Figure 1 Full scale pushover test of 2 bridge piers rested on raft and raft with SSPW [4]

Efficiency Investigation of steel sheet pile wall permanent use for improving the stability

of multi-story buildings supported on liquefiable soil foundation Ahmed. M. Y. Mohammed

1 and K. Maekawa

2

1Department of Civil Engineering, The University of Tokyo, Tokyo, Japan

1Department of Civil Engineering, The University of Tokyo, Tokyo, Japan

E-mail: mohammed@concrete.t.u-tokyo.ac.jp

ABSTRACT: This paper is an attempt to discuss the nonlinear seismic responses, damage evolution and control of multi-story buildings

supported by rafted piles or only raft in liquefiable soil foundation. Here, group piles driven in fully saturated soft sands are considered. The

focus is directed to the effect of permanent use of steel sheet pile wall (SSPW) to protect the existing structures which are supported by RC

raft with and without piles in liquefiable soil. The results clearly show that, the sheet pile wall could improve the overall stability of the

superstructure , but it leads to a higher base shear to superstructure.

1. INTRODUCTION

During the Alaska and Nigata earthquakes (1964), serious structural

damages due to soil liquefaction have been reported. Likewise,

severe damage and stability failure of multi-story buildings were

also reported during the Hygoken-Nanbu earthquake. Subsequently,

research on the investigation of damage evolution and control has

drawn increasing attention in the structural engineering field.

Accordingly, efforts are being made towards enhanced damage

control techniques and numerous experimental investigations with

different scales have been carried out [1,2, and 3]. Nowadays, the

most common techniques used as a countermeasure for damage

control are soil densification, compaction grouting, and dissipation

of excess pore water pressure by using gravel or pipe drains [4].

These techniques are costly and are practically difficult to be used as

a control for the damage of multi-story buildings. For improved

horizontal seismic resistance, Nishioka et al. have proposed a new

type of foundation that combines RC mat with steel sheet-pile wall

(SSPW) used for earth-retaining works during excavation. They

conducted a series of small scale as well as a large scale bridge

column experiments as indicated in Fig. 1. The results showed an

efficient increase in the lateral seismic resistance of RC mat

foundation when it is combined with the steel sheet-pile wall [5].

Yet, the effect of using SSPW on the superstructure is not discussed.

The current paper is an attempt to address this issue.

While a full scale experiment to investigate the seismic behaviour of

a real structure together with SSPW is costly, an analytical study

with a well verified computational RC and soil model [6] can serve

as a best alternative. Here, the authors use a full three dimensional

finite element analysis of soil-structure-pore water systems. The

applicability of the system is verified by shaking table experiments

of top-heavy piles embedded in model foundation [7]. Using this

analytical platform, the effects of using SSPW as a seismic

countermeasure for both raft and rafted pile foundation is discussed

with regard to transmitted base shear to the superstructure and

overall stability.

2. FINITE ELEMENT MODEL

For the purpose of analytical investigation, a seven story building

supported by nine columns in a soft sandy soil foundation is

considered. The building is 12m wide and 24.5m high and is

supported by nine square columns (70cm x70cm). Two types of

foundation are considered for supporting these columns; one a raft

foundation type and the other a rafted pile foundation type extending

through a 16.5m thick of soft sandy soil to bear on a very dense base

soil. The soft soil is considered to consist of 5 layers from very soft

layer at the surface to a compacted one at the bottom and is assumed

to be deposited on a very dense sandy soil that act as an engineering

base on which the ground acceleration is defined. The soil layer

properties are described in Table 1. For simplicity, all concrete slabs

and foundation mat are considered to have a uniform thickness of

50cm and are modelled as 3D elastic solid elements having density

2.5t/m3, elastic modulus 2800kN/cm2, and Poisson’s ratio 0.2. The

finite element discretization was carried out by using 3D-nonlinear

solid element for soil, 3D-elatic solid element for RC slabs and mat

foundation, and Timoshenko frame elements for piles and columns

as indicated in Fig. 2. The compressive strength of concrete and

yield strength of reinforcing bars are assumed to be 35 MPa and 400

MPa respectively. Scaled Kobe earthquake with a PGA of 0.5g is

used in the current analysis as shown in Fig. 3.

