Deformation of compensated piled raft foundations with deep ...

THE STRUCTURAL DESIGN OF TALL AND SPECIAL BUILDINGS Struct. Design Tall Spec. Build. 24, 521–536 (2015) Published online 22 September 2014 in Wiley Online Library (wileyonlinelibrary.com/journal/tal). DOI: 10.1002/tal.1178

Deformation of compensated piled raft foundations with deep embedment in super-tall buildings of Shanghai Yongjing Tang*,† and Xihong Zhao Department of Geotechnical Engineering, Tongji University, Shanghai, 20092, China

SUMMARY This paper presents a synergetic approach based on a statistical-empirical method, conservation of energy method and superstructure-foundation interaction theory, and this paper aims to estimate the deformation level of a compensated piled raft foundation. The advantages and main characteristics of such a compensated piled raft foundation are described, and a history of the heave, recompression deformation and final settlement data measurements is provided. Case studies of four super-tall buildings, the 88-story Jinmao Building, 66-story Henglong Plaza, 101-story Shanghai World Financial Center and 121-story Shanghai Center Tower in Shanghai, all of which are engineering projects that the second author participated in, are provided to illustrate the effectiveness of different calculations for heave, recompression deformation and final settlement. This study demonstrates that the deformation process can be reasonably projected for a piled raft foundation with deep embedment in Shanghai using superstructure-foundation interaction methods, statistical-empirical formulas and a method based on the conservation of energy. The coefficients in the statistical-empirical method are also further optimized. This deformation estimation considering compensation for deep embedment unloading is reasonable and can be used to avoid excessively conservative designs, and the synergetic approach is applicable to any compensated piled raft foundation with deep embedment in Shanghai. Copyright © 2014 John Wiley & Sons, Ltd. Received 18 December 2013; Revised 26 July 2014; Accepted 8 August 2014 KEY WORDS: compensated piled raft foundations; heave; recompression; settlement; statistical-empirical method; superstructure-foundation interaction method

1. INTRODUCTION In the early 1980s, Professor Zeevaert pioneered the concept of a compensated foundation with friction piles (Zeevaert, 1957) and visited Tongji University to introduce such a foundation in 1980s. More attention has gradually been directed toward compensated foundations during the 21st century. The deformation of an overcompensated foundation for two dry docks measuring 41 000 m2 and 89 000 m2 in area and with depths of 13 m in the Shanghai Outer Ring Tunnel Project was further studied, and the investigation of these dry docks comprised the second such project in the world and the first in Asia (Zhao et al., 2005). Tang and Zhao (2014) have reanalyzed that a fully compensated piled raft foundation with deep embedment in the 121-story Shanghai Center Tower using compensated pile foundation theory enhanced the future usefulness of this theory. In 1957, Professor Zeevaert presented the paper ‘Compensated friction pile foundation to reduce settlement of buildings on the highly compressible volcanic clay of Mexico City’, elevating the profile of compensated pile foundations. Poulos (2005) and Sales et al. (2010) have also thoroughly researched compensated piled raft foundations and played a significant role in expanding the practical application of compensated pile foundations. *Correspondence to: Yongjing Tang, Department of Geotechnical Engineering, Tongji University, Shanghai, 20092, China † E-mail: [email protected] Copyright © 2014 John Wiley & Sons, Ltd.

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Y.J. TANG AND X.H. ZHAO

To use a compensated pile foundation with deep embedment (D ≥ 15 m) in practice, it is necessary to briefly introduce the relevant theory and method and to discuss the characteristics and advantages of this system. One recognized characteristic of piled rafts, or box foundations, is the ratio of pile spacing to diameter, which must be larger than 5 to fully mobilize the soil’s bearing capacity potential (Tang et al., 2013). Compensated pile foundations can reduce the building load on a foundation due to the foundation pit’s excavation load, reducing the number of piles and the foundation deformation as a result. In practice, a deep embedment always exists in the piled raft or piled box foundations of super-tall buildings, reducing the overturning moment caused by wind loads (Tang and Zhao, 2014). Consequently, using the method of superstructure-foundation interaction and the iterative method with variable rigidity (Zhao, 1998; Xu and Zhao, 2010), piled raft and piled box foundations with deep embedment can be feasibly designed for super-tall buildings to ensure their safety and obtain the best economic results. The advantages of compensated foundations with deep embedment are as follows: (1) to fully mobilize the soil’s bearing capacity potential, (2) to reduce the number of piles and the deformation, (3) to reduce the overturning moment caused by wind loads and (4) to feasibly design piled raft and piled box foundations with deep embedment. Understanding the heave and recompression at the bottom of a foundation pit is very important to the design of compensated piled raft and piled box foundations in practice and has always been important to the geotechnical community. Nevertheless, such calculations are very difficult to solve, both in theory and practice, because the factors influencing the magnitude of heave and recompression include the dimensions of the plane and depth of the foundation pit (or excavation), the soil conditions below the base of excavation, the ground water level, dewatering conditions, excavation speed, exposure time after excavation, pile foundations and the shape of the foundation pit structure. Heave data have been collected by researchers for past studies (D’appolonia et al., 1971; Focht et al., 1978). The entire process of foundation deformation in four Shanghai buildings (Zhang et al., 1980), including pre-compression due to dewatering, heave due to excavation, recompression due to foundation loading, heave due to the cessation of dewatering and compression due to superstructure and live loads, is shown in Figure 1. Statistical-empirical equations from real projects including piled raft foundation and box foundation without piles have been suggested based on these measurement data, including SH = (0.5–1%) D and SR = 1.2 SH, in which SH is heave, SR is recompression settlement and D is the depth of the foundation pit. In practice, heave and recompression are rarely considered for super-tall building settlement, which leads to conservative designs.

