Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

Effect of Pile Diameter on Plugging Phenomenon of Open-ended Piles
Mizue KANBE
Graduate Student, Department of Civil Engineering, Tokyo University of Science, Chiba, Japan
Email: 7616608@ed.tus.ac.jp

Yoshiaki KIKUCHI
Professor, Department of Civil Engineering, Tokyo University of Science, Chiba, Japan
Email: kikuchi_y@rs.tus.ac.jp

Taichi HYODOAssistant Professor, Department of Civil Engineering, Tokyo University of Science, Chiba, Japan
Email: t.hyodo@rs.tus.ac.jp

Hiromu OTSUBO
Undergraduate Student, Department of Civil Engineering, Tokyo University of Science, Chiba, Japan
Email: 7614018@ed.tus.ac.jp

Hiroyoshi YAMAZAKI
Undergraduate Student, Department of Civil Engineering, Tokyo University of Science, Chiba, Japan
Email: 7614106@ed.tus.ac.jp

ABSTRACT
Nowadays deep embedded and large diameter steel pipe piles have been widely used in Japanese port facilities for supporting large vertical load, as growing sizes or changing structural types of port facilities. Estimation for bearing capacityof large diameter and deep embedded piles has been complex problems such that bearing capacity is increased becauseof deep embedment and plugging effect is decreased because of using large diameter piles. To investigate the inner
friction force mechanism development with soil plugging of open-ended piles was the main aim of this study. In thisresearch, open-ended piles with different pile outer diameters were penetrated into dry sand. The plugging situation in
the model pile penetration experiment was evaluated from two viewpoints of the plugging phenomenon. As a result, it
was found that if the ratio of the wall thickness to the pile diameter is the same, there is not much difference in the degreeof plugging due to the pile diameter.
Key words: Open-ended piles, End bearing capacity, Soil plugging, Inner friction

1. Background
Steel pipe piles have been used for a long time inratio. The plugging ratio is considered to be affected by

Japan's port facilities. Nowadays deep embedded anddetailed mechanism of the plugging has not been clarified.

large diameter steel pipe piles have been widely used in

As shown in Fig. 1, theoretically, the toe bearing re-port facilities for supporting large vertical load, as grow-sistance of an open-ended pile can be separated into theing sizes or changing structural types of port facilities.

resistance of the annular part, Rp, and the inner friction be-

Therefore, it is required to accurately estimate the end

tween the pile wall and soil, RfI. Considering this, the the-bearing capacity of one pile. According to the design

oretical plugging effect, , is written in Eq. (1). (AIJ,
2001)

standards of Japanese port structures, the design bearing

pile diameter and embedment length to the bearing layer,

capacity of the open-ended pile incorporates a plugging- 395 -

Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

100

Summation percentage (%)

Tohoku silica sand #5

RfI
Rp
Fig. 1

Schematic diagram of the bearing capacity of an openended pile

Rp +RfI=
Rclose

(1)

80
60
40
20
0
0.01

0.1
1
10
Particle size (mm)100

Fig. 2 Particle size distribution of Tohoku silica sand #5

where Rclose is the resistance of a closed-ended pile.
However, it is difficult to estimate the inner frictional
resistance because the mechanism of the soil plugging of
the open-ended pile is unknown. For this reason, a method
for estimating the plugging ratio has not been adopted inpractice.
In this study, the mechanism of inner friction force
development with soil plugging of open-ended piles wasinvestigated. In order to investigate the effect of the pileouter diameter on the plugging phenomenon of an openended pile, model piles with different pile outer diameters
were penetrated into dry sand in this paper. The results ofmodel pile penetration experiments were evaluated for the

Fig. 3

plugging situation from two viewpoints. One was the bear-

Schematic diagram of installation method of measuring

equipment

ing capacity, the other was a phenomenon where plugging
can be made.
2. Material and test methods
The model piles used in this study were made ofstainless steel. One closed-ended pile and two open-ended
piles had an outer diameter (D) of 50 mm and a length (L)of 380 mm. Apart from them, one closed-ended pile andtwo open-ended piles had an outer diameter of 101.6 mm
and a length of 900 mm. For both open-ended piles with

Fig. 4The measurement method of inner soil height

D of 50 and 101.6 mm, diameter-thickness ratio (D/t) was
the soil particles of Tohoku silica sand #5 was 2.658 g/cm3,

12.5 and 25.
When using model piles with an outer diameter of 50

the mean diameter was 0.55 mm, and the maximum andmm, the model ground was prepared in a soil tank of 300

minimum dry density were 1.718 g/cm3 and 1.479 g/cm3

mm inner diameter. A soil tank with an inner diameter ofrespectively. The model ground was prepared with sand of

