Shanghai center project excavation induced ground surface movements and deformations

doi:10.1007/s11709-017-0439-1

Front. Struct. Civ. Eng.

2018, Vol. 12

Issue (1) : 26-43 https://doi.org/10.1007/s11709-017-0439-1

RESEARCH ARTICLE

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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Abstract

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 Author(s): 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.

URL:

https://academic.hep.com.cn/fsce/EN/10.1007/s11709-017-0439-1
https://academic.hep.com.cn/fsce/EN/Y2018/V12/I1/26

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	53
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	45
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	18
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	28
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	14
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	25
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
9	Base plate construction	Construct the base plate framework and cast concrete; 02/08/2010–04/19/2010 End dewatering; 04/05/2010	71
10	Underground Construction	Construct the underground structure and facilities; 04/20/2010–09/29/2010	161

Tab.1 Main stages of the construction of the central foundation pit

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

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

H d / H

versus H ; (b) depth where

δ h m

occurred versus H ; (c) relationship between H and

δ h m

δ v m

, and

δ b s

, respectively

Fig.11 (a) Embedded depth ratio

H d / H

versus D ; (b) depth where

δ h m

occurred versus D; (c) relationship between D and

δ h m

δ v m

, and

δ b s

, respectively; (d) relationship between

H d / H

and

δ h m

δ v m

, and

δ b s

, 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);

E_m_:pressure meter modulus(MPa);

G_m: pressure meter shear modulus(MPa);

P_s:bearing capacity of static penetration test(MPa);

E: dynamic elastic modulus (MPa);

G: dynamic shear modulus (MPa);

H: excavation depth of the pit(m);

δ h m

: the maximum lateral movements of the walls (mm);

H m

: the depth where

δ h m

occurred (m);

D: foundation pit diameter (m);

H_d: embedded length of the retaining walls (m);

δ h s

: the maximum lateral movement of the circumferential soil (mm) ;

δ v m

: the maximum layered soil settlement (mm) ;

δ b s

: the maximum basal heave (mm) ;

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