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

Evaluation of Deformation Behavior of Self-Standing Retaining Wall Using
Large Diameter Steel Pipe Piles into Hard GroundYoshiro ISHIHAMA
Senior Researcher, Steel Structures Research Lab., Nippon Steel and Sumitomo metal Corporation, Chiba, Japan
Email: ishihama.86m.yoshiro@jp.nssmc.com

Kakuta FUJIWARA
Manager, Construction Products Development Div., Nippon Steel and Sumitomo metal Corporation, Tokyo, Japan

Jiro TAKEMURA
Associate Professor, School of Environment and Society Department of Civil and Environment Engineering, Tokyo
Institute of Technology, Tokyo, Japan

V. KUNASEGARAM
Student, School of Environment and Society Department of Civil and Environment Engineering, Tokyo Institute ofTechnology, Tokyo, Japan

ABSTRACT
Steel pipe pile walls are utilized for many projects. Recently, the application of the walls has increased especially forhigh walls. In such a case, the pile diameter should be larger in order to gain high flexural rigidity and the embedded
ground should be stiff enough to satisfy the requirement for the wall displacement. A conventional method such as
Chang’s formula has been used in the design of such high walls, but several difficulties in design and construction are
arising due to the natures of larger diameter pile. With respect to the design issues, the embedment of the walls
determined by the conventional method becomes longer beyond necessity for stability, since the higher flexural rigidityof larger diameter of piles is one of the critical conditions for the minimum embedment depth. In case of harder groundconditions, the longer embedment is likely to lead to difficulties in installing piles and hereby causes extra construction
time and cost. In this paper the behavior of wall with large-diameter steel pipe piles embedded into a soft rock is
investigated by a simple analysis using a beam-spring model targeting the wall embedment length as the main
parameter. The calculated results were compared with those observed in centrifuge models. The results of this study
suggest that the conventional method could require unnecessary embedment length and then the calculation model with
Elasto-Plastic soil springs can determine more rational embedment length even if the larger diameter piles are used forretaining walls into stiff layers.
Key words: Steel pipe pile, Retaining wall, Soft rock, Frame model analysis, Centrifuge

1. Introduction
Construction projects aiming to make efficient use

performance requirement. Consequently, the diameter ofof small plots of land and mountainside road projects

The embedment length of a steel pipe in the ground ishave increased in recent years, necessitates the use of tall

determined by the larger one between the minimum

self-standing steel pipe retaining walls. As the height ofrequired embedment length and calculated length

retaining wall increases, the need is growing forsatisfying the required wall deformation, such as wall top

high-flexural-rigidity steel pipes in order to achieve wall

displacement. The minimum depth is determined by a

top displacement reduction, which is a critical structuralconventional method, such as Chang's method, using asteel pipes used for such applications becomes larger.

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

Wall top displacement

formula of the steel pipe flexural rigidity and groundrigidity. If, however, a large-diameter (e.g. greater than
2,000 mm) steel pipe is used, there are cases where theWall heightrequired embedment length becomes very large, even for
Water level(loading height)

the hard ground, because high steel pipe flexural rigidity
makes the minimum required embedment length by
Chang's or other method so large. For example, 2,000

Embedment
depth (de)mm diameter piles require embedment length over 10 m
Elasto-Plastic spring(Bi-linear)even in the ground consisting of sand and gravel layers
Fig. 1

with SPT N-value greater than 50, regardless of the wallheight. Such large embedment depth would place a very

Calculation model of Elasto–Plastic design method

Table 1. Calculation and experimental conditions
Case name
C2
C3
C4
C7
Wall thickness
1.0
2.5
2.5
2.5
(=pile diameter) (m)heavy burden on the constructor. The authors conducteda series of centrifuge tests focusing mainly onembedment in soft rock (Kunasegaram et al., 2018) andWall height (m)

9.0

12.0

12.0

12.0

1.8

9.8

3.0

2.5

1/3) compared to the minimum length determined by theEmbedment depth (de) (m)Embedment requirement by
Chang’s method (dc) (m)

6.4

16.3

11.2

11.2

conventional design method. When evaluating the

Ratio of de to dc

28%

60%

27%

22%

behavior of a retaining wall with a shorter embedment

kH (MPa)

