1

The Influence of Tunnel Construction on the Performance of Shallow Foundation Bridge

Shuying Wang1, Ronaldo Luna2 and Junsheng Yang3

1Graduate Research Assistant, Missouri University of Science & Technology, Rolla, 65409; sw896@mst.edu 2 Associate Professor, Missouri University of Science & Technology, Rolla, 65409; rluna@mst.edu 3 Professor, Central South University, Changsha, 410075, China; jsyang@mail.csu.edu.cn

ABSTRACT: The development of urban tunnels has resulted in the construction of several tunnels under bridges, which influence their performance. It is important to assure the safety and performance of the bridge during and after tunnel construction. The analysis and measurement of the bridge performance is researched herein. The Jinshazhou Tunnel crosses below the foundation of Guangfu Overpass which was built 18 years ago. To avoid damage of the bridge due to the construction of Jinshazhou Tunnel, the influence of tunneling on the performance of the shallow foundation bridge has been analyzed, and then the bridge damage assessment was performed. Finally, the influence of Jinshazhou on Guangfu Overpass was analyzed and the critical values of settlement and ground loss were predicted. INTRODUCTION

The performance of bridges can be influenced by tunneling directly underground. It is very important to evaluate the potential damage due to tunneling to ensure the safety of bridges. Burland & Wroth (1974) presented some parameters to define building displacement and deformation, two important ones of which are relative deflection and average horizontal strain. Burland et al (1977) stated that there were three criteria when considering building damage, including visual appearance, serviceability, and stability. Mair et al (1996) presented the three-stage building damage assessment approach. In the preliminary assessment, the presence of the building is not considered. In the second stage, the building is represented as an elastic beam whose foundation is assumed to follow the settlement profile. In the third stage, the details of the building and of the tunnel construction should be taken into account. This three-stage assessment approach was adopted successfully for the Jubilee Line Extension, London. Potts & Addenbrooke (1997) presented a relative stiffness approach to consider the influence of building stiffness on the tunnel-induced building deformation. This approach can consider the effects of soil-structure interaction. The majority of researchers and engineers simply apply the critical ground surface settlement such as 30cm to assess structure damage due to tunneling, developed from the project experience without analytical justification. Although many scholars have presented different approaches to assess the damage of existing structures, there are still some limitations. This previous research has focused on building performance. There are few research results on the influence of tunnel construction on the bridges, especially those supported on shallow foundations. In many projects, the engineers and researchers take an empirical value as the critical ground surface settlement. The influence of tunneling on the performance of shallow foundation bridges is presented. Additionally, the influence of the Jinshazhou on the Guangfu Overpass is analyzed and the critical values of settlement and ground loss are predicted.

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OUTLINE OF JINSHAOZHOU TUNNEL AND GUANG-FU OVERPASS BRIDGE Spatial Relation between Tunnel and Overpass Bridge

The Jinshazhou Tunnel is located west of Guangzhou city. The length of the tunnel and the one of its structure are respectively 4056m and 4428m. The tunnel crosses the Guangfu Overpass at the DK2194+675.7 (Fig. 1). The overpass and the tunnel are located in east-west and south-north direction, respectively. The center lines cross at an angle of 83¡05′45″.

Huancheng Freeway

service roadservice road

4.10

8 4.61

53.

832

3.72

5

DK

2194

+650

DK

2194

+550

7.79

9

Tunnel centerline

1?

¡e

¨￠

??

??

?D

¦?

0?¨

000

DK2194+675.7Joint

83¡

5′45

"

Guang-Fu Overpass

Jinshazhou Tunnel

N

Bridge centerline

Ramp bridge

DK

2194

+750

DK

2194

+450

DK

2194

+410

DK

2194

+835

Fig. 1 Horizontal Layout of Project The tunnel is located 18.83m below Pier 7# foundation level. The height and width of the

tunnel is 12.98m and 15.10m, respectively. In the horizontal direction, the tunnel goes below the 7# pier. The distance between the central line of the tunnel and the one of 7# pier is 4.30m. The details of the vertical cross-section along the center line of the overpass bridge are shown in Fig. 2. Guangfu Overpass Bridge Structure

The Guangfu Overpass (Fig.3) was built in 1989. The current condition of the bridge is good before tunneling. Except for the two-span continuous girdle beams at the central Pier 8#, the portions on the two sides are simply supported girdle beams. The spans of the simple supported beams and the continuous beam are 16.94m and 26.57m, respectively. The beam cross-sections are T-shape and have a depth of 0.9m and 1.4m for the simple supported and continuous beams, respectively (Fig. 4). The foundation types under the piers are all shallow spread footings supported on the alluvial clay strata (Fig. 5).