772 mm was used when using model piles with an outer

65% relative density. The particle size distribution ofdiameter of 101.6 mm. The model ground was made of dry

Tohoku silica sand #5 is given in Fig. 2. Internal friction

sand and the height was 270 mm and 800 mm in each soil

angle of the sand measured by drained triaxial compres-tank. It was made of Tohoku silica sand #5. The density ofsion test under the confining pressure of 50 kN/m2 was 40- 396 -

Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

degree at the relative density of 80%.
The pile was penetrated into the model ground at the0

Penetration depth, z (mm)rate of 5mm/min in experiments with a soil tank of 300
mm inner diameter, 30 mm/min in experiments with a soiltank of 772 mm inner diameter. No effects were observedin the difference of penetration rates in these series of experiments. The penetration resistance and penetration
depth were measured using external load cell and displacement transducer respectively as shown in Fig. 3.
When the open-ended pile with an outer diameter D of 50

0

Inner soil height, h (mm)
50
100
150
200

250

D=50mm, Dr=65%

50

h=z
t=2mm
(D/t=25)t=4mm(D/t=12.5)

100
150
200
250

mm was penetrated into the model ground, the inner soil(a) D = 50 mm

height, h, was measured using a scaled-mark string connected to a small weight at the bottom by stopping pene-0

Penetration depth, z (mm)tration at 25 mm intervals as shown in Fig. 4. For openended piles with an outer diameter of 101.6 mm, inner soilheight was measured with a tape measure type displacement transducer connected to a weight. Inner soil height
was measured continuously by placing the weight on thesoil surface in the open-ended pile and measuring thewithdrawal amount of the wire with penetration of the pile.

0

Inner soil height, h (mm)100 200 300 400 500

600

D=101.6mm, Dr=65%

100
200
300

t=4mm (D/t=25)

400
500

h=z
t=8mm (D/t=12.5)600

Penetration depth, z (mm)00Penetration resistance, R (N)1000 2000 3000 4000 5000 6000

Fig. 6

D=50mm, Dr=65%

Relationship between the penetration depth and innersoil height50

3. Results and discussion

100

Fig. 5 (a) and (b) show the relationship between the

t=4mm(D/t=12.5)

150

penetration depth and the penetration resistance in anouter diameter of 50 and 101.6 mm. In the case of open-

200
t=2mm(D/t=25)

ended piles with outer diameter D of 50 mm as shown inclosed-ended pileFig. 5 (a), the inner soil height was measured by stopping

250

penetration and released the load at around 25 mm inter-(a) D = 50 mm

Penetration depth, z (mm)00Penetration resistance, R (kN)51015

vals. The results indicate that there was a certain relation20

D=101.6mm, Dr=65%

100

ship between the ratio of the penetration resistance of
open-ended pile to the penetration resistance of the closedended pile. The results also indicate that the relationship200

varied depending on the diameter-thickness ratio, regard-

300

less of the pile diameter. Fig. 5 (a) and (b) show that the400

closed-ended pilesmaller the diameter-thickness ratio is, the lower penetration resistance at the same penetration depth becomes.

500
t=4mm (D/t=25)

Fig. 6 (a) and (b) show the relationship between the

t=8mm (D/t=12.5)

600

penetration depth and the inner soil height in an outer di(b) D = 101.6 mm

Fig. 5(b) D = 101.6 mm

Relationship between the penetration depth and thepenetration resistanceameter of 50 and 101.6 mm. When the tangential line of
the z-h curve is in parallel with the dotted line (z=h), innersoil was unplugged. When the inner soil height was- 397 -

Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

smaller than the penetration depth, there was a situation inwith the penetration of the pile is related to the soil plug-

which soil was difficult to be filled into the pile. The re-ging, incremental filling ratio (IFR) (Lehane and Gavin,sults show that the inner soil height was smaller than the2001) was defined as shown in Eq. (6).

penetration depth with the penetration depth more than(5)

IFR=dh/dz

twice the pile diameter (referred to as 2D) when the diameter-thickness ratio was small regardless of the pile diameter. When the diameter-thickness ratio is small, it waswhere dh is change of inner soil height for a penetrationconsidered that a plugging phenomenon was occurring at

depth of dz.

the penetration depth deeper than 2D.
In this research, the soil plugging behavior of open--0.5
0ended pile was evaluated from two viewpoints. One was aplugging effect to be evaluated from penetration resistance.

1

The other was a plugging phenomenon which evaluates

2z/D

whether the inner soil had formed a plug from the relationship between the inner soil height and the penetration

4

uate the plugging effect. Rr was defined by Eq. (2).

