efficiency investigation of steel sheet pile wall...
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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: [email protected]
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
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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.
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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
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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.