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PRACTICE AND RESEARCH ON MICROPILE GROUPS AND NETWORKS

Explore recent developments in micropile construction including types, designs, and applications in various soil conditions. Learn about case studies and testing methodologies in this informative lecture from Prof. François Schlosser. Dive into topics like group behavior, foundation reinforcement, and design methodologies to enhance your understanding of micropiles.

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PRACTICE AND RESEARCH ON MICROPILE GROUPS AND NETWORKS

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  1. 2nd LIZZI lectureTokyo IWM August 2004 PRACTICE AND RESEARCH ON MICROPILE GROUPS AND NETWORKS Prof. François SCHLOSSER ENPC - CERMES

  2. PRACTICE AND RESEARCH ON MICROPILE GROUPS AND NETWORKS • 1) Development in micropile construction • 2) Examples of micropile groups under vertical loading • 3) Behaviour and design of A-shape micropiles under horizontal loading • 4) Micropiles in liquefiable soils

  3. RECENT DEVELOPMENT IN MICROPILE CONSTRUCTION 1) Types of micropiles tested in the Forever project 2) Driven and grouted micropile 3) Self -drilling injected micropile

  4. FrenchBored Micropile Classification

  5. GROUTING WITH THE “TUBE A MANCHETTE” ( Type IV : Repeated and Selective Injection)

  6. Main type of micropile tested at the FOREVER experimental site:  Fontainebleau sand (Dr = 0.5)  Boring, Grouting by gravity (Type II ) Iia : complementary grouting from the top iib : complementary grouting from the bottom  Main parameter:  and qs(side friction stress)

  7. R-SOL MICROPILE

  8. Comparative Results

  9. EXAMPLES OF MICROPILE GROUPS UNDER VERTICAL LOADING • Reinforced foundation of the Uljin nuclear power plant • Micropiled raft withstanding water uplift pressures at A86 urban highway in Rueil (near Paris) • Foundation reinforcement of the old Pierre bridge in Bordeaux

  10. ULJIN NUCLEAR POWER PLANT

  11. Micropile reinforced foundation in the fault zone

  12. DESIGN METHODOLOGY: 1) Equivalent homogeneous material assumed for the plug of reinforced faulted rock . 2) Elastic isotropic FEM calculations for determining the required modulus Ev. 3) Homogeneization of a group of micropiles in 1 D deformation using the results of load tests on isolated micropiles. DESIGN OF THE PILE GROUP

  13. HOMOGENEIZATION METHODS 1-D method : (Blondeau et al., 1987) 2-D and 3-D methods : (deBuhan et al., 1995-7)

  14. RUEIL MICROPILED RAFT Traction load test Reinforcement : tube Ø = 89 mm e = 9.5 mm Borehole : Ø = 125 mm Soil : alluvium + chalk Total length : L = 19 m Free length : Lf = 4 m

  15. GOUPEGMETHOD ( Hybrid model taking into account the micropile interaction ) 1) Load transfer functions model (GOUPIL - LCPC) : p-y, t-z, q-z ( Frank, 1983 – Degny and Romagny, 1987) 2) Mindlin’s equations for evaluating the micropile interaction (O’Neill, 1977)

  16. Load (kN) Settlement (mm) Comparison between measured and calculated load - settlementcurves of the micropiles of the group

  17. FOUNDATION REINFORCEMENT OF THE PIERRE BRIDGE IN BORDEAUX

  18. _______ Movement of the water level ( sea tide, river flow) _______ Wooden piles : B = 0,30 m s/B = 4 Micropiles : B = 0,22 m s/B = 10

  19. MICROPILES : • Bored micropiles • Reinforced tube (178/154 mm) • Type IV (injection with “tube à manchettes”) in the marl • Type II ( global injection at low pressure ) in the masonry • Measured load transfer 5 to 20 %

