1. Utilising composite action to
achieve lining thickness
efficiency for sprayed concrete
lined (SCL) tunnels
Dr. Jiang Su
BTS 2016 11th Oct 2016

2. • Background of this research
• What is composite SCL and why use composite SCL
• Lining optimisation study
• Conclusions and suggestions
Content of this presentation

3. SCL Tunnel Lining Efficiency
Platform Tunnel Lining Configuration Heathrow
Express
Crossrail
Primary
Lining
Thickness (mm) 300 400
Type of reinforcement Steel mesh Steel fibres
Secondary
Lining
Thickness (mm) 300 300
Type of reinforcement Steel rebars Steel fibres (steel
rears in the invert)
Tunnel Total Thickness (T) (mm) 600 700
External diameter (D) (m) 9 11
Efficiency T / D (mm/m) 67 64

4. Composite SCL – Physical Components
• Composite SCL
 Permanent sprayed concrete primary lining (including a regulating layer)
 Sprayed waterproofing membrane
 Permanent sprayed (or cast in-situ) concrete secondary lining
 Composite SCL has been constructed for recently projects (e.g. Crossrail)
a b Ground
Permanent sprayed primarylining
Sprayed waterproofing membrane
Permanent sprayed secondarylining

5. Composite SCL – Design Approaches
• Composite SCL – Current Design
Approach
 Only compression are considered
 Designed as “unbonded double shell
lining” tunnel
 Not realise the full potential of
composite SCL
Permanent sprayed
primary lining
(a) Sprayed membrane interface
currently assumed in the design
Permanent sprayed or
cast secondary lining
Compression
(b) Sprayed membrane interface
actual behavior
Compression TensionShear
• Composite SCL – Actual Behaviour
 Compression, tension and shear all
considered
 Designed for composite action
 Hope to reduce the overall lining
thickness

6. Composite SCL – Key features of this study
• Composite SCL – Previously
 Limited laboratory tests for sprayed membrane interface
 Only one structural numerical analysis performed for composite SCL tunnel
• Composite SCL – This Study
 Finite Difference Package FLAC used
 Interface parameters based on results from extensive laboratory tests
 A verified numerical modelling technique for simulating composite action
 Full numerical analysis considering key factors
1) Different stress histories between primary and secondary linings
2) Age-dependent stiffness for sprayed concrete
3) Stage construction of the SCL primary lining
4) Non-linear small strain stiffness constitutive model for the ground
5) Long-term consolidation of the ground

7. Composite SCL – Criteria of an Efficient and Robust Design
• Robust and Efficient Design Criteria
 Minimise the use of traditional steel
reinforcement
 Reduced overall lining thickness
 Sufficient robustness of interface
• Evaluation Method
 Axial force
 Ratio between bending moment and
axial force (RBM/AF)
 Interface stress
𝑅 𝐵𝑀/𝐴𝐹 = 𝑀 (𝑁 × 1𝑚)
BM/AF =0.20
BM/AF =0.40
BM/AF =0.13

8. Composite SCL – FLAC Model

9. Composite SCL – Modelling Approach for Lining
• Primary and secondary linings modelled using zone elements
 Allows for the development of composite action at the membrane interface

10. • Waterproofing membrane interface modelled using interface elements
 Modelled as normal and tangential springs between the two linings
 Variations in membrane thickness, interface roughness and others can be
considered by varying interface parameters
 Interface parameters based on laboratory testing, as shown below
Composite SCL – Modelling Strategy for Membrane Interface
Interface
parameter
Normal stiffness
(GPa/m)
Tangential sitffness
(GPa/m)
Tensile strength
(MPa)
Shear Strength
(Mpa)
Value 4 2 0.8 2

11. • Use “dummy” beam element
 Beam element with 1/1000 actual lining stiffness
 Placed at the centre of the lining
 Ease to extract the results
Composite SCL – Extraction of the Results

12. Composite SCL – Presentation of the results
• 6 cases presented based on a typical Crossrail platform tunnel
• Primary lining thickness constant at 400mm
• Secondary lining thickness reduces from 300mm to 50mm
• Axial force check not presented
• Long-term consolidation load presented for load sharing results
• Lining efficiency includes short-term load for the primary lining
• Lining efficiency check against a BM/AF ratio of 0.20
• Interface stress check against interface strength from laboratory tests

