RISK MANAGEMENT:
Tyler Sandell
The Robbins Company
H A R D R O C K T B M D E S I G N F E AT U R E S F O R
D I F F I C U LT G R O U N D C O N D I T I O N S
PRESENTATION OUTLINE
RISK MANAGEMENT IN DIFFICULT GROUND
OVERVIEW
Introduction
Risk Management:
• Identify
• Assess and Monitor
• Response –Taking Control
Conclusions
Q & A
AN OUNCE OF PREVENTION IS WORTH A POUND OF CURE
-Benjamin Franklin
Properly Installed Ground Support Using the McNally System and Steel Sets
A L I T T L E R I S K M A N A G E M E N T S AV E S A L O T O F FA N C L E A N I N G - U n a t t r i b u t e d
INTRODUCTION
IDENTIFY:
WHAT RISKS DOES THE
GROUND PRESENT?
WHAT IS MEANT BY
DIFFICULT GROUND?
Particular Geological Features:
+ Water inflows
+ High water pressures
+ Fault zones
+ Rock bursting
+ Hard, abrasive rock
+ Squeezing ground
+ Fractured rock
+ Mixed face conditions
+ Cobbles and boulders
BEGINNINGS OF DIFFICULT GROUND SOLUTIONS (DGS):
COLLAPSING/SQUEEZING GROUND
K A R G I H E P P
G E O L O G Y AT T I M E O F T B M O R D E R
G E O L O G Y O F P R O J E C T AT 5 0 % C O M P L E T E
+ Difficult Ground Solutions (DGS) is a suite
of options for non-pressurized, shielded
TBMs in hard rock and mixed ground
+ Features are customized for known
geologic conditions including squeezing
ground, fault zones, water inflows, and
collapsing ground
INTRODUCTION
DIFFICULT GROUND SOLUTIONS
WHAT IS IT?
ASSESS and MONITOR:
TOOLS AND STRATEGIES FOR
LEARNING WHAT’S
AHEAD
Risk Comes From Not Knowing
What You’re Doing
- Warren Buffet
Heavy Water and Muck Inflow
Veligonda, India – 10 m Double Shield TBM
TBM FEATURES FOR DIFFICULT GROUND
STRATEGY
• Good geological advance investigation
within the tunnel is cost effective
• Probe drilling in advance of face
• Multiple probe holes in faulted areas
Probe drilling in advance of face
GOOD GROUND KNOWLEDGE
DETECTION
TUNNELING IN ROCK WITH WATER
PROBE DRILLING
Capable of accurate drilling at long distances: 60 to 100 m ahead of the TBM
TBM FEATURES FOR DIFFICULT GROUND
TBM DESIGNS
PROBE DRILLING
Multiple drill holes: Need fast, accurate drilling at long distances 60 to 100 m ahead of the TBM
Down-the-hole Hammers: + Ideal for drilling multiple
holes for water cut-off
+ Straighter drilling compared to top hammer drilling
PROBE DRILLING EQUIPMENT
• Wasarra DTH water hammers
• Ideal for drilling in water
environment
• Straighter drilling
• Drill tests completed near
jobsite
• Ripamonti Drill Feeds
• Blowout preventers
TBM FEATURES FOR DIFFICULT GROUND
TBM FEATURES FOR DIFFICULT GROUND
STRATEGY
MEASUREMENT WHILE DRILLING (MWD) &
OTHER SYSTEMS
• MWD system and TBM data interprets geological model
• Understanding the rock mass, improving general performance
• Documentation of the existing rock formation
• Amberg TSP System
• One or more shot lines w/small explosive charges
• Four receivers
• Geoelectrical BEAM System
• Whole cutterhead or single cutting tools can act as measuring electrode
TBM FEATURES FOR DIFFICULT GROUND
FACE COLLAPSE
• Purpose – To
see the cut face
in front of the
TBM
• Allows
understanding
of ground
stability
• Uses pre-
positioned ports
that pass
through the
back of the
cutterhead
FACE INSPECTION
CAMERA
TAKING CONTROL:
TOOLS AND
STRATEGIES FOR
MITIGATING THE
RISKS OF DIFFICULT
GROUND
TBM FEATURES FOR DIFFICULT GROUND
CHEMICAL GROUTWands pushed into face and chemical additive (Polyurethane) is pumped into
the wands to consolidate the face
STRATEGY
TBM FEATURES FOR DIFFICULT GROUND
STRATEGY
Typical overlapping forepoling arrangement
FOREPOLING
SMOOTH CUTTERHEAD DESIGN+ Purpose – A smoother surface does not permit the cutterhead to become stuck due to
changing ground conditions and collapse.
+ Grilled bucket openings
+ No face buckets
TBM FEATURES FOR DIFFICULT GROUND
TBM FEATURES FOR DIFFICULT GROUND
STRATEGY
• Purpose – When loose material comes against the cutterhead higher torque
is required to commence rotation.
