Deep Excavation - Diaphragm Wall - Dr.M.muttharam

DEEP EXCAVATION-DIAPHRAGM WALL

by

Dr. M. Muttharam, Associate Professor,CEG,Anna university, Chennai

Ms. J. Jasmine Nisha, Research Scholar, CEG,Anna university, Chennai

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INTRODUCTION

Due to rapid economic growth, numerous deep excavation

projects for infra-structure and high-rise buildings were in

progress

Deep excavations are often carried out in congested areas

to increase the underground usable spaces

Excavation alters the stresses and disturbs the existing

equilibrium and become unstable cut is deep and nearly

vertical

To improve the stability supported systems are used


Diaphragm walls

Temporary and permanent supporting

system

Reduced number of joints in the wall

which ultimately improves the walls

water tightness of walls

Deflection of the wall is less can be

used in congested areas


DIAPHRAGM WALLS - APPLICATIONS

Retaining structure and load bearing element for

deep basements of buildings traffic under passes under ground mass transit stations cut and cover tunnels parking garages underground industrial facilities docks and water front installations water works


ADVANTAGES

Can be made in any soil and to any depth, regardless of the groundwater

Fulfill simultaneously the task of sheeting, waterproofing and load bearing

Every phase of operation can be mechanizedVery little noise on vibrationEven a confined space can be entirely usedMaterial of the wall may vary within wide

limitsHas excellent properties as far as load

bearing is concerned


ADVANTAGES

Its stiffness might be increased by buttresses to carry high moments.

It is very suitable for tie-backsWork can be carried out freely in sections.

No major surface gradings are required prior to the trenching

It provides a simple and clear site as compared with the traditional foundation pit full of Braces


DISADVANTAGES

The surface quality of the diaphragm walls depends on the equipment used and the type of soil to be excavated

In order to prevent pollution caused by the slurry at the site and its vicinity, special precautions must be taken.

Any inspection during construction is only possible by indirect means


DISADVANTAGES

In the following cases it can be made only after preparatory work

In open water In layers bearing artesian water In poorly compacted fillNear existing buildings, or if the existence

of unknown sewers, cellars, caves, public utilities is suspected

In a soil where a significant and rapid loss of the slurry is anticipated


CONSTRUCTION SEQUENCE


DIAPHRAGM WALL CONSTRUCTION


STABILITY OF THE TRENCHo Technological requirements

The guide wall must not move or be deformed

There must be nor deformations or cave-ins in the trench

The slurry level must not sink to such an extent or at such a rate as to endanger the technological procedure


STABILITY OF THE TRENCH-CONT

Stability requirements concerning the vicinity of the slot

There must not occur any greater subsidence or damage of the surrounding buildings, structures or public utilities than the considered values

Traffic in the vicinity must remain unhindered

The safety of the workers, machinery and equipment must be protected


FACTORS INFLUENCING THE STABILITY OF THE SLOT

The forces stabilizing the trench The support of the guide wall and the

slurry the internal strength of the soil

The forces acting in opposition to cause failure of the slot Hydrostatic pressure Weight of the soil The surcharges and other forces or their

combined effect


FUNCTIONS OF THE GUIDE WALL FROM THETECHNOLOGICAL ASPECT ARE

To ensure the guidance of the trenching tool

To ensure the specified horizontal state of the diaphragm wall

To serve as a baseline for staking outTo serve as a conduit for filling in the

necessary slurry during excavation or for its removal during concreting


ROLES OF THE GUIDE WALL AS FAR AS SLOTSTABILITY IS CONCERED ARE

It protects the edge of the slot from being damaged by the trenching equipment

It prevents the dangerous seepage of slurry into the upper soil layers of high porosity

It supports the upper portion of the trench like a bracing on that part where the slurry pressure is insufficient to ensure the stability

If required, it can be raised above the working surface to increase the slurry level

It prevents the horizontal deformation of the upper soil strata by its rigidity and by activating some arching effect, reducing the vertical stresses in the surrounding soils


