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GZA GEOENVIRONMENTAL, INC.1 EDGEWATER DRIVENORWOOD, MA 02062

AUTHOR/PRESENTER: ERIC P. BREGMAN

OWNER: Massachusetts Water Resources Authority (MWRA)

CONTRACTOR: Barletta Heavy Division

GZA GEOENVIRONMENTAL : Geotech ConsultantContractor Support Services

PROJECT TIMELINE: 2008 – 2009

PROJECT LOCATION: East Boston, MA

PROJECT COST: $50 Million

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PURPOSE:

Upgrade & Improve Existing Local Sewer System Capacity

Reduce Discharge Into Boston Harbor & Chelsea Creek By 40 Million Gallons Annually (90% Reduction)

GOAL: Comply with Federal Clean Water Act of 1972

SCOPE: 11,800 LF of 36” to 66” Micro-tunnelCSO Relief Piping

DESIGN SERVICES:

Structural & Geotechnical Engineering • 20 Deep Structure Shafts• 8-ft Wide x 96-ft Long Trench Support Design• MBTM Jacking Thrust Blocks

Aerial View of Project SiteREF: Google Maps (Satellite View)

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BENEFITS OF RE-SEQUENCING SHAFT CONSTRUCTION

• Reduced Number of MBTM Mobilizations

• Eliminated Five (5) Shafts

• Expedited Shaft Installation Increased Efficiency

• Resulted In Schedule and Cost Savings

BENEFITS OF SELECTING THE RIGHT EQUIPMENT

• AVN Model Automatic Tunneling Machine and Hydraulic Pipe Jacking Drive Unit

• Many of the Required Shaft Sizes Were Reduced

GROUND CONDITIONS & SITE CONSTRAINTS:

Contaminated Soils& Groundwater

Existing Utilities

Headroom Restrictions

Tie-ins to Existing Sewer

Structures

Difficult Ground Conditions

• Wide Variations inthe Soil Strata

Stability of Nearby Structures

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TRENCHLESS TECHNOLOGIES (MBTM)

Greatly Reduces Local Impact ToCommunity & Environment

Construction Related Traffic

Construction Related Pollution

(Sight, Noise, Air, Water, Etc.)

GEOTECHNICAL & STRUCTURAL CONSULTING SERVICES:

Eleven (11) Impermeable Shafts

Interlocking Drilled Secant Piles

Steel Sheet Piles

Jet Grout Invert Seals, Plugs & Ground Improvement

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GEOTECHNICAL & STRUCTURAL CONSULTING SERVICES:

Soldier Piles & Lagging

Drilled Micro-Piles & Contact Lagging

Reinforced Concrete Thrust Blocks

DRILLED SOLDIER PILE & LAGGING SHAFTS

40-ft Deep Max.

Groundwater Table

30-ft Above BOE

15-ft of Native Fill

atop Glacio Marine Clay

Clay Extended

Below BOE

Local Sumping

Numerous

Underground Utilities

Speed, Precision &

Ease of Construction

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CIRCULAR SHEET PILE SHAFTS

31-ft Deep Max.

Groundwater Table 25-ft Above BOE

15-ft of Native Fill atop Organics Over Glacio Marine Clay (w/ Sand Lenses)

CIRCULAR SHEET PILE SHAFTS

Jet Grout Invert Plug

Reduced Treatment of Contaminated

Groundwater

CIP Reinforced Concrete Ring Beams

Limited Groundwater Treatment and

T & D of Contaminated Soils

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DRILLED MICRO-PILE & CONTACT LAGGING SHAFTS

Low Headroom

Proximity to Utilities & Structures

Restricted Work Hours in Residential Area

Low Profile Track Mounted Drill Rig w/ Articulating Mast

DRILLED MICRO-PILE & CONTACT LAGGING SHAFTS

Accurately Locate & Install Vertical Support Members

9-5/8”Φ x 1/2” Wall Flush Joint Steel Casing

Contact Lagging Designed

Avoided Existing Utilities

Reduced Vibrations Typical of Pile Driving

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CIRCULAR SECANT PILE SHAFTS

45-ft Deep Max.

Groundwater

Table 39-ft

Above BOE

9-ft of Native Fill

Atop Glacio Marine

Clay to Below BOE

Contaminated

Groundwater & Soil

Water-Tight

Impermeable Design

CIRCULAR SECANT PILE SHAFTS

Technically Innovative

Interlocking Primary &

Secondary Secant

Piles Design

1 Meter Diameter (3’-3”)

Drilled Steel Casing

14-ft to 27-ft Inside

Diameter of Shaft

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CIRCULAR SECANT PILE SHAFTS

Quantity of Secants a Function of MBTM

Size (Overall Shaft Diameter) & Min.

Required Wall Thickness

22 to 38 Secants

Required w/

Center-to-Center

Spacing of 2’-6”

9” Min. Wall

Thickness

2500 PSI

Rapid Curing Concrete

CIRCULAR SECANT PILE SHAFTS

Stresses Due to Overburden & Surcharge Transmitted & Distributed Along

Circumference of Shaft

Hoop Stresses Acted as Compression Force

Lateral Earth Pressures of 4500 PSF (278 PSI) Across 25-in Secant Overlap

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CIRCULAR SECANT PILE SHAFTS

Quality Control & Installation Techniques of Contractor

No Bracing Due to Geometric Properties (Arching Effect)

Reduction in Shaft Diameter, Construction Material & Excavation Quantity

400% Increase in Efficiency & Speed of Continuous Excavation

PRACTICAL ADVANTAGES RECOGNIZED

Innovative & Constructible Solutions for Deep Shaft Design

Flexible Design Approach

Minimized Impact to Surrounding Residential Urban Environment

Construction Efficiency

Schedule & Cost Savings Resulting From:

• Reduction in Shaft Quantity & Size

• Limit Bracing Required

• Contaminated Groundwater and Soil Treatment & Disposal

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Barletta Heavy Division, Inc. of Canton, MA (General Contractor)

Cruz Contractors, LLC of Holmdel, NJ (Micro-Tunneling Sub-Contractor)

Hayward Baker of Providence, RI (Specialty Sub-Contractor)

Herrenknect AG of Germany (Micro-Tunneling Equipment Manufacturer)