Volume 3, Issue 1 March 2018

ReportActivities for the Reinforcement of Existing Foundations
Tomoyuki Suzuki
Group Leader of Steel Pipe Sheet Pile Foundation Team,Technical Committee of Road and Railway,
Japanese Technical Association for Steel Pipe Piles and Sheet Piles
Much infrastructure, including roads, bridges and rivers, had been constructed during a period of rapid economic growth
in Japan. It is thought that the age-related problems of these structures will become more tangible and accelerated, andmeasures to mitigate them are imperative. According to the Ministry of Land, Infrastructure, Transport and Tourism(MLIT), the percentage of road bridges over 50 years after construction was about 18 % in 2013 and is expected to beabout 65 % in 2033. Under these circumstances, MLIT began to issue a “basic infrastructure life elongation plan” and tocarry out intensive examinations and inspections. Accordingly, they have started taking measures such as renovation andreinforcement.
In response to this trend, the Japanese Technical Association for Steel Pipe Piles and Sheet Piles (JASPP) has conductedvarious studies for the reinforcement of existing foundations. As one of the main activities, utilization of steel pipe sheet
pile foundation will be introduced in the next sections.
1．Characteristics of Steel Pipe Sheet Pile Foundation
The structural characteristics of steel pipe sheet pilefoundation (Fig. 1) is that steel pipe sheet piles are
installed in an enclosed form of circle, oval orrectangle, and the rigidity of the structure is increasedby filling materials such as concrete mortar in the P-P
shaped interlock. Features from the behaviouralcharacteristics of wall structures such as those madeof steel pipe sheet piles are that they depend mainlyon the horizontal resistance of the ground, while thesteel pipe sheet pile foundation depends on verticalresistance from the pile toe resistance and skinfriction as well as horizontal resistance. From thisviewpoint, the behaviour of steel pipe sheet pilefoundation is closely related to the ground condition,
and a more careful ground evaluation and morereliable construction are both required to securehighly reliable foundation structures. Therefore,
several evaluations of the foundation performanceFig. 1 Schematic view of steel pipe sheet pile foundation
including on-site loading test have been carried out,that is simultaneously used as temporary cofferdam
and standardized application methods have beenshown only for structures and construction methods of which the execution management methods are specified in theJapanese Bridge Standard and all that. For the steel pipe sheet pile foundations, the pile driving method or foot protection
method with inner excavation is currently regarded as the standard construction method, whereas the Press-in Method
and the Press-in Method assisted with water jetting have not been generally used. For these two methods, it is prescribedthat the pros and cons of their use and the design application be evaluated by carrying out construction tests and loading
tests at each construction site. From the advantage that the cofferdam to build a bridge pier can be co-used, the steel
pipe sheet pile foundation has shown itself to be highly economical as a foundation construction method in water areas,
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and its application has increased. To further increase its use, it is indispensable issue to develop a construction methodthat is highly applicable and reliable, so that the method can cope with many different ground and construction conditions.
2．Activities for Reinforcement of Bridge Pier Foundation
Reinforcement methods of existing foundations may be divided into those increasing bearing capacity of foundation, e.g.,
by ground improvement, and those increasing bearing capacity structurally. Typical examples of the latter case maybe amethod to add foundation piles by enlarging footing, and steel pipe sheet pile foundation extension method 1), 2). In thesteel pipe sheet pile foundation extension method, steel pipe sheet piles are installed in such a way as to enclose anexisting foundation, and a combined footing structure is formed by connecting the piles with the existing foundation
using pile caps and so on. Table 1 shows main past records by the steel pipe sheet pile foundation extension method,while Fig. 2 depicts a reinforcement case. The reinforcement cases by the steel pipe sheet pile foundation extension
method have increased since the restoration works of the Great Hanshin Earthquake Disaster. As described earlier, thesteel pipe sheet pile foundation has an advantage that it can be used as a temporary cofferdam in reinforcement woks inwater. In addition, there are key advantages of the Press-in Method, such as construction conditions of limited overhead
clearance under bridge girders, and piling with limited harmful effect on existing foundations.
Table 1 Main reinforcement records by steel pipe sheet pile foundation extension method