150

56

250

250

Upper limit of subgrade
reaction coefficient (MPa)*

1.1

0.07

1.4

1.4

confirmed that stability requirements could be met even
if a substantially shorter embedment length (about 1/2 tolength by using a calculation model, it is necessary toevaluate ground behavior including the transition fromthe elastic range to the plastic range in the embedment
zone, and such behavior cannot be evaluated by applying
the beam-on-elastic-foundation theory. In this study,

Calculation Water level (m)0→6.0 0→7.0 0→8.03 0→9.8(=Loading height)

therefore, the validity of applying the Elasto-Plastic*: Rankine passive pressure determined by qu (unconfinedcompressive strength) for soft rock and ' for sand.

design method to a retaining wall with a shortembedment length was verified by comparing calculation
results based on the Elasto-Plastic design method withthe centrifuge test results. Furthermore parametric study
was made on the embedment length in the calculation.
2. Calculation model of Elasto–Plastic method
In accordance with JASPP's design manual (JASPP

Fig. 2

Horizontal subgrade reaction model

2008), the calculation model shown in Fig. 1 and theWater feeding

calculation conditions shown in Table 1 were defined.
Sand

The retaining wall was modeled as an elastic beam

Rubber bag

9,000 or 12,000mm

element whose lower end is connected to a pin-roller

Rubber bag

Water

Water

support. The reason why the elastic beam element was

1,800~3,000mm

drainageused is that under the calculation conditions assumed, themember stresses in all cases were within the elastic

Soft rock or sandrange.

35,000mm

11,500mm
Note: Values in prototype scale

For the embedment zone, a bi-linear elastic andFig. 3

perfectly plastic soil spring as shown in Fig. 2 wasExperimental setup in centrifuge

defined. The setup for the centrifuge test (Kunasegaram

A sealed rubber bag containing water was placed in front

et al., 2018) conducted for comparison is shown in Fig. 3.

of an aluminum wall secured to the embedment zone,- 154 -

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

4.0

Horizontal load ratio, Moment ratio

and an open-top rubber bag containing dry Toyoura sandwas placed at the back of the wall. The test was
conducted in two stages: excavation and loading. At the
excavation stage, the water in the rubber bag in front of
the wall was drained into a tank to let the pressure fromthe dry sand act on the wall. At the loading stage, thewater in the tank was poured into the rubber bag at theC2 Moment

3.0

C2 Horizontal load

2.0

C7, C3,C4 Horizontal load
1.0

C7, C3,C4 Moment
0.0

back of the wall so that the water level rose gradually so

0

2

4

Fig. 4process leading to the ultimate state was examined by

C3(Sand,2500mm)

Wall top displacemnt (δt)(mm)test results and past experiment results (Koda et al.,2000), respectively. In the calculation, attention was paid
to the water level, and the load condition at the end of theloading (water level = 0 m; hereinafter referred to as

14

C7(Rock,2500mm)

400

C2(Rock,1000mm)
300

200

100

C4(Rock,2500mm,"loading height") was defined as the initial condition.

3m embedded)00Thereafter, retaining wall deformation taking place in

4

8

12

Loading hight (m)Fig. 5

response to the loading height rise was calculated by theRelationship between wall top displacement andloading height

Elasto-Plastic design method, and the results thus

3. Calculation result and discussions
3.1. Yielding and influence of embedment depth

consist of water pressure and earth pressure. The earth
angle, φ, of 40°, a cohesion, c, of 0 kN/m2 and a

12

ExperimentCalculation

determined with reference to unconfined compressive

pressure was calculated by assuming an internal friction

10

500

The properties of the soft rock and sand used were

The load acting from behind the wall was assumed to8

Moment and horizontal load with loading heightobserving the deformation behavior of the retaining wall.

obtained were compared to the centrifuge test results.

6

Loading height (m)as to increase the load acting on the wall. Thus, theFig. 5 compares the calculated and measured values
showing the relationship between loading height and wall
top displacement. Case C2 and Case C3 show slightcoefficient of Rankin active earth pressure, Ka, of 0.215.

differences in initial displacement at the start of loading

In Case C3, a horizontal load corresponding to the(loading height = 0 m; upon completion of excavation in

overburden

thefront of the wall). This is thought to be because in C3

embedment layer is composed of sand. For comparison,rigidity was assumed to be constant in the depth direction,

Fig. 4 shows the horizontal load ratio and the moment

while in the test rigidity varied in the depth direction. In

ratio at each loading height. Horizontal load ratio and theall cases in the centrifuge test, displacement increased as

moment ratio are the relative values to the water level ofthe loading height rose, but the changes in displacement