Case study on Diaphragm wall


STUDY AREA- NOIDA

Plan area of site 24000m2Ground + 13 stories with a combined

basement of 3 levelsAll floors (except basement floors) to be

used as office spaceBasement floor 1 and 2 are to be used

for double level car parkingBasement 3 is used for conventional

single level parking


SITE LAYOUT


BOREHOLE LOCATION


BOREHOLE PROFILEDepth

(m) BH-1 BH 2 BH 3 BH 4 BH 5 BH 6 BH 7 BH 8 BH 9 BH 10 BH 11 BH 12 BH 13 BH 14 BH 15 BH 16 BH 17 BH 18 BH 19 BH 20 ABH 1 ABH 2 ABH 3

00.5 4 5 6 4 4 12 4 6 4 91 7 6 4 6 4 6 9 7 8 9

1.52 5 9 8 6 6 9 7 8 7 13 8 9 9

2.5 7 8 6 7 7 10 8 12 11 133

3.5 16 9 16 9 9 10 9 15 12 17 9 15 104 13 11 11 9 10 8 19 16 16 20

4.55 12 10 11 8 14 9 11 8 9 17 14 13 15

5.5 11 12 12 13 9 10 8 11 10 186

6.5 11 13 12 13 15 11 15 13 13 15 17 28 177 13 17 10 20 14 13 11 14 12 14

7.58 11 15 15 21 21 14 21 19 19 17 22 25 22

8.5 16 26 16 24 16 15 17 19 16 209

9.5 16 18 17 27 23 21 22 29 23 22 24 33 3310 17 28 22 29 21 15 16 20 19 20

10.511 33 32 21 30 34 39 35 31 28 30 21 27 25

11.5 20 33 31 42 32 20 20 25 20 2312

12.5 25 30 2713

13.514 36 44 46 33 48 39 33 40 33 37 30 35 32

14.5 31 43 39 43 39 32 32 26 28 2615

15.5 37 39 3616

16.517 45 49 52 42 46 46 43 42 42 42

17.5 38 46 43 46 34 42 37 36 41 3318

18.5 42 44 4219

19.5 50 49 4320 49 61 46 45 47 47 45

20.5 50 48 43 50 37 42 4121

21.5 31 48 4822

22.523 61 43 52 58 48 51 54

23.5 55 50 49 51 41 53 5224

24.5 48 49 5325

25.526 50 57 50 55 56 46 55

26.5 56 52 53 53 50 42 4727

27.5 58 49 4928

28.529 61 62 58 67 61 57 61

29.5 68 66 63 57 53 39 53

Filled up Soil Silty sand Sand


02

4

6

8

10

12

14

16

18

20

22

24

26

28

30

32

0 10 20 30 40 50 60 70

Average SPT 'N'

Sand 'Average N Value - 14

Silty sand 'Average N Value -8






Borehole Chart


GENERALIZED SOIL PROFILE

Layers (m)Layer

Thickness (m)

Soil Descriptio

n

Unit weight of soil

(kN/m3)

Saturated Unit

weight of soil

(kN/m3)

SPT N

Value

Youngs Modulus (kN/m2)

Poisson's ratio ()

Friction Angle ()Top Bottom

0 4 4 Silty Sand 15 16 8 22900 0.25 27

4 8 4 Sand 16 17 14 35900 0.25 29

8 11 3 Sand 18 19 20 47500 0.25 29

11 17 6 Sand 19 20 32 64400 0.25 30

17 22 5 Sand 19 20 46 78400 0.35 30

22 28 6 Sand 19 20 52 80000 0.35 30

>28 - Sand 20 21 60 85000 0.35 31


GUIDE WALL LAYOUT


GUIDE WALL DETAIL


DIAPHRAGM WALL LAYOUT


INSTRUMENTATION SCHEME FOR DIAPHRAGM WALL


EXCAVATION SCHEME - 1 (800 MM THICK D-WALL)


