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

BRADSHAW CONSTRUCTION CORPORATION

ELDERSBURG, MARYLAND

Alternative Title – “Luke. Let Go. Use the

Force” LESTER M. BRADSHAW, JR . / TODD BROWN / JORDAN BRADSHAW

BRADSHAW CONSTRUCTION CORPORATION

ELDERSBURG, MARYLAND

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

• Bradshaw’s 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

Owner’s 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

Engineer’s Design for this Project ◦ Six (6) jacked drives totaling 2,500’ x

48”or 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)

Contractor’s 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

BIGGER IS BETTER….IF IT FITS 11” 15” 17”

11.5” Disk Cutters

14” Disc Cutters

Tunnel Launches HEADER TUNNELS WERE INSTALLED BY DRILL- AND-BLAST METHOD

JACKING FRAME UTILIZED UNTIL TBM GRIPPER COULD BE USED

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!

www.Bradshawcc.com

QUESTIONS?