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

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

24. Failure Mechanism for Micropile systems in Liquefying soils

25. Main Analysis Considerations