Volume 6, Issue 1 March 2021

Report12th IPA Press-in Engineering Seminar in Tokyo 2020

(1) TC1 “Application of Cantilever Type Steel Tubular Pile Wall embedded to
Stiff Grounds”
Jiro Takemura
Associate Professor, Tokyo Institute of Technology
Director, IPA / Chair, TC1
IPA-Technical Committee (TC)1 (Chaired by Dr. Jiro Takemura, the author) was set up in 2017 to figure out the issues forfurther application of cantilever type steel tubular pile wall embedded to stiff grounds and establish a rational design
procedure of embedded cantilever steel tubular pile wall as the final goal. This report overviews the research activities
done by TC1, i.e., case study, physical modeling, numerical analyses, parametrical study by design models, which were
presented in the seminar.

1. Background and objectives
Thanks to the innovative pile installation method, like rotary cuttingpress-in method (e.g., Gyropress), the applicability of steel tubular
pile walls (STPW) retaining systems has increased significantly forvarious structures (road, harbor, railway) and objectives, not only
ordinary retaining structures (Miyanohara et al., 2018, Suzuki andKimura, 2021), but also restoration, rehabilitation and reconstructionof disaster areas (Takada, 2016, He, 2018). The installation ability oflarge steel tubular pile (STP) into very stiff grounds is a criticaladvantage of the rotary cutting press-in method. The combination oflarge diameter and high rigidity STP, and the stiff embedded groundwidening
enables to construct cantilever type walls with large retained height(Fig. 1). By the combination, the wall top displacement caused by theFig. 1. Application of STPW (H=13m, lp=23m)
wall bending deflection and the wall rotation in the embedment canfor road widening projects. (Miyanohara et
be controlled below the required displacement. However, the current
al.2018)
design method of embedded cantilever wall has been developed forthe relatively flexible steel sheet pile wall into soft grounds for small
retained height (e.g. less than 4m, JRA (1999)). Therefore, simple
application of the current design method to the cantilever type STPW
embedded in stiff grounds (Fig. 2) may require unnecessary
embedment depth, or increase a risk of failure caused by theunexpected performance of the wall. Several concerns can bepointed out such as,1) The minimum embedment depth (d0) requirement using
characteristic value (β), such as d0≧3/β (ASP, 2009; IPA,2014&2016)
should be verified, as it is based on long flexible wall behavior in an
infinite uniform elastic media, which conflicting the rigid nature ofdelarge diameter pile;
Stiff layer2) As the pile diameter (Φ) increases, the relative embedment depth(de/Φ) and wall thickness and diameter ratio (t/Φ) tend to decrease.
Fig. 2. Cantilever STPW embedded in stiff
Furthermore, near the surface of stiff ground, especially rock, theground and conditions used in the design.
stress concentration could occur on the front side of tubular pile.
These particular conditions could enhance local and 3D behavior,
which is not taken into account in the conventional 2D analytical/numerical models;
3) High confinement or fixity of the piles by the stiff ground could generate the large resilience of pile, which affects thewall-soil interaction, the wall pressure from the retained soil, and the residual wall displacement after the temporalloading event, e.g., earthquake.
To answer the above-mentioned concerns and establish a rational design procedure, four working groups were created15

Volume 6, Issue 1 March 2021
in TC1 with several tasks as shown below. Note: some findings related to the tasks underlined were presented in theseminar.
- WG1 on design method:
Tasks 1: to analyze present design methods, and identify the issues such as embedment depth, soil characteristics,
seismic design.
Task 2: to analyze the design procedure of existing large diameter tubular steel pipe walls.
Task 3: to propose a new rational design method of large diameter tubular steel pipe wall including seismic design.
- WG2 on centrifuge model tests:
Task 1: to clarify mechanical behavior of large diameter tubular steel pipe wall in stiff ground under static loads.
Task 2: to analyze influences of critical conditions such as embedment depth, ground stiffness and strength on thewall behavior.
Task 3: to discuss difference between the behavior of actual structures and that predicted by the simplified designmodel.
Task 4: to simulate the deformation and failure behavior under earthquake loading.
- WG3 on numerical analyses:
Task 1: to verify and calibrate 3D FEM method by centrifuge modeling.
Task 2: to analyze the detail and local behavior of wall and ground, which cannot be observed in the centrifuge model
tests.
Task 3: to analyze the influence of parameters on behavior of large diameter tubular steel pipe wall using simple flame
analysis and 2D FEM.
- WG4 on case study of construction:
Task 1: to collect construction cases with design details as many as possible.
Task 2: to collect the data observed during and after construction, if available, with the collaboration of TC2.
Task 3: to identify the concerns in the actual construction, in particular on the cost and time.