5
6

(1)

1.0

1.5
Dr=65%

D/t=12.5

3depth. The inner stress intensity ratio(Rr) was used to eval-

Rr = qfI ⁄qb

Rr
0.5

0.0

Fig. 7

D/t=25

D=101.6mm
D=50mmRelationship between the penetration depth and Rr

where qfI is the resistance per unit area acting on the bot*

tom of the inner soil of the pile, qb is the resistance of the-0.2
0annular part per unit area.

0.2

0.6

0.8

1.0

Dr=65%The previous research suggests that the soil pressure

1

distribution at the tip of the closed-ended pile is almost

D=101.6mm
D=50mm2

z/D

equally distributed load at the model experiment level(Kikuchi, 2011). In this paper, qb was calculated from Eq.
(3) using a measured value of penetration resistance of the3

D/t=12.5

4closed-ended pile.

5

qb = Rclose ⁄A

0.0

IFR
0.4

(2)

D/t=25

6
Fig. 8Relationship between the penetration depth and IFR*

where Rclose is the resistance of a closed-ended pile, A is
the total area covered by the pile outer diameter.

As Eq. (6) implies, a fully-plugged open-ended pile

qfI was calculated by Eq. (4) and Eq. (5) using measured values of penetration resistance.

produces a zero value of IFR due to no changes in the soil
plug height respective its penetration depth. At the otherextreme end, an unplugged open-ended pile produces 1

qfI = RfI ⁄Ain

(3)

value of IFR due to an equal height of soil plug to its penetration depth. However, a fully-plugged open-ended pile

RfI =Ropen − qb Ap(4)

produces 1 value of Rr, and an unplugged open-ended pile
produces zero value of Rr. To clarify the relationship be-where RfI is inner frictional resistance, Ain is internal area

tween the plugging effect and the plugging phenomenon,of open-ended pile, Ropen is the resistance of an open-ended

the plugging phenomenon was evaluated by IFR* shown

pile, Ap is annular area.

in Eq. (7). A fully-plugged open-ended pile produces 1

Since the degree of the change in the inner soil heightvalue of IFR*, and an unplugged open-ended pile produces- 398 -

Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

zero value of IFR*. In this paper, IFR* was referred to as

1.0
z/D=2

incremental filling ratio.
0.8
∗

(6)

Dr=65%

0.6

Dr=80%IFR*

IFR =1 − dh/dz

Dr=0%Fig. 7 shows the relationship between the penetration

0.4

depth and Rr calculated from Eq. (2)-(5). In Fig. 7, the0.2

penetration depth was normalized by the pile outer diam-

0.0

eter. The result shows that Rr increased with penetration-0.2

when the penetration was shallow. The result also shows△ D=50mm▲ D=101.6mm

0

10

20

that Rr became almost constant irrespective of the penetration depth when the model pile was penetrated into theFig. 10ground more than about 2D. In addition, Rr is slightly big-

30
D/t

40

50

60

Relationship between incremental filling ratio and diameter-thickness ratio

ger for larger diameter piles at any diameter-thickness ratio until the penetration depth reaches 2D.

different relative densities (Kanbe et al., 2017).

Fig. 8 shows the relationship between the penetration*

Fig. 9 shows that Rr tended to decrease as the diame-

depth and IFR calculated from Eq. (7). In Fig. 8, the pen-

ter-thickness ratio increased in both cases of pile diameter

etration depth was normalized by the pile outer diameterof 50 and 101.6 mm. Focusing on the difference in pile

as in Fig. 7. The result indicates that the same tendency as

diameter, Fig. 9 shows that Rr became slightly larger as the

Rr could be seen with IFR*. In other words, the result

pile diameter increased in both diameter-thickness ratio of*shows that IFR increased until the penetration depth

12.5 and 25. However, since the difference in Rr due to thereached 2D, and it showed a generally constant value

pile diameter was smaller than the difference in Rr due towhen it was penetrated deeper than 2D.

the diameter-thickness ratio, it was considered that the in*Fig. 7 and Fig. 8 show that both Rr and IFR appeared

fluence on Rr is larger in the diameter-thickness ratio thanto be affected by both the pile diameter and diameter-in the pile diameter. Fig. 10 shows that IFR* decreased

thickness ratio. In order to clarify the influence of the pilewith the diameter-thickness ratio as in Rr. Focusing on the

diameter and diameter-thickness ratio, the relationship be-difference depending on the pile diameter, Fig. 10 shows*

tween the diameter-thickness ratio and Rr or IFR was in-that IFR* decreased as the pile diameter increased whenvestigated as shown in Fig. 9 and Fig. 10. The data when

the diameter-thickness ratio was 12.5. Fig. 10 also shows

the penetration depth reached 2D was plotted in Fig. 9 andthat IFR* was less than zero with the small pile diameter