3

Elev

atio

n: 1

4.19

Guangfu Overpass

6# 7# 8# 9# 10#

3.13 3.13 3.13 2.334.83

7.49 7.02 6.694.83 4.674.88

B

430 1382

1883

1510

R755

Jinshazhou Tunnel

1298

1369

excavation line

-28.68

3.13

Fig. 2 Vertical Cross-section

(Unit of Dimensions: cm; Unit of Stations and Elevations: m)

Centerline of Guang-Fu OverpassCenterline of

Huancheng Freeway

Stat

ion

0+0

00

2567 2567 16941694

6# 7#8#

9# 10#

2.33

7.49 6.694.80

E

E

750 1000

610

900

610

900

ground surface

15.1715.17

150

15.36

Elevation View

Plan View

3.13 3.13 3.13

Stat

ion

0-12

7.31

16941694169416941694

1# 2# 3# 4# 5#

3.43 3.135.73 5.13

B

B

C

C

975

5075

40

35

900

450

12.27 13.71

4.88

Stat

ion

0+14

4.25

1694 1694 1694 1694 1694 1694

11# 12# 13# 14# 15# 16#

4.31

450

900

975

7550

12.5411.08

2.37 1.20

Fig. 3 Guangfu Overpass

(Unit of Dimensions: cm; Unit of Stations and Elevations: m)

60

70 15

60 124

65

6050

170 180 180 180 2451565

10

15

10

60

90

60

70 15

60 124

115

6050

170 180 180 180 2451511

510 1510

60

140

(a) Simple Supported Beam (b) Continuous Beam

Fig. 4 Cross-sections of Girdle Beams

(Unit of Dimensions: cm)

4

60

90450

300

65

The piers' height (m)： 2＃：6.21 11＃：8.45 3＃：6.78 12＃：8.06 4＃：7.26 13＃：7.58 5＃：7.65 14＃：7.01 6＃：7.94 15＃：6.41

900

150

150

120

120

610300

90

60 763813

900

150

150

120

120

11

4646

763

60

90

60

550750

1000

150

150

120

120

874

500

60

90

900

120

120

150

150

Elevation View

Plan View

65

Fig. 5 Substructure Dimensions

(Unit of Dimensions: cm)

Jinshazhou Tunnel Engineering geology The section of Jinshazhou Tunnel that crosses the Guangfu Overpass is located in an alluvial plain. The tunnel¡s vertical change in elevation is small and the vertical alignment has a 2% grade dipping to the south. The cross section of DK2194+650~DK2194+700 of Jinshazhou Tunnel along the strike of the tunnel is shown as Fig.6. The soil characters are described in Table.1, and cross-referenced with Fig. 6.

Table.1 Soil Characters During the DK2194+650~DK2194+700

Code Stratum State Bearing capacity

(kPa)

Cohensive strength

(kPa)

Internal friction

angle ( ¡ )

Natural density (g/cm3)

(1) Filling Loose -- -- -- --

2(4) Clay High plasticity 120 8.54 17.83 1.86

2(5) Clay Medium plasticity 150 28.57 13.53 1.96

7(1) Carbon limestone

Complete weathering

200 18.2 4.20 1.95

7(2) Carbon limestone

Strong weathering

300 -- -- --

8(2) Limestone Strong weathering

500 -- -- --

8(3) Limestone Weak weathering

1000 -- -- --

10(1) Breccia Complete weathering -- 46.75 27.50 2.01

5

(1)filling

2（4）Soft plastic slity clay

2（5）Stiff plastic slity clay

2（4）Soft plastic slity clay

2（5）Stiff plastic slity clay

10（1）Breccia

8（2）Limestone

Border line of different weathering degreesabove：complete weathering below：weak weathering