Figure 1. Entire deformation process. Copyright © 2014 John Wiley & Sons, Ltd.

Struct. Design Tall Spec. Build. 24: 521–536 (2015) DOI: 10.1002/tal

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In this paper, we primarily investigated the deformation, including heave, recompression deformation and total final settlement with deep embedment (D ≥ 15 m), of super-tall buildings in Shanghai.

2. ANALYTICAL METHODS FOR DETERMINING HEAVE, RECOMPRESSION, AND SETTLEMENT As mentioned in Section 1, many factors that can influence heave are often difficult to be isolated. Furthermore, the data measured on this aspect of foundations are insufficient. Given this condition, feasible and practical applications for solving this difficult problem depend on engineering experience. Based on the experience gained from 1970s onward, the authors engaged theory and practice for tall and super-tall buildings, including deep excavation engineering. The analytical methods used for heave, recompression and settlement are presented in the following sections. 2.1. Statistical-empirical method 2.1.1. Heave and recompression SH ¼ k1 D

(1)

SR ¼ k 2 SH

(2)

where k1 is a coefficient that is primarily relative to the size and the shape of the excavation: SH = 0.15% D for a circular structure with a diameter not larger than 100 m and SH ≤ 0.20%D for a circular structure with a diameter greater than 100 m and for a bracing structure. k2 is a coefficient relative to the weight of excavated soil and is taken as 1.2 based on engineering experience of Shanghai. 2.1.2. Settlement The measured settlement data taken over three decades in Shanghai have illustrated the development of settlement from the beginning of construction until the service period. Taking the Jinmao Building as an example, the statistical ratio among the settlements occurring during the whole process, including SS for the completion of the structure, SB for the completion of the building and SF for the final settlement, is 1.0:1.4:1.7 based on field measurement data. However, it is normal for the coefficients of settlement in different stages to have small differences. Therefore, the general statistical-empirical equations are expressed as follows: pffiffiffi A

(3)

SB ¼ k3 SS

(4)

SS ¼ k 4 SS

(5)

SS ¼

where A is the piled raft (box) foundation area in square meter and SS, SB and SF are in millimeters. k3 and k4 are coefficients that are relative to the local field data in Shanghai soft soil, with k3 = (1.2–1.4) and k4 = (1.5–1.7). 2.2. Conservation of energy method Based on several decade of excavation engineering project’s measured data, participated by the second author, the relationship among the maximum values of horizontal displacement along the depth of diaphragm wall, Sh, of settlement on the back of the diaphragm wall along the ground surface, Sd, and of heave at the bottom of the foundation pit, SH, is shown in Figure 2. Sh ≈Sd ≈SH

(6)

It is found that this relationship is similar to the concept of conservation of energy. Thus, the statistical-empirical formula is called conservation of energy method. Copyright © 2014 John Wiley & Sons, Ltd.


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Figure 2. Application of the conservation of energy to excavation engineering. The heave can be easily obtained from the horizontal deformation of the diaphragm wall, Sh, as SH = Sh. The value of Sh is obtained either via the horizontal deformation of the diaphragm wall or the nonlinear space theory and method calculation (Zhao et al., 2000, 2001), and SR = 1.2 SH. 2.3. Superstructure-foundation interaction method The concept of the analytical method for superstructure-raft–pile-soil interactions was based on the finite element method, used to obtain the stiffness matrices of the superstructure, foundation and pile-soil system. The superposition of these three stiffness matrices was carried out one by one, and the force equilibrium and deformation compatibility conditions were used to establish the basic equation. Nevertheless, this method (Zhao, 1998) treats the raft as a whole plate and designs a displacement function according to the deformation state and boundary condition of the raft, which is based on the nodal force of the superstructure and pile-soil system applied to the raft. The basic equations for the interaction analysis were established based on the principle of potential energy. As a result, the nodal forces of the superstructure and pile-soil system, the bending moment, torsion moment, normal stress and shear stress at any point in the raft foundation could be calculated. The derivation of this method is given in detail by Zhao (1998). When combined with the Mindlin equations, this method allows the entire deformation process of the building to be calculated, from heave (SH) to final settlement (SF).

