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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
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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
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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
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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
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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
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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
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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
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CONSTRUCTION SEQUENCE
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CONSTRUCTION SEQUENCE
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DIAPHRAGM WALL CONSTRUCTION
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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
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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
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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
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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
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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
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Case study on Diaphragm wall
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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
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SITE LAYOUT
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BOREHOLE LOCATION
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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
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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
Sand 'Average N Value - 20
Sand 'Average N Value - 32
Sand 'Average N Value - 46
Sand 'Average N Value - 52
Sand 'Average N Value - 60
Borehole Chart
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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
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GUIDE WALL LAYOUT
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GUIDE WALL DETAIL
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DIAPHRAGM WALL LAYOUT
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INSTRUMENTATION SCHEME FOR DIAPHRAGM WALL
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EXCAVATION SCHEME - 1 (800 MM THICK D-WALL)
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PLAXIS MODEL FOR 800 MM THICK D-WALL
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SHEAR FORCE FOR 800 MM THICK D-WALL
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BENDING MOMENT FOR 800 MM THICK D-WALL
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WALL DEFLECTION FOR 800 MM THICK D-WALL
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TOTAL DISPLACEMENTS FOR 800 MM THICK D-WALL
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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
4 Excavation upto -6m from NGL 66.31 -86.72 53.46 -106.01 5
5 Excavation upto -7.5m from NGL 46.4 -194.28 68.09 -127.62 7
6 Installation of soil anchors @ -7 from NGL 59.09 -87.26 85.6 -104.11 7
7 Excavation upto -10m from NGL 45.9 -218.72 90.28 -115.86 11
8 Excavation upto -11.5m from NGL 106.3 396.49 154.02 -127.91 20
9 Installation of soil anchors @ -11 from NGL 55.08 -340.58 153.41 -126.69 19
10 Excavation upto -14.2m from NGL 93.18 -503.56 186.19 -142.89 40
Design forces 106.3 -503.56 186.19 -142.89 40
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TYPICAL STAAD MODEL FOR 800 MM THICK D-WALL
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SCHEMATIC REPRESENTATION OF 800 MM THICK D-WALL WITHLOADS AND EARTH PRESSURE
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SHEAR FORCE FOR 800 MM THICK D-WALL
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BENDING MOMENT FOR 800 MM THICK D-WALL
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-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
Basement slab - 3 at -9.0m below EGL
Diaphragm Wall
Raft slab at -12.7m below EGL
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EXCAVATION SCHEME - 2 (600 THICK D-WALL)
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PLAXIS MODEL FOR 600 MM THICK D-WALL
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SHEAR FORCE FOR 600 MM THICK D-WALL
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BENDING MOMENT FOR 600 MM THICK D-WALL
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WALL DEFLECTION FOR 600 MM THICK D-WALL
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TOTAL DISPLACEMENTS FOR 600 MM THICK D-WALL
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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
2 Excavation upto -7.5m from NGL 86.54 -9.57 44.77 -22.36 8
3 Installation of soil anchors @ -7 from NGL 111.84 -16.9 84.04 -57.34 7
4 Excavation upto -10m from NGL 56.89 -78.33 61.22 -104.82 12
5 Excavation upto -11.5m from NGL 113.34 -164.38 109.13 -123.96 21
6 Installation of soil anchors @ -11 from NGL 85.79 -100.1 109.79 -108.5 21
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
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TYPICAL STAAD MODEL FOR 600 MM THICK D-WALL
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SCHEMATIC REPRESENTATION OF 600 MM THICK D-WALL WITHLOADS AND EARTH PRESSURE
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SHEAR FORCE FOR 600 MM THICK D-WALL
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BENDING MOMENT FOR 600 MM THICK D-WALL
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-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
Basement slab - 2 at -4.5m below EGL
Basement slab - 3 at -9.0m below EGL
Raft slab at -12.7m below EGL
Diaphragm Wall
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GUIDE WALL - BORING
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GUIDE WALL REINFORCEMENT
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GUIDE WALL CONSTRUCTION
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REINFORCEMENT CAGE
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REINFORCEMENT CAGE CORNER PANEL
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LIFTING HOOK - REINFORCEMENT
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ANCHOR SLEEVE
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ANCHOR PLATE
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ANCHOR SLEEVE W.R.T. SPACING
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ANCHOR SLEEVE W.R.T. SPACING
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CRABBING FOR D-WALL & STOP END INSTALLATION
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KODEN TEST
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SONIC LOGGING INSTALLATION
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SONIC LOGGING INSTALLATION
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SONIC LOGGING & REINF. WITH STOP END
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DIAPHRAGM WALL WITH STOP END
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SONIC LOGGING TEST
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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.
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THANK YOU
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