Among the records of which design procedure were confirmed, theminimum embedment depth (d0≧3/β) were adopted especially forthe road construction projects. Although the number of applications
has increased significantly, very limited record is available on themonitored behavior of the wall during and after the construction. The
data related to serviceability limit state (SLS) and the ultimate limit
state (USL), and the wall performance from SLS and ULS under various
actions, e.g., static and seismic loadings are critically important torationalize the design procedure.
16

Number of projects

Pile dimeter, Φ [mm]Pile length, lp [m]Number of projects

Since the Gyropress method was developed by Nippon Steel and
GIKEN LTD and first applied in 2004, it has been applied more than 400
projects till 2019 (Hirata & Matsui, 2016; IPA, 2019; Suzuki & Kimura,2021). Fig. 3 shows some summary of the case records, giving thenumber of projects in terms of pile diameter, pile length with the joint
number and maximum converted SPT N-values with the site groundtype. As for the pile diameter, 1m piles have been most commonlyused about 40%, but the large diameter piles over 1m have been used
more than 30% with 2.0m maximum. The project shown in Fig. 1 is an
example of the 2.0m pile wall. While for the pile length, the mostfrequently used length is about 18m and very long piles over 30m wereconstructed. The number of welding joint depends on the site
condition, such as upper space clearance, and the required pile length.
The most of piles have been embedded in the ground with maximum
N value over 50. About 20 % of recorded cases, the walls wereconstructed in gavel or rock ground with the converted N-value of 300
or higher. The application of large diameter pile in the stiff grounds forlarge height retaining walls is an increasing trend especially for the sitewith severe conditions, such as spatial restriction, low noise andvibration requirements, and short construction period.

Number of projects

2. Case study

Max converted SPT N-value

Fig. 3. Summary of case records of STPW
installed by rotary cutting press-in method.
(Suzuki & Kimura, 2021)

Volume 6, Issue 1 March 2021
3. Behavior of large diameter STPW investigated by physical models and numerical models
To fill the gap or limitation of field records and investigate the critical behavior of large diameter STPW embedded in stiff
grounds, several series of centrifuge model tests and numerical analyses have been carried out to discuss the effects ofcritical conditions, such as embedment depth, and ground conditions, 3D effect of tubular pile wall, and static anddynamic loading.
(1) Centrifuge model study
Three series of centrifuge model tests were conducted, 1) Simulation of excavation and loading using cantilever plate wall
embedded in soft rock (Kunasegaram et al., 2018 and Kunasegaram & Takemura, 2019), 2) Horizontal loading tests tosingle STP pile and STP wall socketed in a soft rock with and without overlying sand, and 3) Dynamic loading tests to STPW
in a soft rock. The main parameter studied is the socket depth to the stiff layer (dr,). For the uniform soft rock ground, thewall embedment depth (de) is equal to dr, while for the two-layers ground de is the sum of the top layer depth and dr(Fig. 2). To generalize the embedment or socket depth, normalized embedment depth (deβ or drβ) were estimated. The
de and dr adopted in the centrifuge tests were all far below the minimum embedment depth (d0=3/β).
a) Series I model: 2D retaining wall
Model test setup shown in Fig. 4 can simulate an excavation process and an extreme loading for a cantilever type retaining
wall in a geotechnical centrifuge. In other words, it can model the high stiffness wall behavior with large retaining heightfrom the serviceability limit state (SLS) to the ultimate limit state (ULS). In this series, several centrifuge model tests wereconducted on plate walls with per width flexural rigidity (EI) equivalent to STPW with Φ=2.5m and 1.0m, embedded insoft rocks and sand (Kunasegaram et al., 2018; Kunasegaram & Takemura, 2019). Observed wall top displacements androtations of 12m high rigid walls (Φeq=2.5M) with de=2.5m (deβ=0.86) and 3.0m (deβ=1.05) are compared in Fig. 5. As aunified loading index in the two processes, the moment load applied at the excavation bottom is used in the horizontal
axis. Though deβs are much smaller than the minimum requirement (d0β=3), the wall displacements by the excavation
were well controlled below the target allowable displacement (δt=50mm, 0.4% wall height). Assuming ULS at δt=5%H,
the safety margin at SLS against the failure are about threefold in terms of the moment load. Backward slip failure wasconfirmed for de=2.5m wall after the test, but for de=3.0m wall, the embedment portion was securely fixed by the softrock, preventing the catastrophic failure. A half meter increment of the embedment for this case can significantly increase
the safety of the wall.
RW1: de=2.5m, deβ~0.86, RW2: de=3.0m, deβ~1.05