3. CASE STUDIES We considered case studies of four super-tall buildings containing deep embedment to examine the feasibility and practicality of the analytical methods introduced in the previous section: the Jinmao Building, Henglong Plaza, Shanghai World Financial Center (SWFC) and Shanghai Center Tower, which are the tallest buildings in Shanghai. The soil layers information for these four super-tall buildings are listed in Table 1 and 2. It is necessary to describe these buildings’ backgrounds before detailing the analysis. In 1990s, buildings in excess of 30 stories experienced rapid development in Shanghai. The tallest of these buildings, the Jinmao Building in the Pudong region, has 88 stories and is 420.5-m high, and its construction began on 1 May 1994 and completed on 28 August 1998. Henglong Plaza in the Puxi region, a 66-story, 288-m building, began construction on 1 March 1998 and was completed in April 2001. Both buildings had complete settlement deformation data already presented (Zhao et al., 1996; Zhao, 1999). The construction of super-tall buildings has continued to increase into the 21st century. The 101-story, 492.0-m SWFC was considered the first landmark in the Pudong region and has mostly complete data, including the installation of instruments beginning on 31 December 2004 for field testing described in detail in ‘A Comprehensive Study on Field Experiment of Piled Raft Foundation for Shanghai World Financial Center’ with 101 stories (Zhao et al., 2014). Finally, the construction Copyright © 2014 John Wiley & Sons, Ltd.



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Table 1. Major physical mechanical properties of soil layer for Jinmao Building. No.

Name of soil layer

Thickness (m)

Bulk density (kN/m3)

Cohesion (kPa)

Friction angle ϕ (°)

① ② ③ ④ ⑤ ⑥ ⑦1 ⑦2

Fill Silty clay Soft silty clay Soft clay Silty clay Silty clay Sandy clay Fine sand

0.90 2.18 4.20 9.72 8.59 3.22 6.94 28.32

18.0 18.5 18.1 17.3 18.5 20.1 18.6 18.9

11.0 17.0 11.5 14.0 13.0 51.0 4.3 0.0

17.0 20.8 22.0 13.5 20.0 21.0 32.7 33.6

Note that the soil properties in SWFC and Shanghai Center are similar to Table 1.

Table 2. Major physical mechanical properties of soil layer for Henglong Plaza. No.

Name of soil layer

Thickness (m)

Bulk density (kN/m3)

Cohesion (kPa)

Friction angle ϕ (°)

① ② ③ ④ ⑤1 ⑤2 ⑥ ⑦1

Fill Silty clay Soft silty clay Soft clay Silty clay Silty clay Silty clay Sandy clay

1.60 1.70 2.90 10.30 3.80 8.90 3.20 2.40

18.0 18.9 17.8 17.0 17.9 18.5 20.3 19.3

0.0 25.0 10.0 12.0 15.0 13.0 53.0 4.3

20.0 19.7 23.5 10.7 11.2 24.0 23.2 40.0

of the 121-story, 632-m Shanghai Center Tower has been completed of structure on 3 August 2013 and will be completed in 2015. All of these data, especially the field measurements data on the four tallest buildings in Shanghai, present optimal conditions for the deformation studies presented in this paper. 3.1. Jinmao Building 3.1.1. Heave and recompression deformation analysis The Jinmao Building’s diaphragm wall structure is a bracing structure with four levels of trusses and is composed of reinforced concrete (RC). The foundation pit depth D = 19.65 m, the diaphragm wall depth H = 36 m, the depth ratio of the diaphragm embedded in the soil to the excavation depth (H–D)/D = 0.83 and the diaphragm wall thickness t = 1 m. (a) Statistical-empirical method SH = 0.20%D = 39.3 mm (b) Conservation of energy method According to the diaphragm’s horizontal deformation, as shown in Figure 3, Sh = 48.5 mm, which means SH = Sh = 48.5 mm. (c) Superstructure-foundation interaction method In Section 2.3, the superstructure-foundation method was primarily focused on the reference (Zhao, 1998). The Jinmao Building was built prior to the emergence of the superstructure-foundation method, and its heave was calculated indirectly using finite element method and the statisticalempirical method. The horizontal deformation of the diaphragm wall calculated with the program SAP 90 was Sh = 50.0 mm. By employing the conservation of energy method described in Section 2.2, we obtained SH = Sh = 50.0 mm. Copyright © 2014 John Wiley & Sons, Ltd.


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deformation (mm) 20

10

0

30

40

50

60

5

depth (m)

10 15 20 25 30 35

Figure 3. Deformation-depth curve of the diaphragm wall in the Jinmao Building. The heave based on the superstructure-foundation interaction method from Section 2.3 was 30 mm, while the recompression obtained from the statistical-empirical method was 36 mm. (d) Deformation versus time curve Based on the deformation versus time curve, as shown in Figure 4, SR = 40 mm. Then, SH = SR/1.2 = 33.3 mm. The values of heave obtained using the different methods were concluded to be similar.

07/12/31

06/12/31

06/03/30

05/01/01

04/03/31

03/04/01

02/09/30

98/05/25

97/08/28

97/04/01

96/09/01

96/03/01

95/12/09

95/10/05

3.1.2. Settlement (a) Statistical-empirical method A = 3 519 m2 in the Jinmao Building. Based on Equation 3)–(5, the predicted settlements SS, SB and SF were 59.3 mm, 83.02 mm and 95.36 mm, respectively, and the corresponding measured settlements were 50 mm, 70 mm and 85 mm, respectively, as shown in Table 3. pffiffiffi Using Equation (5), SF = k4SS = (1.5–1.6) A = (1.5–1.6) × 59.30 = 88.95–94.9 mm. At that time, the Jinmao Building was the first super-tall building to be constructed in the Pudong region. To ensure safety, we assumed SF = 94.9 mm. (b) Superstructure-foundation interaction method By using the superstructure-foundation interaction method, the final settlement SF = 95 mm.