0 m. As shown, the horizontal load increases more gently

were gentler than in the calculation results. In contrast, inthan the moment as the loading height increases. The

the calculation results, displacement began to increase

flexural rigidity of the wall and the embedment length

sharply at a particular loading height (5.0 m in C2, 5.8 m

used in the test were determined in advance through thein C3, 9.6 m in C4, 6.8 m in C7) showing a clear

preliminary design so that the wall top displacement at a

infection point. The reason for this is that because theloading height of 0 m would not exceed 50 mm, which issoil spring at the embedment zone is modeled as a

the limit under normal conditions used in the design ofbi-linear elastic and perfectly plastic element as ariver structures such as revetments. However, in thiscondition for calculation (Fig. 2). Deformation continues

calculation and experiment, it is not considered that theto increase even after the yielding without increase of thelimit of the minimum embedment length was determinedhorizontal resistance. It is thought that in the test, passivefrom the characteristic value by Chang's formula.

resistance increased, regardless of the type of ground

load

was

also

appliedbecause(soft rock or sand), as ground deformation in the- 155 -

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

embedment zone could increase after the yielding. From

indicate that the pivot point of rotation is located at athese results, it can be inferred that calculation by thedepth corresponding to 56% to 57% of the embedment

Elasto-Plastic design method could make it possible todepth in the soft rock cases and at a depth corresponding

estimate deformation behavior conservatively until theto about 80% of the embedment depth in the sand case.

point of inflection was reached. The load at the loading

These calculation results agree fairly well with the test

height at the point of inflection was greater than the

results.

design load under normal conditions (at a loading heightof 0 m) by a factor of about 1.6 to 1.8 in the horizontal
value by a factor of about 1.3 to 1.5.
3.2. Bending moment – deflection and failure
Fig. 6 shows bending moment distributions per unit
width in the retaining wall. Although the calculation andHeight from embedment level (m)direction, and the moment was greater than the design

15.0

test results show fair agreement in tendency, in all cases

4.0m(□)In the calculation, Rankin active condition was assumedon the earth pressure acting on the wall from thebackfilled sand from the beginning of the loading. But
the actual wall earth pressure after the excavation process

Plot :ExperimentLine :Calculation0

In the cases where the ground in the embedment
zone consists of soft rock (C2, C4 and C7), the maximum
bending moment occurred in the region just under thesurface of the embedment zone. Both test and calculation

gradually deeper. Table 2 shows the location of the pivot
point of rotation. In the centrifuge tests of soft rockground, the measured pivot points of rotation werelocated slightly below the midpoint of the embedment
length. In the sand cases with relatively deep embedment,

Loading Height=0.0m(○)
5.0

5.0m(□)
6.0m(×)0.0

3.0m(△)-5.0- 156 -

7.0m(＊)
500

1,000

1,500

2,000

2,500

3,000

C4, Rock, φ2,500mm(Embedment=3.0m)

10.0

Loading Height=0.0m(○)
6.0m(□)
5.0

9.0m(×)0.0

9.5m(＊)

3.0m(△)-5.0

Plot :ExperimentLine :Calculation

-10.0
0

500

1,000

1,500

2,000

2,500

Bending moment (kNm/m)
15.0

C7, Rock, φ2,500mm(Embedment=2.5m)

10.0

Loading Height=0.0m(○)
6.0m(□)

5.0

7.0m(×)3.0m(△)

0.0

8.0m(＊)-5.0

Plot :ExperimentLine :Calculation-10.0
0

the pivot point of rotation was located close to the lower
end of the embedded wall. The calculation results

C3, Sand, φ2,500mm

Plot :ExperimentLine :Calculation

15.0

Height from embedment level (m)where the maximum bending moment occurred became

800

Bending moment (kNm/m)by soft rock with very high rigidity (See Table 1). Inof sand (C3), as loading height increased, the location

600

10.0

0

results indicate that the retaining wall is firmly confined
contrast, in the case where the embedment zone consists

400

-10.0

Height from embedment level (m)the calculations and measurements.

200

Bending moment (kNm/m)

was needed to get the active condition. This could be a
the beginning of loading and better agreement between

6.0m(＊)-5.0

might not reach the active condition and additional load
possible reason of overestimation of bending moment in

3.0m(△)

0.0

15.0

Height from embedment level (m)calculated values were greater than the measured values.