Border line of different stratums

Ran

g of

tunn

el2％

DK

2194

+650

DK

2194

+700

4.23

2.35

-0.75

-3.95

-16.19

4.48

0.80

-2.00

-6.00

-9.50

-13.60

-17.19

Elevation of inside train track: 28.49

997

73

359

301

173

188

3

1096

Elevation 14.19

Fig. 6 Geology of Tunnel

(Unit of Dimensions: cm; Unit of elevations: m)

Construction method The tunnel will be advanced using a double-wall pit construction technology for the

section DK2194+650～DK2194+700 of Jinshazhou Tunnel. A curtain grout technology is used to strengthen the stratum before excavation. The

strengthening boundary is located in the 5m away from the face of the excavation in the transverse direction (Fig. 7). The 10.8cm diameter grouting pipes are used to inject neat cement and other special cement. Support structure

Compound linings are used to support the adjacent ground after excavating ground. Due to the different soil conditions, different support structures are used in section DK2194+650~675 and DK2194+675~700. The detail of the support structures are shown in Fig. 8.

6

grouting boundary line

excavation line

grouting holes

central line of every circle holes

0123456

106

7575

7575

7575

Tunn

el c

ente

rline

755

5m

Fig. 7 Curtain Grout (Unit: cm)

Note：1、Unit:cm 2、systemic bolts arch: grouting hollow bolt side: common mortar bolt

60

50

665

250

665

1567250

Centerline

50

4646

Secondary support:C35 reinforced concrete

Preliminary support: steel net: 20cm*20cm（radial*longitudinal） anchor : 4.0m(length),80cm*100cm（radial*longitudinal） steel frame: I20a,80cm(longitudinal) sprayed concrete

2828 70

49

250

665 665

250

1567

60

49

Note：1、Unit:cm 2、systemic bolts arch:grouting hollow bolt side:common mortar bolt

Secondary support:C35 reinforced concrete

Preliminary support: steel net: 20cm*20cm（radial*longitudinal） anchor : 4.0m(length),80cm*100cm（radial*longitudinal） steel frame: I22a,50cm(longitudinal) sprayed concrete

3030

(a) DK2194+650~675 (b) DK2194+675~700 Fig. 8 Tunnel Support Structure

GROUND SURFACE MOVEMENT DUE TO TUNNELING Prediction of Ground Settlement

To predict the settlement due to tunneling, there are mainly three methods, including (1) empirical method, (2) analytical method (Sagaseta, 1987, 1998; Verruijt and Booker, 1996; Bobet, 2001; Gonzalez and Sagaseta, 2001; Park, et al. 2005), (3) numerical method (Lee

7

K.M., Rowe, et al. 1990). The random medium method is a numerical method that is also used to predict the settlement, which was presented by Litwiniszyn (late 1950s), and then Liu (1993) contributed to the development of this method.

However, compared to the analytical and numerical methods, the empirical methods are convenient to predict ground settlement. Peck (1969) stated that transverse settlement trough or dip could be described by a Gaussian error function, and the settlement could be calculated as follow.

2 2

2exp2 4 2

LV

V D xS xi i

(1)

Where， vS x －settlement at the location with horizontal distance x to tunnel centerline;

LV －ground loss; D－diameter of tunnel; i－trough width. O¡Reilly and New (1982) presented that the horizontal displacement in the transverse

direction can derived from the Peck¡s formula, with the assumption that the resultant displacement directs toward the center of the tunnel. Liu (1991) presented the concept of underground loss and modified the Peck¡s formula to predict the settlement in the longitudinal direction. Hou (1993) modified Peck¡s formula considering influence of construction and time.

The inclination, ( )T x , and horizontal displacement, hxS x , in the transverse direction are expressed as:

2 2

2 2( ) ( ) exp2 4 2

v LdS x V D x xT xdx i i i

(2)

0

vhx

xS xS x

Z (3)

Where, Z0－tunnel depth.

Equivalent Radius

When deformation and failure of adjacent rock are analyzed, the non-circle shape tunnels

with straight side wall tunnels or curved side wall tunnels are usually assumed to be circle shape tunnels with equivalent radius (R=D/2). This is called equivalent circle method, which is usually applied to the analysis of tunnel displacement. This includes two type approaches, such as the equivalent geometric method and equivalent displacement method (Li, 1986 and Li, 1999). With the advantage of considering geometric shape, dimension, stress conditions and lateral stress coefficient, the equivalent displacement method is applied in this study. The equivalent radii are calculated using the following rules: a. radius of circumcircle (Fig.9.a); b. radius of arch (Fig. 9.b.); c. half of the sum of large and small dimensions (Fig.9.c); d. 1/4 of sum of height and span (Fig.9.d-f).