0 10

Date (Y/M/D)

Settlement (mm)

20 30 40 50 60 70 80 90 100

Figure 4. Measured settlements versus time curve in the Jinmao Building. Copyright © 2014 John Wiley & Sons, Ltd.



527

Table 3. Summary of measured or predicted settlements for four super-tall buildings, mm. SS/date*

SB/date*

SF/date*

50.00/(97/08/28) 51.00/(00/03/16) 97.79/(07/09/14) 79.08/(13/08/03)

70.00/(98/05/25) 59.00/(01/04/15) 126.30 (08/05/13) 94.90**

85.00/(07/12/31) 75.00** 150** 120**

Building name Jinmao Building Henlong Plaza SWFC Shanghai Center Tower

SS : SB : SF 1:1.4:1.7 1:1.2:1.5 1:1.3:1.6 1:1.2:1.5

*Date is expressed in year/month/day, **expressed predicted settlements.

(c) Deformation versus time curve The measured value of SF stabilized between 2006 and 2013 and did not change. According to the data shown in Figure 4, SF was estimated as 85 mm. It was observed that the predicted and calculated values were closer to the measured values. 3.2. Henglong Plaza 3.2.1. Heave and recompression deformation analysis The Henglong Plaza’s diaphragm wall structure is a bracing structure with four levels of trusses; three of which are composed of RC. The fourth truss is made of steel pipe to reduce the quantity of RC used and to enhance stiffness in case of emergency. The foundation pit depth D = 18.95 m, diaphragm wall depth H = 33 m, depth ratio of the diaphragm embedded in soil to the excavation depth (H–D)/D = (33–18.95)/18.95 = 0.74 and diaphragm wall thickness t = 1 m. (a) Statistical-empirical method SH = 0.20%D = 36.4 mm (b) Conservation of energy According to the horizontal deformation of the diaphragm, as shown in Figure 5, Sh = 58.5 mm, and then SH = Sh = 58.5 mm. It should be noted that the diaphragm’s horizontal deformation was larger because of the leakage of water occurring somewhere between the walls. (c) Superstructure-foundation interaction method This method was similar to that used for the Jinmao Building at the time to calculate the stress and strain in the soil, wall and bracing system. Sh = 43.0 mm, and then, SH = 43.0 mm. The heave based on the superstructure-foundation interaction method described in Section 2.3 was 28 mm, while the recompression calculated using the statistical-empirical method was 33.6 mm.

deformation (mm) 0

0

10

20

30

40

50

60

-5

depth (m)

-10

-15

-20

-25

-30

Figure 5. Deformation-depth curve of the diaphragm wall in the Henglong Plaza. Copyright © 2014 John Wiley & Sons, Ltd.


528


(d) Deformation versus time curve Based on the deformation versus time curve shown in Figure 6, the recompression SR corresponding to the reload equaling the weight of excavation, 18 mm, and then SH = SR/1.2 = 15.0 mm. Note that the data measured at 2 months after excavation, the data listed in Figure 6 should be added 6 mm. 3.2.2. Settlement (a) Statistical-empirical method pffiffiffi By using Equation (5), k4SS = SF = (1.5–1.6) A = (1.5–1.6) × 60.20 = 90.32–96.32 mm. The listed weight of Henglong Plaza, 4 245 000 kN, was greater than that of the Jinmao Building, at 3 000 000 kN, while its area A of 3 622 m2 and its embedment D of 18.95 m were nearly equal to those of the Jinmao Building, 3 519 m2 and 19.65 m, respectively. However, the higher friction of the bored piles in Henglong Plaza compared with that of the steel pipe piles in the Jinmao Building resulted in less settlement occurring in Henglong Plaza than in the Jinmao Building, as shown in Table 3. Thus, we assumed k4 ≤ 1.5, after which SF ≤ 1.5 × 60.20 ≤ 90.32 mm. (b) Superstructure-foundation interaction method By using the superstructure-foundation interaction method, the final settlement was 75.0 mm, which was similar to the measured settlement. (c) Deformation versus time curve According to the measured data (shown in Fig. 6), the value of SF was predicted to be less than 8.0 cm. 3.3. SWFC 3.3.1. Heave and recompression deformation analysis The SWFC’s diaphragm wall structure was a circular arc with an outside diameter of 100 m, foundation pit depth D = 18.45 m, diaphragm wall depth H = 32.6 m, depth ratio of the diaphragm embedded in the soil to the excavation depth (H–D)/D = 0.77 and diaphragm wall thickness t = 1 m. (a) Statistical-empirical method Based on Equation (1), SH ≤ 0.15%D = 27.7 mm. (b) Conservation of energy method The value of Sh obtained using the nonlinear space theory and method calculation (Zhao et al., 2001) was as follows:

2001/7/1

2001/4/1

2001/1/1

2000/10/1

2000/7/1

2000/1/1

2000/4/1

1999/10/1

1999/7/1

1999/4/1

1999/1/1

1998/10/1

1998/7/1

0

1998/4/1

Sh ¼ 30:0 mm

Date (Y/M/D)

Settlement (mm)

10

20

30

40

50

60

Figure 6. Measured settlements versus time curve in the Henglong Plaza. Copyright © 2014 John Wiley & Sons, Ltd.



