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

In-situ Load Test of Press-in Steel Pipe Pile for Seismic Isolation Retrofit
Koji WATANABE
Research Engineer, Technical Research Institute, Obayashi Corporation, Tokyo, Japan
Email: watanabe.koji.ro@obayashi.co.jp

Hiroyuki KISHI
Section Manager, Structural Engineering Department, Tokyo, Japan

Fumikazu OHASHI
Section Manager, Structural Engineering Department, Tokyo, Japan

ABSTRACT
There are several projects with relatively small construction space to retrofit the old building in narrow spaces andareas with low overhead clearance. Pile construction for existing structures to strengthen the seismic resistance such as
the seismic isolation retrofit is subjected to constraints on the construction site and process. Furthermore, noise andindustrial waste need to be considered with regard to their effects on the surrounding environment. A construction of aseismic isolation retrofit for an old building was planned in Kagawa prefecture, Japan. The compressive load dominates
because it is needed to support the dead load of existing building. In this project, a press-in steel pipe pile which
supports the existing old building was applied. Appropriate estimation of the bearing capacity of the press-in steel pipe
pile against the dead load was a major concern in the foundation design. Therefore, an in-situ compression load test was
carried out to confirm the bearing capacity of press-in steel pipe pile. The paper describes the results of in-situ pile load
test for foundations supporting an existing building, also presents the empirical design method for a press-in steel pipe
pile.
Key words: Seismic Isolation Retrofit, Building, Press-in Pile, Bearing Capacity, In-situ Load Test

surrounding environment.

1. Outline of the projectIn this project, the seismic isolation retrofit will be

1.1. Place
A construction of a seismic isolation retrofit for an

carried out as the building is being used before the retrofit

old building was planned in Kagawa prefecture, Japan.

construction. Thus, the temporary pile supports theThe planned building is located in the center of Takamatsubuilding after the excavation under the building. The

city, Kagawa prefecture.

schematic view of press-in process for the in-situ load
test indicates in Fig. 1.
The compressive load dominates because it is needed

1.2. Background and objectives of the project
There are several projects with relatively small

to support the dead load of existing building. In thisconstruction spaces to retrofit old buildings in narrowproject, a press-in steel pipe pile which supports thespaces and areas with low overhead clearance. Pile

existing old building will be applied. Appropriate

construction for existing structures to strengthen theestimation of the bearing capacity of the press-in steel

seismic resistance such as the seismic isolation retrofit ispipe pile against the dead load was a major concern in thesubjected to constraints on the construction site andfoundation design. Therefore, an in-situ compression loadprocess. Furthermore, noise and industrial waste need totest was carried out to confirm the bearing capacity of

be considered with regard to their effects on thepress-in steel pipe pile.

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

N value
050

0

No.1

No.2

Buried soil

Press-inGravel
5

Depth (m)Reactionbeam

10

Sandy silt
GravelSilty sandGravelOrganic clay
Clay15

Clayey sand
Clayey gravel

Gravely sand
ClayPress-in jack

Gravel20

Clayeygravel25(m)Fig. 1: Strain gauge

ClayFig. 2

Steel pipe pile

: LVDT

Soil profile and test piles

Steel pipe pile

Schematic view of press-in process

Reaction beam
2. Structural type and piling method
2.1. Site condition
There are some buildings such as offices andFig. 3

apartment buildings near the planned building. The

Arrangement of test piles and reaction beam

construction condition of seismic retrofit construction
required consideration for the neighboring environment.

15.0m depth. However, the ground surface is located at

Therefore, noise, vibration and industrial waste need toGL -1.0m because the load tests were carried out at thebe considered with regard to the construction of pilebasement floor of existing building. Thus, the actual pile

construction.

length is 14.0m. The reaction beam system wasemployed to apply loads on the test pile by using theexisting building structure. The test pile consisted of2.2. Ground condition
Fig. 2 shows the soil profile and test pile. The test

1.5m length steel pipe pile which was connected 15.0m

ground was composed of gravel and silty sand up tolength. The welded joints were applied to the steel pipe

about GL −9.0m, of organic clay and clay from GL -9.0

pile joints when the upper pile was connected to theto 12.0m, and of gravely sand and gravel below GL

lower pile. Because the piles constructed with this-12.0m. The bearing stratum was adopted to be N=50

method were assumed to be for construction in narrowfrom the results of ground investigation. The test piles

spaces, the steel pipes were joined by short pieces into

were embedded in the bearing stratum of SPT N value oflengths of 1.5 m. In order to make such short joints, there

50.