Fig. 10. In addition, these figures also include past re-and it was slightly more than zero with the large pile di-search results of penetrating model piles into grounds ofameter. If IFR* is less than zero, it means that the increment of the inner soil height is larger than the increment

1.5

Rr

1.0

z/D=2

of the penetration depth. There are at least two factors that

Dr=0%

can affect the inner soil height. One is that mass of soil

Dr=65%

penetrated a little from the outside of the inner of the pile.

Dr=80%The other is that the volume of soil changes after soil pen-

△ D=50mm

etrating into the pile. When the diameter-thickness ratio▲ D=101.6mm

0.5

was 25, it is difficult to judge which cause affected the difference in the tendency of IFR* depending on the pile di-0.0

Fig. 9ameter only by this result.
0

10

20

30
D/t

40

50

60

As shown in Fig. 9 and Fig. 10, there was a slightdifference in tendency between Rr and IFR* due to differ-

Relationship between inner stress intensity ratio and di-ences in the pile diameter and the diameter-thickness ratio.

ameter-thickness ratio- 399 -

Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

Fig. 11 shows the relationship between Rr and IFR* to in-

into the ground. The degree of the soil plugging in the ex-vestigate how these relationships change. This figure in-periment results was evaluated from two viewpoints. The

cludes the results at the penetration depth of 1D, 1.5D, 2D,

first evaluation method was to judge the plugging effect

2.5D. Fig. 11 also includes the past research results

based on the bearing capacity, which was evaluated by Rr.

*(Kanbe et al., 2017). On the dotted line, Rr and IFR are

The other was IFR*, which was to judge whether a soil

equal. As shown in Fig. 11, the past experiment results

plug was formed from a change in the inner soil height.

*

show that Rr and IFR had a one-to-one relationship in

The results suggest that Rr slightly increased with theloose sands regardless of the difference in the diameter-

pile diameter, while IFR* tended to decrease with the pilethickness ratio. In addition, the past experiment results

diameter. Although this tendency was seen, it was deduced*

also show that Rr became larger than IFR in dense sand.

that the effect of the diameter-thickness ratio on the soil

The relationship between the overall Rr and IFR* obtained

plugging was larger than that of the pile diameter underfrom the experiment results this time was located between

this experiment condition.

the past experiment results. This is probably because the

The results also suggest that there was not much

relative density of the model ground was 65%. Focusingchange in the relationship between Rr and IFR* if the di-on the difference in the diameter-thickness ratio, it could

ameter-thickness ratio was the same even if the pile outerbe seen that the diameter-thickness ratio did not havediameter was about two times different.

much influence on the relationship between Rr and IFR*

although the values of Rr and IFR* themselves varied depending on the diameter-thickness ratio. Focusing on the

5. Acknowledgements
The financial supports for the research works pro-difference in the pile diameter, the relationship between Rr

vided by the Japan Iron and Steel Federation (JISF) is*and IFR had almost the same trend regardless of the pile

gratefully acknowledged.

diameter at the diameter-thickness ratio of 12.5. When the
diameter-thickness ratio was 25, it was considered that
there was not much difference depending on the pile di-References
Architectural Institute of Japan. 2001. Recommendations

ameter although it could not be clearly judged because offor design of building Foundations. 207. (in Japa-

the range of Rr varying somewhat by the pile diameter.

nese)
Kanbe, M., Kikuchi, Y., Hyodo, T., Okubo, M., Onozawa,K. 2017. Estimation of inner friction distribution of

*

-0.5
-0.5

0.0

IFR
0.5

Rr

open-ended piles. Proceeding of PILE 2017, I1.1-

1.5

I1.10.

D=50 mm
Dr= 0

0.0

1.0
65

80 %
: D/t=12.5: D/t=16.7: D/t=25: D/t=50

Kikuchi, Y. 2011. Mechanism of inner friction of an openended pile. Press-in Engineering 2011, 65-83.
Lehane B. M. and Gavin K. G. 2001. Base resistance of

D = 101.6 mm

0.5jacked pipe piles in sand. J. of Geotechnical and Ge-

Dr= 65%: D/t=12.5: D/t=25

oenvironmental Engineering, 127 (6). 473-480.

1.0
1.5
Fig. 11

Relationship between Rr and IFR*

4. Conclusions
In this research, model experiments were conductedto penetrate open-ended piles with different pile diameters- 400 -