MICROPILES RESEARCH AT WASHINGTON STATE UNIVERSITY Dr. Adrián Rodríguez-Marek, Dr. Balasingam Muhunthan, and Dr. Rafik Itani Civil and Environmental Engineering Department. Pullman, WA International Workshop on Micropiles Venice, Italy June 1, 2002

Organization FHWA $600,000+ TRAC (Washington State Transportation Center) WSDOT FHWA Turner Fairbanks Hwy. Research Center Local FHWA office Technical Advisory Committe Technical Review HPC for floating bridges Post-EQ bridge evaluation MICROPILES $280,000 DYNAMIC Dr. Adrian Rodriguez-Marek Wong Joo Chai (Ph.D. Student) STATIC Dr. Balasingam Muhunthan 1 Ph.D. Student

Objectives Comprehensive literature review Update to FHWA State of the Practice State of the Art in analytical methods Experimental data Develop and validate analytical tools for Micropile networks Static loading Dynamic loading Design Guidelines Design guidelines for battered micropiles Take systematic advantage of network effects (static and dynamic)

Research Approach MICROPILE PERFORMANCE DATA NUMERICAL MODELS Finite Element Ousta and Sharour WSU FE implementation (e.g. Modak 2000) Finite Difference Pseudo-Static (e.g. LPILE, GROUP) Dynamic (e.g. FLAC) Empirical p-y curves Calibration and Validation SIMPLIFIED ANALYTICAL APPROACH -Center of rotation/Elastic Center -Transfer Matrix Calibration DESIGN GUIDELINES

Outline Of Presentation Focus on: Experimental needs (Rodríguez-Marek) Considerations for static design of Micropiles (Muhunthan)

Available Data on Micropile Performance Vertical, static loading Extensive availability of data Static lateral loading Field test: Bruce, Weinstein, and Juran Dynamic lateral loading Centrifuge tests with seismic loading (Juran et al. 1998) Shaking table tests (Kishishita 2001) NEEDS Full scale lateral load tests with dynamic loads Field instrumentation

National Earthquake Simulation Network NSF funded network of test facilities for advancing the understanding of earthquake engineering Objective: Develop test facilities that will become available to the earthquake engineering community in general (to be ready by 2004) OPPORTUNITY: Greater access to test facilities (e.g. centrifuge testing) and field testing equipment

Eccentric shaker, MK-15 Uni-directional eccentric mass vibrator Operating frequency range:.25 – 25 Hz Force capability: 440 kN (100,000 lbs) Weight: 27 kN (6000 lbs) Dimension: 1.8 m x 3 m Eccentric Mass Shaker UCLA NEES equipment site (PI: Dr. John Wallace)

Dynamic Lateral-Load Field Tests: Objectives Quantify the effects of inclination, configuration, and spacing on load transfer mechanism and foundation response of micropile groups (and networks) To obtain ultimate lateral capacities for single micropiles and micropile groups Obtain field p-y curves Effect of cyclic loading at varying strain levels “Scale” effects Comparison with commonly used p-y curves Validation of pseudo-static analyses (e.g. GROUP) Characterize dynamic impedance functions for micropile foundations

Tentative Test Site Site: Caltrans’ property Low marginal cost for Micropile tests Fully-characterized site Field tests: SCPT, SPT, PMT, and down-hole suspension logging Laboratory tests: Atterberg Limits, Consolidation & UU Triaxial Tests Extensive field tests of Drilled Shafts performed at this site

Tentative Configurations  1 x 2  ( 2 x 2 ) A 2 piles  = 0 , 10  & 30  Case  = 0 , ultimate capacity will be tested Parameters to study: Load-deflection Inclination Spacing ( 2 x 2 ) B  4 piles  = 0 , 10  & 30  Parameters to study: Load-deflection Inclination Configuration Spacing

Load-deflection at the Pile Head Only 1x2 configuration can be tested for its ultimate lateral capacity. Vertical micropiles in (2x2)A and (2x2)B configurations and battered micropiles in 1x2, (2x2), & (2x2)B configurations might be too strong to be tested their ultimate lateral capacity at this site. Predictions using GROUP software with “generic” p-y curves

Summary Full scale dynamic lateral load tests of micropiles are important Assess “Scale Effects” associated with: Model tests Design formulas based on large-diameter piles Field tests will be performed side by side to full-scale tests of drilled shafts One tentative test site has been identified (other sites will be explored) Sand Site: Group efficiency factors as a function of construction methods Soft-Clay sites: Evaluation of ultimate capacities

Summary Other issues Include pile non-linearity in evaluation of field p-y field curves Incorporation of measurement errors into back-calculation of p-y curves Quantification of lateral soil pressures during testing

Static Design Of MICROPILES PROBLEM: PILE CAPACITY & SETTLEMENT SINGLE GROUP VERTICAL RETICULATED NETWORK

CURRENT STATE (Capacity) Most design based on relative density (D r or I D ) Influence of stress level on strength of soil (rarely taken into account) No account of compressibility (intended for quartzitic sands; other weak minerals?) Contradictory results (Literature)

SOIL BEHAVIOR (Critical State Soil Mechanics) Zones of stable plastic yielding

Capacity of piles in sands is a function of the “in situ state” of soil as defined by the “state parameter, R s ” as compared with the relative density, D r, used in the conventional practice. Normalized pile capacity tends to decrease with increasing R s or increasing depth. Normalized pile capacity tends to converge or remain constant when the in situ soil state nears critical state or R s converges to unity. Constant R s, would yield constant pile capacity, stiffness, and compressibility Even Constant Cyclic strength of sand

Parallel contours of normalized cyclic strength of Ottawa sand (Pillai and Muhunthan 2001)

State Parameter R s < 1 - dilative behavior R s >1 - contractive behavior

Summary NEED TO INTERPRET Single, Group, Network effects based on STATE BASED SOIL MECHANICS Soil parameters (Capacity, stiffness) as functions of R s