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The French National Research Project Soil Reinforcement by Micropile Systems

The French National Research Project FOREVER aimed to assess, develop & design micropile systems for soil reinforcement. The study tested micropile groups & networks under static and seismic loads, exploring design methods and practical applications. Conclusions highlighted the importance of group and network efficiency for bearing capacity and loading behavior. Learn more about the innovative findings and advancements in micropile technology.

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The French National Research Project Soil Reinforcement by Micropile Systems

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  1. FOREVER The French National Research Project Soil Reinforcement by Micropile Systems François SCHLOSSER - Roger FRANK Ilan JURAN - Roger ESTEPHAN 1993-1999

  2. PARTNERS CERMES CERCSO DDE DE LA MANCHE FOREZIENNE SOCASO SCETAUROUTE MENARD TERRE ARMEE

  3. SPONSORS French Government 1 100 000 USD(15%) French Partners 5 150 000 USD(73%) F.H.W.A Contribution 850 000 USD(12%) Total Budget 7 100 000 USD

  4. OBJECTIVES • Technology & Performance Assessment • Evaluation and Development of Design Methods • Isolated, groups and networks behavior (static and seismic) • New Fields of Applications

  5. FOREVER 1 - Introduction and Objectives 2 - Experimental Tools 3 - Main Experimental Results

  6. FOREVER 2 - Experimental Tools

  7. FOREVER 3 - Main Experimental Results

  8. Micropile Number Ø (mm) Length (m) Spacing (Ø) Spacing (mm) 3x3=9 6 0.5 10 60 4x4=16 6 0.5 6.5 39 5x5=25 6 0.5 5 30 6x6=36 6 0.5 4 24 MICROPILE GROUPS AND EQUIVALENT COMPOSITE FOUNDATIONS (CENTRIFUGE TESTS - 20G)

  9. MICROPILE GROUPS AND EQUIVALENT COMPOSITE FOUNDATIONS (MICROPILE GROUPS)

  10. MICROPILE GROUPS AND EQUIVALENT COMPOSITE FOUNDATIONS (COMPOSITE FOUNDATIONS)

  11. Conclusions • The creep unit load (per micropile) decreases with the spacing of micropiles within the group. • Under axial loading, the behavior of the 6 x 6 (e=4B) is close to that of the monolithic bloc. • The Bearing Capacity of the composite foundation is closely equal to that of the micropiles increased by the Bearing Capacity of the footing.

  12. Double A-Shaped Micropiles Network (FULL SCALE TESTS)

  13. VERTICAL LOADING

  14. LATERAL LOADING

  15. LIZZI MODELS (CENTRIFUGE TESTS)

  16. LIZZI MODELS (CENTRIFUGE TESTS)

  17. EFFICIENCY OF MICROPILE GROUPS & NETWORKS CENTER Ce group Ce network Network / Group MICROPILE L/D Inclination s/D CERMES 50 15° 4 - - 1.28 (I) 50 15° 4 - - 0.9 3S-(98) 100 20° 3.5 2 1.65 0.83 100 20° 7 2.2 2.05 0.93 3S-(99) 100 20° 3.5 1.86 1.69 0.91 100 20° 7 1.6 1.74 1.09 100 20° 7 2.55 > 1 LCPC 100 7.3° & 9° 7 1.61 1.31 0.81 Lizzi 100 7.3° & 9° 7 1.68 2.22 1.31 (I) with confining pressure h = v = 50, 100 or 150 kPa

  18. FOREVER Some Main Conclusions (1) 1. Many Experimental Tools - Experimental Site - Full Scale Foundations - Calibration Chambers - Centrifuge

  19. FOREVER Some Main Conclusions (2) 2. Micropile Groups in Sand - Group Effect : maximum obtained when spacing equals 4 diameters (group equivalent to the block) - Composite Foundation (micropile foundation + cap) : the bearing capacity is equal to the sum of the independent bearing capacities

  20. FOREVER Some Main Conclusions (3) 3. Micropile Networks in Sand (ID 0.5) under Vertical Loading - Double A-Shaped Network : less efficient than the equivalent group - Lizzi’s Network Efficiency not found in the centrifuge (ID 0.8)

  21. FOREVER Some Main Conclusions (4) - Simple reticulated networks are more efficient than groups only at large displacements - Sophisticated (more reticulated) networks seem to be more efficient than groups

  22. DESIGN OF MICROPILE GROUPS & NETWORKS UNDER STATIC LOADING 1) Large influence of the installation method, difficult to assess 2) PDA tests appear to provide a reliable quality control method 3) Group effect : important parameter for both axial and lateral loadings 4) Network effect : important parameter for lateral loading, not obvious for axial loading 5) Seismic performance discussed in the next Session

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