8

BD

AD

R0α

R0

b

a1

a2

a1a2

a2

a1

b

hh

b b

h R0

R0

R0

(a) (b) (c)

(d) (e) (f) Fig. 9 Equivalent Radius, R

Trough Width

Trough width is the horizontal distance between central line and point of inflection. Many scholars have presented empirical formulae for different ground conditions (Table 2).

Table 2 Empirical Formulae of Trough Width

Scholar Year Trough width, i Ground conditions 1969 0/ ( / 2 ) ( 0.8 ~ 1.0)ni R Z R n --

Peck 0 /[ 2 tan(45 / 2)]i Z --

Attewell & Farmer 1974 0/ ( / 2 ) ( 1.0)ni R Z R n --

0/ ( / 2 ) ( 0.8)ni R Z R n -- Clough & Schmidt 1981

00.43 1.1i Z 0Clay, 3m Z 34m

Loose sand Atkinson & Potts 1977 00.25( )i Z R

00.25(1.5 0.5 )i Z R Dense sand & OC clay

Mair et. al. 1983 00.5i Z Clay

Leach 1985 0(0.75 0.47 ) 1.01i Z Obvious consolidation

Qu, J. L. 2006 9 84.35 7.29 10i x Shanghai soft soil

Clay soil, a=0.65 Han X. 2007

00

0

0.5 0.325 / ( )1 /

Z Zi Z aZZ Z

A=0~1 Sandy soil，a=0.50

Note：R－Equivalent tunnel radius; －Internal angle of fiction; Z0－Tunnel depth.

Ground Loss

Ground loss is the percentage of total volume of the settlement trough with respect to the

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theoretical volume of the tunnel excavation. Burland (2006) stated that ground loss is dependent on a numbers of factors such as the ground type, groundwater conditions, tunneling method, and length of time in providing positive support, and the quality of supervision and control. So its quantification is usually based on the past experience in a given area employing a particular tunneling method. According to reported experience, it is usually 0~5% (Franzius, J.N., 2003; Burland, 2006).

DAMAGE ASSESSMENT OF SHALLOW FOUNDATION BRIDGE DUE TO TUNNELING Description of Bridge Damage

The damage induced by tunneling consists of direct damage and indirect damage. The

direct damage is the activity caused by settlement due to tunneling, but the indirect damage comes from other factors such as changes of groundwater level. The direct damage is main damage for bridge. The direct damage of bridge is induced by the following factors. Uniform settlement does not have serious consequences, but may impact the surface drainage of the overall structure. Horizontal displacement can cause the bridge foundation to move and the beam may come off its bearing to eventually produce a collapse of the bridge. Differential settlement will induce stresses in the continuous beam and to a lesser extent in the simple supported beams.

In addition to the above mentioned factors, horizontal deformation also will also induce some damage to the bridge foundations. However, bridge foundations are usually made of reinforced concrete, with a capacity of bearing horizontal deformation. It is important to mention that the damage of bridge is not caused by only one of the above factors, these factors usually occur simultaneously and combined. Analysis of Bridge State Superstructure

Because the simple supported beam is a determinate structure, ground surface settlement

will not induce stresses unless the settlement is too large so that it is changed into an indeterminate structure. The Chinese bridge code (JTJ024-85, 1985) demands that uniform settlement and differential settlement are respectively less than 2.0 L (cm) and 1.0 L (cm), where L is the span of the beam. If the span is less than 25m, L should be assumed to equate 25m herein.

On the other hand, the continuous beam is an indeterminate structure, and ground settlement will induce stresses and deformations. It is necessary to analyze the influence of ground settlement to ensure the demand on the continuous beam. The Chinese bridge code (JTJ024-85, 1985) requires verification of the ultimate state for bearing normal service. Exceeding the ultimate bearing state results in a collapse condition. Some cracks or large deformations will appear. The ultimate state for bearing ability includes bearing ability at the right section and oblique section. The ultimate state for normal service includes anti-cracking capacity at the right section, anti-cracking capacity at the oblique section, and deflection.

