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

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

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

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

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

FOREVER 2 - Experimental Tools

FOREVER 3 - Main Experimental Results

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

MICROPILE GROUPS AND EQUIVALENT COMPOSITE FOUNDATIONS

MICROPILE GROUPS AND EQUIVALENT COMPOSITE FOUNDATIONS

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.

Double A-Shaped Micropiles Network (FULL SCALE TESTS)

VERTICAL LOADING

LATERAL LOADING

LIZZI MODELS (CENTRIFUGE TESTS)

LIZZI MODELS (CENTRIFUGE TESTS)

EFFICIENCY OF MICROPILE GROUPS & NETWORKS CENTER MICROPILE Ce group Ce network Network / Group 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

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

Some Main Conclusions (2) 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

Some Main Conclusions (3) 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)

Some Main Conclusions (4) 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

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