Location
In Japan

Existing
foundation

Reason forreinforcement

Steel pipe sheet piles
OD(mm)/Length(mm)OD of coffer
damConstruction
methodMiyazaki

Caissonfoundation

Wash out

612.8/25500

Oval11835 x 7593

Inner excavation +pre-boring

Wakayama

Caissonfoundation

Upper work
extension

600/10000

Oval
16254 x 6834

Hyogo

Caissonfoundation

Aseismic
reinforcement

600/15500

Circular
7634 x 7634

Hyogo

Caissonfoundation

Aseismic
reinforcement

600/13500

Circular
11635 x 7593

Caissonfoundation
Directfoundation

Aseismic
reinforcement

600/44600

Wash out

600/8500

Hyogo

Caissonfoundation

Bridgewidening

Hyogo

Caissonfoundation

Osaka

Inner excavation(cement milk)

Circular
8711 x 8711
Oval
22078 x 11600

JV(Vibro with WJ* )Inner excavation(cement milk)

600/21500

Circular
14821 x 14821

Press-in Method(with WJ* )Wash out

600/14000

Rectangular
14460 x 7200

Inner excavation

Caissonfoundation

Wash out

600/28500

Oval
15216 x 6834

Press-in Method(with WJ* )NaraCaisson
foundation

Upper work
extension

600/20500

Circular10158 x 10158--TokyoPile foundation

Aging

1000/36500

Oval
20079 x 42539

Press-in Method

Hyogo
Hyogo

*WJ: Water jetting

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Unit: mmExisting foundation: Caisson foundation Circular 10000 x 10000 x L21500
Reason of reinforcement: Reinforcement of the foundation for the increase in the vertical load after widening thebridge
Specification of the steel pipe sheet piles: 800mm dia. x t12 x L21500 Circular 14821x14821
Installation method: Press-in associated with water jetting

Fig. 2 Reinforcement example by the steel pipe sheet pile extension method
On the other hand, from a structural design viewpoint, a clearer understanding of the behavior has been regarded
important in Japanese bridge foundations. Combined foundations, in which foundations with different resistantcharacteristics are combined, have not been generally used. For this reason, there are no unified design methods for thesteel pipe sheet pile foundation extension method. In the actual design, evaluation has been carried out in each case. It
seemed often the case that the design for the actions arising during earthquake was performed in such a way that only
steel pipe sheet pile foundation would carry the seismic load, because not enough was understood regarding theresistance exhibiting ratio between the existing and extended parts, and on the stability of the structure as a combined
foundation. Consequently, in consideration of more economical foundation reinforcement works, establishment of arational design method became an issue, in which the load exhibiting ratio between the existing and extended portions
is clarified. As a result, JASPP organized a study group to build a design method of the steel pipe sheet pile foundation
extension method, and to develop more rational structures. The study group conducted centrifuge model experiments
and a 3-D FE-analysis. In addition, based on the results of the study, applicability of the 2-D analysis was examined. All
the study summary will be described in the following sections.
2.1 Centrifuge Model Test
Centrifuge model tests were carried out for 3 models, paying attention to the bonding structure of the steel pipe sheet
pile foundation for existing caisson foundations: 1) rigidly fixed structure with pile caps; 2) semi-rigidly fixed structurewith pile caps; and 3) unconnected structure without pile caps. Schematic diagrams of rigidly fixed and semi-rigidly fixed
structures are observed in Fig. 3a and 3b, respectively. The following behavioral characteristics became clear:1) Rigidly fixed structure
From the beginning of loading, large reinforcement effect, horizontal yield strength of combined foundation divided bythat of existing caisson foundation only, is shown. In the end, horizontal yield strength more than about 2.7 times theoriginal value was obtained, compared with the situation before reinforcement by extension.

