1 excavation methods and support system

8/9/2019 1 Excavation Methods and Support System

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3.1 Introduction3.2 Excavation Methods

3.3 Retaining Walls

3.4 Strutting Systems

3.5 Selection of the

Retaining Strut System

3.6 Case History of the

TNEC Excavation

Excavation Methods and Lateral SupportingSystems

3.2.1 Full Open Cut Methods3.2.2 Braced Excavation Methods3.2.3 Anchored Excavation Methods3.2.4 Island Excavation Methods3.2.5 Top-down Construction Methods

3.2.6 Zoned Excavation Methods

3.3.1 Soldier Piles3.3.2 Sheet Piles3.3.3 Column Piles3.3.4 Diaphragm Walls


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Definition of deep excavation

Terzaghi(1943)Whose excavation depths were larger thantheir widths

Terzaghi and Peck (1967) Peck et al.(1977)Whose depths were deeper than 6 meters

Introduction (in chapter 1)


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A complete deep excavation design

includes a retaining system, a strutting

system, a dewatering system, excavation

procedure, a monitoring system, building

protection , etc. Figure 1.1 illustrates the

general course of deep excavation design.


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Adjacent propertyinvestigation

Set the criteria fo r design

Confirm the conditions of

the excavation site

Decide excavationmethod

Decide auxiliary method

Decide depth of retainingwall

Whether economic ?

Strut design

Determination of theexcavation procedure

Deformation analysis

Meet the designcriteria ?

Stress analysis

Geologicalinvestigation

Boiling analysis

Push - in fa il ur eanalysis

Basal heaveanalysis

Detailed design of theretaining strutting system

Arrangement of monitoringsystems

Dewatering analysis

Uplift analysis

FIGURE 1 . 1 Flow chart for analysis and design of an excavation

Yes

Start

End

No

No


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Flow chart for analysis anddesign of an excavation

Adjacent propertyinvestigation

Set the criteria for design

Confirm the conditions ofthe excavation site

Decide excavationmethod

Decide auxiliary method

Decide depth of retainingwall

Whether economic?

Geologicalinvestigation

Boiling analysis

Push-in failureanalysis

Basal heaveanalysis

Yes

Start

No

No


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Strut design

Determination of the

excavation procedure

Deformation analysis

Meet the design

criteria?

Stress analysis

Detailed design of theretaining strutting system

Arrangement of monitoringsystems

Yes

End

No

Dewatering analysis

Uplift analysis


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3.2 Excavation Methods

3.2.1 Full Open Cut Methods

FIGURE 3.1 Sloped open cut method

a


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Retaining wall

3.2 Excavation Methods3.2.1 Full Open Cut Methods

FIGURE 3.2 Cantilevered open cut method


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3.2.2 Braced Excavation Methods

Excavation surface

BracketWale

Strut

Mat

Slab

Center post

Retaining wall

FIGURE 3.3 Braced excavation method (a) profile


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Retaining wallHorizontal strut

Brace

Wale

3.2.2 Braced Excavation Methods

FIGURE 3.3 Braced excavation method (b) plan


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3.2.2 Braced Excavation MethodsFigure 3.4


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3.2.3 Anchored Excavation Methods

Retaining wall

Anchor head

Anchor seat

Tendon

FIGURE 3.6 Basic configuration of an anchor


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Slab

Excavation surface

Anchor head

Free sectionAnchorage section

Mat foundation

3.2 Excavation Methods3.2.3 Anchored Excavation Methods

FIGURE 3.7 Profile of the anchored excavation method


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Water flow

FIGURE 3.8 Problem of the anchored excavation method when applied inthe cohesionless soil with high groundwater level

Retaining wall



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3.2.4 Island Excavation Methods

q

o35q

Retaining wall

Raker Wale

FIGURE 3.9 Island excavation method with single level of struts


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3.2.4 Island Excavation Methods

FIGURE 3.10 Island excavation method with multiple levels of struts

Main structure

Center post

Wale

Retaining wall

Raker


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3.2.5 Top-down Construction Methods

FIGURE 3.12 Top down construction method

Bearing stratum

Pile

Steel columnRetaining wall

Excavation surface

Excavation surface

Final excavation surfac

Floor slab


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Diaphragm wall

Wall deformation

FIGURE 3.13 Plan of an excavation


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A zone B zone

Diaphragm walla b


FIGURE 3.14 Plan of the zoned excavation method


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3.3 Retaining Walls

3.3.1 Soldier Piles3.3.2 Sheet Piles

3.3.3 Column Piles3.3.4 Diaphragm Walls


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3.3.1 Soldier Piles

WedgeSoldier pile

Lagging

(b)(a)

Backfill

FIGURE 3.15 Soldier piles (a) front view (b) section view


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3.3.1 Soldier Piles

h l


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3.3.2 Sheet Piles

Excavation bottom

FIGURE 3.17 Steel sheet pile method


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3.3.2 Sheet Piles3.3 Retaining Walls

3 3 2 Sh Pil


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( a )

( b )

( c )

3.3.2 Sheet Piles

FIGURE 3.19 Sections of steel sheet piles (a) U pile (b) Z pile (c) straight pile


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3.3.3 Column Piles

(1) Packed In Place pile. The diameter of PIP pile isaround 30 cm to 60 cm.

