Consideration for End Shape of a Pile forPre bored Pile Construction Method
Sena MIYAZAKI1) ,Hideto SATO2)
Katsuhiro KANUKA3) ,Yuuki HARIGAYA4)
1) Graduate Student of Nihon Univ.,
3) Kanuka Design Co.,Ltd,

2) Nihon Univ.
4) Noix Co.,LtdINTRODUCTION- The cement milk pile construction method isclassified as the prebored pile construction
method.
- The application number of this method has
increased in Japanese urban areas because ofLow
the low construction noise and vibration.
- Recently, small size steel piles are often used Noisefor foundations of house or retaining wall.

LowVibration

Retaining wall with small steel pile
constructed by cement milk method
ISOPE 2015, Hawaii, USAINTRODUCTION- If the pile end is fixed in soft or medium clay,
vertical resistance might decrease.
- Accordingly, it is important to ensure thestiffness of a consolidation of pile end.
- In this study, we propose to attach a holed disk
plate to the pile end in order to improve the end
bearing capacity of a small sized steel pipe pile.

Soft clay
Small sized steel pile with end disk plate
ISOPE 2015, Hawaii, USAINTRODUCTION
Laboratory Experiments
We examine the characteristics of the end bearing
capacity and the effectiveness of the end disk plate.

Design the End Disk Plate
The dimensions of the plate to apply to the cement
milk method are discussed.

Loading Test in the Field
Actual size loading tests are performed to confirm
the validity of the improved pile end.
ISOPE 2015, Hawaii, USALABORATORY EXPERIMENT
Test Pile- A steel pipe is used as a test pile.

上下用シャフト

制御盤

杭頭軸力計

テフロンシート
φ650
テフロンシート 1,400
1,4002,300 2,300

回転装置

先端軸力計
先端軸力計
先端軸力計
先端軸力計

1,100
1000
1,100

杭頭軸力計

回転装置

700

- No. 5 silica sand in dry condition is used.
- Model ground is prepared by the air
pluviation technique with double nets
for dispersion.
- The N-values of the pile end is N=2.

杭頭軸力計
圧入装置
杭頭軸力計

700

Model Ground

回転装置

243
(H)

- A steel circular test tank is used.
Diameter is 650 mm.
Depth is 700 mm.

回転装置

圧入装置

5D

Test Tank

上下用シャフト480mm（ 10D）
480mm（ 10D）
480mm（10D）10D）
480mm（制御盤

圧入装置

600

- To eliminate the frictional resistance, 制御盤
the pile surface is coated with Teflon.

2,3002300
2,300

上下用シャフト

圧入装置

1,100 1,100

制御盤576mm（12D）
576mm（12D）
576mm（12D）
576mm（12D）

Diameter is 48.6 mm (D).
Length is 600 mm.
Embedment length(H) is 243 mm (5D).

上下用シャフトFig. 3 Experimental apparatus
テフロンシート

ISOPE 2015, Hawaii, USA

LABORATORY EXPERIMENT

3.2(t)

93.2(t)93.2(t)3.2(t)

15~30
48.6
(De)
Open end pile(OP)

48.6(De)
Closed end pile(CP)

48.6(De)
S-series

932.2
58.3~75.9(Do)
P-series- We performed 4 kinds of model tests.
- S-series : To discuss the influence of the pile end opening.
Opening diameters (Do) are 15, 25 and 30 mm.

- P-series : To investigate the effect of the pile end area.
External diameters (De) are 58.3, 67.6 and 75 mm.
ISOPE 2015, Hawaii, USA

LABORATORY EXPERIMENT

Pシリーズの杭先端

Pile tip (P-series)

載荷時の全景の写真

Loading scene

Situation of the pile head

- For axial loading, we used displacement controlling type loading device.
Loading speed is 1 mm/min.
Measurement interval is 3 seconds.