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2) Semi-rigidly fixed structure
Horizontal resistances at the beginning and the end of loading increased by 60 % and more than 20 %, respectively.

a）Rigidly fixed structureb）Semi-rigidly fixed structure

Fig. 3 Schematic view of pile cap connection method
3) Without pile caps
Effect by extension reinforcement was not noticeable.
From the result of the centrifuge model experiments, it may be concluded that the rigid fixing of extended structure withthe existing foundation is the most effective connection method, and that the semi-rigidly fixed structure can be rational
due to its simple connection structure, depending on the level of reinforcement effect required.
2.2 Three-Dimensional FE-analysis
To verify the reinforcement effect on real structures, a 3-D FE-analysis was conducted. The following points were clarified:
1) From the simulation analysis of the centrifuge model experiment, analytical conditions suitable for the steel pipe
sheet pile foundation extension method were identified, and it was confirmed that the reinforcement effect could bequantitatively evaluated in the 3-D FE-analysis.
2) Though the increment ratio in horizontal yield strength may decrease for both rigidly fixed and semi-rigidly fixed
structures as displacement increases, an increase in the yield strength of 1.5 to 2.0 times the original value was obtained.
In the cases where pile caps were not used, the increase in horizontal yield strength was about 1.1 times the originalvalue, not as good a reinforcement effect as in the centrifuge model test.
2.3 Two-Dimensional Analysis
To build a more simplified design method in lieu ofa 3-D FE-analysis, 2-dimensional simulation analysis
was carried out using real structural models, and its
applicability was examined. The following points
were clarified:1)
Load-deformation curves are compared
between the 3-D FE-analysis and the 2-D analysis inFig. 4. It may be seen in the figure that the loaddeformation curves are generally in goodagreement with each other. They are in good
agreement, especially in the quasi-elastic range,
where the horizontal seismic intensity is small.
After the yield point, deformation in the 2-Danalysis is somewhat larger.
Fig. 4 Load-deformation curves: comparison of 2-D and 3-D analyses
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2) As shown in Fig. 5, distributions of section force of the steel pipe sheet piles are generally consistent with each other,though there are some discrepancies between the two. There is a tendency that the absolute value of the section force
is larger in the 2-D analysis result.

A）axial force distributionB）Bending moment distribution

C）Shear force distribution

Fig. 5 Distribution of section forces exerted on steel pipe sheet pile
From the results obtained above, it may be concluded that the 2-D analysis can simulate relatively well the behavior of
the foundation reinforced by the steel pipe sheet pile foundation extension method, that it gives more conservativeresults, and that it is applicable as a practical design method. Research results to date on aseismic reinforcement ofexisting foundations by the steel pipe sheet pile foundations have been discussed. From the findings obtained throughthis study, design method (draft) on reinforcement has been compiled as “Design manual for the steel pipe sheet pilefoundation extension method (draft)”. For details, reference 2 may be referred to.
3．Activities for Reinforcement of Bridge Abutment Foundation
As a collaborative research with Research and development agency, Public Works
Research Institute (PWRI), in a 4-year plan since 2015, JASPP has been developing
reinforced structures of bridge abutment foundation on ground susceptible toliquefaction. The activities of this research have been carried out in a publicprivate partnership, as a “resilient reinforcement of disasterprevention/mitigation performance”, one of the Cross-ministerial Strategic
Innovation Promotion Program (SIP)3) (termed SIP collaborative research,hereinafter). With the damage experienced at the time of the Great East Japan
Earthquake as lessons learned, it is aimed to build a resilient society and reinforce
disaster prevention/mitigation performance against the Nankai Megathrust
Earthquake and any future earthquake that directly hits the Tokyo area. Fig. 6shows a case study where a bridge abutment was damaged by the lateral
movement due to liquefaction of the ground.

The abutment wasdeformed frontward.

Limited working space

Fig. 6 Example of structure damaged by lateral movement due to liquefaction of groundIn this study, as a premise of taking reinforcement measurements while using road bridges, considered are thereinforcement methods that can produce a specified effect under the conditions such as no hindrance of common use ofexisting bridges, and limitation of construction area depending on road and structure conditions. An image of thereinforcement method is illustrated in Fig. 7.
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A. steel pipe sheet pile wall, laterally integral type

B. steel pipe sheet pile wall, front isolated typeFig.7 Image of reinforcement method
As concrete activities, centrifuge model tests and shaking table experiments have been performed to date. Here, anoverview of the shaking table tests and their results are explained 4). Schematic overview of the shaking table test isshown in Fig. 8, while two of the test cases performed are listed in Table 2. No reinforcement measure was taken in Case1, whereas reinforcement by the laterally integrated type steel pipe sheet pile wall was made in Case 5. In the latter case,
it is intended to suppress the deformation of the abutment by the steel pipe sheet pile wall during earthquake, and tosecure the passability of the bridge after strong shake owe much to its vertical bearing capacity. Note that the shaking
table tests were carried out using the 3-dimensional large-scale shaking table and a large scale rigid chamber withdimensions of 6 m wide, 3 m deep and 2 m high, both owned by PWRI.

