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Frontiers of Structural and Civil Engineering

Front. Struct. Civ. Eng.    2018, Vol. 12 Issue (1) : 26-43
Shanghai center project excavation induced ground surface movements and deformations
Guolin XU1(), Jiwen ZHANG2, Huang LIU2, Changqin REN3
1. Department of Civil Engineering, Southwest Forestry University, Kunming 650224, China
2. Department of Civil Engineering, University of Kentucky, Lexington, KY 40506-0281, USA
3. Shanghai Geotechnical Investigations & Design Institute Company Limited, Shanghai 200032, China
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Empirical data on deep urban excavations can provide designers a significant reference basis for assessing potential deformations of the deep excavations and their impact on adjacent structures. The construction of the Shanghai Center involved excavations in excess of 33-m-deep using the top-down method at a site underlain by thick deposits of marine soft clay. A retaining system was achieved by 50-m-deep diaphragm walls with six levels of struts. During construction, a comprehensive instrumentation program lasting 14 months was conducted to monitor the behaviors of this deep circular excavation. The following main items related to ground surface movements and deformations were collected: (1) walls and circumferential soils lateral movements; (2) peripheral soil deflection in layers and ground settlements; and (3) pit basal heave. The results from the field instrumentation showed that deflections of the site were strictly controlled and had no large movements that might lead to damage to the stability of the foundation pit. The field performance of another 21cylindrical excavations in top-down method were collected to compare with this case through statistical analysis. In addition, numerical analyses were conducted to compare with the observed data. The extensively monitored data are characterized and analyzed in this paper.

Keywords deep excavation      foundation pit      soft clay      top-down method      field observation      ground surface movements      ground deformations     
Corresponding Authors: Guolin XU   
Online First Date: 01 August 2017    Issue Date: 08 March 2018
 Cite this article:   
Guolin XU,Jiwen ZHANG,Huang LIU, et al. Shanghai center project excavation induced ground surface movements and deformations[J]. Front. Struct. Civ. Eng., 2018, 12(1): 26-43.
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Guolin XU
Huang LIU
Changqin REN
Fig.1  Site location and adjacent structures
Fig.2  Cross section of the foundation pit with the soil profiles
Fig.3  Soil properties along the depth at the site
Stage Operation Activity Day
1 The first level strut (Elevation−1 to−8.5 m)

Construct the first level wall and retaining structure framework with 1 m height as preparation work; 07/27/2009–08/24/2009

Cast concrete; 08/25/2009–08/27/2009

2&3 The Second level strut (Elevation−8.5 to−14.5 m)

Remove the first level soil to form a pit with a size of 50m (length) × 15m (width) × 5m (depth) around the lift platform No. 1; 09/16/2009–09/22/2009

Excavate to the bottom of the second level strut with a depth of 10 m around the lift platform No. 3 in a direction of north-south from peripheral to central; 10/05/2009–10/11/2009

Change excavation sequence, excavate in the direction of east-west from central to peripheral;10/11/2009–10/23/2009

Construct the second level wall and retaining structure framework and cast concrete; 10/24/2009–10/30/2009

4 The Third level strut (Elevation−14.5 to−19.5 m)

Excavate to the third level along the circumference but do not remove the central soil; 10/31/2009–11/03/2009

Construct the third level wall and retaining structure framework and cast concrete; 11/04/2009–11/16/2009

5 The Fourth level strut (Elevation−19.5 to−24.0 m)

Remove the central soil at the third level; 11/17/2009–11/21/2009

Begin to dewater; 11/22/2009

Excavate along the circumference to the fourth level but do not remove the central soil; 11/22/2009–11/29/2009

Construct the fourth level wall and retaining structure framework and cast concrete; 11/30/2009–12/07/2009

Remove the central soil at the fourth level; 12/08/2009–12/14/2009

6 The Fifth level strut (Elevation−24.0 to−28.0 m)

Excavate along the circumference to the fifth level but do not remove the central soil; 12/15/2009–12/20/2009

Construct the fifth level wall and retaining structure framework and cast concrete; 15/21/2009–01/04/2010

