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