Fig. 5. Effect of embedment depth observed in Series I
centrifuge tests (Kunasegaram & Takemura, 2019).

Fig. 4. Centrifuge model test setup on rigid
plate wall (Kunasegaram & Takemura, 2019).

b) Series II model: parametric study on rock sock depth and ground conditions
To investigate the effect of embedment depth under clear loading conditions, lateral loading tests were performed for
Φ=2.0m single STP (SP) and STP wall (RPW) socketed in the soft rock with and without overlying sand. The load –displacement curves are compared in Fig. 6. Details of the tests are given in Kunasegaram et al. (2019), but the test
conditions, e.g., ground conditions and socket depth with normalized depth [dr, drβ] are shown in the figure. From Series
II tests, several findings are derived. 1) Lateral resistances of wall and single pile increase with dr, but the trend of theincrease depends on imposed displacement, ground condition, and types of failure (ground failure or pile failure, Fig. 7).
2) Optimum socket depth, over which the effect of dr is insignificant is much smaller than 3/ β. 3) As shallow rock part
mainly resists to the horizontal load in the early stage of loading, the effect of socket depth may not be so apparent.
17Volume 6, Issue 1 March 2021
However, once the rock initiates yielding at the shallow depth, the influence of socket depth becomes eminent. 4) The
single piles have higher lateral resistance per unit width than the walls both for the initial subgrade reaction and theultimate resistance. 5) The effect of socket depth and the difference between the pile and the wall are more significant
for the single soft rock layer than the sand/soft rock layers. 6) In the two layers, the complicated interaction between
pile/wall and soil determines the residual displacement and lateral stiffness of wall. The above findings are all criticallyconcerned to the issues for the rational design procedures, such as, critical embedment depth, non-linearity of p-y curves,and accumulation of residual displacement of the wall subjected to various loading history.
2000[4m, 2.1]

SP in soft rock

SP in sand/soft rock

Lateral(P(PLateralload
loadL) (kN/m)
L) (kN/m)[4m, 2.1][2m, 1.1]

1500[3m, 1.2] [3m, 1.6]

[3m, 1.6]

1000

RPW insand/soft rock

[4m, 1.6]

RPW in soft rock

[3m, 1.2]500[2m, 1.1][dr,drβ],
0

0

200

400

SP in sand (de=6.5m)
Difference of PL at large δt

600

800

1000

Loading
direction[4m, 1.6]δtPLCompressive
failurehL=6.5m
SP-SR-2*
drSP-SR-3
SP-SR-4
Soft rock
RPW_SR_3
δRPW_SR_4
PLthL=6.5m
SP_MS_6.5
SP_MS_SR_2
deds =6.5m
SP_MS_SR_3
dr
SP_MS_SR_4
RPW_MS_SR_
Sand/softrock
RPW_MS_SR_

1200

1400

Wall/ Pile
displacement) (mm)
Wall/Pile
toptopdisplacement(δ(δL)t (mm)Fig. 6. Effect of embedment depth observed in Series
II centrifuge tests (Kunasegaram et al., 2019).

