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Conditions Where Diaphragm Walls Are Used

Marco D. Boscardin, PhD, PE, DGE

Boscardin Consulting Engineers, Inc.

DFI Seminar - 16 October 2012

What Drives Basement Construction Practices? Economy

Local Experience and Expertise

Local Tradition

Local Geology

Groundwater

Right-of-Way Issues

Other Site Constraints

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Why Use Diaphragm Walls?

Improved Control Ground Loss During Wall Construction

Improved Control Adjacent Ground Movements During Mass Excavation and Load Transfer

Control Groundwater Infiltration

To Serve as Final Walls and Load Bearing Elements

Alternatives such as T-Panels and Post Tensioning

Concrete Diaphragm Walls

Advantages Temporary and Perm. Groundwater Control

Less Vibration and Better Movement Control

Flexibility in Construction Sequence and Ground Conditions Accommodated

Limitations Work Area Needed

Cost

Specialized Equipment

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Where Diaphragm Walls are Used

When Large, Deep Basements are Needed

BCEICourtesy Nicholson and

Architect of The Capitol

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BCEI

Courtesy Nicholson and Architect of The Capitol

Where Diaphragm Walls are Used

When Large, Deep Basements are Needed

Dense Urban Settings Where Impact on Adjacent Properties a Concern

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Where Diaphragm Walls are Used

When Large, Deep Basements are Needed

Dense Urban Settings Where Impact on Adjacent Properties a Concern

To Eliminate the Need for Underpinning Existing Structures

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10 St. James

Braced Cut for Building

Where Diaphragm Walls are Used

When Large, Deep Basements are Needed

Dense Urban Settings Where Impact on Adjacent Properties a Concern

To Eliminate the Need for Underpinning Existing Structures

To Expedite Construction Schedule Serve as Final Walls Top-Down Construction Serve as Foundation Elements

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Russia Wharf Project

Where Diaphragm Walls are Used

When Large, Deep Basements are Needed

Dense Urban Settings Where Impact on Adjacent Properties a Concern

To Eliminate the Need for Underpinning Existing Structures

To Expedite Construction Schedule Serve as Final Walls Top-Down Construction Serve as Foundation Elements

Special Cases

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Circular Diaphragm Wall

Soft eye –Fiberglass piles

Diaphragm Wall for Tunnel Eye

North Shore Connector, Pittsburgh - AECOM

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T-Panels and Post-Tensioned Panels

Geotechnical Conditions and Diaphragm Walls

Compatible with Most Soil Conditions (Mechanical and Hydraulic Clam Rigs) Loose to Dense Sands

Soft to Stiff Clays

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Herbert Hoover Dike Rehabilitation

Hydraulic clamshell – Soilmec SM-870 with BH12 21

Herbert Hoover Dike Rehabilitation

Mechanical Clamshell

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Geotechnical Conditions and Diaphragm Walls

Compatible with Most Soil Conditions (Mechanical and Hydraulic Clam Rigs) Loose to Dense Sands

Soft to Stiff Clays

Compatible with Weaker Rocks (Hydromill) Hard Clay, Chalk, Shale, Sandstone

Hydromill Rig

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Herbert Hoover Dike Rehabilitation

Hydromill Cutter

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Cutter Soil Mixing (CSM) Rig

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Geotechnical Conditions and Diaphragm Walls

Compatible with Most Soil Conditions (Mechanical and Hydraulic Clam Rigs) Loose to Dense Sands

Soft to Stiff Clays

Compatible with Weaker Rocks (Hydromill) Hard Clay, Chalk, Shale, Sandstone

Difficulties with Soils Containing Many Boulders

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Drop Chisel for Rock Excavation

Vibrations and Wall Construction

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Geotechnical Conditions and Diaphragm Walls

Compatible with Most Soil Conditions (Mechanical and Hydraulic Clam Rigs) Loose to Dense Sands Soft to Stiff Clays

Compatible with Weaker Rocks (Hydromill) Hard Clay, Chalk, Shale, Sandstone

Difficulties with Soils Containing Many Boulders

Difficulties where Slurry is Lost – e.g. Karst, Coarse Gravels

Typical Goals for a Diaphragm Wall

Use Slurry to Counterbalance Lateral Ground and Water Pressures and Provide Support to Limit Ground Loss During Wall Excavation and Placement

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BCEI

Courtesy Nicholson

Typical Goals for a Diaphragm Wall

Use Slurry to Counterbalance Lateral Ground and Water Pressures and Provide Support to Limit Ground Loss During Wall Excavation and Placement

Place a Stiff Element in the Ground so that a Wider Support Spacing and a More Open Work Space are Possible

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Typical Goals for a Diaphragm Wall

Use Slurry to Counterbalance Lateral Ground and Water Pressures and Provide Support to Limit Ground Loss During Wall Excavation and Placement

Place a Stiff Element in the Ground so that a Wider Support Spacing and a More Open Work Space are Possible

Limit Water Inflows

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Russia Wharf Project

Diaphragm Walls and Water

Better than Other Conventional Walls Soldier Piles and Lagging Driven Sheet Piles

But Not Perfect, Shrinkage, Movement

Each Joint is a Potential Source of Leakage

Walls Flex and Joints Open and Close with Excavation and Filling

Can be Addressed with Special Joint Details

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LD-IV-1-10-39

Slurry Walls Not Totally “Watertight”

Soil Between Walls Excavated and “Dry” Side Exposed to Changes in Temperature and Humidity

P = Primary SPTC Wall Panel

S = Secondary SPTC Wall Panel

Gaps Grows Larger Between Concrete and Steel Pile on Dry Side Due to Shrinkage of Concrete as it Dries and is Subjected to Large Temperature Fluctuations

Surface Cracking Develops in Response to Cyclic Drying and Cyclic Freeze-Thaw

Example of an Improved Joint

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Diaphragm Wall Considerations

Panel Size Affects Ground Loss Affects Cost of Construction

Number and Types of Joints Affects “Water Tightness” Affects Load Transfer Between Panels

Support Spacing and Subgrade Soil Strength Overall System Stiffness Controls Ground Movements and Impacts on

Adjacent Structures

Opencut Movements

BCEIClough & O’Rourke, 1990

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Horizontal Wall Movement vs. Stiffness

BCEIClough & O’Rourke, 1990

Adaptable to Special Construction

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Jacked Tunnel Access Pits

Schematic Section of Jacking Pit Looking East

Cross Lot Bracing

Relief Holes

Frozen Soil

Post TensionSlurryWalls

Jet Grout In Situ Bracing

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Moveable Diaphragm Wall

Relief Holes Along Post-Tensioned Panels

Control of ground freeze pressures unique application in U.S.

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Summary

Diaphragm Walls a Competitive Alternative

Provides Enhanced Ground Loss Control During Wall Construction

Provides a Stiffer Support System to Better Control Ground Movements

Provides Improved Ground Water Control

Can Serve as Load Bearing Elements

Can be Reconfigured and Post-Tensioned for Greater Stiffness.