Table 1 Soil properties used in analysis

Soil

Layer

Gs(MPa) Relative

density

density

(kg/cm3)

friction

angle φ

A 740 100 2.2 45

B 150 42 1.8 37

C 90 40 1.8 35

D 70 36 1.7 34

E 50 30 1.7 31

F 30 20 1.6 25

Figure 2 model of multi-story building

Figure 3 Scaled Kobe earthquake

3. CONSTITUTIVE MODELING

A nonlinear path-dependent constitutive model for soil, mainly

dependent on shear stress-shear strain relationship which is extended

to three-dimensional generic condition and assumed to behave

according to Masing’s rule to fulfil the soil hysteresis. The soil is

idealized as an assembly of a finite number of elasto-perfectly

plastic elements connected in a parallel pattern. The nonlinear

behaviour of the soil system in liquefaction is assumed as undrained

state, since its drainage time is much longer than the duration time

of earthquake [4]. The soil undrained behaviour is as shown in Fig.

4, and 5. The Full details of the constitutive model of soil, RC-solid

element, and frame element is explained by Maekawa et al [6].

Figure 4 Experimental confinement dependent soil model under

undrained condition

Figure 5 Analytical confinement dependent soil model under

undrained condition

4. STEEL SHEET PILE WALL EFFECT

The analytical investigation was carried out using four different

types of foundation as shown in Fig. 6. These include only raft (R),

rafted piles (R.P), raft and SSPW (R.S), rafted piles and SSPW

(R.P.S). Stability of the superstructure is defined by the settlement,

lateral movement, and tilting and the relative performance of each

foundation type are presented in the subsequent subsections.

4.1 Building lateral movement

The structure lateral displacement during earthquake is an important

stability factor to assess how the use of the steel sheet pile wall

would help to control stability. The raft and rafted pile foundation

have no significant effect on reducing the lateral displacement as the

structure moves with the soil in both cases as shown in Fig. 7-R ,

and 7-R.P. When the steel sheet pile wall is embedded into the soil

as a control measure, the maximum lateral displacement of the

building reduces from 36 cm to 17 cm in case of raft foundation as

indicated in Fig. 7-R , and 7-R.S. Likewise, the lateral displacement

reduces from 51 cm to 12 cm in the case of rafted pile foundation as

indicated in Fig. 7-R.P , and 7-R.P.S. Thus, the steel sheet pile wall

is really necessary for both types of foundations (Raft and Rafted

pile) to minimize the lateral movement.

4.2 Building tilting

In the current research, the tilting angle is calculated for the four

different cases and listed in Table 2. As indicated in Table 2, the

titling angle in case of raft foundation is about 1.68 degree and in

case of rafted pile foundation is about 0.35 degree. That declares

importance of rafted pile foundation which has less tilting angle.

Consistently, during the Nigata earthquake in 1964, severe tilting of

a number of Kawagishi-cho apartment buildings which were

supported by only raft foundation on a potentially liquefiable soil

was captured and reported [8]. Whereas nearby to those buildings,

other buildings which were supported by rafted pile foundation still

stand vertically as clearly indicated in Fig. 8.

4.3 Building Vertical settlement

Liquefaction in soft deposited soil during earthquake may cause

floating of underground structure and it may cause subsidence of on

ground structures. These kinds of movement have been experienced

by the past earthquakes in reality and by experimental and analytical

investigations [3, and 7]. Here, the vertical settlement of the

superstructure for the four types of foundations is presented in Fig. 9.

The vertical settlement of the building due to soil liquefaction when

it is supported only by a raft foundation is about 82 cm. When the

steel sheet pile wall is embedded surrounding the multi-story

building, the vertical settlement reduces to 30cm. The pile

foundation strongly resist the superstructure subsidence during and

after the soil liquefaction. The vertical settlement for the rafted pile

foundation is about 3 cm and reduced to 2 cm after embedding the

steel sheet pile wall. It is clear that the pile foundation has a

sufficient resistance against the subsidence in a liquefiable soil.