Substructure

In order to ensure the superstructure safety, the horizontal displacement at the top of the pier should be controlled, or else the superstructure will move off its bearing. In addition,

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bearing capacity at the bottom of the foundation should be checked to ensure the safety of foundation, including eccentric loading and stability.

To satisfy the safety of bridge, each effect should be less than the corresponding resistance ( 0r S R , where, 0r －coefficient of importance of a structure; S－design value for action effects; R－design value for ultimate bearing capacity). And the factor of safety is defined as:

0

RNS

(4)

From the above simple analysis, the bridge damage assessment system is established in Table 3.

Table 3 Assessment System of Bridge Damage due to Tunneling Structure type Assessment parameters

Uniform settlement Free beam

Differential settlement Bearing capacity at the right section

Bearing of capacity at the oblique section Anti-cracking capacity at the right section

Anti-cracking capacity at the oblique section

Upper structure Continuous

beam

Deflection Horizontal displacement at the top of pier Eccentricity at the bottom of foundation Substructure

Stability at the bottom of foundation Wang (2007) presented that the anti-cracking capacity of right section decreased rapidly with increasing differential settlement at the supports. Additionally, the horizontal displacement at the top of the pier increased rapidly to the point of substructure collapse. With these results, the bridge damage assessment system is modified to focus on the governing parameters, as shown in Table 4.

Table 4 Modified Assessment System Bridge Damage due to Tunneling Structure type Assessment parameters

Uniform settlement Free beam

Differential settlement Anti-cracking capacity at the right section

Upper structure Continuous

beam Deflection Substructure Horizontal displacement at the top of pier

ASSESSMENT OF INFLUENCE OF JINSHAZHOU TUNNEL ON PERFORMANCE OF GUANG-FU OVERPASS

The tunnel height (12.98m) and the span (15.10m) result in an equivalent radius of (H + b) /4=7.02m. Because the ground consists of different layers, the trough width coefficient is

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selected carefully. The coefficients of each layer are shown Table 5.

Table 5 Trough Width Coefficients for Jinshazhou Tunnel Layers

Layer High

plastic Clay

Medium plastic Clay

High plastic Clay

Medium plastic Clay

Complete weathering

Breccia

Strong weathering Limestone

Thickness (m) 1.73 3.59 3.01 0.73 9.77 0 Trough width

coefficient 0.25 0.45 0.25 0.45 0.9 －

Considering the different layers, the trench width is:

0 =0.60 25.85=15.10mi kZ (5) According to Peck¡s formula, the ground surface settlement is:

2( ) 3.982 exp( 0.002 )V LS x V x (6) So, the ground surface curvature and horizontal displacement are respectively:

2( ) arctan ( ) tan( 0.017 exp( 0.002 ))Lx T x arc xV x (7) 2( ) 0.154 exp( 0.002 )hx LS x xV x (8)

The above equations include ground loss. In the following assessment, they will be assumed to analyze the influence of ground loss on performance of Guangfu Overpass. a. Simple supported beam

The critical values of settlement and differential settlement between two adjacent foundations are 10cm (= 2.0 25 cm) and 5cm (=1.0 25 cm), respectively. From the Table 6 and Table 7, the settlement on location 7# and the settlement difference between location 7# and location 6# increase to the critical values respectively when the ground loss increase to 2.6% and 2.2% respectively. So, for the simple supported beam, ground loss should not exceed 2.2% in order to ensure satisfactory performance.

Table 6 Settlements at the Piers of Simple Supported Beams (Units: cm)

Ground loss Location Distance

（m） 0.5％ 1.0％ 2.0％ 2.6％ 1~3# － 0.00 0.00 0.00 0.00

4# -55.12 0.00 0.01 0.02 0.02 5# -38.18 0.11 0.22 0.43 0.56 6# -21.24 0.81 1.62 3.23 4.20 7# -4.3 1.92 3.84 7.67 10.00 9# 47.04 0.02 0.05 0.10 0.12

10~16# － 0.00 0.00 0.00 0.00

b. Continuous beam For continuous beam, it is necessary to check the anti-cracking capacity at right section

and deflection. The safety coefficient of the anti-cracking capacity at right section and deflection is shown in Table 8, and it can be found that when ground loss increases to 0.9%, the factor of safety decrease to about 1.