- The resistance and the displacement of the pile end are almost equal
the values of the pile head, because the length is short and the surface
is coated by the Teflon.
Pile head load＝Pile end load
Pile head displacement＝ Pile end displacement
ISOPE 2015, Hawaii, USA

LABORATORY EXPERIMENT

Rp= α・N・Ap(1)

Rp： End bearing capacity (kN)
α :Bearing capacity factor (kN/ m2)
N :Average of N-value of the tip

δ = 0.1D

Ap: Sectional area of the pile tip (m2)

- The end bearing capacity (Rp) of a single pile is calculated by Eq. 1.
- The end bearing capacity (Rp) is given when the pile-end
displacement (δ ) reaches 10 % of the pile diameter (D).
- The standard value of the bearing capacity factor (α) for the prebored construction method is α=200.
ISOPE 2015, Hawaii, USA

LABORATORY
EXPERIMENT
杭先端荷重～基準化変位関係(R－δ/D曲線）
Displacement of pile end δ/DPile end resistance R (kN)

Rp = 1.84 kN
Closed end pile
(α=495)- As for the closed end pile (CP), the pile end resistance(R) is increasing
Test end
from the loading initial stage.
- The end bearing capacity is Rp = 1.84 kN, and the end bearing capacity
factor is α = 495. These are sufficient values for end resistance of theprebored construction method.
ISOPE 2015, Hawaii, USALABORATORY
EXPERIMENT
杭先端荷重～基準化変位関係(R－δ/D曲線）
Displacement of pile end δ/DPile end resistance R (kN)

Rp = 0.15 kN(α=11.5)

Rp = 1.84 kN
Closed end pile
(α=495)

Open end pile

- In the case of the open end pile (OP), the pile end resistance (R) does
Test end
not large even if the displacement (δ/D) reaches 0.1.
- The end bearing capacity is Rp = 0.15 kN, and the bearing capacity
factor is α = 11.5.
- These values are only 8 % of the closed end pile's.
ISOPE 2015, Hawaii, USA

LABORATORY
EXPERIMENT
杭先端荷重～基準化変位関係(R－δ/D曲線）
Displacement of pile end δ/DPile end resistance R (kN)

Rp = 1.71 kN(α=461)

Rp = 1.84 kN
Closed end pile(α=495)

S-30

S-25
S-15

Do
S-series- In the S-series, the larger the opening diameter (Do) , the smaller thepile end resistance (R).
- The end bearing capacity of S-15 is almost same as CP's. (93% of CP's)

ISOPE 2015, Hawaii, USA

LABORATORY
EXPERIMENT
杭先端荷重～基準化変位関係(R－δ/D曲線）
Displacement of pile end δ/DPile end resistance R (kN)

Rp = 1.84 kN(α=495)
Rp = 3.31 kN(α=893)
Closed end pile

S-75
S-67
P-58

32.2

58.3~75.9(De)

P-series- In the P-series, the larger the external diameter (De) , the larger thepile end resistance (R).
- We suppose that this phenomenon is caused by the area of the pile end.
- In case of P-58, the pile tip area is same as CP's.
- The end bearing capacity of P-75 is 1.7 times larger than CP's.
ISOPE 2015, Hawaii, USALABORATORYEXPERIMENT
杭先端荷重～基準化変位関係(R－δ/D曲線）
Displacement of pile end δ/DPile end resistance R (kN)

Rp = 0.85 kN(α=229)Closed end pile

Rp = 1.84 kN(α=495)

32.2

58.3

P-58

P-58

- In case of P-58, the pile tip area is same as CP's.
- But the Rp value of P-58 is only 40% of CP's.
- This phenomenon shows that the end bearing capacity is affected bythe opening even if the end area is the same.
ISOPE 2015, Hawaii, USA

LABORATORYEXPERIMENT
杭先端荷重～基準化変位関係(R－δ/D曲線）
Displacement of pile end δ/DPile end resistance R (kN)
Rp = 0.51 kN(α=138)
Rp = 0.85 kN(α=229)

S-30

P-58
32.2
30
48.6

58.3

S-30

P-58

- Furthermore in P-58, the opening area is almost same as S-30's.
- However, the Rp value of P-58 is about 1.6 times larger than S-30.
- This result is signifies that the end disk plate contributes to provide forthe large end bearing capacity.
ISOPE 2015, Hawaii, USABearing capacity factor α [kN/m2]
Bearing capacity factor α (kN/m2)

