Underground Excavation Behavior of the Queenston Formation

Geomechanics ColloquyWorkshop on Failure Prediction in GeotechnicsSalzburg, Austria

Austrian Society for Geomechanics

Underground Excavation Behaviour of the Queenston Formation - Tunnel back analysis

Matthew Perras, Prof. Mark Diederichs (Queen’s University) and Helmut Wannenmacher (Marti Tunnelbau AG. formerly Strabag Inc.)

Presentation Outline

• Introduction • Geomechanical Settings • Rock Mass Behaviour • Tunnel back analysis • Lessons learnt!

Tunnel

The Falls Whirlpool

Intake The TBM

St David’s

Escarpment

Niagara GorgeNiagara Falls

Rapids

Whirpool

Introduction NTFP _ The Niagara Region

Construction of two tunnel back in the 1950 ties

Introduction NTFP _ Tunnel Alignment

Introduction NTFP _ Geological Section

The NTFP: Excavation and Support

The NTFP: Problem Statement

Problem Statement

Geomechanical Settings What is the trigger for this adverse rock mass conditions?

Southern Ontario

Niagara Tunnel

CanadaCanada

Geomechanical Settings_ Regional Setting

DGRNiagara Tunnel

Geomechanical Settings _ The Queenston Formation

Bois Blanc

Salina

Niagara Group

Cataract Group

Queenston

Georgian Bay

Blue MountainCollingwoodCobourg

Bass Island

Amherstburg

Geomechanical Settings _ Variances in Stiffness

Geomechanical Settings _ Variances in UCS and CI

Geomechanical Settings _ Influence of Siltstone Layers

Tunnel

Geomechanical Settings _ Stress Field at the NTP

Tunnel

Rock Mass Behaviour

Rock Mass Behaviour _ Classification of Rock Mass Behaviour

Observed area

Zone 4 Zone 3 Zone 2 Zone 1

Irondequoit

Age Formation Brief Description

Grey crystalline dolomitic Limestone Lockport

Grimsby

Power Glen

Whirlpool

Queenston Red shale and argillaceous limestone

Light grey crossbedded sandstone

Grey shale to white calcareous sandstone

Green, irregularly bedded sandstone with red shale

interbeds

Grey to reddish dolomitic limestone

Crystalline dolomite &grey mudstone

Ordov- ician

Light grey crystalline dolomite

Neahga

Thorold

Reynales

White sandstone

Rochester

Green shale

Dark grey calcareous shale dolomite interbedded

Approx.

Thickness (m)

Symbol

3.6 – 7.6

1.2 – 3.1

2.1 – 4.0

2.4 1.8

Shallow Chimeny

Gravity Raveling

Localized Haunch Fractures

Haunch Failure

Rock Mass Behaviour _ Zone 1

Irondequoit

Grimsby

Power Glen

Whirlpool

interbeds

Ordov- ician

Neahga

Thorold

Reynales

White sandstone

Rochester

Green shale

Approx.

Thickness (m)

Symbol

3.6 – 7.6

1.2 – 3.1

2.1 – 4.0

2.4 1.8

Joints

Irregular Profile

Large Blocks

Stress concentration from

stiff to weak layer

Shear failure along the planes of

weakness

Contact Area of Sandstone and Mudstone

Irondequoit

Grimsby

Power Glen

Whirlpool

interbeds

Ordov- ician

Neahga

Thorold

Reynales

White sandstone

Rochester

Green shale

Approx.

Thickness (m)

Symbol

3.6 – 7.6

1.2 – 3.1

2.1 – 4.0

2.4 1.8

Rock Mass Behaviour _ Depth of Overbreak

1.5km3.5 km 2.5 km3.0km 2.0 km

Irondequoit

Grimsby

Power Glen

Whirlpool

interbeds

Ordov- ician

Neahga

Thorold

Reynales

White sandstone

Rochester

Green shale

Approx.

Thickness (m)

Symbol

3.6 – 7.6

1.2 – 3.1

2.1 – 4.0

2.4 1.8

Rock Mass Behaviour _ Comparison of Zones

Tunnel back analysis

• Damage Initiation and Spalling Limit “DISL” (Diederichs 2007)– Without dilation– With dilation

• Ubiquitous Joint - Spalling – As above, with addition of ubiquitous joints

• Laminated Anisotropic MethodJoint elements used to induce anisotropy

Isotropic No Laminations

Anisotropic Laminations

Tunnel back analysis

Niagara Tunnel Project NTP – Laminated Model

Tunnel back analysis _Failure Envelops

Isotropic – No Laminations Anisotropic – With Laminations

Far Field

Sigma 1 = 12 MPa

Crown Stress Concentration

Tunnel back analysis _Elastic Stress Comparison

Anisotropic – With Laminations

Far Field

Sigma 1 = 12 MPa

Crown Stress Concentration

Transversely Isotropic – No Laminations

Numerical Approach_Elastic Stress Comparison

Deformed Boundary

Far Field

Sigma 1 = 12 MPa

Isotropic – No Laminations Anisotropic – With Laminations

Tunnel back analysis _Plastic Displacement Comparison

3.95 m3.78 m

Tunnel back analysis _Ubiquitous Joint

Tunnel back analysis _ NTP Back Analysis

Lessons learnt !

• Queenstone shale as a brittle material demands for more sophisticated analyses to capture realistic rock mass behaviour.

• Mineralogical differences are the source of the planes of weakness and trigger the failure process.

• DISL / Ubiquitous Joint method can capture overbreak dimensions, but were unable to capture chord closure measurements.

• LAM method can capture both overbreak dimensions and chord closure measurements.– The anisotropic stiffness plays an important role in the failure mechanism

when beam deflect can occur

Lessons learnt!

Thanks for your audience.

Underground Excavation Behavior of the Queenston Formation

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