Fig. 8 Schematic view of shaking test
Table 2 Experimental cases considered
Case15Foundation dimensions
Prefabricated RC pile
Diameter 450 mm, 8 x 3

Reinforcement method

Prefabricated RC pile
Diameter 450 mm, 8 x 3

Steel pipe sheet pile wall (laterally integrated type)No reinforcement

8 no. 600 mm dia., t = 9 mm piles (4 on each side)

Distributions of bending strain of existing piles at maximum response are shown in Figs. 9a and 9b, while that ofreinforcement steel pipe sheet pile is shown in Fig. 9c. From the figures, the following observations may be made:1) Distribution of bending strain of existing pile at maximum response
From Figs. 9a and 9b, it is shown that the magnitude and the distribution pattern of bending strain of the existing pile areboth similar to those in Case 1, suggesting a similar range of earth pressure to that in Case 1 acted on the existing pile inCase 5. In addition, as in Case 1, at the top and in the middle section of the existing pile in Case 5, bending strain largely
exceeded the yield strain.
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2) Distribution of bending strain of reinforcement steel pipe pile at maximum response
Most bending strain of reinforcement steel pipe pile stayed within an elastic range.
From the results above, it may be said that even though bending strain of the existing pile largely exceeded the yieldstrain, aseismic property was still secured as a whole foundation after the existing pile was damaged, since reinforcementby the laterally integrated steel pipe sheet pile wall was a structure consisting of integrated steel pipe sheet pile wall andexisting bridge abutment. Note that following these test results, a demonstration test with a large-scale model was carriedout in February 2018, at a full-scale 3-dimensional vibration failure test facility (E-defense) owned by the research anddevelop agency, National Research Institute for Earth Sciences and Disaster Prevention (NIED). The test results are
currently under compiling.

(a)

(b)

(c)

Fig. 9 Results of non-reinforcement (Case 1) and reinforcement by laterally integrated

4．Summary and Conclusions ‒ Things Expected for the Press-in Method
When considering retrofitting of existing structures, the Press-in Method is expected to be one of the most effective
construction methods, from the points of view of construction environmental conditions and effect on existing structures.
In this case, the capacity that can install objects at a specified location is naturally required. In addition, another importantfactor may be the capacity to be able to accomplish this without disturbing the ground that is supporting the structures.
More concretely, required for the construction method selected may be minimization of scattering the effects of theconstruction method on the ground, reduction in the vertical and horizontal resistance characteristics of constructed piles
and steel pipe sheet pile, and improvement in reliability of load bearing performance. Specifications for highway bridges
in Japan has been revised in a partial coefficient format based on reliability technique. Unfortunately, the observation
data and analysis evaluation in views described above are not sufficient. As discussed in Section 1, the Press-in Method
has not been regarded yet as a standard construction method for the Specification adopted for Road Bridges. Regarding
further development of steel pipe sheet pile foundation in future and foundation piles installed by the Press-in Method,
it is felt the urgent issue is to establish an execution management method that can guarantee standardization ofconstruction and demonstration of specified performance and accumulate data on load bearing performance and its
reliability.
Translated by Mr Masafumi Yamaguchi, IPA Secretariat
Reference[1] Japan Road Association: Reference material on reinforcement of existing road bridge foundations, February 2000 (inJapanese).
[2] Study group of aseismic reinforcement, JASPP: Research report on steel pipe sheet pile foundation extension method,March 2007 (in Japanese).
[3] Cabinet Office of Japan: Website http://www8.cao.go.jp/cstp/gaiyo/sip/ Cross-ministerial Strategic Innovation
Promotion Program (SIP) (in Japanese).
[4] Civil Engineering Journal: Shaking table experiment on aseismic reinforcement technology of existing bridge abutment
foundation in liquefiable ground, Volume 59, No. 9, 2017 (in Japanese)
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