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SEISMIC BEHAVIOR OF MICROPILE SYSTEMS CENTRIFUGAL MODEL STUDIES and FE Analyses Prepared By

SEISMIC BEHAVIOR OF MICROPILE SYSTEMS CENTRIFUGAL MODEL STUDIES and FE Analyses Prepared By Isam Shahrour Ilan Juran & Sherif Hanna FOREVER - FHWA International Center for Ground Improvement Polytechnic University May 31 2002. Cooperative Highway Research Project

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SEISMIC BEHAVIOR OF MICROPILE SYSTEMS CENTRIFUGAL MODEL STUDIES and FE Analyses Prepared By

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  1. SEISMIC BEHAVIOR OF MICROPILE SYSTEMS CENTRIFUGAL MODEL STUDIES and FE Analyses Prepared By Isam Shahrour Ilan Juran & Sherif Hanna FOREVER - FHWA International Center for Ground Improvement Polytechnic University May 31 2002

  2. Cooperative Highway Research Project On Soil Reinforcement with Micropiles FOREVER - Direction Des Routes - FHWA Calibration Chamber Tests CERMES - ENPC France Seismic Response Analysis of Micropile Systems Centrifuge Model Tests Polytechnic Univ. USA Shaking Table Tests Canterbury Univ. New Zealand

  3. Basic Design Philosophy for Deep Foundations for Liquefaction Mitigation

  4. Analysis Considerations for Conventional Piles in Liquefying Soils (I) 1- Foundation stiffness (rotational & lateral) 2- Moment Capacity of pile group 3- Lateral capacity of foundation system 4- The above considerations lead to large diameter piles, high strength, and large deeply embedded pile caps.

  5. Analysis Considerations for Conventional Piles in Liquefying Soils (II) Ground motion amplification Bending Moment Resistance (near stiff layers) Cap / pile connection Flowing soil characteristics between and around the piles Ductility of pile material Flexibility of the superstructure and force phasing

  6. Basic Behavior of Micropile Systems Case I - Micropile Group as Direct Structural Support

  7. Basic Behavior of Micropile Systems Case II - Micropile Network - Circumscribe and Internally Reinforce a Coherent Composite Reinforced Soil Structure

  8. Overview • Dynamic Behavior of Micropile Systems in Dry Sand • (Omar BenSliman, 1998) • Dynamic Behavior of Micropile Systems in Liquefying • Soils (Sherif Hanna, 2002?)

  9. FOREVER - Centrifuge Test Results Dry Sand • Objectives • Development of Experimental database for • seismic retrofitting assessment • Parametric evaluation of the effect of the main system • parameters on the structure response, such as pile • diameter, pile inclination, and group and network • effects • Evaluation of Existing Analysis Codes

  10. FOREVER - Centrifuge Test Results • Main Parameters • Natural Frequency of Soil / Micropile Systems • Soil - Pile Interaction (Dynamic p-y curves) • Axial Load transfer • Analytical Simulations - pseudo-static • (LPILE & GROUP codes)

  11. Typical Micropile Configuration Tested in the Centrifuge

  12. Seismic Behavior of Micropile Systems Parametric effect of pile inclination (a ) on recorded pile bending profile (0.5 FL ; a/g = 0.3 ; s/D = 3 )

  13. Seismic Behavior of Micropile Systems Parametric effect of pile inclination (a ) on recorded pile displacement profile (0.5 FL ; a/g = 0.3 ; D = 0.13 m)

  14. Seismic Behavior of Micropile Systems • GROUP PROGRAM (Reese et al., 1994) • 1- Static analysis of symmetrical Pile Groups including • batter piles • 2- Soil-Pile-Interaction is modeled using t-z and p-y • approach (Winkler model) • 3- Group effect under lateral loading is modeled using • p-y multipliers. • 4- GROUP program predicts a negative group effect

  15. Seismic Behavior of Micropile Systems Parametric effect of s/D on pile bending profile for 2x2 vertical pile group using GROUP program (0.9 FL - a/g = 0.3)

  16. Research Objectives Behavior of the composite Micropile-reinforced soil systems Behavior of Micropile Systems Effect of the main group and network system parameters Basic load transfer mechanisms Experimental database and numerical analysis Evaluation and calibration of available analysis approaches & State of Practice Review

  17. Analysis Considerations for Micropiles in Liquefying Soils Ground motion amplification Excess pore pressure mitigation Lateral spreading pressure Ductility of pile material Force phasing Micopile Tension capacity

  18. Assessment of Micropile Network Systems in Liquefied Soils • Objectives • * Excess Pore Pressure • 1- Seismic Response of the composite • micropile- reinforced soil system * Acceleration Profile • and ground motion • * Surface settlement • Profile • * Overall system stiffness • (apparent natural frequency) • 2- Load Transfer Mechanisms * Kinematical and Inertial loading • * Micropile resisting forces (tension) • * Dynamic p-y and t-z curves

  19. Assessment of Micropile Network Systems in Liquefied Soils • Objectives • * Pile inclination • 3- Effect of the main group and • network parameters * Relative flexibility between • micropiles & the surrounding • soil (ductility, axial stiffness, & • micropile cap connection) • * Density of micropile • reinforcement (spacing) • * Geometric configuration • of the reticulated system • 4- Evaluation of the available analysis approaches through comparisons of • method predictions with the experimental results of the centrifuge model • tests • 5- Review of the Current State of Practice & Annual Review Board Meeting

  20. Assessment of Micropile Network Systems in Liquefied Soils Typical 2x1 pile network configuration for liquefaction studies

  21. Failure Mechanism for Micropile systems in Liquefying soils

  22. Main Analysis Considerations

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