Small Diameter Rock TBM Tunneling in Baltimore .Small Diameter Rock TBM Tunneling in Baltimore...

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Small Diameter Rock TBM Tunneling in Baltimore LESTER M. BRADSHAW, JR . / TODD BROWN / JORDAN BRADSHAW



Alternative Title Luke. Let Go. Use the




Presentation Agenda

Organizational History Project Overview Choosing Means & Methods Construction Details Lessons Learned

Bradshaw Construction History Family tunneling firm since 1963

Specializing in tunnel & shaft construction

Florida to Maine to Colorado to Texas

Extensive tunneling experience: Hand & NATM Tunneling TBM Tunneling Microtunneling

Project Overview

Name: Lower Gwynns Run Interceptor Phase II

Owner: City of Baltimore, MD Engineer: Dewberry Consultants, LLC Design Bid Build Contract Bradshaws Low Bid $11.9 million

Project Requirements Meet 2002 EPA Consent Decree Replace 1904 Infrastructure Increase sewer capacity Complete failed microtunnel

Project Challenges Downtown urban setting Extremely variable geology Existing utility conflicts Community relations

Downtown Urban Setting

Downtown Urban Setting Restricted Access Limited Work Areas

Project Geology Baltimore Gneiss

UCS Values Max 37,002 psi Average 20,199 psi

RQD Ranging from 25% (poor) to 95% (excellent), averaging out at 60% (fair)

Highly abrasive Cerchar from 3.2 to 5.6 High quartz content (23% - 35%) High feldspar content (46% - 59%) Strike of foliation between 25 to 75 degrees NE Dipping from 25 to 45 degrees to the NW

Geotechnical Report Bid Package

Initial report provided with bid documents High UCS = 26,812 psi Average UCS = 14,429 psi TBM proposals based on this

Geotechnical Report by Addendum

Geotechnical data from previous failed microtunnel contract issued by addendum 9 days before bid: Average UCS = 20,199 psi High UCS = 37,002 psi 38% higher TBM suppliers do not respond

Baltimore TBM Rock Experience Upper Jones Falls Interceptor (2004)

6,000 x 48 PCP by one pass microtunnel Contract specified rock (UCS) < 18,000 psi Actual rock (UCS) peaked at 43,500 psi MTBM rescued on 1 of 6 drives Open main beam type TBM tried & failed Result: 50% DSC cost overrun of bid price

Owners Experience All previous sewer tunnels over budget

and over time Used design engineers with limited rock

tunneling experience Used highly prescriptive specifications Result: Paid significant claims and

incurred substantial delays tunneling for the past 15 years

Engineers Design for this Project Six (6) jacked drives totaling 2,500 x

48or 60 OD steel casing Installed by mechanized tunneling

(method unspecified) Drill and blast rescue tunneling

allowed Carrier pipe - 30 FRP (two pass) 8 access shafts 7 manholes + tie-in

Structure in Baltimore Street

Contractor Must Make the Decisions

Choose the tunneling method Choose the TBM Choose the TBM cutter wheel Make it work!

How Did We Decide Means & Methods? Evaluated the geology Reviewed previous TBM experience Evaluated TBM capabilities Evaluated tunnel support risk Adjusted design to TBM capabilities Offered improved capacity (win:win)

Contractors Means & Methods Upsized tunnel diameter to 72 Chose Double-Shield Rock TBM Chose 14 disk cutter wheel Tunnel support as needed or required Lengthened several tunnels Eliminated 2 access shafts & manholes Larger tunnel allowed Owner to upsize

sewer pipe

MTBM vs Double-Shield TBM Microtunneling Advantages:

Better capability for weathered rock Smaller diameter excavation

Microtunneling Limitations: MTBM rock mining efficiency limited Pipe jacking required

MTBM vs Double-Shield TBM

Double-Shield TBM Advantages TBM RPM is faster and disk cutters are

much larger Self-propelled option allows for

multiple tunnel support choices Longer drives & fewer access shafts

Double-Shield TBM Disadvantages Slower production in highly-

decomposed zones

Choosing the Correct TBM Cutter Wheel Robbins Standard Cutter Wheel - 11.5

Cutters Easier to change Production rate slower Lower life

Robbins Heavy Duty Cutter Wheel - 14 Cutters Harder to change Production rate higher Longer life


11.5 Disk Cutters

14 Disc Cutters



Competent Rock Zones

1,540 LF of unsupported rock Mining production = 20 LF/shift Excludes launches, cutter changes, TBM repairs and delays

Competent Rock Zones No Supports

Decomposed Rock Supported Tunnel

500 LF of rib-and-board supported tunnel

Mining production = 10 LF/shift Excludes launches, cutter changes, TBM repairs and delays

Decomposed Rock & Soft Ground

Permit Requires Tunnel Supports

240 LF of 68 liner plates for crossing underneath AMTRAK right-of-way

Mining production = 15 LF/shift Excludes launches, cutter changes, TBM repairs and delays

Tunnel Production Summary Production Analysis

Overall Average = 11.5 LF/shift Peak Shift = 36 LF

Cutter Wheel Analysis 11.5 Cutters = 7 LF/shift 14 Cutters = 12 LF/shift

Access Shafts Rib-and-board supports in soft ground Wire mesh & shotcrete in rock Rock excavation by drilling and blasting Six mining/receiving shafts

16 to 32 diameter 18 to 57 deep

Complex Existing Utilities in Baltimore St

32 ID Recovery Shaft in Baltimore St

Extensive existing utilities: 4 storm drains 1 gas line 1 concrete duct-bank 2 water mains Multiple communication cables Live 33 brick sanitary sewer

Restricted TBM Recovery Baltimore St

Safe TBM recovery required extra utility support to create a window

TBM broken down into its shortest segments

Restricted TBM Recovery Baltimore St

Tie-In Structure Baltimore St

Junction structure for new 36 and existing 33 sanitary lines

15 x 15 x 13 cast-in-place structure constructed around live brick sanitary sewer and below active utility lines

Lessons Learned Benefits of owner / engineer flexibility on means and methods

Benefits of contractor input on means and methods, even design

Trust local geologic knowledge Baltimore Tunneling Firsts:

Completed on time Under budget

Lessons Learned

As the Millennials take over, look out for the inexperienced!


Small Diameter Rock TBM Tunneling in BaltimoreAlternative Title Luke. Let Go. Use the ForcePresentation AgendaBradshaw Construction HistoryProject OverviewProject RequirementsProject ChallengesDowntown Urban SettingDowntown Urban SettingProject GeologyGeotechnical Report Bid PackageGeotechnical Report by AddendumBaltimore TBM Rock ExperienceOwners Experience Engineers Design for this ProjectContractor Must Make the DecisionsHow Did We Decide Means & Methods?Contractors Means & MethodsMTBM vs Double-Shield TBMMTBM vs Double-Shield TBMChoosing the Correct TBM Cutter Wheel11.5 Disk Cutters14 Disc CuttersTunnel LaunchesCompetent Rock ZonesCompetent Rock Zones No SupportsDecomposed Rock Supported TunnelDecomposed Rock & Soft GroundPermit Requires Tunnel SupportsTunnel Production SummaryAccess ShaftsComplex Existing Utilities in Baltimore StRestricted TBM Recovery Baltimore StRestricted TBM Recovery Baltimore StTie-In Structure Baltimore StLessons LearnedLessons LearnedQUESTIONS?