engineering issues related to mined...
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Society of Myanmar Civil Engineers (Singapore)
Engineering Issues Related to Mined
Tunnels
Dr. Oskar SIGL – Geoconsult Asia Singapore
Singapore; 16 October 2016
2 2
Mined Tunnels – SCL/NATM/SEM
Content
Latest Developments on mined tunneling supporting
method
Controlling soft ground
3 3
Mined Tunnels – SCL/NATM/SEM
Terminology
SCL – Sprayed Concrete Lining
NATM – New Austrian Tunneling Method
SEM – Sequential Excavation Method
Observational Approach
Shotcrete Sprayed Concrete
4 4
Example: Mined Station; Seattle
SoundTransit
Beacon Hill Station
5 5
Example: Mined Station; London
LUL Jubilee Line Extension
Contract 102 Waterloo Station
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Example: DTSS Advance Tunnel; Singapore
North East Line
Contract C705
7 7
Example: Overrun Tunnels; Singapore Orchard Road
Circle Line 1 – Overrun Tunnels
Contract C825 Dhoby Ghaut Station
8 8
Example: NS3 Cable Tunnel; Singapore
Tunnels for TBM operation and cable
enlargements
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Example: EW1 Cable Tunnel; Singapore
Mined tunnel
10 10
Key Issues
Are not rocket science
Understand the general sequence of tunneling and
the staging of excavation & support application
Pay attention to deformation control and ground
confinement
Recognize the importance of design adjustments
during construction
Maintain stability of the excavation face at all times
Understand why people call it “high risk”
Mined Tunnels
11 11
Characteristics of Work Processes
Linear development of the work zone with limited
space and accessibility
Repetition of working steps (work cycles)
Transient intermediate stages (sections with
incomplete liner)
Mined Tunnels
12 12
Mined Tunnel - Construction
Sequencing of Excavation & Support
Constitutes major part of the design
13 13
Sequencing/staging DETAILING
Staged Excavation
Lattice girder, full round in soft ground
Shotcrete & wire mesh
Mined Tunnel - Construction
14 14
Top Heading
Bench
Invert Bench
Typical sequencing/staging
Mined Tunnel - Construction
15 15
Mined Tunnel - Construction
16 16
Typical sequencing/staging
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Typical sequencing/staging
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Steel Rib / Arch
Not embedded in shotcrete
Function Load distribution
Support of “green” shotcrete
Profile control
Support for forepoling
Traditional Types H-beams
Channels with sliding connection
Lattice girder
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Channel with sliding connection
20 20
Layout Options:
“Standard”
“Optional”
Lattice girder – For embedment in shotcrete
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Face Stability
Advance support of excavation face
Forepoling / pipe umbrella / spiling
22 22
Advance support ahead of excavation face
Provide support for exposed round
Needs support (soil and lattice girder)
Ground Support
Forepoling DETAILING
23 23
Special Equipment – Tunnel Excavator
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Special Equipment – Tunnel Excavator
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Pipe Umbrella / Pipe Roof
Same concept as forepoling
but stronger & heavier & longer
Advance Support Ahead of Excavation Face
26 26
Pipe Umbrella / Pipe Roof
Advance Support Ahead of Excavation Face
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Pipe Roof
28 28
Casagrande Rig
Pipe Roof
29 29
Jumbo
Pipe Roof
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Pipe Roof
31 31
Forepoling – Soft ground
Support soil in front of the “next” face
Reduce soil loading for the soil wedge defining face
stability
Spacing typically 150-300mm c/c
T25 rebars, mostly grouted
Length > advance length (typically 1.5 x)
Tied into lattice girder of previous round
Advance Support Ahead of Excavation Face
32 32
Face Stability
Effects of Advance Support
Wedge 1 & Wedge 2
33 33
Face Stability – Design of Advance Support
Wedge 1 situation
Support of free
advance length
34 34
Face Stability – Design of Advance Support
Wedge 2 situation
Supporting load
on top of wedge
35 35
Spiling – Rock
Same concept as forepoling but in rock
Rock bolting inclined forwards in order to avoid
overbreak in the next blasting round
Spacing typically >500mm c/c
Length ≈ advance length
“Does not need a lattice girder”
Advance Support Ahead of Excavation Face
36 36
Spiling to reduce overbreaks
37 37
EXAMPLE: Face stability in Praxis
38 38
39 39
Loose Gravel
Dense Gravel
Silt Stone
Dense Gravel
Tunnel
EXAMPLE: Face stability in Praxis
40 40
Face stability in Praxis
Subdivide excavation face
Increase immediate support by reduction of
excavation area
Start where it is worst, use the better area for
support
FACE
SUPPORTING
BODY
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Example – Face Stability Recover, small faces
42 42
Recover, small faces
43 43
Recover, small faces
44 44
Drainage
Forepoling
Face bolts
Face
Dumpling
45 45
103.03m
101.48
Existing 1.2m Water Pipe
PIPE
800mmx11mm thk
Ground Level 109.43 (approx.)