• Two speed gearboxes allow both high torque and high speed without
increasing HP/KW.
HIGH-TORQUE MAIN DRIVES
Dual Range Gearbox:
Low RPM/High Torque
High RPM/Low Torque
0
2000
4000
6000
8000
10000
12000
14000
0 2 4 6 8 10
Cu
tte
rhea
d T
orq
ue
(kN
m)
Cutterhead Speed (RPM)
Gerede Torque CurveTwo-Speed Gearbox
Low Speed
High Speed
TBM FEATURES FOR DIFFICULT GROUND
STRATEGY
HIGH-TORQUE MAIN DRIVES
TUNNELING IN ROCK WITH WATER
WATER INFLOW PREVENTION
Three-axis main bearing with
35 bar static pressure
protection
Outer Seal Layout
Inner Seal Layout
TBM FEATURES FOR DIFFICULT GROUND
TUNNELING IN FAULTED & FRACTURED ROCK
SEALABLE/REPLACEABLE
SCREW CONVEYOR
• Screw conveyor can be sealed
off so the TBM can continue to
advance in water-bearing
ground
• Sequential operation of screw
conveyor
• Replaceable wear plates and
sections of screw for use in
rock conditions
Screw conveyor designed in removable and
replaceable sections, with wear plating for use in
abrasive ground
TBM FEATURES FOR DIFFICULT GROUND
TBM FEATURES FOR DIFFICULT GROUND
MUCK CHUTE CLOSURE DOORS• Purpose is to reduce the volume of incoming water and fines passing through
the muck chute
• Can be flapper door type or guillotine type
STRATEGY
TUNNELING IN ROCK WITH WATER
WATER INFLOW PREVENTIONSealable Pressure Bulkhead
TBM FEATURES FOR DIFFICULT GROUND
TBM FEATURES FOR DIFFICULT GROUND
Alternative To Muck Chute Closure Doors
METHODS & LESSONS LEARNED
STRATEGY: SEALING OF DOUBLE SHIELD GAPS
WATER
TBM FEATURES FOR DIFFICULT GROUND
RAPID ADVANCE SHIELDS
Rapid Advance Shield Design for difficult ground entails a number of
features to effectively excavate in squeezing conditions:
• Shorter shield design
• Stepped/tapered shields
• Convergence measuring system
• Peripheral shield lubrication
• Hydraulic shield breakout system
STRATEGY
TBM FEATURES FOR DIFFICULT GROUND
FACE COLLAPSE
• Purpose – Identifies ground when it has started to collapse onto the forward
shield of the TBM.
• Temposonic cylinder to measure distance from shield to ground
• Read distance measurement from operators screen
COLLAPSE DETECTION CYLINDER (CDC)
TUNNELING IN ROCK WITH WATER
RAPID ADVANCE SHIELDSStepped Shield Design
Considerations:
• Fines and muck
flow
• Steering
• Protection
against
squeezing
ground
• Shimming of
gage cutters
Nominal overcut
and 50 mm overcut
shown
TBM FEATURES FOR DIFFICULT GROUND
TUNNELING IN ROCK WITH WATER
RAPID ADVANCE SHIELDS
TBM FEATURES FOR DIFFICULT GROUND
TUNNELING IN ROCK WITH WATER
RAPID ADVANCE SHIELDSPeripheral Shield Lubrication
TBM FEATURES FOR DIFFICULT GROUND
TBM FEATURES FOR DIFFICULT GROUND
STRATEGY
• Purpose – When needed additional thrust force can be generated to move the TBM in
difficult ground
• Additional hydraulic rams are used to increase the total available machine thrust to
break the TBM free
HIGH PRESSURE JACK
SUPER THRUST
+ Reduces risk to contractors
and owners when a
challenge is encountered
+ Like buying risk insurance:
A small initial investment
can pay off if a difficult
feature is encountered
INTRODUCTION
DIFFICULT GROUND SOLUTIONS
BENEFITS
Image credit: Bilgin & Algan (2012). The performance of a TBM in
squeezing ground in Uluabat, Turkey. Tunnelling & Underground Space
Technology 32: 58-65.
CONCLUSIONS
DIFFICULT GROUND SOLUTIONS
TAKEAWAY POINTS
+ Identify the risk – it’s important to know as much about the ground as possible before you start and equip the TBM with the right tools for the job.
+ If you’re tunneling in the mountains, your geotech will probably not be accurate so it’s best to be prepared for everything!
+ The DGS features should be built into the TBM, rather than being added in the tunnel.
+ Assess and monitor the risk – We have probe drills and many other tools to provide information about what we will be encountering. Use them!
+ Contractors and project owners must work with the equipment manufacturer from the beginning to develop a solution for challenging projects.
THANK YOU!
SIDE NOTE:
MAIN BEAM TBM
TBM FEATURES FOR DIFFICULT GROUND