TBM Face Pressure Calculation

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  • DOWNTOWN LINE 2 CONTRACT C918 Revision B Bored Tunnel between TKK and BTN - TBM Face Pressure Calculation

    Job No. S4922 Geoconsult Asia Singapore 01/08/2012

    Table of Contents

    0 REVISION RECORD ........................................................................................................................... 2

    1 INTRODUCTION ................................................................................................................................. 3

    2 ALIGNMENT AND GROUND CONDITIONS ..................................................................................... 4

    2.1 Alignment ............................................................................................................................................ 4

    2.2 Ground Conditions .............................................................................................................................. 4

    3 CALCULATIONS ................................................................................................................................ 5

    4 CONCLUSIONS & RECOMMENDATIONS ....................................................................................... 6

    4.1 General ................................................................................................................................................ 6

    4.2 TBM Operation .................................................................................................................................... 6

    4.3 Recommendations .............................................................................................................................. 6

    5 REFERENCES .................................................................................................................................... 8

    APPENDIX: Appendix 1 Ground Information Appendix 2 Design Parameter and Input Data Appendix 3 Recommended Face Pressure Values Appendix 4 Cutter Head Intervention

    Page 1

  • DOWNTOWN LINE 2 CONTRACT C918 Revision B Bored Tunnel between TKK and BTN - TBM Face Pressure Calculation

    Job No. S4922 Geoconsult Asia Singapore 01/08/2012

    0 REVISION RECORD

    Revision Description of Amendments Date

    -

    First Issue 20/06/2011

    A

    Final Submission 13/09/2011

    B

    Final Submission Revised According to LTAs Comments 01/08/2012

    File: W:\wo0_job\49\22-C918-DD Alpine\TECH-DOC\Reports\Face Pressure\TKK to BTN\Rev. B\DOC-918-TUN-DCS-9101_B.doc

    Page 2

  • DOWNTOWN LINE 2 CONTRACT C918 Revision B Bored Tunnel between TKK and BTN - TBM Face Pressure Calculation

    Job No. S4922 Geoconsult Asia Singapore 01/08/2012

    1 INTRODUCTION

    Contract 918 consists of design and construction of station at Tan Kah Kee, the twin bored tunnels from the cross over box northwest of Tan Kah Kee Station (TKK) to the station at Sixth Avenue (SAV) within C917, and another twin bored tunnels between the Tan Kah Kee station (TKK) and the station at Botanic Garden (BTN) to be constructed under the C919.

    The Tunnel works include twin bored tunnel with inner diameter of 5.8m and outer diameter 6.35m as well as two mined cross passages. The total length of the twin bored tunnel is about 1.483 kilometres. The length of twin bored tunnel from Cut Cover Tunnel to Sixth Avenues Station is 0.558 kilometres and the length of twin bored tunnel from Tan Kah Kee Station to Botanic Garden Station (BTN) is 0.925 kilometres.

    This report provides estimate of required face pressures to be applied and controlled during driving from TKK to BTN station only. The estimated TBM face pressure for bored tunnels between CCT and SAV station is covered by a separate report.

    The twin bored tunnel will be constructed by slurry tunnel boring machines (slurry TBMs). The slurry TBM is designed to allow excavation in the varying soft ground conditions. Pre-cast concrete segmental lining, designed to provide the final permanent support, will be installed at the tail section of the TBM as it advances though the ground.

    The report shall be read in conjunction with drawing and geotechnical data presented in Appendix 1 and Appendix 2.

    The overall site plan of Contract C918 is presented in Figure 1-1 below.

    Figure 1-1: Site Plan of Contract C918

    Page 3

  • DOWNTOWN LINE 2 CONTRACT C918 Revision B Bored Tunnel between TKK and BTN - TBM Face Pressure Calculation

    Job No. S4922 Geoconsult Asia Singapore 01/08/2012

    2 ALIGNMENT AND GROUND CONDITIONS

    2.1 ALIGNMENT

    As stated above, contract C918 bored tunnel alignment features twin bored tunnels.

    At Launching area:

    Expo Bound Track tunnel (Left tunnel from TKK to BTN) Bukit Panjang Bound Track tunnel (Right tunnel from TKK to BTN)

    At Receiving area:

    Expo Bound Track tunnel (Left tunnel from TKK to BTN) Bukit Panjang Bound Track tunnel (Right tunnel from TKK to BTN)

    As mentioned in Section 1 above, the alignment of DTL 2 for C918 commences from the launching area which is located at the TKK station. After the launch, the TBMs will run more or less at the same level throughout the drive.