529

Then, SH ¼ Sh ¼ 30:0 mm (c) Field experimental test The field data are shown in Figure 7. SH ¼ Sd =1:2 ¼ 28:5 mm It should be noted that after the foundation pit was completed, we visited the site to determine whether the heave of the foundation pit matched our expectations. The engineer confirmed the heave to be 27.5 mm, while the predicted heave was 27.7 mm when D = 18.45 m. The predicted and measured values closely resembled the measured data, as shown in Figure 7. (d) Superstructure-foundation interaction method The superstructure-foundation interaction method was used to calculate the deformation during the entire construction process, from the start of excavation to the building’s completion. The calculated results are shown in Figure 8, and the heave SH = 33.0 mm. (e) Deformation versus time curve Based on the deformation versus time curve shown in Figure 9, the recompression SR corresponding to reloading equal to the excavation weight was 28.0 mm. The value of heave was then SH = 23.3 mm. In summary, the values of heave obtained using the different methods were similar. 3.3.2. Settlement The weight of the SWFC, 4 400 000 kN, is slightly higher than that of the Henglong Plaza, at 4 250 000 kN, while its area A of 6 200 m2 is greater than that of Henglong Plaza, 3622 m2, and its embedment D of 18.45 m is very similar to that of Henglong Plaza. However, the 700-mm-diameter steel pipe pile with L/d = 79 000/700 = 113 > 100 has higher slenderness than the 904-mm-diameter steel pipe pile in the Jinmao Building, which has L/d = 86. (a) Statistical-empirical method. By using Equation (5), SF = (1.5–1.6)D = (1.5–1.6) × 78.85 = 118.2– 126.2 mm.However, to compare the conditions in the Jinmao Building and Henglong Plaza with our predictions mentioned above, we decided to take k4 ≥ 1.7, and then SF ≥ 1.7 × 78.85 ≥ 134.0 mm.

35 30

Heave (mm)

25 20 15 10 5

Date (Y/M/D) 04/12/18

04/12/09

04/12/01

04/11/22

04/1114

04/10/24

04/10/05

04/09/21

04/09/08

04/08/29

04/08/20

04/08/06

04/07/27

04/07/16

04/07/05

04/06/24

04/06/17

04/05/28

04/05/18

0

Figure 7. Heave versus time in the SWFC. Copyright © 2014 John Wiley & Sons, Ltd.


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soil raft -3 -2 -1 1 5 10 20 30 40 50 60 70 80 90

40 20

Settlement (mm)

0 -20 -40 -60 -80 -100 -120

A

A

-140 0

5

10 15 20 25 30 35 40 45 50 55 60 65 70 75

Center line along A-A section (m)

Figure 8. Entire deformation process of the SWFC, from the heave to the 101st story.

(b) Superstructure-foundation interaction method By using the superstructure-foundation interaction method, the final settlement was 150 mm, as shown in Figure 8, which was similar to the measured settlement. (c) Deformation versus time curve According to the measured data shown in Figure 9, the value of SF was predicted to be less than 150 mm. 3.4. Shanghai Center Tower 3.4.1. Heave and recompression deformation analysis This building’s diaphragm wall structure takes the form of a circular arc with an outside diameter of 123.4 m, foundation pit depth of D = 31.20 m, diaphragm wall depth of H = 50 m and depth ratio of the diaphragm embedded in the soil to the excavation depth (H–D)/D = 18.8/31.2 = 0.60.

05/05/29

05/08/22 05/10/18 05/12/28 06/02/22 06/04/26 06/06/28 06/08/16 06/09/25 06/11/28 07/01/12 07/02/21 07/03/29 07/04/26 07/05/28 07/06/27 07/07/30 07/08/31 07/10/30

05/03/17

(a) Statistical-empirical method The soil conditions in the Shanghai Center Tower were similar to those in the SWFC. However,

0 10

Date (Y/M/D)

Deformation (mm)

20 30 40 50 60 70 80 90 100

Figure 9. Settlement versus story curve in the SWFC. Copyright © 2014 John Wiley & Sons, Ltd.