7 The Sixth level strut (Elevation−28.0 to−33.7 m)

Remove the central soil at the fifth level; 01/05/2010-01/08/2010

Excavate along the circumference to the sixth level but do not remove the central soil; 01/09/2010–01/23/2010

Construct the sixth level wall and retaining structure framework and cast concrete; 01/24/2010–01/30/2010

8 Cast concrete under-layer

Remove the central soil at the sixth level and excavate to-33.7m; 01/31/2010–02/03/2010

Cast all concrete under-layer; 02/04/2010–02/12/2010

9 Base plate construction

Construct the base plate framework and cast concrete; 02/08/2010–04/19/2010

End dewatering; 04/05/2010

10 Underground Construction

Construct the underground structure and facilities; 04/20/2010–09/29/2010

Tab.1  Main stages of the construction of the central foundation pit
Level Size, height × thickness (mm × mm) Central elevation (m)
1 3700 × 1500 −1.75
2 2800 × 1500 −9.30
3 2800 × 1600 −15.30
4 3000 × 1600 −20.30
5 3000 × 1800 −24.90
6 3000 × 1800 −28.90
Tab.2  Size and location of the struts
Fig.4  Instrumentation layout of the circular pit
Fig.5  Lateral movements of the walls at P01 and P05: (a) variations in different stages along the depth;(b) variations at different depths along the excavation progress
Fig.6  Vertical movements of the peripheral soil in layers at R1 and R5: (a) variations in different stages along the depth; (b) variations at different depths along the excavation progress
depth (m) accumulative settlement (mm) average (mm)
R1 R2 R3 R4 R5 R6 R7 R8
−6.0 −57 −48 −49 −49 −58 −46 −41 −41 −48
−11.0 −24 −41 −48 −48 −60 −42 −44 −39 −42
−16.0 -−20 −19 −41 −41 −46 −38 −38 −29 −33
−21.0 −5 −7 −29 −29 −37 −27 −27 −17 −21
−26.0 −5 4 −20 −20 −4 −4 −7 −12 −7
−31.0 4 10 −5 −5 3 -2 -5 1 1
−36.0 7 9 8 8 4 4 2 −2 5
−41.0 13 19 12 12 15 7 −1 4 10
-46.0 18 15 15 15 20 12 9 3 13
-51.0 17 10 13 13 20 17 17 3 14
-56.0 18 16 20 20 22 18 19 10 18
Tab.3  Layered vertical movements of the soils behind the walls at different depths at the end of the excavation
Fig.7  Cross sections showing the relationship between the surrounding ground vertical settlements and the distance to the perimeter of the pit
Fig.8  Basal heave along the depth for all arrowhead magnets
Fig.9  Relationship between the heave amount and the distance from the center of the pit to the measured points
Fig.10  Embedded depth ratio Hd /H versus H ; (b) depth where δhm occurred versus H ; (c) relationship between H and δhm , δv m, and δbs, respectively
Fig.11  (a) Embedded depth ratio Hd /H versus D ; (b) depth whereδh m occurred versus D; (c) relationship between D and δh m , δvm, and δb s, respectively; (d) relationship between Hd /H and δhm , δv m, and δbs, respectively
Fig.12  The simulation models for estimating the ground movements and deformations duringconstruction process
Fig.13  The simulation results in different construction stage corresponding to each strut level
γ: unit weight of soil (kN/m3);
c': effective cohesion(kPa);
ϕ': effective friction angle(°);
v: Poisson’s ratio (dimensionless unit);
K: permeability coefficient(10-4cm/s);
Em: pressure meter modulus(MPa);
Gm: pressure meter shear modulus(MPa);
Ps:bearing capacity of static penetration test(MPa);
E: dynamic elastic modulus (MPa);
G: dynamic shear modulus (MPa);
H: excavation depth of the pit(m);
δhm: the maximum lateral movements of the walls (mm);
Hm: the depth where δhmoccurred (m);
D: foundation pit diameter (m);
Hd: embedded length of the retaining walls (m);
δhs: the maximum lateral movement of the circumferential soil (mm) ;
δvm: the maximum layered soil settlement (mm) ;
δbs: the maximum basal heave (mm) ;
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