    The length of the bored tunnels is about 0.925 kilometers for each drive. Both tunnels will be driven along decreasing chainages.

    2.2 GROUND CONDITIONS

    The ground conditions are interpreted based on GIBR attached in LTA consolidated working document documents Ref [1]. The project site is located primarily in Fill underlying by Kallang Formation and the bottom layers are comprised of Bukit Timah Granite.

    The subsurface layering can be classified into the following layers:

    Fill Estuarine Clay (E) Fluvial Clay (F2) Fluvial Sand (F1) Residual soil of Grade VI (GVI) and Grade V (GV) Various grades of Rock, i.e. Grade IV (GIV), Grade III (GIII), Grade II (GII)

    and Grade I (GI)

    For easy reference, the soil profile along the tunnel alignment is presented in Appendix 1.

    Page 4

  • DOWNTOWN LINE 2 CONTRACT C918 Revision B Bored Tunnel between TKK and BTN - TBM Face Pressure Calculation

    Job No. S4922 Geoconsult Asia Singapore 01/08/2012

    3 CALCULATIONS

    The calculation approach investigates the stability of tunnel face by considering limit equilibrium of a sliding wedge at the face loaded by a prismatic body.

    The imposed loads comprise of surface surcharge of 20 kPa and gravity loading of soil above the sliding wedge. Ground water table at 1m below the ground surface is considered in calculations. Both drained and undrained behaviours of relevant soil materials are examined. Generally, recommended face pressures are derived from the more conservative drained case.

    A total of 38 sections for each TBM drive have been calculated. Selection of sections for calculations is based on variations of overburden, and geology at the tunnel face. The distance between the analysis sections is generally about 25m.

    The calculation approach is based on Anagnostou and Kovari, Ref.[7]. This approach has previously been applied successfully to the TBM tunnel drives for other projects in Singapore including, the North East Line, the Deep Tunnel Sewerage System (DTSS), the Circle Line Stages 2, 3, 4 & 5 and the Downtown Line 1.

    The following design considerations are mentioned in particular:

    1. The ground conditions at tunnel level and above are taken from the geotechnical interpretive report and the geotechnical soil profile which is presented in Appendix 1.

    2. TBM face pressures are derived by calculations based on the approach presented in Ref.[7], considering the local ground conditions as well as groundwater seepage forces at the face.

    3. Seepage pressure and related temporary depressurisation at the excavation face were considered in the analyses using drained soil parameters. Since the TBM will be advancing at an average rate of about 10m per day, this is considered conservative.

    The input parameters used in calculation are summarized in Appendix 2 and the results of calculations are summarised in Appendix 3.

    Page 5

  • DOWNTOWN LINE 2 CONTRACT C918 Revision B Bored Tunnel between TKK and BTN - TBM Face Pressure Calculation

    Job No. S4922 Geoconsult Asia Singapore 01/08/2012

    4 CONCLUSIONS & RECOMMENDATIONS

    4.1 GENERAL

    Based on existing ground conditions at tunnel level, the required face pressures are calculated and presented in Appendix 3.

    4.2 TBM OPERATION

    The twin bored tunnels will be driven using two slurry TBM for each drive. The TBM is expected to be operated with the pressure chamber fully filled and pressurized, such that the recommended face pressure range as provided in Appendix 3 is maintained at all times.

    The tables in Appendix 3 provide the following information:

    Recommended face pressure range at tunnel axis level Recommended tail void grouting pressure range Recommended compressed air pressure during cutterhead interventions

    Hydrostatic groundwater pressure at tunnel axis level

    4.3 RECOMMENDATIONS

    The recommended face pressure ranges are proposed in Appendix 3.

    The proposed values are based on the understanding that during TBM driving, the following strategy will be adopted in principle:

    In general, the applied face pressure shall be within the recommended face pressure range at all times

    Shop Houses: From the findings of the CIAR, Ref. [9], the tunnel excavation needs to limit the volume loss to 1.0% in the zone of the Shop Houses. The conclusion from that assessment is that the volume loss of 1.0% needs to be applied for Bukit Panjang bound tunnel only between chainage 46+020 and 45+950. According to Rep