531

compared with the SWFC, the diameter of the Shanghai Center Tower (123.4 m) was larger and the depth ratio of the diaphragm embedded in the soil to the excavation depth (0.60) was smaller than that in the SWFC (0.77). However, the wall thickness was 1.2 m, 0.2 m greater than that of SWFC. For such conditions and based on Equation (1), we assumed that the calculated heave could be taken as k1 = 0.20% and SH = 0.20%D. SH ¼ 0:20%D ¼ 62:4 mm (b) Conservation of energy method The value of Sh obtained using the field data was 68.5 mm, as shown in Figure 10. Based on Equation (6), SH = Sh = 68.5 mm. (c) Superstructure-foundation interaction method By using the superstructure-foundation interaction method, the heave was 60 mm. (d) Field deformation measurement Based on the recompression deformation in March 2013, SR = 68.42 mm in survey, at that time, the load was equal to the excavated soil weight (6 716 582 kN). Thus, the value of heave, SH = SR/1.2 = 68.42/1.2 = 57.01 mm. In summary, the values of heave obtained using different methods for the Shanghai Center Tower were similar. Thus, these data on the four tallest buildings in Shanghai proved that a synergetic approach consisting of the statistical-empirical method, conservation of energy method and superstructurefoundation interaction method could easily predict heave and recompression deformation in practice. 3.4.2. Settlement (a) Statistical-empirical method The area of the Shanghai Center Tower A = 8 250 m2. By using the statistical-empirical method, Equation 3)–(5 show that the predicted settlements for SS, SB, and SF were 90.82 mm, 118.07 mm and 136.23 mm, respectively, and that the corresponding measured settlements were 79.08 mm, 103.0 mm and 120 mm, respectively, as shown in Table 3. By using Equation (5), SF = (1.5–1.6)

pffiffiffi A = (1.5–1.6) × 90.82 = 136.23–145.31 mm.

010

1 Miscellaneous fill 2 Silty clay 3 Very soft silty clay

4 Very soft clay 5 1a Clay

0

20 30 40 50 60 70 80

-5 -10 -15

5 1b Silty clay

-20

6 Silty clay

-25

7 1 Sandy silt

-30 -35

7 2 Silty sand

-40 -45 -50

Figure 10. Deformation-depth curve of the diaphragm wall at a typical point. Copyright © 2014 John Wiley & Sons, Ltd.


532


However, to compare this with the conditions for the Jinmao Building, Henglong Plaza and SWFC mentioned above, we assumed k4 ≤ 1.5, and then SF ≤ 1.5 × 90.82 ≤ 136.2 mm. (b) Superstructure-foundation method The conditions in the Shanghai Center Tower were somewhat different because the heave had not been measured and the structure was already completed. Thus, the analytical methods adopted were as follows. The unequal pile length (82 m and 86 m) in this building (Tang and Zhao, 2014) was considered when using the superstructure-foundation interaction method. The heave did not need to be calculated, and the final settlement was 100 mm, while that by using the iterative method with variable rigidity balance of the pile foundation (Xu and Zhao, 2010) was 124 mm. (c) Field deformation measurement Based on the deformation of completion of structure in August 2013, SS = 79.08 mm. Thus, SF = (1.5–1.6)SS = 118.6–126.5 mm. The average SF = 120.00 mm. It was observed that the predicted values SF (120 mm) were closer to the measuring values expected.

4. DISCUSSION 4.1. Heave and recompression

49.05 m

Centerline of Tunnel I

I

Huangpu River

As previously mentioned, many factors that influenced the heave value, such as pile material type, the depth ratio of the diaphragm embedded in the soil to the excavation depth and the excavation diameter, were complicated because of their interaction. The data from the field measurements were obviously not sufficient to regress the function of the heave value with diverse factors. Therefore, the most important factor, excavation depth, was chosen to predict heave and recompression in the statistical-empirical method. It is very important to gather data from the field to improve this method’s usefulness. We used examples to assess the various methods of calculating heave and recompression based on lateral deformation of filed measurement. For instance, in the Puxi Section of Shanghai Outer Ring Tunnel Project, the depth of 30.4 m on both the opening of one side and the closing of another side of the rectangular pit was noted and is shown in Figure 11 and 12 (Zhao et al., 2005). The calculated (Zhao et al., 2005) and measured heaves were 69 mm and 70 mm, respectively, or SH ≈ 0.20%D. In other words, the result obtained from the statistical-empirical method, SH = 0.20%D, was found to be close to that in practice. Regarding the analyses of the Jinmao Building, SWFC and the Shanghai Center Tower, the selection of a value from the statistical-empirical method for each diaphragm wall’s circular structure still showed a slight difference, SH = 0.15%D and SH = 0.20%D. As shown in Table 4, these results were similar to those obtained from the superstructure-foundation interaction method, conservation of energy method and field measurements. In other words, they were found to be close to that in practice.

47.00 m

Figure 11. Excavation engineering plan view in Puxi Section. Copyright © 2014 John Wiley & Sons, Ltd.



-2.20

-2.20

-6.80

-6.80

-10.80 -14.30 -18.40 -22.10

-10.80 -15.00

533

-19.40 -23.80 -25.20

-25.20

-30.40

I-I

Figure 12. Excavation engineering section view in Puxi Section.

