Transcript Training
Concrete Institute of Australia Soil-Structure Interaction Seminar Sydney March 2007
Design of Buried Arch 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 Longitudinal differential settlement Longitudinal loads Examples Conclusions
Influence of high fills on structural actions Axial loads High fill = high axial load Effect of foundation stiffness on axial load
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
Influence of high fills on structural actions Bending moments and shear forces Effect of arch profile on arch actions Morwell Tunnels - alternative cross sections
100 0 -100 -200 -300 -400 -500 -600 -700 -800 -8
Influence of high fills on structural actions Bending moments
Morwell Tunnels Compa rison of Arch S ha pe s Be nding Mome nts -6 -4 -2 0
X-Axis
2 4 6 8 Actual Circular Elliptical
Influence of high fills on structural actions Shear Forces
Morwell Tunnels Compa rison of Arch S ha pe s S he a r Force s 1000 500 0 Actual Circular Elliptical -500 -1000 -8 -6 -4 -2 0
X-Axis
2 4 6 8
Influence of high fills on structural actions Bending moments and shear forces Effect of arch profile on arch actions Oman Southern Expressway; 20 m span under 25m high fill
Influence of high fills on structural actions Bending moments Ultimate Bending Moments -400 -600 -800 -1000 0 400 200 0 -200 5 10 15 X-Axis 20 25 30 35 Circular K = 0.4
Influence of high fills on structural actions Shear Forces Ultimate Shear Forces 800 -200 -400 -600 0 600 400 200 0 5 10 15 X-Axis 20 25 30 35 Circular K = 0.4
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
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.
Include concrete and geometric non linearity for large structures.
Design of foundation structures for high vertical loads Morwell Conveyor Tunnels Alternative foundation treatments
Design of foundation structures for high vertical loads Detail of finite element mesh Alternative simplified model
Design of foundation structures for high vertical loads Design actions in actual raft under maximum load
Type A Raft 1000 500 0 -500 -1000 -3 -2 -1 0 1 2 3 Moment Shear Axial
Design of foundation structures for high vertical loads Comparison of bending moments in flat and tapered rafts
Bending Moment Flat raft vs. Actual 1000 500 0 -500 -1000 -1500 -2000 -3 -2 -1 0 1 2 3 Flat raft Actual raft
Design of foundation structures for high vertical loads Alternative raft models: bending moments
Bending Moment Alternative analysis methods 600 500 400 300 200 100 0 -100 -200 -3 -2 -1 0 1 2 3 R E P L FE A S tra nd7 FE A S tra nd7 simplifie d
Design of foundation structures for high vertical loads Alternative raft models: axial forces
Axial Load Alternative analysis methods 0 -100 -200 -300 -400 -500 -600 -700 -800 -900 -3 -2 -1 0 1 2 3 R E P L FE A S tra nd7 FE A S tra nd7 S implifie d
Design of foundation structures for high vertical loads Larger spans
Design of foundation structures for high vertical loads Larger spans
Longitudinal Differential Settlement
Long Section - Morwell Tunnels
Longitudinal Differential Settlement
Morwell conveyor tunnels analysis Deep brown coal deposits + uncompacted fill
Vertical Settlement
Horizontal Movements
0 -0.5
-1 -1.5
-2 -2.5
-200
Longitudinal Differential Settlement
Settlement and Longitudinal Movement Minimum stiffness all layers 0.2
-100 0
X-Axis
100 0.1
0 -0.1
200 -0.2
0 -0.1
-0.2
-0.3
-0.4
-0.5
-0.6
-0.7
-0.8
-200 DX DY Settlement and Longitudinal Movement Maximum differential stiffness -100 0
X-Axis
100 200 -0.15
0.1
0.05
0 -0.05
-0.1
DX DY
Longitudinal Differential Settlement
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
Longitudinal Loads
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
Examples - Morwell Conveyor Tunnels
Examples - Mt Arthur, Olympic Dam
Examples - Oman S Expressway
Examples - Spain
Conclusions
High axial loads, possibly high bending moments and shear forces Consider upper and lower bound foundation stiffness Consider concrete and geometric non linearity for large structures Design raft foundations for soil-structure interaction Consider longitudinal effects: – Differential settlement – Foundation spreading – Longitudinal loads due to fill slopes and/or inclined structure