Sand surface

Backward
slip failure

Pilefailure
failurepile(a) Wall in soft rock: dr=4m(b) Wall in sand/SF: dr=4m

Fig. 7. Failure mode observed in wall loading in Series
II centrifuge tests (Kunasegaram et al., 2019).

Normalized cumulative wall top
displacement after shaking [δt/H][%]c) Series III model: Dynamic loading on STP retaining wall embedded in soft rockA 12m high cantilever walls embedded in the soft rock with backfill sand,δt
Dry shaking
which is similar to the model in Series I, were made using the same STP
5
Wet shaking
H=wall in Series II. Several dynamic loadings were applied to the models
4.5
Water feeding
12m
sand
4
with different embedment depths (Shafi et al., 2021). In the loadingde3.5
soft rocksequence, water was fed in the backfill to rise the water level. The
3accumulated wall displacements observed were plotted against the
2.5
Case 3, de=2.5m
cumulative Arias intensity for the wall with de=2.5m (drβ=1.2) and 3.0m
2(drβ=1.6) in Fig. 8. Similar to Series I, the dynamic stability of the wall is
1.5
Case 1, de=3.0m
1
significantly increased by a half meter increase of the embedment into
0.5
the soft rock. It was also found that high confinement or fixity of the piles0by the stiff ground could generate the large resilience of pile, which
0
20
40
60
80
100
120
Cumulative arias intensity, A [m/sec]
resulted in the increase of wall earth pressure after shaking. This pressure
should be considered as an action to examine the structural safety of theFig. 8. Effect of embedment depth underpile and wall residual displacement after the earthquake.
dynamic loading Series III centrifuge tests(Shafi et al., 2021).
(2) Numerical and analytical studies
Though the centrifuge model tests could provide valuable results on themechanical behavior of the cantilever type STPW embedded in stiff
grounds, there are still many remaining concerns which might affect thewall behavior or be critical in the rational and safe design procedure,such as plugging of rock in the socket part, local 3D effect of deformationof thin wall tubular pile. In particular, the pile structural failure with local
buckling (Fig. 7) could be a common ULS for the wall relatively large de,even deβ are well below the minimum requirement (d0β=3). Using 3D
FEM, Ishihama et al. (2019) investigated the plugging effect, the local
stresses at the pile tip, and pile deformation at the pile tip and the rocksurface, and found that the plugging effect and 3D effects could not
significantly affect the overall behavior of laterally loaded STPW in softrock. TC1_WG3 further conducted 3D and 2D FEM analyses for the wallmodel embedded in the soft with dr=4.0m (Centrifuge test Series II). In
the 3D analysis, the actual tubular pile was modeled by solid element,
while in the 2D analysis, the pile was modeled by a beam element withequivalent EI of the actual STP wall. The load – displacement curves
18

Lateral load PL (kN/m)i

2D FEM (PW: beam element)
Yielding

3D

3D FEM (PW: solid element)
Centrifuge test

Yielding(back(tension)side)

Yielding(front (compression)side)

Wall top displacement δt (mm)Fig. 9. 2D and 3D FEM results of laterally
loaded STPW embedded in soft rock withcentrifuge model result: dr=4m.

Volume 6, Issue 1 March 2021

The top wall displacements analyzed by subgrade reaction method usingbi-linear p-y relation is plotted against to the relative embedment depth
to the minimum requirement (deβ/3) in Fig. 10. This is the common
analytical model for the design of retaining wall called “elasto-plastic
analysis” in Japan (JRA, 1999). The wall and ground conditions modeledin the centrifuge test Series I were assumed in the analyses, which areindicated in the figure with the centrifuge experiment results. The
elasto-plastic analysis could predict the wall defection with reasonableaccuracy. From the figure the critical embedment depth, over which thedisplacement markedly increases can be confirmed. For the soft rockcases, the critical depths are much smaller than the minimum required
depth (3/β), 20 to 30%, especially for the large diameter and highretaining wall. While for sand case the critical depth is about 60% of 3/β.
These trends of the de effect were also confirmed by rigid-plastic FEM(Mochizuki et al., 2019).

