Australian Geomechanics Society Mini-symposium Sydney October 2005

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

26. 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

27. Longitudinal Loads

28. 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

29. Examples - Morwell Conveyor Tunnels

30. Examples - Mt Arthur, Olympic Dam

31. Examples - Spain

32. 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