13. Composite SCL – Sharing of long-term consolidation axial force
0
200
400
600
800
1,000
Axialforce(kN)
Position around the lining
SEC_50mm SEC_100mm SEC_150mm
SEC_200mm SEC_250mm SEC_300mm
Crown Shoulder Axis Knee Invert
a
0
200
400
600
800
1,000
Axialforce(kN)
Postition around the lining
SEC_50mm SEC_100mm SEC_150mm
SEC_200mm SEC_250mm SEC_300mm
Crown Shoulder Axis Knee Invert
b
-200
-100
0
100
200
300
400
500
600
Axialforce(kN)
Position around the lining
SEC_50mm SEC_100mm SEC_150mm
SEC_200mm SEC_250mm SEC_300mm
Crown Shoulder Axis Knee Invert
c
-20%
0%
20%
40%
60%
80%
Axialforceloadsharingratio
Position around the lining
SEC_50mm SEC_100mm SEC_150mm
SEC_200mm SEC_250mm SEC_300mm
Crown Shoulder Axis Knee Invert
d

14. Composite SCL – Sharing of long-term consolidation bending moment
-50
0
50
100
150
200
Bendingmoment(kN.m)
Position around the lining
SEC_50mm SEC_100mm SEC_150mm
SEC_200mm SEC_250mm SEC_300mm
Crown Shoulder Axis Kne Invert
a
-15
-5
5
15
25
35
Bendingmoment(kN.m)
Position around the lining
SEC_50mm SEC_100mm SEC_150mm
SEC_200mm SEC_250mm SEC_300mm
Crown Shoulder Axis Knee Invert
b
0.0001
0.001
0.01
0.1
1
10
100
1000
Bendingmoment(kN∙m)
Position around the lining
SEC_50mm SEC_100mm SEC_150mm
SEC_200mm SEC_250mm SEC_300mm
Crown Shoulder Axis Knee Invert
c
0%
20%
40%
60%
80%
100%
Bendingmomentloadsharingratio
Position around the lining
SEC_50mm SEC_100mm SEC_150mm
SEC_200mm SEC_250mm SEC_300mm
Crown Shoulder Axis Knee Invert
d

15. Composite SCL – Evaluation of Lining Efficiency – Total Lining
Force
0.00001
0.0001
0.001
0.01
0.1
1
BM/AFratio
Position around the lining
SEC_50mm SEC_100mm SEC_150mm
SEC_200mm SEC_250mm SEC_300mm
Crown Shoulder Axis Knee Invert
a
1E-05
0.0001
0.001
0.01
0.1
1
10
100
BM/AFratio
Position around the lining
SEC_50mm SEC_100mm SEC_150mm
SEC_200mm SEC_250mm SEC_300mm
Crown Shoulder Axis Knee Invert
bBM/AF=0.2
BM/AF=0.2

16. Composite SCL – Interface Stress
-150
-100
-50
0
50
100
Interfacestress(kPa)
Position around the lining
SEC_50mm SEC_100mm SEC_150mm
SEC_200mm SEC_250mm SEC_300mm
Crown Shoulder Axis Knee Invert
a
-200
-150
-100
-50
0
50
100
Interfacestress(kPa)
Position around the lining
SEC_50mm SEC_100mm SEC_150mm
SEC_200mm SEC_250mm SEC_300mm
Crown Shoulder Axis Knee Invert
b
Interface stress in normal direction Interface stress in tangential direction
Tension
Compression

17. Composite SCL – Typical Lining Behaviour
Interface stress Lining deformation
Maximum
interface
tension
Maximum
interface
tension
Maximum interface
compression
Original circular tunnel lining
Primary lining in deformation
Secondary lining in deformation
Crown
Invert
Axis level
Secondary lining being “pulled apart”
by the primary lining via bonded
interface – tension in interface
Secondary
lining being
“pushed
down” by the
primary
lining via
bonded
interface –
compression
in interface

18. Composite SCL – Conclusions and Suggestions
• Conclusions
 Utilising the composite action could significantly reduce the secondary lining thickness,
improving the lining efficiency
 The interface is sufficiently robust to resist the interface stresses
 One pass SCL tunnel is possible from a structural point of view
• Suggestions
 Design a secondary lining that is much thinner than the primary lining
 Secondary lining mainly designed for internal loads, durability, etc
 More laboratory and in-situ test results for the long-term behavior of the membrane interface

19. Composite SCL Tunnel Publications
Interface parameters of composite sprayed concrete linings in soft ground with spray-
applied waterproofing - Tunnelling and Underground Space Technology Oct 2016
Primary-secondary lining interactions for composite sprayed concrete lined tunnels
using sprayed waterproofing membrane - World Tunnel Congress 2016 April 2016
Utilizing composite action to achieve lining thickness efficiency for sprayed concrete
lined (SCL) tunnels - World Tunnel Congress 2016 April 2016

20. Thanks
• This study is part of the PhD research in University of Southampton
• Financial support from Mott MacDonald and Normet
• Supervisor Dr. Alan Bloodworth and Professor Chris Clayton
• Ross Dimmock for inspiring my PhD research

21. Thank You
Jiang.Su@AECOM.COM
BTS 2016 11th Oct 2016