5.0m(×)-10.0

the calculated moments at loading heights from 0.0 to 3.0
bending moment were more or less the same or the

Loading Height=0.0m(○)

5.0

the measured bending moment tended to be greater thanm. Thereafter, the calculated and measured values of

C2, Rock, φ1,000mm

10.0

500

1,000

1,500

2,000

Bending moment (kNm/m)Fig. 6

Bending moment profiles at the loadingProceedings of the First International Conference on Press-in Engineering 2018, Kochi

Pivot points of rotation at failure

C3
C4
C7

Exp

1.05

Cal

7.70

Exp

6.80

Cal

1.70

Exp

1.56

Cal

1.42

Exp

dp/de
0.561

1.8

-1.2

Inflection point

0.0

0.694

1.0

2.0

0.568
0.510

4.0

5.0

-4.8
-5.8
-1.5

C3, Sand, φ2,500mm-6.8

Plastic area

-9.8
-2.5
6.0
0.0
0.0

C4, Rock, φ2,500mm

-0.6

0.521

3.0

Loading height (hw)(m)

-0.3

0.567

2.5

-3.8
-1.0

-7.8
-2.0

-1.8
0.0

3.0

1.28

Plastic area

-0.9

-2.8

-8.8

0.786

9.8

-0.6

-1.5

0.581

-1.8
-0.5

C2, Rock, φ1,000mm
Embedded depth (m)

1.01

-0.3

Embedment
length (de)
(m)

-0.5

(Embedment=3.0m)

Embedded depth (m)

C2

Cal

-0.8

Embedded depth (m)Pivot point (dp)from embedment
level (m)

0.0

0.0

Embedded depth (m)Table 2.

-0.9

-1.2
-1.5

Plastic area

-1.8
-2.1

1.0
1.0

2.02.03.0 3.0 4.0 4.0 5.0

5.06.0

6.0
7.0

7.0
8.0

7.0

8.0

Loadingheight(hw)(m)Loadingheight(hw)(m)C7, Rock, φ2,500mm(Embedment=2.5m)-1.0

Plastic area

-1.5

-2.0

-2.4
-2.7

-2.5

-3.0

3.3. Plastic area development in the embedment

0.0

2.0

4.0

6.0

0.0

8.0

2.0

1.0

Fig. 7 show how the plastic region increases withloading height. Here the plastic region is defined as theFig. 7

6.0

5.0

4.0

3.0

Loading height (hw)(m)Loading height (hw)(m)Development of plastic region in the embedded depthwith loading

depth at which the horizontal sub-grade reaction reaches
100%

Ratio of plastic area of embedment (%)

the upper limit (See Table 1). The plasticization ratios,
defined by ratio of the thickness of plastic region to theembedment depth, are plotted to the loading height in
Fig.8. In Case C2 with smaller equivalent pile diameter(φ1,000 mm), the plasticization occurs in the shallower
region, while in Cases C4 and C7 with larger pile
diameter (φ2,500 mm), the plasticization occurs more or

C7,Rock,φ2,500mm
Embedment 2.5m

80%

C3,Sand,φ2,500mm

60%

40%

20%

C2,Rock,φ1,000mm
C4,Rock,φ2,500mm
Embedment 3.0m

0%less uniformly in the shallow and deep depth in the

0.0

2.0

4.0

6.0

8.0

10.0

12.0

Loading height (m)embedment zone. In Case C3, as can be seen, theplasticization begins and occurs to a considerable extent

Fig. 8in the shallow region until loading height reach 6.0 m atTable 3.

the stage close to the ultimate state, when theplasticization begins near the lower end of the pile.

Calculation Case
Wall thickness (m)

C2’
1.0

C3’
2.5

C7’
2.5

Comparison of the calculation results on Cases C2, C4

Wall height (m)

9.0

12.0

12.0

and C7 (soft rock cases) with that of Case C3 (sand case)

Embedment (m)

1.8→

9.7→

2.5→

reveals that in the soft rock cases the plasticization(Experiment→Calculation)

1.3~6.0

8.3~18.0

1.8~8.0

kH (MPa)

150

56

250

Upper limit of subgrade
reaction coefficient (MPa)

1.1

0.07

1.4

Loading height (m)

0.0

0.0

0.0

occurs rapidly, while in the sand case the plasticization
begins and occurs gradually from the shallow depth untiltheultimate

state

was

reached

soon

after

the

plasticization develops near the lower end of the pile.
This is thought to be closely connected to the fact that in

Ratio of plastic area of embedment
Calculation condition changing embedment

the soft rock, the pivot point of rotation was shallow andlength is reduced by about 1 m from the length used inlocated near the midpoint of the embedment depth as

the experiment, while for the conditions of Case 2 ashown in Section 3.2.

sharp increase only 0.3 m embedment depth reduction.
Fig. 10 shows the relationship between the

3.4. Horizontal subgrade reaction

embedment

ratio

and

the

amount

of

wall

top

Fig. 9 shows the effect of embedment on the wall

displacement. The embedment ratio is relative value totop displacement calculated for the conditions of Case 2,

the tested embedment length in Cases C2, C3 and C7.