Supporting Steel Frame
~ 94.00m
Change of shallow cover pipe pile box
tunnel to a mined tunnel with shotcrete
Application to Complicated Problems
SUBWAY STRUCTURE
46 46
Pipe Roof Cross Section – Pipe Pile Box
47 47
Existing 1.2m Water Pipe
Application to Complicated Problems
SUBWAY STRUCTURE
One tunnel too shallow
48 48
SCL Cross Section - Sequencing
49 49
SCL Cross Section - Sequencing
50 50
SCL Cross Section - Sequencing
Half of permanent
structure
Temp. props
51 51
SCL Cross Section - Sequencing
52 52
SCL Cross Section - Sequencing
53 53
SCL Cross Section - Sequencing
54 54
Longitudinal Section & Ground Condition
Pipe Roof Sections
Water Pipe
FILL & Peaty clay
Silty Clay
Cemented silty sand
55 55
Sequential Excavation with Pipe Roof
Install Pipe roof Sections overlap more pipe layers
Top heading
Temporary invert
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Construction
Pipe Roof
57 57
Ground Treatment
Details of face grouting arrangement
Design of drilling / grouting pattern
58 58
2D Analysis
Mined Tunnel 2 (Staged Top Heading &
Bench/Invert excavation)
Face & pipe roof grouting
Temporary Prop
“Fill concrete”
Permanent Structure
Connection DETAIL
Tunnel 2
Horizontal face grouting + Pipe Roof
installation and grouting
Staged excavation of Top Heading &
Bench/Invert (short ring closure)
Casting of second half permanent
structure
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3D Analysis
60 60
Pipe Roof Drilling
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Excavation
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SECTION 2 double pipe roof
SECTION 1 double pipe roof
Construction
63 63
Excavation – Top Heading
64 64
Pipe roof pipe
Construction
65 65
Excavation – Top Heading
Face grouting pipes
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Face Support – Top Heading
67 67
Face Grouting – Top Heading
68 68
Drilling of Face Grouting – 1st Drift
69 69
“Weak” support resistance of Lattice girder and temporary invert
Construction Issue
70 70
Excavation – 2nd Drift
71 71
2nd Drift Completed
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Application to much Larger Schemes
73 73
Singapore Jurong Caverns
74 74
Storage Schematics and Terminology
Inlet shaft Pump Shaft
Water Curtain Tunnel & dill holes
Access tunnel
Water Curtain Tunnel & drill holes
Access tunnel Storage cavern
20 x 30 x 650m
75 75
Storage Schematics and Terminology
76 76
Water Curtain System
Permanent pressure gradient towards the cavern
Oil floats on top of a water cushion
Thickness of water cushion is regulated by water
pumps in pump shaft
77 77
Oil pump
Water pump
Water cushion
Crude Oil
Hot oil pipe
Storage of Crude Oil
78 78
Storage Principle
Hot oil pipe
79 79
Engineering
Engineering during construction
Geological Mapping
Geotechnical Documentation
Rock Support Classification
Rock support application
Geological prediction during construction
80 80
Implementation During Construction
Geological
Mapping sheet
81 81
Distribution of rock quality – Padur/A
82 82
Data Management
Geological documentation
83 83
Construction Sequencing
Gallery – Pilot and Slashings
Pilot Gallery Side Slashing - LEFT Side Slashing - RIGHT
84 84
Construction Sequencing
Bench 1
Side Slashing
Pilot Bench
Bench 2
85 85
Construction Sequencing
3 Benches
Gallery
Bench 1
Bench 2
Bench 3
86 86
Gallery
Bench 1
Bench 2
Bench 3
Excavation Stages
87 87
Pilot
Side slashing
Excavation Stages
88 88
Pilot Side slashing
Bench 1
Excavation Stages
89 89
Bench 2 Pilot Side slashing
Excavation Stages
90 90
Bench 3
Excavation Stages
91 91
21m
30m
12m
Excavation Stages
Pump sump
92 92
Cavern
Construction
93 93 Access tunnel portal
Construction
94 94
Access tunnel junction
95 95
Pump Shaft
Inlet Shaft
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97 97
Inlet shaft
Vishakapatnam – Construction
98 98
Inlet shaft
99 99
Pump shaft
100 100
Pump shaft
101 101
Major Wedge Failure
102 102
Major Wedge Failure
103 103
Major Wedge Failure
Shear
Tension
Shear
Tension
Both
Sigma 1
MPa
0.00
1.80
3.60
5.40
7.20
9.00
10.80
12.60
14.40
16.20
18.00
0-1
0-2
0-3
0-4
0-5
0-6
0
-70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80
104 104
Major Wedge Failure
105 105
Major Wedge Failure
106 106
Thank You
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