Table 4. Comparison of heave and recompression obtained using various methods, mm. Building Method Superstructure-foundation interaction Conservation of energy Statistical-empirical method Field measurements

Jinmao Building

Henglong Plaza

SH

SR

SH

SR

30.0

36.0

28.0

33.6

48.5 39.3 33.0

56.2 47.2 40.0

58.5 36.4 15.0

70.2 43.7 18.0

SWFC SH

SR

Shanghai Center Tower SH

SR

33.0 39.6

60.0

72.0

30.0 36.0 27.7 33.2 28.5 34.2

68.5 62.4 57.0

82.2 74.9 68.4

However, the values of heave obtained for Henglong Plaza via various methods were influenced by two factors, as shown in Table 4. The horizontal deformation was too large because of poor construction quality. In summary, based on comparisons of the heave and recompression values in Table 4, the values obtained using the superstructure-foundation interaction, conservation of energy and statisticalempirical methods were similar to the field data and had practical utility. 4.2. Final settlement Like heave value, the buildings’ final settlements depend on many factors, including the pile type and length/diameter, especially, the heave and recompression in the compensated piled raft foundations with deep embedment in super-tall buildings. Herein, the authors discuss how pile type and length/diameter influence the final settlement. 4.2.1. Influence of pile type and length/diameter on the final settlement Until now, it has been observed that the superstructure-foundation interaction method and statisticalempirical method are satisfactory and that the relationship between SS : SB : SF could be used to assist in calculating the final settlement of a super-tall building with deep embedment. We also determined the real final settlement according to the concrete conditions listed in Table 5, for which the effects of pile type and length/diameter on final settlement were also significant. In other words, it was difficult to accurately determine the final settlement. However, we could predict it by making a concrete analysis of a concrete problem. Copyright © 2014 John Wiley & Sons, Ltd.


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Table 5. Influence of pile type and length/diameter on the final settlement, mm. Building name Embedment, m

Jinmao Building 19.65 Henglong Plaza 18.95 SWFC 18.45 Shanghai Center Tower 31.2

Design weight of building, kN

Pile type

Measured or predicted SF, mm

Area of foundation, m2

Length, m/diameter, mm

Measured SS, mm

3 000 000 3519 4 240 000 3622 4 400 000 6200 6 709 468 8250

Steel pipe pile (81/904) = 89.6 Bored pile (78/800) = 97.5 Steel pipe pile (78/700) = 111.4 Bored pile (82, 86/1000) = 82, 86

SF = 85 SS = 50 Predicted = 70 SS = 51 Predicted > 150 SS = 97.79 Predicted = 120 SS ≈ 82.00

4.2.2. Actual final settlement If the elevation of the pit bottom was unchanged in the survey, then the real deformation was equal to the recompression deformation SR minus the heave SH. Thus, when using a compensated piled raft foundation, the deformation was less than that experienced when using a typical piled raft foundation. The final settlement calculated using the statistical-empirical method for the Shanghai Center Tower (Tang and Zhao, 2014) was changed. The final settlement was as follows: SF ¼ SH þ SR þ SL þ SD ¼ 68:5 þ 82:2 þ 11:0 þ 28:0 ¼ 52:7 mm where heave SH due to the weight of excavation soil. Herein obtained by concept of conservation of conservation, SH = 68.5 mm; recompression, SR = 82.2 mm, due to the dead load of the structure, DL = 6 709 000 kN; recompression, SL, due to the live load of the structure, LL = 900 000 kN, thus, SL = (900 000/6 709 000) × 82.2 mm = 11.0 mm. Recompression, SD, due to constant load, according to observation for tall buildings in Shanghai, SD ≈ 0.3(SR + SL) ≈ 0.3(82.2 + 11.0) = 28.0 mm. In conclusion, the methods presented in this paper not only are applicable to the soft soil of Shanghai but can also provide a useful reference for soil in other regions. A Dubai building can serve as an example of this applicability. Equation (5) was used to predict settlement prior to the completion of the 160-story, 828-m Burj Khalifa Tower in Dubai. According to a 3-D analysis performed by the consulting company Hyder (UK), the maximum settlement was approximately 80 mm (Baker et al., 2006; Russo et al., 2013). pffiffiffi A = 3380 m2, SS = A = 58 mm, SF = (1.5–1.6) SS = 87–93 mm. Dubai soil, which is more stiff than Shanghai soil, had SF values lower than the range of 87–93 mm. Therefore, Equation 3)–(5 were determined to be practical. 5. CONCLUSIONS Four main conclusions were drawn from this study based on the detailed deformation analyses described above. (1) The useful method for determining the heave and recompression of compensated piled raft or box pile foundations with deep embedment has become an important subject in geotechnical engineering. A synergetic approach was generated by summarizing the calculated heave values, SH, using the superstructure-foundation interaction method, the conservation of energy method, the statistical-empirical method and the corresponding field data. Based on the research results, the synergetic approach was found to be useful in practice. (2) The statistical-empirical method used to predict the heave and recompression of piled raft or box foundations with deep embedment in super-tall buildings was as follows: SH ≤ 0.15%D for a circular structure with an outside diameter not larger than 100 m and SH ≤ 0.20%D for a circular structure with an outside diameter >100 m and a bracing structure. For all cases, the recompression can be estimated by SR = 1.2 SH. (3) Calculating the final settlement for super-tall buildings is very important and is considered a building’s lifeline. The superstructure-foundation interaction method and the statistical-empirical Copyright © 2014 John Wiley & Sons, Ltd.