3 and 7 (Table 3). For the conditions of Cases C3 and C7

Fig. 11 shows the relationship between the embedment

the displacement increases sharply as the embedment

ratios relative to embedment requirement based on- 157 -

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

600

C3’

Wall top displacement (δt)(mm)

Wall top displacement (δt)(mm)

500

400

C2’
C7’

300

Exp. C2(Rock,φ1000mm)

Exp.C3200(Sand, φ2500mm)

Exp.C7(Rock,φ2500mm)

100

Exp.C4

C7’

500

C2’

C3’
400

Exp. C2300

Exp.C3 (Rock,φ1000mm)(Sand, φ2500mm)
Exp.C7200(Rock,φ2500mm)

Exp.C4
100
0

0
0

5

10

15

0.6

20

0.7

0.8

0.9

1.0

1.1

1.2

Embedment ratio to basic case (C2,C3,C7=1.0)

Embedment (m)Fig. 10

Fig. 9 Relationship between wall top displacement and embedment

Relationship between wall top displacement andembedment ratio

Chang's method and normalized wall top displacementby the wall height.
As shown in Fig. 10, in Case C3 (embedded inC7’sand), the displacement begins to increase sharply when

C2’

C3’

Exp. C2(Rock,φ1000mm)

the embedment ratio decreases by about 10%. In Cases

Exp.C3(Sand, φ2500mm)

C7 and C2, the displacement begins to increase after the
Exp.C7

embedment ratio decreases by about 20% to 25%. From
the results on(Rock,φ2500mm)

the soft rock (i.e. hard ground) cases

Exp.C4

shown in Fig.11, it can be confirmed that no significant
change in the wall displacement is obtained over acertain embedment. This embedment can be considered

Fig. 11

Relationship between wall top displacement and relativeembedment to the required one by conventional method

as a critical depth, over which wall behaves similar to theone with semi-infinite length. These critical lengths areorder to enhance the accuracy of retaining wall behavior

about 30% to 40% of the embedment length required byestimation, it is necessary to refine the modelingthe conventional method. In the sand case, however, theapproach by, for example, expressing ground behavior

criticalwith a tri-linear model instead of a bi-linear model.

embedment length is about 60% to 70% therequired embedment length. This indicates that theminimum embedment

length requirement by the

5. Acknowledgements

conventional method based on Chan's formula could be

The authors gratefully acknowledge the invaluable

an over conservative in the assessment of wall

advice and guidance provided by the members anddisplacement for the large diameter steel pipe wall

advisers of the IPA TC1 (Committee on Application of

constructed in the stiff ground, like soft rock.

Self-retaining Tubular Pile Wall to Stiff Ground) inconnection with the preparation of this paper.

4. Concluding remarks
・The plasticized length of embedment calculatedby the Elasto-Plastic design method using a soil spring ofReferences
Kunasegaram, V. et al. 2018. Behavior of self-standing

a bi-linear elastic and perfect plastic element is not morehigh stiffness steel pipe sheet pile walls embedded

than 50% under a horizontal load and a moment loadin soft rocks. Proceeding of the 1st International

greater than those assumed in design for normal load

Conference on Press-in Engineering.

conditions by a factor of up to about 1.6 to 1.8 and by aJapanese Association for Steel Pipe Piles. 2008. Deignfactor of up to about 1.3 to 1.5, respectively. If applied

manual of self-standing steel sheet pile wall. Try, co.

loads are within those ranges, retaining wall behavior canltd. (in Japanese)be evaluated by the Elasto-Plastic design method.

Koda, M. et al. 2000. Modeling and evaluation of p-y

・Under larger loads, the amount of displacement
tends to be overestimated (i.e. to be on the safe side). In- 158 -

curves of single pile in sand. Journal of Japan
Society of Civil Engineers, pp. 191-207.