LABORATORY
EXPERIMENT
杭先端荷重～基準化変位関係(R－δ/D曲線）
1000
900
800
700
600
500
400
300
200
100
0

P-76

S
P

P-68

CPＩ

S-15

S-25
00.2

P-58

α=200

S-30

OP

0.4
0.6
Aperture ratio(r) r
ApertureRatio

0.8- The aperture ratio r is the ratio of the opening area to the whole areaof the tip.
- In the S-series, when r is larger than 0.27, α-value become smaller than
the standard value of the prebored construction method.
- However in the P-series, all test results are larger than S-series, andthey are also larger than the standard values.
ISOPE 2015, Hawaii, USADESIGN MANNER OF THE END DISK PLATE- According to the results of the laboratory experiment, the end disk
plate is effective for improvement in the end bearing capacity.
- However, the larger disk plate might scrape the soil off a bored hole
- An enough opening is needed to fill the inner space of the pile with thecement milk.
- The dimensions of the plate are designed as follows;1. The area ratio (rA) should be more than 1.0 (rA>1.0).
rA=A/A0 , A : Whole area of pile end
A0 : Sectional area of pile body.
2. The digging diameter ratio (rD) should be less than 0.8 (rD<0.8).
rD=De/DD , De : External diameter of end disk plate
DD : Digging diameter

3. The opening diameter (Do) should be more than 80 mm (Do >80 mm)
4. The aperture ratio (r) should be less than 0.3 (r<0.3).
r =Do2/De2 , Do : Opening diameter of end disk plate
DD : Digging diameter
ISOPE 2015, Hawaii, USAFIELD EXPERIMENT
Test Site- Two kinds of loading tests wereperformed in Morokawa-city located in
mid area of the Kanto plane.

Test Pile- We used an general small-diameter steel
pipe piles.
Diameter is 165.2 mm (D).
S-pile : Embedded in Clayey Sand. N is 5.8.
C-pile: Embedded in Sandy Clay. N is 8.8.

End Disk Plate- Holed disk plate were melded on the end.
External diameter is 225.2 mm (De).
Opening diameter is 85.2 mm (Do).

Boring logs of field test
ISOPE 2015, Hawaii, USAFIELD EXPERIMENT
Reaction beam

Test pile
Anchor pile system
Reaction
End disk plate on pileendbeam method

Loading system of the anchor pile system- Static axial load tests are executed according to the test manual
using theDisplacement
Jack(produced by the Japanese Geotechnical Society).
anchor-pile-systemgauge- The strain and displacement of the pile tip are measured.
Test pile- The pile end load is converted by values of the strain gauges.
ISOPE 2015, Hawaii, USAFIELD EXPERIMENT0Pile end resistance R (kN)
50100150

Displacement of pile end δ/D00.01

0.02
10.3m

0.03

12.1m

0.04

0.05
0.06

C-Pile0.07

S-pile0.08

Rp = 104 kN(α=307)

0.09

S-PileC-pileRp = 128 kN(α=680)0.1- S-pile : The end bearing capacity (RP) indicates 104 kN and thebearing capacity factor (α) is 307.
- C-pile : RP is 128 kN and α-value is 680.
- We can confirm the validity of the disk plate added to the pile tip.
ISOPE 2015, Hawaii, USA

FIELD EXPERIMENT

Digging out investigation

Pile tip situation (S-Pile)- We could not find any damage and crack.
- Some small lump of soil are exist on the surface, but we could confirm thatthe pile tip has solidified united with cement milk.
ISOPE 2015, Hawaii, USACONCLUSION- In the cement milk pile construction method, there is somepossibility of decreasing the end bearing capacity due to theinsufficient stiffness of pile end.
- In this paper, we proposed to attach a holed disk plate to thepile end in order to improve the end bearing capacity of asmall sized steel pipe pile.
- We examined the influence of the disk plate and the openingof the pile end by the laboratory experiments.
- We proposed the design manner of dimensions of the diskplate.
- In actual sized field tests, two test results showed large andsufficient end bearing capacities.

ISOPE 2015, Hawaii, USAThank you very much for your kind attention