  20. STABILIZATION OF THE SETTLEMENTS AFTER MICROPILES INSTALLATION

  21. BEHAVIOUR AND DESIGN OF A-SHAPED MICROPILES UNDER HORIZONTAL LOADING 1) Results of the Forever full scale load tests 2) St Maurice anti-noise wall 2) Slope stabilization at the site of the Millau viaduct

  22. FOREVER RESULTS THE THREE A-SHAPED NETWORKS

  23. HORIZONTAL LOADING • Bearing capacity of the networks largely exceeding bearing capacity of the group

  24. Horizontal loading test of an A-shaped micropiles network

  25. ST MAURICE ANTI-NOISE WALL

  26. LATERAL LOADING TEST

  27. MICROPILE LOAD – DISPLACEMENT CURVES Vertical Inclined ( traction) Axial force at the top( kN ) Displacement at the top (mm)

  28. ROTATION ( R ) VERSUS APPLIED LOAD ( F ) R : rotation of the footing F : (lateral) load applied to the wall R (rad) F (kN)

  29. COMPARISON BETWEEN MEASUREMENTS AND GOUPEG CALCULATIONS Rotation (rad) Measurement Goupeg 1 Goupeg 2 Applied load ( kN)

  30. SLOPE STABILIZATION AT THE MILLAU VIADUCT SITE

  31. LANDSLIDE ON THE SOUTH WORKS TRACK (2001)

  32. A – SHAPED MICROPILES • Type 3 (global injection) • Tube : Ø = 157/178 mm • Inclination :  = 20° • Borehole diameter :B = 0.30 m • Spacing : s = 1.70 m •Soil : alluvium, altered marl, marl Global safety factor against sliding : F = 1.13 with q = 46 kPa F0 = 1.00 with q = 0

  33. SOIL – MICROPILES INTERLOCKING EFFECT Present design methods do not take it into account ( Ce  1 ) F = K .  M = k . (  f)  = G . ( f) Energy equation : K.H2 = 4k + G.V f< f Plasticity of the soil without flow, then failure at  = f f = f Failure f > fPlasticity of the micropiles without flow, then failure at  = f

  34. MICROPILES IN LIQUEFIABLE SOIL • 1) Behaviour of single micropiles and micropile groups in liquefiable soil (FEM modelling) • 2) Behaviour of A-shaped micopiles in liquefiable soil (centrifuge modeling)

  35. F.E.M. MODELLING Shahrour and Ousta. (1997,1998) Shahrour, Sadek, Ousta. (2001)

  36. SOIL LIQUEFACTION WITH AND WITHOUT MICROPILE

  37. MICROPILE GROUPS IN LIQUEFIABLE SOIL (FEM)

  38. CENTRIFUGE MODELLING ON A-SHAPED MICROPILE GROUPS Juran I. ( New York Polytechnic University)

  39. MAX. ACCELERATION IN THE VICINITY OF THE A-SHAPED MICROPILES amax = 0,4 g at the base

  40. EXCESS PORE PRESSURE IN THE VICINITY OF THE A-SHAPED MICROPILES ru = u / σ’v0 Max. value = 0,6 compared to 1 in free field.

  41. CONCLUSIONS 1) The main parameter in micropile vertical bearing capacity is the side friction stress qs. Grouting with the “tube à manchettes” gives the best results. 2) Present design methods of micropile groups are conservative, leading to Ce 1. They neglect the soil/micropiles interlocking. 3) A-shaped micropiles (elementary networks) quite well withstand lateral loading. In slope stabilization, interlocking has a beneficial effect on the global safety. 4) In seismic events A-shaped micropiles are well withstanding horizontal movements and thus prevent liquefaction of saturated loose sands.

  42. THANK YOU FOR YOUR ATTENTION !

  43. Micropile and nail launcher using compressed air ( Myles and Bridle, 1991 )  Metallic bar  Energy at the tip  Relatively large penetration  Apparently good lateral friction, but further research needed

  44. RAILWAY EMBANKMENT STABILIZED BY MICROPILES : Additional settlement due to the installation of the micropiles

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