Field Static Load Testing of Concrete Free Reticulated Micropiles System

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1 Field Static Load Testing of Concrete Free Reticulated Micropiles System A. Mehdizadeh 1, M. Disfani 2, R. Evans 3, E. Gad 4, A. Escobar 5 and W. Jennings 6 1 Research Assistant in Geotechnical Engineering, Swinburne University of Technology 2 Senior Lecturer in Geotechnical Engineering 3 Senior Lecturer in Geotechnical Engineering, Swinburne University of Technology 4 Professor in Structural Engineering, Swinburne University of Technology 1 5&6 Civil/Structural Engineer, Pandoe Pty Ltd. (Surefoot)

2 Introduction Project Description Site Description Test Results Discussion and Conclusions 2

3 3 What is Surefoot footing?

4 Surefoot comprises of A steel pile cap that sits either on or above the ground A number of inclined stainless steel or galvanised hollow micropiles (40 mm diameter) 4

5 Surefoot is a new steel micropile group footing system Braced Batter Micropile Group Light enough to be manually handled by a single operator Quick installation using very simple power tools (10 to 30 mins per footing) 5

6 No need for excavation, drilling or use of any concrete (minimum site disturbance and low Carbon foot-print) Versatile footing system to cover a wide range of loading magnitudes and patterns. Highly suitable for areas with limited access 6

7 Introduction Project Description Site Description Test Results Discussion and Conclusions 7

8 Performance of Surefoot system in terms of ultimate load capacity under: - Axial compression - Axial tension loads 8

9 9 Testing Methodology: Quick Maintained Pile Load Test Method (ASTM D1143/D1143M-07, 2013 and FHWA NHI-05) Increment load: 10 per cent of the anticipated ultimate capacity Maintained for 15 minutes for each increment Soil/system creep assessment

10 Unloading in three or four steps based on the achieved ultimate load The ultimate load: Continuous jacking to maintain the applied load Footing Type Embedment Depth (mm) Type of Footing Number of Micropiles Surefoot Footing Details Pile Cap Dimensions (mm) Pile Cap Thickness (mm) 10 SF SF SF SF SF Reaction Test Test Test Test x x x x x

11 11 SF100

12 12 SF300

13 13

14 14

15 Introduction Project Description Site Description Test Results Discussion and Conclusions 15

16 Site location: Melbourne s western suburb of Braybrook in Victoria Tests Location 16

Depth (m) 0 0.3 0.5 0.7 1 Soil properties 1.

21 Fill cu (kpa) Φu (⁰) c (kpa) 13 14 0 Φ (⁰) E50 (MPa) 13.

Stiff, Slightly calcareous Clay (CH), Dark grey to light grey, Very stiff, Very

17 Depth (m) Soil properties Description w (%) LL (%) PL (%) Fill cu (kpa) Φu (⁰) c (kpa) Φ (⁰) E50 (MPa) 13.5 Clay (CH), Brown, Stiff, Very slightly calcareous Clay (CH), dark grey, Stiff, Slightly calcareous Clay (CH), Dark grey to light grey, Very stiff, Very slightly calcareous Legend Clay (CH), Light grey, Very Stiff 5 17 Organic root matter was also noted in both layers down to a depth of 1000 mm

Effective Internal Friction, φ' ( ) Secant modulus of Elasticity, E 50 (MPa) Fill 450 75 28 13.5 8.

18 Soil Type Depth (mm) Liquid Limit, LL (%) Plastic Limit, PL (%) Moisture Content, w (%) Undrained Shear Strength, S u (kpa) Cohesion, c (kpa) Internal Friction, φ ( ) Effective Cohesion, c' (kpa) Effective Internal Friction, φ' ( ) Secant modulus of Elasticity, E 50 (MPa) Fill Fill Clay Clay Clay Clay Clay

19 The average undrained shear strength (Su) was selected 12 kpa and 23 kpa for the fill material and clay, respectively. The average measured penetration per blow: 14 at a depth of 200 mm down to 1700 mm No water table was observed down to 2 m. 19

20 Introduction Project Description Site Description Test Results Discussion and Conclusions 20

21 21 SF

22 22 SF

23 23 SF & 1500

24 Ultimate Bearing Capacity (kn) Ultimate Pullout Capacity (kn) 150 Mazurkiewics (1972) Fuller and Hoy s (1970) Butler and Hoy s (1977) Brinch Hansen s 80% Criterion (1963) Chin-Konder Extrapolation (1970) DeBeer (1972) 100 Mazurkiewics (1972) Fuller and Hoy s (1970) Butler and Hoy s (1977) Brinch Hansen s 80% Criterion (1963) Chin-Konder Extrapolation (1970) DeBeer (1972) SF SF SF SF Bearing Capacity Pullout Capacity SF SF SF SF

25 Introduction Project Description Site Description Test Results Discussion and Conclusions 25

26 Current design approach: 26 Bearing Capacity: - Bearing capacity of shallow foundations - Skin friction of deep foundations Pullout Capacity: Bearing Capacity (kn) - Skin friction and lateral passive forces Skin Friction (kn) Passive Forces (kn) SF Ultimate Bearing Capacity (kn) Ultimate Pullout Capacity (kn) Field Bearing Capacity (kn) Field Pullout Capacity (kn)

27 What other factors need to be considered in the design approach? 27 - Micropiles and restricted soil in between may work as a block - Reinforcing effect of micropiles improves shear strength at local failure planes - Effect of root system on interaction between soil and micropiles - Arching effect presented by Mason (1997)

28 28 3D finite element modelling is required to study the influence of different parameters

29 Thanks for your attention ACKNOWLEDGEMENT: This research is funded by the State Government of Victoria, Department of Economic Development, Jobs, Transport and Resources. R&D Voucher Program IVP-BRD-264A.1. In addition, the authors would like to thank Pandoe Pty Ltd (Surefoot) for their financial and in-kind support. 29

30 Field Static Load Testing of Concrete Free Reticulated Micropiles System A. Mehdizadeh 1, M. Disfani 2, R. Evans 3, E. Gad 4, A. Escobar 5 and W. Jennings 6 1 Research Assistant in Geotechnical Engineering, Swinburne University of Technology 2 Senior Lecturer in Geotechnical Engineering 3 Senior Lecturer in Geotechnical Engineering, Swinburne University of Technology 4 Professor in Structural Engineering, Swinburne University of Technology 30 5&6 Civil/Structural Engineer, Pandoe Pty Ltd. (Surefoot)

NPTEL Course GROUND IMPROVEMENT USING MICROPILES

Lecture 22 NPTEL Course GROUND IMPROVEMENT USING MICROPILES Prof. G L Sivakumar Babu Department of Civil Engineering Indian Institute of Science Bangalore 560012 Email: gls@civil.iisc.ernet.in Contents