1Geotechnical Investigation for the

Second Avenue Subway in New York

Verya Nasri, PhD, PE

Planning and Development of Underground Space,

HKIE and HKIP

PROJECT PHASING PLAN

Phase 2125th to 96thPhase 3

63rd to Houston

Phase 196th to 63rd

Phase 4

Houston to Hanover

272nd ST. and 86th ST. STATIONS

72nd ST. STATION

372nd ST. STATION

72nd ST. STATION

4PUBLIC CAVERN

ANCILLARY CAVERN

5FOLIATED METAMORPHIC ROCK

180 new borings in Phase 1 Area

Cavern crown centerline borings (rock cover)

Two inclined borings in cavern at 72nd St

Historic borings

Environmental borings

GEOTECHNICAL BORINGS

6SUBSURFACE TESTING AND

EXPLORATION PROGRAM

Orientation and frequency of fracturesShear strength properties of fractures

Abrasivity of rock

Faults and shear zones

Intrusions and alteration

Rock material properties

Rock mass properties

Soil-rock interface profile and condition

GENERAL TESTS

Uniaxial Compression

Point Load Strength

Deformation Properties

Brazilian Tensile Strength

Direct Shear of Joints

MACHINE TESTS

Cerchar Abrasivity

Petrographic Analyses

Drill Rate Index

Bit Wear Index

Cutter Life Index

LABORATORY TESTING - ROCK

7The quality of the

rock can change

in very small

distances

VARIABILITY IN ROCK QUALITY

ATV image

Core

CORRELATION OF CORE AND

ACOUSTIC IMAGE

8GEOLOGIC INTERPRETATION

Interpreted conjugate faults

JOINT WAVINESS

Manhattan Schist

9ROCK WEDGE

Deep wedge

stable with irregular joints

Deep wedge

can be unstable if friction angle &

dilatancy is low, occurs with:

continuous, sheared, planar joints.

EMPIRICAL DESIGN (Q)

Span

Span

Span

Crown

Zone used for determining representative

Q values, obtained using the weighted

average of the raw Q values for each core

run within the zone.

Rock

Surface

10

CONTINUUM ANALYSIS

2D modeling Hoek-Brown Failure Criterion 50 % Relaxation, Shotcrete Strength Varied With Excavation Sequence

ROCK MASS PARAMETERS

Input- Intact Uniaxial Compressive Strength (UCS)- Intact Rock Modulus (Ei)- Disturbance Factor (D)- Geological Strength Index (GSI)- Intact Rock Parameter (mi)

Output- Hoek-Brown Strength Parameters- Rockmass Deformation Modulus

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EXCAVATION SEQUENCE

CONTINUUM ANALYSIS RESULTS

No Yielding of Initial Support Small Ground Surface Deformations (5 to 10 mm)

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TYPES OF DISCONTINUITIES

FOLIATION

SUBVERTICAL STRUCTUREFAULT / SHEAR ZONE

CONJUGATE JOINTS

CLUSTER

CONSTITUTIVE MODELS

Rock constitutive model: Mohr-Coulomb elastic/plastic failure

Joint constitutive model: Barton-Bandis joint model

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No Axial Failure

Local Axial Failure

Bolt Axial Load

Bolt Axial Load

BOLT AXIAL LOADS AND FAILURE

Maximum Settlement3.4 mm

EXPECTED CASE SETTLEMENT

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Maximum Settlement14 mm

WORST CASE SETTLEMENT

Expected Case

Maximum Settlement3.4 mm

Maximum Settlement14 mm

Worst Case

SETTLEMENT AT TOP OF ROCK

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TRIDIMENSIONAL CONTINUUM (FLAC3D)

MODELING

TRIDIMENSIONAL CONTINUUM (FLAC3D)

MODELING

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TRIDIMENSIONAL CONTINUUM (MIDAS)

MODELING

TRIDIMENSIONAL DISCONTINUUM

(3DEC) MODELING

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TRIDIMENSIONAL DISCONTINUUM

(3DEC) MODELING

Stress Distribution in Shotcrete Liner

EXCAVATION SEQUENCE

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STATION CAVERN

Excavation Sequence and Support

STATION CAVERN

Excavation Sequence and Support

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STATION CAVERN

Excavation Sequence and Support

No need for final lining

Drained, no water pressure (%25 assumed)

Rock load, capacity of bolts

Rock-liner interface

FINAL LINER DESIGN

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Design for Environment

Architecture: 96th St. Entrance 3

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Architecture: 86th St. Entrance 2

Architecture: 72nd St. Entrance 3

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Architecture: 86th St. Ancillary 1

Secant Pile Walls

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Secant Pile Walls, Toe Anchors

Slurry Walls, Permanent Station Walls

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Rebar Cage Lift

100 Right of Way

41 Travel Way 42 Work Zone

10 ft

96th St. Station, Street Cross Section

25

94th to 95th Streets, Temporary Decking

Launch Box Excavation

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Starter Tunnels

TBM

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TBM Tunnel

72nd Street Shaft

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72nd Street Shaft

Drill and Blast Design

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Overbreak and Profile Control

Vibration and Damage Control

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Vibration Control

Center Drift of Top Heading

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Side Drift of Top Heading

Penetration

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TBM Tunnel Enlargement

East Side Access Station Caverns in New York

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East Side Access Station Caverns in New York

East Side Access Station Caverns in New York

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Updated 0508

Trans Hudson Express Station Cavern

Trans Hudson Express Station Cavern

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High Speed Train Station in New York (Concept)

Indianapolis Pump Station Cavern

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Designed by Santiago Calatrava

World Trade Center, New York

The Future