should be a welded part with a pitch of 1.5m. The piles
were used to be fabricated from JIS standard STK400

2.3. Structural type
The test steel pipe pile had a diameter of 0.4m insteel pipe to ensure a low cost and certain level ofquality.

axial part. The pile base sat on the gravel layer below- 572 -

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

1000

Load (kN)
2000

0

3000

002000

2000

4000

4000

60006000Displacement (mm)Displacement (mm)

08000

10000
12000

1000

Load (kN)
2000

3000

8000

10000
12000
14000

14000
Displacement at pile top
Displacement at inner soil

16000

16000

18000

Displacement at pile top
Displacement at inner soil

18000(a) Test pile: No. 1
Fig. 4(b) Test pile: No. 2

Relationships between load and displacement in press-in process

The difference of displacement between the pile top and2.4. Piling method
The standard press-in steel pile method was applied

the inner soil means the plugging effect in the steel pipe

to the construction of test pile because it was assumed

pile. Thus, it is said that the inner part of steel pipe pilethat the pile would be constructed under the basement of

was partially plugged during the installation process.

existing building. The existing building is used to theThe data obtained by the press-in process which

reaction when the press-in of pile is carried out. Because

indicates the relations between displacement and time are

there is possibility to break the soil plug inside steel pipeshown in Fig. 5. These data provides the creep

pile, the water jet technology is not applied to thedisplacement in the press-in process. From Fig. 5, theconstruction of test piles.

displacement slightly increases in the initial press-inprocess such as the depth of GL-2.0m when the press-in

3. Press-in pilingload holds. However, it is found that the creep

3.1. Layout

displacement does not occur as the press-in process

Fig. 3 shows the arrangement of the test andproceeds.

reaction piles. The influence range for the each test piles

The static load tests were carried out after theconformed to the Japanese Geotechnical Society standard

press-in of steel pipe pile until the gravel soil layer which(2001). Specifically, each test piles were separated by 3

is predetermined depth of GL -15.0m. The static load

times the pile diameter.

tests were carried out based on the standards of theJapanese Geotechnical Society (“Methods for vertical

3.2. Piling data
The relationships between the load and theload test of piles”) (2001). A stepwise multi-cycle

displacement in press-in process are shown in Fig. 4.

period of 30min, hysteretic load holding duration of 2min,According to Fig. 4, the both piles are inserted into theand zero load holding duration of 2min. The measured

gravel soil layer which is located at depth below

parameters were the pile top load, displacement at pile

GL-14.0m. Moreover, the press-in load increases when

top, and strain of the steel pipe. The pile tip displacement

the test piles reach the depth of GL -7.0m. This is due towas calculated by the displacement at pile top and strain

the stiff gravel soil which is located at the GL-6.0~8.0m.

of steel pipe.

loading system was employed with a new load holding- 573 -Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

Time (min)
500
10000

1500

002000

2000

4000

4000

6000

6000

Displacement (mm)Displacement (mm)

0

8000

10000
12000

1500

8000

10000
12000
14000

14000
16000

Pile top

16000

Inner soil

Pile top

Inner soil

18000

18000
(a) Test pile: No. 1
Fig. 5(b) Test pile: No. 2

Relationships between displacement and time in press-in process

3000

3000

2500

2500

2000

2000
Load (kN)

Load (kN)Time (min)
500
1000

1500

1500
1000

1000

500

Pile top

500

Pile top

Pile tipPile tip000

102030Displacement (mm)040(a) Test pile: No. 1
Fig. 6100200Displacement (mm)300(b) Test pile: No. 2

Relationships between load and displacement in load tests process

Fig. 6 indicates the relationships between load andAxial force distribution in load tests process isdisplacement at pile top and pile tip. The displacement atpresented in Fig. 7. The axial force was calculated bypile tip is the calculated value although the displacement

considering only the steel pipe; the strain of the steel pipeat pile top is the measured value. The load and stiffness

obtained from the test was multiplied with the Young’s

increase as the displacement increases. This trend ismodulus and cross-sectional area of the steel pipe. For

noticeable in test pile No.1. In test pile No. 2, the large

the both test piles, the axial force reaching the pile tip

displacement occurs in the load test. This is believed toincreased with the applied load. Furthermore, thebe due to the influence of inhomogeneity for the gravelly

difference of axial force from pile top to pile tip shows

sand layer which is located below GL -15.0m to -17.0m.