4. Toward rational design procedure and practiceNormalized wall top displacement δt /Hobtained by the 3D and 2D analyses were compared with the centrifuge test result in Fig. 9. At the relatively small
displacement less than 50mm, which corresponds to allowable value or SLS, no significant difference can be seen in the
3D and 2D models. Over this SLS, the resistance of 2D model becomes larger than that of the 3D model. This can be
attributed to local yielding of the ground and pile due to stress concentration at the front toe near the rock surface andback toe near the pile bottom. The analyses overestimate the ultimate resistance, as the FEM cannot simulate the crack
formation and back slip failure (Fig. 7). However, from Fig. 9 it can be said that the 2D model can be applied without
specific consideration of 3D effects of STPW for the displacement prediction till the SLS.
Soft rock

C7’
H=12m
Φ=2.5mt=25mm3/β=11m

C2’
H=9m
Φ=1.0mt=10mm3/β=6.4m

Exp: de=1.8m

Toyoura sand
Dr=80%
C3’
H=12m
Φ=2.5mt=25mm3/β=16m
Exp: de=9.8m

Exp:
de=2.5m
de=3.0m
Relative embedment depth to minimum requirement: deβ/3

Fig. 10. Result of subgrade reaction
methods using bi-linear p-y relation(Ishihama et al., 2018).