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Table 7 Differential Settlement between the piers of free beams (Units: cm) Ground loss Location Distance

（m） 0.5％ 1.0％ 2.0％ 2.2％ 1~3# － 0.00 0.00 0.00 0.00

4～3# -55.12 0.00 0.01 0.02 0.02 5～4# -38.18 0.10 0.21 0.41 0.45

6～5# -21.24 0.70 1.40 2.80 3.08 7～6# -4.3 1.11 2.22 4.44 5.00

9～10# 47.04 0.01 0.02 0.03 0.04 10~16# － 0.00 0.00 0.00 0.00

Table 8 Safety Coefficients of Anti-cracking Capacity of Right Section Location Settlement

(cm) Ground

loss Factor of

Safety Location Settlement (cm)

Ground loss

Factor of Safety

7# 0 7# 2.69

8# 0 8# 1.12

9# 0

0 1.899

9# 0.03

0.7％ 1.221

7# 1.92 7# 3.45

8# 0.80 8# 1.44

9# 0.02

0.5％ 1.567

9# 0.04

0.9％ 1.007

The deflection is a critical value:L/600＝ 25.67/600m=4.28cm (L is the span of continuous beam). In Table 9, it is found that when ground loss increases to 2.5%, the deflection hasn¡t reached the critical value. Therefore, the ground loss should be controlled below 0.9% to ensure the performance of the continuous beam.

Table 9 Deflections for Different Ratio of Volume Loss Ground loss 0 0.5％ 1.0％ 1.5％ 2.0％ 2.5％

Deflection (cm) 2.65 3.23 3.45 3.57 3.61 3.67

c. Substructure For the substructure, it is only necessary to check for the horizontal displacement at the

top of pier. The critical value for horizontal displacement at the top of pier is: 5 16.94cm=2.53cm . The horizontal displacements for different ground loss are shown in table 10. It can be found that when ground loss increases to 1.8%, the horizontal displacement increases to the critical value. Therefore, the ground loss should be limited below 1.8%.

In summary, to ensure the satisfactory performance of the whole bridge structure, the ground loss should be limited to satisfy the safety of the whole bridge structure, ground loss should be limited to 0.9%. When the ground loss is 0.9%, the settlements for different locations are shown in Table 11.

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Table 10 Horizontal Displacements of Pier Top (Units: cm)

Ground loss Location Distance(m)

0.5% 1.0% 1.8% 1~3# - 0.00 0.00 0.00

4# -55.12 0.02 0.02 0.04 5# -38.18 0.32 0.32 0.58 6# -21.24 1.35 1.43 2.53 7# -4.3 0.66 0.66 1.17 8# 20.592 -1.40 -1.25 -2.35 9# 47.04 -0.09 -0.09 -0.16

10~16# - 0.00 0.00 0.00

Table 11 Critical Settlements When Ground Loss is 0.9% Location 1~3# 4# 5# 6# 7# 8# 9# 10~16#

Settlement(cm) 0.00 0.01 0.19 1.45 3.45 1.44 0.04 0.00

CONCLUSION

This study developed a series of parameters that can be used to evaluate the performance of a bridge structure supported on shallow foundations when tunnels cross directly underneath. The Jinshazhou Tunnel project that crosses under the Guangfu Overpass Bridge was used to exemplify the process. Several settlement performance parameters were calculated using different methods, including: Peck¡s formula, equivalent radius method, ratio of volume loss, and trench width. Bridge damage due to ground surface settlement, horizontal displacement, inclination, curvature and horizontal deformation were also calculated. The critical values of ground surface settlement and ground loss below Guangfu Overpass have been predicted for the construction of the Jinshazhou Tunnel in order to ensure satisfactory performance. After evaluating several parameters it was concluded that for this bridge structure the ground loss should be limited to about 0.9% . ACKNOWLEDGEMENTS The research project presented herein is a portion of a more broad study sponsored by China Tiesiju Civil Engineering Group CO.LTD. The financial and technical support is sincerely appreciated. The technical staff under the direction of faculty and graduate students that helped during the research are also acknowledged as contributors to this paper. REFERENCES

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