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FIGURE 3.21 Construction procedure of a packed in place (PIP) pile

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3.3 Retaining Walls

3 3 3 C l Pil


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(2) Concrete piles

Reverse circulation drill method--

All casing method--

The diameters are around 60 cm to 200 cm.

3.3.3 Column Piles

3 3 3 C l Pil


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(3) Mixed piles.They are also called MIP piles (Mixed In

Place piles). The diameters are around 30 cm to 60 cm.

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(a) swirl the drillingrod and inject mortarinto the soil from the

bottom of thedrilling rod

(b) drill to thedesigned depth andtreat the soilsimultaneously whilekeeping swirling

(d) finish theimprovement

(c) withdraw thedrilling rod andinject the mortar simultaneously

FIGURE 3.22 Construction procedure of a mixed in place (MIP) pile

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3.3.3 Column Piles


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SMW is a typical MIP piles.

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FIGURE 3.23 Soil mixed wall (SMW)


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Layouts of column piles

( a )

( b )

15

24

79

68

3

1 683524 79

32 68 71 954

1 365

2 47

( c )

( d )

( e )

FIGURE 3.24 Layouts of column piles (a) independent pattern (b) S pattern

(c) line pattern (d) overlapping pattern (e) mixed pattern

3 3 4 Diaphragm Walls


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(a) (b) (d)

Groundwater

(c)

FIGURE 3.26 Construction procedure of a diaphragm wall panel(a) construction of the guided wall(b) excavation of the trench

(c) placement of reinforcements(d) concrete casting

3.3.4 Diaphragm Walls

Panel partition


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Panel partition----

Primary panelSecondary panel


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Guided wall construction----


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Trench excavation----

Clamp type----


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31 2

1 3 2

Hydraulic bucket

FIGURE 3.25 Trench excavation by the MHL method


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Rotatory type----


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Placement of reinforcements----


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The joint of diaphragm walls:

Connection pipe method--

End-plate method--

Stable waterConcreteGround Steel pipe


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( a ) ( b )

( c ) ( d )

FIGURE 3.27 Procedure of construction of a diaphragm wall (a) trenchexcavation (b) steel pipe installation (c) steel cage

placement (d) concrete casting

Stabilizer

surfaceConcrete surface

p p(connection pipe)

Tremie concreteStabilizer

Reinforcement cage

Fresh concrete


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Concrete

Connection pipe

FIGURE 3.29 Joint of diaphragm walls: theconnection pipe method

1. excavate trench

2. Place reinforcement cage and insert connection pipe

3. Backfill concrete and pull out connection pipe

4. Excavate secondary unitPrimary unit Secondary unit

Connection pipe method--


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End-plate method--

Angle steel forstopping water

Partition plate

Angle steel for stoping water

#10#5@30

40 50 20

6 0

Vinylon sheet

6-#8#5@60

#5@30#10

Tremie pipe

Short reinforced bar for fixing steel plate#4@60

FIGURE 3.30 Joint of diaphragm walls: the end-plate method (unit: cm)


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3.4 Strutting Systems

According to the material a strut is made of, thereare wood strut, RC strut, and steel strut.

According to the function of a strut, it is classifiedas an earth berm, a horizontal strut, a raker, ananchor, or as a top-down floor slab.


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Berm

Retaining wall

FIGURE 3.31 Earth berm as lateral support

R k


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Main structure

Steel pile

Retaining wall

Retaining wall

Raker

Raker

FIGURE 3.32 Rakers


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3.5 Selection of the Retaining Strut System

: good : acceptable : not good Note (1): should be applied along with special drill and striking device.

(2): if driven into soil by static vibrating, noise and vibration can be reduced.