the large value. It is said that the shaft resistance- 574 -Proceedings of the First International Conference on Press-in Engineering 2018, Kochi

increases as the applied load increases. Thus, the shaft

steel pipe. If the reference displacement at pile tip is 10%

resistance contributes to the pile resistance althoughofthese piles except to calculate only the pile tip resistancedisplacement is maximum displacement when thein the practical engineering because the shaft resistancedisplacement does not reach the reference displacement),

is small between the pile and the soil.

the test pile of No. 1 showed the large bearing capacity of

thesteelpipe

diameter(i.e.,

thereference

Fig. 8 shows the relationships between the bearing

14000kN/m2, and the test pile of No. 2 showed the small

capacity and the displacement at pile tip. The bearing

bearing capacity of 3000kN/m2. This means that thecapacity was calculated by dividing the axial force

bearing capacity of test pile No. 2 is affected by the weakreaching the pile tip as shown in Fig. 8 by the area of thesoil layer which is located below the bearing stratum.

Axial force (kN)
1000
2000

3000

002244668
Applied load (kN)

1800
2000
2200
2400
2600
2800

101214

Axial force (kN)
1000
2000

0

Depth (m)Depth (m)08
Applied load (kN)

10

1800
2000
2200
2400
2600
2800

1214

1616(a) Test pile: No. 1
Fig. 7(b) Test pile: No. 2
Axial force distribution in load tests process

16000

18000

14000

16000

14000

12000

12000
Load (kN)

10000
Load (kN)

3000

8000

6000

10000
8000
6000

4000

4000

No.1
Calculated value: AIJ

2000

No.2
Calculated value: AIJ

2000
00051015Displacement (mm)20(a) Test pile: No. 1Fig. 80100200
Displacement (mm)(b) Test pile: No. 2Relationships between bearing capacity and displacement at pile tip in load tests process- 575 -300

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

However, the maximum bearing capacity in the test pile

pile which supports the existing old building was applied.

of No. 2 exhibits 15000kN/m2. The evaluation formula ofIn this study, the in-situ compression load test wereend bearing capacity as shown in Eq. (1) for the driving

carried out to confirm the bearing capacity of press-in

pile is proposed by the Architecture Institute Japan.

steel pipe pile. The following findings were obtainedq p  300 Nfrom this study.

(1)1) The construction of test piles was completed by

Where, qp: End bearing capacity for sandy soil
2

using only the basic press-in method. Thus, the water jet(kN/m ) and N : Average SPT N value near pile tip
A comparison of Fig. 8(a) with the value calculated

method was not applied in this study.

by the evaluation formula for end bearing capacity shows

was inserted at the deeper depth. And the soil plugging

that the tested piles tend to show the almost same value

effect was confirmed in the press-in process.

2) The press-in load increased as the steel pipe pilein the pile tip displacement of 0.1D or the maximum
bearing capacity. Thus, it may be concluded that the3) The creep displacement did not occur in thepress-in process.

bearing capacity at pile tip is evaluated by the calculated

4) From the results of load tests after the press-in

formula for the driven pile proposed by Recommendation

process, the bearing capacity almost showed the samefor Design of Building Foundations (2001).

value compared to the calculated value which wasobtained by the evaluation formula for the driven pile.

3.3. Productivity
This paper describes the load test to evaluate thebearing capacity for the press-in construction method.

5. Acknowledgements
We appreciate the member of work office in thisThus, two press-in piles were constructed in the site toproject when the load tests were carried out.

carry out the load tests. Two days (i.e. 16 hours = 8hours/day x 2 days) were spent to construct one press-inpile. It can be said that the press-in speed is almost

References
The Japanese Geotechnical Society. 2001. Methods for

1.0m/hours.

VerticalLoad

TestofPiles.

TheJapanese

Geotechnical Society. (in Japanese)
3.4. Encountered difficulties
The press-in load shows the large value as shown inTheArchitecture

InstituteofJapan.

2001.

Recommendationfor

Designof

Building

Fig. 4 when the steel pipe pile reaches the middle section

Foundations. The Architecture Institute of Japan. (inof gravel soil layer in the press-in process. It is needed toJapanese)

use the water jet technology to insert the steel pipe pile.
However, there is a possibility to disturb the soil plug
when the water jet method is used. Therefore, in thisproject, the water jet method is not applied to construct
the pile.
4. Concluding remarks
Pile construction forexistingstructures

tostrengthen the seismic resistance such as the seismic
isolation retrofit is subjected to constraints on theconstruction site and process. The construction of aseismic isolation retrofit for an old building was plannedin Kagawa prefecture, Japan. The compressive load
dominates because it was needed to support the dead loadof existing building. In this project, a press-in steel pipe

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