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Australian Geomechanics Society Mini-symposium Sydney October 2005

Australian Geomechanics Society Mini-symposium Sydney October 2005. Soil Loads on Cut and Cover Tunnels Under High Fills Doug Jenkins Interactive Design Services. Overview:. Influence of high fills on structural actions Design of foundation structures for high vertical loads

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Australian Geomechanics Society Mini-symposium Sydney October 2005

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  1. Australian Geomechanics Society Mini-symposium Sydney October 2005 Soil Loads on Cut and Cover Tunnels Under High Fills Doug Jenkins Interactive Design Services

  2. Overview: • Influence of high fills on structural actions • Design of foundation structures for high vertical loads • Longitudinal differential settlement • Longitudinal loads • Examples • Conclusions

  3. Influence of high fills on structural actions • Axial loads • High fill = high axial load • Effect of foundation stiffness on axial load

  4. Influence of high fills on structural actions • Bending moments and shear forces • Effect of foundation stiffness on axial load • Lower bound stiffness may not be conservative

  5. Influence of high fills on structural actions • Bending moments and shear forces • Effect of arch profile on arch actions • Morwell Tunnels - alternative cross sections

  6. Influence of high fills on structural actions • Bending moments

  7. Influence of high fills on structural actions • Shear Forces

  8. Influence of high fills on structural actions • Use finite element analysis. • Consider the effect of boundary conditions in the model. • Consider the effect of upper and lower bound stiffness values in the foundation materials • Model the footing structure accurately • Optimise the arch shape for the fill height

  9. Essential Features of Finite Element Model • Include foundation layers. • Add arch fill in layers, modelling the actual construction sequence. • Allow slip at the arch/soil interface. • Non-linear Mohr-Coulomb soil model.

  10. Design of foundation structures for high vertical loads • Morwell Conveyor Tunnels • Alternative foundation treatments

  11. Design of foundation structures for high vertical loads • Detail of finite element mesh • Alternative simplified model

  12. Design of foundation structures for high vertical loads • Design actions in actual raft under maximum load

  13. Design of foundation structures for high vertical loads • Comparison of bending moments in flat and tapered rafts

  14. Design of foundation structures for high vertical loads • Alternative raft models: bending moments

  15. Design of foundation structures for high vertical loads • Alternative raft models: axial forces

  16. Design of foundation structures for high vertical loads • Larger spans

  17. Design of foundation structures for high vertical loads • Larger spans

  18. Longitudinal Differential SettlementLong Section - Morwell Tunnels

  19. Longitudinal Differential Settlement • Morwell conveyor tunnels analysis • Deep brown coal deposits + uncompacted fill

  20. Vertical Settlement

  21. Horizontal Movements

  22. Longitudinal Differential Settlement

  23. Longitudinal Differential Settlement

  24. Longitudinal Loads • Steep fill slopes above the structure • Segmental structures on steep slopes • Longitudinal spreading of foundations under high fills • Longitudinal differential settlement effects on continuous structures

  25. Longitudinal Loads

  26. Longitudinal Loads • Use wider precast elements • Provide shear connectors between adjacent elements and/or strengthen crown beam • Provide movement joints in the crown beam and footings • Design for variation in axial load • Detail robust crown joints

  27. Examples - Morwell Conveyor Tunnels

  28. Examples - Mt Arthur, Olympic Dam

  29. Examples - Spain

  30. Conclusions • High axial loads, possibly high bending moments and shear forces • Consider upper and lower bound foundation stiffness • Design raft foundations for soil-structure interaction • Consider longitudinal effects: • Differential settlement • Foundation spreading • Longitudinal loads due to fill slopes and/or inclined structure

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