Current design practice for the embedded cantilever wall using the minimum embedment depth (d0=3/β) adopted in thesimple design method (ASP, 2009; IPA, 2014&2016) is based on the assumption of infinite beam on the uniform linear
elastic subgrade. But the subgrade reaction of the pile and wall are very non-linear and change with depth. As its simplicity,
this simple method could be beneficial for the small height flexible sheet pile wall. However, in the application of STPW
in stiff grounds this minimum embedment depth requirement tends to be over conservative and not economical, andeven inconsistent with limit states design concept, especially for the high retaining height and large diameter STP wall.
Structural pile failure becomes dominant ultimate limit state over a certain embedment depth (de). This can be considered
as a critical depth, over which no significant contribution of the de increase can be expected for ULS, and this criticaldepth might be much less than the minimum required embedment depth. The common practice using minimum
embedment depth in the simple method should be considered as an option, not requirement and the required
performances of the limit states, e.g., SLS and ULS should be examined by reasonable methods, considering the nonlinearity of soil – structure interaction.
Combination of elasto-plastic analysis and limit equilibrium method should be a common design practice for the large
diameter STPW in stiff ground. However, in the application of the non-linear subgrade reaction method, there are several
issues remained for the further research. For examples, modeling of p-y relation, including the evaluation of theparameters used in the p-y curves. The estimation of modulus and strength of soil/rock is key issues for the very stiff
ground with very large STP-N values. The variability of ground conditions are also major uncertainties in the design andconstruction of the wall. Especially as the depth of stiff layer could significantly control deformation as shown in Fig. 6.
The data recorded in the press-in process of the pile could contribute to the reduction of the effect of uncertainty andeconomical and safe construction (Suzuki et al., 2021a and 2021b). To establish the more reliable methods, accumulating
field data is of critical importance, as reliable database on site ground conditions, wall specifications, and wall behavior
during and after the construction should be the sources for identifying the critical issues and for updating the design
method.
As for the earthquake loading, two issues can be pointed out, one is dynamic earth pressure and the other the residual
earth pressure after the loading. Even for the large flexural rigidity of the wall with secured fixity by the stiff ground, a
relatively large dynamic wall deflection could be generated in the cantilever wall, which might cause the seismic earthpressure different from the one on the rigid wall and increase the residual earth pressure. They are closely related to thewall stress and residual displacement. To have answers on these issues, the further researches should be performed by
the physical and numerical studies and field study of the wall after the strong earthquake.
The outcome derived from the TC1 activity will be summarized and reported as a form of final report soon.
19Volume 6, Issue 1 March 2021
5. References
Association of Steel Pile (ASP), 2009. Design Manual of Self-Standing Steel Sheet Pile Wall. (in Japanese).
He, H., 2018. Gyropress (Rotary Cutting Press-in) method in Disaster Recovery Project (Kagoshima Prefecture, Japan), IPA
Newsletter, Vol.3, No.1, pp.11-15.
Hirata, H. and Matsui, N., 2016. Expanding Applications of the Gyro-press Method, Nippon Steel & Sumitomo Metal
Technical Report, No.113, 42-48.
International Press-in Association (IPA), 2014. A handbook of Steel Tubular Pile Retaining Wall Constructed by Gyropress(Rotary Cutting Press-in) Method.
International Press-in Association (IPA), 2016. Press-in retaining structures: a handbook (First edition)
International Press-in Association (IPA), 2019. Press-in Piling Case History (Volume 1)
Ishihama, Y., Fujiwara, K., Takemura, J., and Kunasegaram, V., 2018. Evaluation of Deformation Behavior of Self-Standing
Retaining Wall Using Large Diameter Steel Pipe Piles into Hard Ground. Proceedings of 1st International Conference on
Press-in Engineering, Kochi, pp. 153-158.
Ishihama, Y., Takemura, J., and Kunasegaram, V., 2019. Analytical evaluation of deformation behavior of cantilever typeretaining wall using large diameter tubular piles into stiff ground, Proceedings of the 4th International Conference on
Geotechnics for Sustainable Infrastructure Development, Hanoi, pp. 91-98.
Japan Road Association (JRA), 1999. Road Earthwork, Guideline for the Construction of Temporary Structures, (inJapanese)
Kunasegaram, V., Takemura, J., Ishihama, Y., and Ishihara, Y., 2018. Stability of Self-Standing High Stiffness-Steel Pipe Sheet
Pile Walls embedded in Soft Rock. Proceedings of 1st International Conference on Press-in Engineering, Kochi, pp.143152.
Kunasegaram, V., Shafi, SM, Takemura, J. and Ishihama, Y., 2019. Centrifuge model study on cantilever steel tubular pilewall embedded in soft rock, Proceedings of the 4th International Conference on Geotechnics for Sustainable
Infrastructure Development, Hanoi, pp. 1045-1052.
Kunasegaram, V. and Takemura, J., 2019. Deflection and failure of high stiffness cantilever retaining wall embedded insoft rock. International Journal of Physical Modelling in Ge-otechnics, https://doi.org/10.1680/jphmg.19.00008
Miyanohara, T., Kurosawa, T., Harata, N., Kitamura, K., Suzuki, N., and Kajino, K., 2018. Overview of the Self-standing andHigh Stiffness Tubular Pile Walls in Japan, Proceedings of the First International Conference on Press-in Engineering,
Kochi, pp. 167-174.
Mochizuki, K., Isobe, K., Takemura, J., and Ishimhama, Y., 2019. Numerical simulation for centrifuge model tests on thestability of self-standing steel pipe pile retaining wall by Rigid Plastic FEM. Proceedings of the 4th International
Conference on Geotechnics for Sustainable Infrastructure Development, Hanoi, pp. 481-488.
Shafi, S, M., Takemura, J., Kunasegaram, V., Ishihama, Y., Toda, K., and Ishihara, Y., 2021. Dynamic behavior of Cantilever
Tubular Steel Pile Retaining Wall Socketed in Soft Rock. Proceedings of 2nd International Conference on Press-in
Engineering, Kochi (to be published).
Suzuki, N. and Kimura, Y, 2021. Summary of case histories of retaining wall installed by rotary cutting press-in method,
Proceedings of 2nd International Conference on Press-in Engineering, Kochi (to be published).
Suzuki, N., Nagai, K, and Sanagawa, T., 2021a. Reliability analysis on cantilever retaining walls embedded into stiff ground(Part 1: contribution of major uncertainties in the elasto-plastic subgrade reaction method), Proceedings of 2ndInternational Conference on Press-in Engineering, Kochi (to be published).
Suzuki, N., Ishihara, Y. and Nagai, K, T., 2021b. Reliability analysis on cantilever retaining walls embedded into stiff ground(Part 2: construction management with piling data), Proceedings of 2nd International Conference on Press-in
Engineering, Kochi (to be published)
Takada, H., 2016. Restoration and Reconstruction of Kyu-Kitakami River, IPA Newsletter, Vol.1, No.1, pp.3-5.

20