A presentation for 13th Australia New Zealand Conference on Geomechanics 2019 in Perth

1. 13th Australia New Zealand Conference on Geomechanics 2019
The design evolution of
replacement motorway bridge
approach embankments
N. Campbell and C. Bridges

2. 13th Australia New Zealand Conference on Geomechanics 2019
Brisbane
Airport
Gateway
Motorway
Gateway Upgrade North
N

3. N/B
S/B
September 2016
New N/B
Abutment B
New N/B
Abutment A

4. 13th Australia New Zealand Conference on Geomechanics 2019
May 2018

5. 13th Australia New Zealand Conference on Geomechanics 2019
October 2017

6. 13th Australia New Zealand Conference on Geomechanics 2019

7. Design Inputs
• Loading History
• Previous construction details
• Performance criteria
• Ground Model
(Site investigation)
13th Australia New Zealand Conference on Geomechanics 2019
June 2017

8. Design Inputs
• Loading History
• Previous construction details
• Performance criteria
• Ground Model
(Site investigation)
13th Australia New Zealand Conference on Geomechanics 2019
Time Activity
1m/week Construct existing embankment
24 years Current embankment
1 week Infill Median (Nov 2016)
Pause
1m/week Commence Widening (April 2017) Hold at
piling platform (RL +7)
Abutment A: 3 weeks
Abutment B: 3 weeks
Preloading NB widening, install piles (A then
B)
4 weeks Continue widening, raise to Abutment soffit
(RL +8.1)
3 days Install end spans of structure
1m/week Widen and raise to Final Surface Level (FSL)
1 month Preload at final level
1 week Apply final pavement load (Set as PCS
Reference)
40 years Measure Post Construction Settlement (PCS)

9. Design Inputs
• Loading History
• Previous construction details
• Performance criteria
• Ground Model
(Site investigation)
13th Australia New Zealand Conference on Geomechanics 2019

10. Design Inputs
• Loading History
• Previous construction details
• Performance criteria
• Ground Model
(Site investigation)
13th Australia New Zealand Conference on Geomechanics 2019
Slope Stability
Short term factor of safety ≥ 1.3
Long term factor of safety ≥ 1.5
Settlement
Post construction settlement (PCS) < 50mm over 40 years
Differential settlement limited to 0.5% over any 5m length

11. Design Inputs
• Loading History
• Previous construction details
• Performance criteria
• Ground Model
(Site investigation)
13th Australia New Zealand Conference on Geomechanics 2019
Year Investigation Type No. of Test Points
1984 CPT 1
1985 Boreholes 11
1985 CPT 5
2011 Borehole 1
2016 Borehole 8
2016 CPT 4
2017 Test Pits 2
2017 Test Pits during
construction 3

12. Design Inputs
• Loading History
• Previous construction
details
• Performance criteria
• Ground Model
(Site investigation)
13th Australia New Zealand Conference on Geomechanics 2019
Abutment A
Abutment B
Abutment A
Abutment B

13. Abutment B
Abutment A

14. 13th Australia New Zealand Conference on Geomechanics 2019
Additional SI
Load Transfer
Platform
Expanded
Polystyrene
Pulverised Fly
Ash
Preolading
Update
Ground
Model
Calibrate
Model
Updated
Contractor
Input
Preolading
Construction
Verification
Monitoring
Tender Design Detailed Design Construction

15. 13th Australia New Zealand Conference on Geomechanics 2019

16. 13th Australia New Zealand Conference on Geomechanics 2019
Criteria Outcome
Durability No structural elements 
Aesthetics Temporary: no screens required
Permanent: Unchanged

-
Whole of Life Improvement to rideability, no hard to soft pavement interface between piled vs
non piled section

Sustainability No emissions intensive elements (reinforced concrete, transportation, heavy plant
and machinery). Use of existing ground’s load carrying potential

Design Life Unchanged -
Safety Eliminated heavy plant operations to handle, pitch and drive piles. Eliminate
constructability issued with piling under existing high voltage power lines

Functional
Performance
No closely spaced piles which would have limited or constrained future works or
installations (eg. Poles, gantries, light fittings)

Program Less time required for earthworks compared to load transfer platform / piling
installation. Adjacent works could continue during preloading period

Cost Decreased cost in materials, time and equipment 
Comparison between concept and current design

17. Lessons Learnt
• Confirm the design assumptions at the outset (i.e.
following the Tender Phase)
• Seek input from construction team early in the design
process
• Undertake additional ground investigation to fill in the
gaps
• It is useful to have new investigation positions adjacent to
historic locations, to calibrate settlement models
• Update the analysis with ‘as encountered’ conditions
during construction
• There is great value in regular monitoring, enabling back
analysis and greater confidence in forward predictions.
13th Australia New Zealand Conference on Geomechanics 2019