PLAXIS MODEL FOR 800 MM THICK D-WALL


SHEAR FORCE FOR 800 MM THICK D-WALL


BENDING MOMENT FOR 800 MM THICK D-WALL


WALL DEFLECTION FOR 800 MM THICK D-WALL


TOTAL DISPLACEMENTS FOR 800 MM THICK D-WALL


PLAXIS OUTPUT FOR 800 MM THICK D-WALL

SI.No Stage of Excavation Bending Moment (kNm/m) Shear Force (kN/m)Horizontal

Deformation (mm)SF EF SF EF

1 Excavation upto -2m from NGL 26.62 -14.72 21.34 -9.42 2

2 Excavation upto -3.5m from NGL 60.65 -20.16 37.23 -10.38 4

3 Installation of soil anchors @ -3 from NGL 99.68 -72.61 71.56 -69.86 3





8 Excavation upto -11.5m from NGL 106.3 396.49 154.02 -127.91 20



Design forces 106.3 -503.56 186.19 -142.89 40


TYPICAL STAAD MODEL FOR 800 MM THICK D-WALL


SCHEMATIC REPRESENTATION OF 800 MM THICK D-WALL WITHLOADS AND EARTH PRESSURE


-25

-23

-21

-19

-17

-15

-13

-11

-9

-7

-5

-3

-1

-600.000 -500.000 -400.000 -300.000 -200.000 -100.000 0.000 100.000 200.000 300.000D

epth

(m)

Shear Force (kN/m) & Bending Moment (kN-m/m)

Net Maximum Bending Moment and Shear Force from PLAXIS and STAAD for 800 mm thick D-wall

Net Max. Shear force

Net Min. Shear force

Net Max. Bending moment

Net Min. Bending moment

Basement slab - 2 at -4.5m below EGL


Diaphragm Wall

Raft slab at -12.7m below EGL


EXCAVATION SCHEME - 2 (600 THICK D-WALL)


PLAXIS MODEL FOR 600 MM THICK D-WALL


WALL DEFLECTION FOR 600 MM THICK D-WALL


TOTAL DISPLACEMENTS FOR 600 MM THICK D-WALL


PLAXIS OUTPUT FOR 600 MM THICK D-WALL

SI.No Stage of ExcavationBending Moment

(kNm/m)Shear Force

(kN/m)Horizontal

Deformation (mm)SF EF SF EF

1 Excavation upto -5.5m from NGL 29.04 -5.27 23.9 -7 5






7 Excavation upto -14.2m from NGL 73.85 -270 121.68 -124.5 55

Design forces 113.34 -270 121.68 -124.5 55


TYPICAL STAAD MODEL FOR 600 MM THICK D-WALL


SCHEMATIC REPRESENTATION OF 600 MM THICK D-WALL WITHLOADS AND EARTH PRESSURE


-22

-20

-18

-16

-14

-12

-10

-8

-6

-4

-2

0-400 -300 -200 -100 0 100 200

Dep

th (m

)

Moment (kN-m/m) & Shear force (kN/m)

Net Max. Bending moments and Shear force from PLAXIS and STAAD for 600 mm thick D-wall

Net Max. Bending momentNet Min. Bending momentNet Max. Shear forceNet Min. Shear force



Raft slab at -12.7m below EGL

Diaphragm Wall


GUIDE WALL - BORING


GUIDE WALL REINFORCEMENT


GUIDE WALL CONSTRUCTION


REINFORCEMENT CAGE


REINFORCEMENT CAGE CORNER PANEL


LIFTING HOOK - REINFORCEMENT


ANCHOR SLEEVE


ANCHOR PLATE


ANCHOR SLEEVE W.R.T. SPACING


CRABBING FOR D-WALL & STOP END INSTALLATION


KODEN TEST


SONIC LOGGING INSTALLATION


SONIC LOGGING & REINF. WITH STOP END


DIAPHRAGM WALL WITH STOP END


SONIC LOGGING TEST


CONCLUSIONDiaphragm wall was used as support

system for deep excavation and its performance is monitored by instrumentation, which reveals that diaphragm wall is one of the best solutions for supporting deep excavation.

PLAXIS-2D and STAAD Pro software are effective tools for the analysis and design of diaphragm wall.


THANK YOU


Documents

Deep Excavation - Diaphragm Wall - Dr.M.muttharam