tunnel construction method

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2nd Seminario Internacional de Tuneles y aplicaciones ITS26 de Marzo de 2010 Buenos Aires

Tunnel Construction Methods:Conventional vs Mechanized

March 26, 2010

Prof. Andre P. Assis, PhD(ITACET / UnB)

Harvey W. Parker, PhD(ITA / Consultant)


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Huge Diverse Demand for Tunnels Worldwide Motorways & Ring Roads to reduce traffic congestion

Long and/or Deep Road Tunnels to connect populations

By-Pass Historic, Cultural, Scenic, & Congested Locations

Underground Parking

Mass Transit Systems

Public Utilities & Flood Control

City Center Revitalization

Construction Method is Affected by the Purpose

and Numerous other Factors, Especially the

Geology


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Factors to Consider inSelection of Construction

Method

Geology

Rock or Soil

Mountain or River Crossing

Urban or Rural

Number of Lanes ~ Tunnel Size

Length

Safety & EnvironmentalConstraints

Schedule & Cost

Risk Tolerance

Two Basic Categories

Technical Feasibility

Cost & Schedule


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Better Exploration & Understanding of Ground Behaviour

Ground/Groundwater Pressures

Evaluation & Control of Induced Movement

Minimize Potential for Damage

Modern Technology Results in Tunnels

Better, Faster, Cheaper, Safer

Quality Mechanization of the construction process

New Generation of Pressurized TBMs TBMs now routinely used in ground conditions considered inappropriate a few years ago

Innovations Provide our Industry with More Choices than just the traditionalChoice Between Conventional vs Mechanized. In Continuous State of Change

Recent Tunnel Engineering Advances ImproveSelection of Construction Method


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Geology & GeoHydrology

Priority of surface space

Long term (type of infrastructure)

Short term (during construction)

Type, cross-section size and length of the tunnel Location andsurrounding environment of the tunnel. Potential for Public Disruption

Local tradition and experience, schedule, type of contract and

contractual stability

Cost & Schedule

Must PredictProductivity

Labor & Material Costs

Construction Methods and Technology


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Evaluate on RiskManagement Principles

Select Con


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Road Tunnel Types

Varies 80' - 103'53'

20'

22

Var

93'+/-

NBSB

53'

Different configurations,technologies, standards


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Tunnel Size

Alaskan Way, Seattle

~17m OD for Four (4) Lanes


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Now, Several 3 LaneRoads in ~14m Tunnels


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A86 in Paris

11.6 m diameter for 4, possibly u ltimately, more lanes!!- small vehicles only, 3m clearance


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Tunnelling in Soft Ground (Soils)

Cut-and-Cover

TunnellingMethods

Conventional Tunnelling

Special Methods

Mechanized Tunnelling

Conventional CC

Immersed & Other


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Cut-and-Cover vs Tunnel


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Difficult to build from surface

Urban constraints (alignmentsdefined by demand andinterferences)

Cost of relocation

Construction costs

Cost of Public Disruption

Cut-and-Cover


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Door Frame Tunnel in Metro Brasilia


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"Submerged" Cut-and-Cover:Immersed Tunnels

Mo nt Baker Ridge


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Mount Baker RidgeSeattle

Stacked-Drift

InnovativeIncrementalconstruction - small

parallel drifts (likebarrel staves)

Inside diameter 19m

Five through lanes

plus pedestrian, bike

Ventilation and lifesafety systems


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Conve

ntionalT

unnellin

g


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Tunnelling in Soil

Conventional Tunnelling Sequential Excavation Methods (SEM)

Mechanized Tunnelling Full-Face Excavation

Open-face

Pressured-face TBM

Door Frame or Special Construction

Challenge: Stability & Settlement

Sequential Excavation


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Sequential ExcavationMethod (SEM)

Low Mobilization time & cost

Rate of Advance slower than TBMbut sometimes competitive in totalproject time

Various, flexible shapes possible

Quality & Workmanship is Crucial

Practice now accepted as safebut image is not universally good

Transitions / off-ramps easier


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TcnicasAlternativas:

CongelamentoGround

Improvement

and Reinforcement


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MechanizedTunnelling

General Mechanized


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General MechanizedSelection Flow Chart

Source: ITA Working Group 14, Mechanized Tunnelling, 2000


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Pressurized-Face TBMs:

EPB, Slurry and Mix Shield

Sl


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2nd

Seminario Internacional de Tuneles y aplicaciones ITS26 de Marzo de 2010 Buenos Aires

EPB vs Slurry

Selection Between


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Selection BetweenEPB and Slurry

Not an Easy Question

Past Years: Slurry for Sands; EPB for Silts & Clays

Must know geology and conduct soil tests

Now newer Conditioning Agents injected at the face extend the range of bothmethods of construction

Disk Cutters extend use of both for Boulders & Variable Rock

Slurry TBMs commonly used for higher water pressures

Careful not to create a blow to surface

Face stability is generally more robust with EPB

Other Issues Prediction of Rate of Advance

Abrasion and/or Clogging=maintenance or repair in Interventions

Plant Size & Muck disposal issues


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Tunnelling in Rock

Tunnelling

Methods

Drill and Blast

Full-Face TBM

- Gripper

- Double Shield

Partial-Face TBM


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Drill and Blast Technology Has Improved Extending

Range of Drill & Blast Projects

Almost no mobilization time. Often Still Used forShorter Projects with variable ground & changing cross

section in remote areas without power


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Mechanized Tunnelling in Rock

Challenge:


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gCutting Tools and Power


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Combined Methods:Conventional and

Mechanized

Tunnelling


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Conventional vs. Mechanized Tunnelling Good for Geometric flexibility

Adaptable to broad range ofground conditions

Temporary exposure tounsupported ground

Contractual flexibility

Lower mobilization & plant costs

Suitable for political risk or lack

of contractual stability Lower costs for short tunnels &

where labor is inexpensive

Often slow but not expensive

New Technology is adaptable tomore ground conditions

Less disturbance to theremaining ground

Better and more regular quality(industrial process)

Mechanization better for workers

Safer because generally under

protective shield Faster rate of advance

Significant mobilization & Plantincreasing Cost & Schedule

Costs and schedule more

favorable for longer tunnels


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Final Remarks


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Final Remarks

Significant increase of the demand of underground structureseverywhere

Two Basic Issues are

Technical Feasibility

Cost & Schedule

Underground structure feasibi lity depends on global costanalyses (construction costs + indirect benefits)

Road Tunnels demand a large cross section

Trend is toward larger diameters

Conclusions


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2nd


Conclusions

Construction methods and technology depend ongeology, tunnel location, size, local tradit ion etc.

A large number of factors must be considered

Not just a decision between conventional & mechanized

Combination of mechanized and sequential excavationmethods or Special Methods may be beneficial

Conclusions


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2

nd


Conclusions

Mechanized tunnelling for long tunnels andurban areas (industrial process, quality andcontrol of costs and schedule)

Trend is for greater innovation giving greater applicability anduse of mechanized in the future.

Conventional tunnelling for short tunnels andvariable conditions (geometry, geology and

political flexibility, and inexpensive labour)


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Mucho Gracias

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tunnel construction method