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method introduced in this paper could be used in this calculation. The settlement pffiffiffirelationship between different cases, the settlement after the completion of the structure SS = A, the settlement after completion of the building SB = (1.2–1.4) SS, the final settlement SF = (1.5–1.7) SS and SS : SB : SF were also very useful for determining the final settlement. (4) The effective factors for heave and recompression are more complex than uncertain settlement and will require further theoretical and practical study, especially for the accumulation of field data. ACKNOWLEDGEMENTS

This paper was supported by funds from the NSFC Project (grant 51278359), the Kwang-Hua Fund for the College of Civil Engineering, Tongji University and the Program for Changjiang Scholars and Innovative Research Teams in Universities (PCSIRT, IRT1029). The authors express their sincere thanks to Chief Engineer, Professor S. Chao of the Architectural Design and Research Institute of Tongji University and Chief Engineer and Professor J. Gong of the Shanghai Construction Group for their support in this paper. The authors also wish to acknowledge the two reviewers unknown whose insightful suggestions helped shape this paper. REFERENCES Baker WF, Korista DS, Novak LC. 2006. Structure design of the Burj Dubai Tower. In Proceedings of 2006 Shanghai International Seminar of Design and Construction Technologies of Super High-Rise Buildings, Shanghai, China; 7–12. D’appolonia DJ, Poulos HG, Ladd CC. 1971. Initial settlement of structures on clay. Journal of Mechanics and Foundation Engineering 97: 1359–1377. Focht JA, Khan FR, Gemeinhardt JP. 1978. One Shell Plaza. Journal of Geotechnical Engineering Division 104: 593–608. Poulos HG. 2005. Piled raft and compensated piled raft foundation for soft soil sites. Geotechnical Special Publication 129: 214–235. Russo G, Abagnara V, Poulos HG, Small JC. 2013. Re-assessment of foundation settlements for the Burj Khalifa, Dubai. Acta Geotechnica 8: 3–15. Sales MM, Small JC, Poulos HG. 2010. Compensated piled raft in Clayey soils: behavior, measurements, and predictions, Canadian Geotechnical Journal 47: 327–345. Tang YJ, Pie J, Zhao XH. 2013. Design and measurement of piled-raft foundations. In ICE Proceedings-Geotechnical Engineering. DOI: 10.1680/geng-13.0004. Tang YJ, Zhao XH. 2014. 121-story Shanghai Center Tower foundation re-analysis using a compensated pile foundation theory. Structural Design of Tall and Special Buildings 23: 854–879. DOI: 10.1002/tal.1087 Xu ZJ, Zhao XH. 2010. Design and Calculation of Pile Foundation for Buildings-design of Variable Rigidity Balance of Pile Foundation. China Machine Press: Beijing (in Chinese). Zeevaert L. 1957. Compensated friction pile foundation to reduce settlement of building on the highly compressible volcanic clay of Mexico City. In Proceedings of 4th International Conference SMFE, London, British; 2: 81–86. Zhang WQ, Zhao XH, Yin YA, Qian YP. 1980. Comprehensive research on field test of box foundation for 4 tall buildings. Chinese Journal of Geotechnical Engineering 2: 12–26 (in Chinese). Zhao XH. 1998. Theory of Design of Piled Raft and Piled Box Foundations for Tall Buildings in Shanghai. Tongji University Press: Shanghai. Zhao XH. 1999. Design Theory and Practice of Superstructure-foundation Interaction with Podium. Tongji University Press: Shanghai (in Chinese). Zhao XH, Chen JM, Gong J, Zhou GR, Zhang QH, Li B. 2000. Deep excavation engineering for tall building in Shanghai. In Proceedings of International Symposium of Civil Engineering in 21st Century, Beijing, China; 1: 517–525. Zhao XH, Chen ZM, Hu ZX. 1996. Practice and Analysis on Excavation Engineering for Tall Buildings. Tongji University Press: Shanghai (in Chinese). Zhao XH, Gong J, Zhang BL, Xiao JH, Tang YJ, Zhou H. 2014. A Comprehensive Study on Field Experiment of Piled Raft Foundation for Shanghai World Financial Center with 101-storey—Theory & Practice of Interaction between Superstructure & Foundation-101. Tongji University Press: Shanghai (in Chinese). Zhao XH, Li B, Yang GX, Li K. 2005. Practice and Theory for Specially Big and Deep Excavation Engineering. China Communication Press: Beijing (in Chinese). Zhao XH, RM Lu, Chen ZM, Gong J. 2001. Non-linear space theory & method & application. In Proceedings of 15th International Conference on SMGE, Istanbul, Turkey; 2: 138–141.

AUTHORS’ BIOGRAPHIES Yongjing Tang received her Bachelor’s Degree in Civil Engineering in 1989, Master’s Degree in Concrete Engineering in 1994, and PhD in Geotechnical Engineering in 1996 at Tongji University. She is currently affiliated with the Department of Geotechnical Engineering, Tongji University. Her research interests include Tunneling and Underground Engineering and Structure of Historical Engineering. Copyright © 2014 John Wiley & Sons, Ltd.


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Xihong Zhao received his Bachelor’s Degree in 1953 at South China University of Technology and Master’s Degree in Bridge Engineering in 1956 at Tongji University. He is currently affiliated with the Department of Geotechnical Engineering, Tongji University. His research interest includes Geotechnical Engineering.

Copyright © 2014 John Wiley & Sons, Ltd.