TABLE 3.1 Application conditions for retaining walls

Wall type Soil type Sealing &Stiffness

Construction Conditions

BudgetSoftclay

SandGravel

soilSealing Stiffness

Noise &Vibration

Treatmentof dump

mud

Surfacesettlement

Soldier pile (1) (2)

Steel sheet pile

(2)

PIP pile

Reinforcedconcretecolumn

pile

MIP pile

Diaphragmwall

E x c a v a t

i o n

D e p

t h

U n

d e r g r o u n

d

O b s t r u c t

i o n

C o n s t r u c t

i o n p e r

i o d


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Retaining wall E (kg/cm 2)

I (cm 4/ m)

E I (t-m 2/ m)

StiffnessratioMethod Type & Dimension

Soldier

pile (1)H300x300x10x15 2.04 106 20,400 4,160 1.0

H350x350x12x19 2.04 106 40,300 8,220 2.0

Steel sheet

pile (2)SP- 2.04 106 16,400 3,350 0.8

SP- 2.04 106 31,900 6,500 1.6

Column

pile (3)30 cm (diameter) 2.1 105 132,500 2,780 0.7

80 cm (diameter) 2.1 105 2,513,300 52,780 12.7

Mip pile (4)SMW method

H400x200x8x132.04 106 59,250 12,090 2.9

Diaphragm

wall (5)50cm thick 2.1 105 1,041,700 21,900 5.3

100cm thick 2.1 105 8,333,300 175,000 42.0

TABLE 3.2 Nominal stiffness (before reduction)


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3.6 Case History of the TNEC ExcavationStreet

Inclinometer Extensometer Tiltmeter Main observation sectionPizometer Rebar stress meter Heave gaugeEarth/water pressure cell

FIGURE 3.33 Excavation of the Taipei National Enterprise Center (a) plan (b) profile

(a)

Scale0 5 10 m

F

E

DC

A

B

P R

Q S


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(b)

densegravel

N>100

compactto densesilty sand

N>14~37

stiff silty clay; N=9~11medium loose silty sand ; N=22~24

soft tomediumsilty clay

N=2~5

loose silty sand N=4~11

soft siltyclay

N=2~4

D e p t h

( m )

5

0

10

20

15

25

30

35

40

45

50

Diaphragm wall

Inclinometer Extensometer Heave gauge

Settlement mark Pizometer Earth/Piezometer cell

FIGURE 3.33 Excavation of the Taipei National Enterprise Center(a) plan (b) profile


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Pile

Steelcolumn

Diaphragm wall

(a) (b)

B1F

GL-19.7m

Strut

GL-19.7m

GL-4.9m

GL-2.8m

GL-35m

FIGURE 3.34 Construction procedure of the Taipei National Enterprise Center

(see Table 3.3 for the description of the construction procedure)


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(c)

B3FB2FB1F1F

6F

GL-19.7mGL-11.7m

GL-8.6m

(d)

GL-19.7m

GL-15.2mGL-17.3m

B4FB3FB2FB1F1F

Strut

FIGURE 3.34 Construction procedure of the Taipei National Enterprise Center(see Table 3.3 for the description of the construction procedure)


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TABLE 3.3 Excavation process of TNEC


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Stage Day Excavation activities

-29~ Installed devices outside of the excavation zone, including in-soilinclinometers, extensometers, observation wells, and electronic

piezometers1~89 Constructed the diaphragm wall, including installation of the earth/water

pressure cells, in-wall rebar strain meters, and in-wall inclinometers

89~147 Constructed piles and the steel columns

147~155 Installed devices inside of the excavation zone, including the piezometers

and heave gauges1 156~162 Excavated to the depth of GL-2.80 m

2 164~169 Installed struts H 3003001015 at the depth of GL-2.0 m. The preload ofeach strut 784.8 kN

3 181~188 Excavated to the depth of GL-4.9 m

4A 217 Constructed B1F floor slab at the depth of GL-3.5 m4B 222~238 Dismantled the first level of strut and constructed the 1F floor slab.

Started the construction of the superstructure


6 279 Constructed the B2F floor slab at the depth of GL-7.1 m


p


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Note The first day of the construction of the diaphragm wall is the datum

8 352 Constructed the B3F floor slab at the depth of GL-10.3 m


10 400 Constructed the B4F floor slab at the depth of GL-13.7 m11A 419~423 Excavated the central zone to the depth of GL-17.3 m

12A 425~429 Installed struts H4004001321 at the depth of GL-16.5 m in the centralzone. The preload of each strut 1177 kN

11B 430~436 Excavated the side zones to the depth of GL-17.3 m

12B 437~444 Installed struts H4004001321 in the two side zones at the depth ofGL-16.5 m. The preload of each strut 1177 kN


457 Finished the superstructure

14 464~468 Cast the foundation slab

15 506~520 Constructed the B5F floor slab at the depth of GL-17.1 m

16 528 Dismantled the second level of struts

1 excavation methods and support system

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