
Figure 7L/D Ratio-Settlement Relationship, Different D
3.2.Load in Similar Settlement as Reference
From the tests and investigations of nine partial skirted models in general, Figures V.1,
V.2, and V.3 no graphs show nothing that is related to peak value. For larger sizes of partial
footing diameter (D), skirt length (L), can be observed in settlements in 3 mm. This shows at the
same diameter as the partial footing, the longer skirt increases also the higher the resistance
because of its greater length. This fact is presented by Figures V.8, V.9, V.10 and table V.2.
-8.0
-7.0
-6.0
-5.0
-4.0
-3.0
-2.0
-1.0
0.0
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2
Set
tlem
ent,
mm
L/D
D = 75 mm D = 100 mm D = 150 mm
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Figure 8Load in Similar Settlement on Footing Diameter 75 mm
Figure 9Load in Similar Settlement on Footing Diameter 100 mm
-4.0
-3.0
-2.0
-1.0
0.0
0.0 1.0 2.0 3.0 4.0 5.0
Set
tlem
ent,
mm
Load, kN
L= 75 mm L = 100 mm L = 150 mm
1.75 0.45 2.38
-4.0
-3.5
-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0.0 1.0 2.0 3.0 4.0 5.0
Set
tlem
ent,
mm
Load, kN
L=75mm L= 100 mm L = 150 mm
1.16 1.79 2.69
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Figure 10Load in Similar Settlement on Footing Diameter 150 mm
Table 2 Load Magnitude in Similar Settlement on 3 mm
Footing diameter
D (mm)
Skirt
length, L
(mm)
L/D Area
Load (P) on
3 mm,
(kN)
75 0 0.00 4419.64 0.54
75 75 1.00 4419.64 0.45
75 100 1.33 4419.64 1.75
75 150 2.00 4419.64 2.38
100 0 0.00 7857.14 0.74
100 75 0.75 7857.14 1.16
100 100 1.00 7857.14 1.79
100 150 1.50 7857.14 2.69
150 0 0.00 17678.57 1.47
150 75 0.50 17678.57 4.72
150 100 0.67 17678.57 7.06
150 150 1.00 17678.57 9.92
It also happened on L/D ratio, which is observed on the similar diameter (D) and different length
(L). The higher L/D ratio the greater the load generated.
-4.0
-3.5
-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0
Set
tlem
ent,
mm
Load, kN
L= 75 mm L= 100 mm L = 150 mm
4.72 7.06 9.92
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4.CONCLUSIONS
According to the research discussion and data analysis, the research conclude a final answer
for the problem formulation, mentioned as following:
Additional skirt would be efficient and good choice to minimize settlement load on clay.
As it could be noticed when is tested on the same load using 1 kN load, using the exact diameter of
partially footing utilizing. The longer skirt the smaller settlement.
The size of settlement for the advantage of skirt length to footing diameter, L/D ratio tested
on the same diameter of footing with different length of skirt. It display that the higher L/D ratio the
smaller settlement, moreover the bigger diameter the smaller settlement.
The load size of loading of the skirted, it is prove that at the exact diameter of footing, the
longer skirt the higher the resist load.
COURTESY
Because of the accomplishment of this final project, the author says thanks to:
Advisor of this final project, Mr. Anto Budi Listyawan, S.T., M.Sc., Yenny Nurchasanah, S.T, M. T.,
Mrs. Ir. Renaningsih, M.T., who have been taking the time to provide guidance and direction to
completion of this final project.
My beloved all my family who always support me. Thanks for the better hope of me a long time,
may Allah gives you all a best reward.
All my friends of Civil engineering, especially in International Program Class, thanks for your time
as my partner.
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REFERENCE
Chandrawanshi, Sareesh, et al. (2014). Effect of Skirt on Pressure Settlement Behaviour of Model
Circular Footing in Medium Dense Sand. Bhopal, India: International Journal of Advanced
Engineering Technology.
El Wakil, Amr Z. (2013). Bearing Capacity of Skirt Circular Footing on Sand. Alexandria, Egypt:
Alexandria Engineering Journal.
Urquhart, Leonard Church. (1959). Civil Engineering Handbook. McGraw-Hill Book Company. p.
8-2. by en.wikipedia.org.
Hardiyatmo, H. C. (2011). Analisis dan Perancangan Fondasi I: Edisi ke-2. Yogyakarta: Gadjah
Mada University Press.
Hardiyatmo, H. C. (2011). Analisis dan Perancangan Fondasi II: Edisi ke-2. Yogyakarta: Gadjah
Mada University Press.
Isvan (2015) “Effect of skirt on the bearing capacity of circular footing on sand”
Nella ( 2016) “Effect of skirt to circular footing on clay subjected on vertical loading”.
Niat (2016) “bearing capacity of skirted footing on sand and clay soil”.