Figure 8 Kawagishi-cho apartment buildings, 1964 [8]

Table 2 Maximum Tilting angle

Case Tilting angle (degree)

Raft 1.68

Raft with SSPW 1.72

Rafted Pile 0.35

Rafted Pile with SSPW 0.67492

R R.P R.S R.P.S

Figure 6 four models considered in analysis

Figure 7 structure and soil lateral displacement

Figure 9 superstructure Vertical settlement

4.4 Base shear transmitted to super structure

The absolute peaks of inter-story shear force are calculated and then

normalized by the whole superstructure weight (7500 kN) as shown

in Fig 10. The inter-story shear force in the first floor is considered

as transmitted base shear to superstructure by the foundation system.

Among the four cases, the transmitted base shear is lowest when

only raft is used. This is because liquefied soil acts as a damping

medium due to the reduction of the shear stiffness after liquefaction

starts. In contrast, the normalized transmitted shear force is higher in

the Rafted pile foundation.

The steel sheet pile wall confine the soil beneath the superstructure

and may prevent the soil liquefaction, thus it reduces the damping

mechanism that may occur due to soil liquefaction. As a result, the

normalized transmitted base shear increases from 0.086 to 0.137 in

case of raft foundation due to the use of SSPW. In case of rafted pile

foundation, the normalized transmitted base shear increases from

0.231 to 0.352 due to the use of SSPW. The SSPW causes more

damage to the superstructure when used with the raft as well as the

rafted pile foundations

Figure 10 Normalized inter-story shear force

5. CONCLUSION

The superstructure-soil interaction by considering different kinds of

foundation under a liquefiable soil is investigated. The influences

due to use of raft foundation and rafted piles is illustrated. The

positive and negative effects of using steel sheet pile wall as a

countermeasure for control of overall stability and damage of

superstructure is elaborated. The effects of using the steel sheet pile

wall could be summarized as follow in Table 3 .

Effect Raft

foundation

Rafted pile

foundation

Lateral displacement

reduction 54 77

Vertical settlement

reduction 64 43

Increasing in Tilting

angle 2.4 92.8

Increasing in base

shear 60 52

In conclusion, the steel sheet pile wall improves the overall stability

of the multi-story building, but it causes more damage to

superstructure which should be considered in seismic design of

superstructure. The Raft with steel sheet pile wall may be a good

alternative instead of the rafted pile foundation due to the efficient

effects, low cost, and less time consumed during construction.

6. REFERENCES

[1] Toshi, I., "Soil liquefaction studies in Japan: state-of-the-art,"

Soil Dynamics and Earthquake Engineering, 5, Issues 1, 1986,

pp 2-68

[2] Finn WDL and Fujita N. "Piles in liquefiable soils: seismic

analysis and design issues," Soil Dynamics and Earthquake

Engineering, 22, Issues 9-12, 2002, pp731-742

[3] Wilson, D.W., "Soil-pile-superstructure interaction in

liquefying sand and soft clay," PHD thesis, 1998.

[4] Towhata, I., “Geotechnical earthquake engineering," Springer,

Germany, 2008

[5] Nishioka, H., Koda, M., Hirao, J., and Higuchi, S.,

“Development of sheet-pile wall foundation that combines

footing with sheet piles,” QR of RTRI, 49, Issues 2, 2008,

pp73-78

[6] Maekawa, K., Pmanmas, A., Okamura, H., “Nonlinear

Mechanics of Reinforced Concrete, " Spon Press, London,

2003.

[7] Maki, T., Maekawa, K., Matsuyoshi, H., “RC Pile-Soil

interaction analysis using a 3D-finite element method with

fiber theory-based beam elements,” earthquake engineering

and structural dynamics, 35, Issues 13,2005, pp1587-1607

[8] Okhovat, M., and Maekawa, K., Damage control of

underground RC structures subjected to service and seismic

loads, PhD thesis, University of Tokyo, 2010

[9] Kawasumi, H., (editor), General report on the Niigata

earthquake of 1964, 1968.