TRENCHLESS TECHNOLOGY ROADSHOW

May 28-29, 2014 – Scotiabank Convention Centre, Niagara Falls, ON

MICROTUNNELLING

OVERCOMES DESIGN AND

CONSTRUCTION CHALLANGES The Keswick Outfall Project

PRESENTATION OUTLINE

• Project Overview

• Design Challenges

• Construction Challenges

• Lessons Learned

PROJECT OVERVIEW

• Where exactly is Keswick, Ontario?

PROJECT OVERVIEW

• Where exactly is Keswick, Ontario?

York Region

PROJECT OVERVIEW

• Where exactly is Keswick, Ontario?

PROJECT OVERVIEW

• Community of Keswick is a growing commuter hub for the Greater Toronto Area

• York Region has been expanding the Keswick Water Pollution Control Plant (WPCP) to accommodate growth

• With expansion of the WPCP came the need to expand the existing outfall

PROJECT OVERVIEW

Keswick WPCP

LEGEND

Existing Outfall Open-Cut

Microtunneling

Dredging

Cook’s Bay

DESIGN CHALLANGES

• Poor ground conditions

• Maintaining traffic flows

• Existing utilities

• Abandoned shoring

• Undercrossing with minimal cover

• Inability to obtain property

• Onshore to offshore transition

DESIGN CHALLANGES

POOR GROUND CONDITIONS

• Groundwater at/near ground surface

• Up to 20ft above tunnel obvert

• Lacustrine deposits of fine sand, silt and clay

• Mainly SPT N = 0 – 4 in the tunnel zone

• Silts and clays highly sensitive

DESIGN CHALLANGES

POOR GROUND CONDITIONS

• Added specification requirements to deal with poor ground

• Soft ground cutterhead

• Minimum length of trailing cans or restrained pipe joints

• Provisional requirement for ground improvement by jet grouting

MAINTAINING TRAFFIC FLOWS

• Key item of concern

• Alignment crossed the town’s main intersection

• “5 Corner” design

• Fire and ambulance stations

• No full closures would be permitted

DESIGN CHALLANGES

DESIGN CHALLANGES

MAINTAINING TRAFFIC FLOWS

• Located shafts outside of intersection

• Limited, partial lane closures only

• Coordinated traffic controls with nearby Fire and Ambulance stations

DESIGN CHALLANGES

EXISTING UTILITIES

• Existing outfall predated many utilities in the intersection

• Original plan was to have the new outfall parallel the existing

DESIGN CHALLANGES

EXISTING UTILITIES

• Reviewed record drawings

• Town’s main trunk sewer (30in) crossed alignment

• Sewer had been constructed using 36ft deep steel sheet pile shoring

• Shoring was abandoned in place

DESIGN CHALLANGES

EXISTING UTILITIES

• Re-routed outfall crossed under existing trunk sewer with less than 18in of cover

• Specification requirements added to protect existing trunk sewer included:

• Advance jet grout support

• Monitoring during grouting and tunneling

• Bypass pumping

• CIPP liner stocked and ready

DESIGN CHALLANGES

INABILITY TO OBTAIN PROPERTY

• If permanent easements were needed, the project would have lost it’s “Pre-Approved” environmental assessment status.

• Locally, separation between the pipe springline and property lines was on the order of 18in

• Microtunnelling was key to maintaining such tight clearances

DESIGN CHALLANGES

ONSHORE TO OFFSHORE TRANSITION

• Traditional cofferdam transition would have significant impacts to shoreline and nearshore aquatic habitat

• Permits would be difficult to obtain

• If obtained, would have onerous conditions of approval.

DESIGN CHALLANGES

ONSHORE TO OFFSHORE TRANSITION

• Design called for transition to be completed by microtunnelling

• MTBM reception to take place 330ft offshore

• MTBM received in a dredged trench

• Shoreline and nearshore habitats unaffected.

CONSTRUCTION CHALLANGES

• Curved Drives

• Wet Reception

CONSTRUCTION CHALLANGES

CURVED DRIVES

• Original design called for straight drives

• Drive length based on 30in pipe installation

4

5 6

7 8 9

ORIGINAL DESIGN

CONSTRUCTION CHALLANGES

CURVED DRIVES

• Contractor proposed curved drives as a means to eliminate two shafts

• Required upsizing from 30in to 48in pipe

REVISED DESIGN

4

6

7 9 Plan Curve Drive Rad. = 22,500ft

Spatial Curve Drive Plan Rad. = 21,650ft Profile Rad. = 2,870ft

CONSTRUCTION CHALLANGES

CURVED DRIVES

• No curved drives had been completed in Canada

• No spatial curved drives had been completed in North America

• Contractor was able to demonstrate Corporate, MTBM Operator and Surveyor experience with curves

• Analysis showed that pipe deflections would be minor

• Credit of $1 million CDN (shared between owner and contractor)

CONSTRUCTION CHALLANGES

CURVED DRIVES

• Once technical (and financial) merit had been established, Owner, Designer and Contractor collaborated to implement the change

• Revisions required to several permits/approvals

• Had to demonstrate that upsizing of pipe was done for constructability reasons, and not to add capacity

CONSTRUCTION CHALLANGES

WET RECEPTION

• Specifications gave contractor flexibility in methods

• Contractor submitted a detailed wet reception plan:

• Hydraulic power pack removed for offshore drive

• Last 30ft of pipe internally restrained with strapping

• Mechanical bulkhead installed at shaft, and water pumped through bulkhead to equalize pressure

CONSTRUCTION CHALLANGES

WET RECEPTION

• Contractor submitted a detailed wet reception plan:

• Suction dredge used to expose MTBM

• MTBM removed and a fabricated tee attached to pipe and grouted in place

LESSONS LEARNED

• Be open to change, and encourage collaboration in implementing change.

• Maintain flexibility for unique or high-risk elements

• A good contractor can make all the difference

QUESTIONS

E-mail: marc.gelinas@hatchmott.com

E-mail: marc.gelinas@hatchmott.com