Small Diameter Rock TBM Tunneling in Baltimore

Transcription

1 Small Diameter Rock TBM Tunneling in Baltimore LESTER M. BRADSHAW, JR. / TODD BROWN / JORDAN BRADSHAW BRADSHAW CONSTRUCTION CORPORATION ELDERSBURG, MARYLAND

2 Alternative Title Luke. Let Go. Use the Force LESTER M. BRADSHAW, JR. / TODD BROWN / JORDAN BRADSHAW BRADSHAW CONSTRUCTION CORPORATION ELDERSBURG, MARYLAND

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

4 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

5 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

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

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

8 Downtown Urban Setting

9 Downtown Urban Setting Restricted Access Limited Work Areas

10 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

11 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

12 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

13 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

14 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

15 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

16 Contractor Must Make the Decisions Choose the tunneling method Choose the TBM Choose the TBM cutter wheel Make it work!

17 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)

18 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

19 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

20 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 highlydecomposed zones

21 Choosing the Correct TBM Cutter Wheel Robbins Standard Cutter Wheel 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

22 11.5 Disk Cutters

23 14 Disc Cutters

24 Tunnel Launches HEADER TUNNELS WERE INSTALLED BY DRILL- AND-BLAST METHOD JACKING FRAME UTILIZED UNTIL TBM GRIPPER COULD BE USED

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

26 Competent Rock Zones No Supports

27 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

28 Decomposed Rock & Soft Ground

29 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

30 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

31 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

32 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

33 Restricted TBM Recovery Baltimore St Safe TBM recovery required extra utility support to create a window TBM broken down into its shortest segments

34 Restricted TBM Recovery Baltimore St

35 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

36 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

37 Lessons Learned As the Millennials take over, look out for the inexperienced!

38 QUESTIONS?