Transcript Washington State University (Prof. Adrian Rodriguez

MICROPILES RESEARCH AT
WASHINGTON STATE
UNIVERSITY
Dr. Adrián Rodríguez-Marek,
Dr. Balasingam Muhunthan, and Dr. Rafik Itani
Civil and Environmental Engineering Department. Pullman, WA 99164-2910
International Workshop on Micropiles
Venice, Italy
June 1, 2002
Objectives

Comprehensive literature review




Develop and validate analytical tools for
Micropile networks



Update to FHWA State of the Practice
State of the Art in analytical methods
Experimental data
Static loading
Dynamic loading
Design Guidelines


Design guidelines for battered micropiles
Take systematic advantage of network effects (static
and dynamic)
Research Approach
NUMERICAL MODELS
MICROPILE
PERFORMANCE
DATA
Empirical p-y curves
Calibration and
Validation
Finite Element
Ousta and Sharour
WSU FE implementation
(e.g. Modak 2000)
Finite Difference
Pseudo-Static (e.g. LPILE, GROUP)
Dynamic (e.g. FLAC)
SIMPLIFIED
ANALYTICAL
APPROACH
- Center of rotation/Elastic
Center
- Transfer Matrix
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


Static lateral loading


Field test: Bruce, Weinstein, and Juran
Dynamic lateral loading



Extensive availability of data
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 Mass Shaker
UCLA NEES equipment site (PI: Dr. John Wallace)
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
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
0 10 20 30 40 50
0
FILL, concrete
and asphalt debris
5


CLAY, silty sandy
10
SILT, fine sands
15

CLAY, silty sandy
Site: Caltrans’ property
Low marginal cost for
Micropile tests
Fully-characterized site

Depth (ft)
20
25
SAND, silty medium
to fine-grained
30

CLAY, slightly silty
35

40
45
wt
50
SAND, fine-grained
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
0
100
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 (Dr
or ID )
 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)

ID(%)
z/(0.5B)
o
D(m)
Nq
Measured
Predicted qc (MPa)
Eq.1 (MPa)
Eq.2
2.84
1.65
58
2
1.4
38.7
133.6
qc(MPa)
1.19
58
4
2.8
37.2
186.3
3.51
7.93
4.73
58
6
4.2
36.2
250.1
6.88
16.0
9.70
80
2
1.4
42.3
227.7
1.2
5.10
2.81
80
4
2.8
40.0
274.6
3.99
12.3
7.03
80
6
4.2
38.7
343.3
8.25
23.07
13.45
80
8
5.6
37.8
417.2
13.31
37.38
22.10
89
2
1.4
43.6
277.4
1.4
6.33
3.42
89
4
2.8
40.9
311.2
5.2
14.20
8.00
89
6
4.2
39.4
371.5
10.91
25.43
14.67
89
8
5.6
38.4
466.7
17.36
42.60
25.00
Comparison of qc between centrifuge and constant –  analysis
(Gui and Muhunthan, 2002)
q  cN   N
u
c
v
Eq. (1)
q
1  2K
q  cN 
 N
3
0
u
c
v
q
Eq. (2)
ID(%)
z/(0.5B)
D(m)
o
Nq
Measured
Predicted qc (MPa)
Eq.1
Eq.2
2.26
1.32
58
2
1.4
38.7
106.3
qc (MPa)
1.19
58
4
2.8
37.2
172.7
3.51
7.35
4.38
58
6
4.2
36.2
248.0
6.88
15.86
9.62
80
2
1.4
42.3
146.6
1.2
3.28
1.80
80
4
2.8
40.0
225.3
3.99
10.09
5.77
80
6
4.2
38.7
303.0
8.25
20.36
11.87
80
8
5.6
37.8
415.6
13.31
37.24
22.00
89
2
1.4
43.6
164.0
1.4
3.74
2.02
89
4
2.8
40.9
247.1
5.2
11.28
6.36
89
6
4.2
39.4
333.1
10.91
22.80
13.15
89
8
5.6
38.4
421.6
17.36
38.48
22.00
Comparison of qc between centrifuge and variable –
 analysis (accounting for stress level) (Gui &
Muhunthan, 2002)
58
2
1.4
38.7
106.3
1.32
2971
0.85
1.19
Predicted
qc(Ir)
Fqc*Eq.2
1.13
58
4
2.8
37.2
172.7
4.38
3999
0.84
3.51
3.67
58
6
4.2
36.2
248.0
9.62
4817
0.83
6.88
8.00
80
2
1.4
42.3
146.6
1.80
4938
0.77
1.2
1.38
80
4
2.8
40.0
225.3
5.77
6655
0.83
3.99
4.77
80
6
4.2
38.7
303.0
11.87
8020
0.85
8.25
10.07
80
8
5.6
37.8
415.6
22.00
9189
0.86
13.31
18.87
89
2
1.4
43.6
164.0
2.02
6193
0.75
1.4
1.51
89
4
2.8
40.9
247.1
6.36
8353
0.85
5.2
5.39
89
6
4.2
39.4
333.1
13.15
10070
0.89
10.91
11.66
89
8
5.6
38.4
421.6
22.00
11540
0.91
17.36
19.92
ID(%)
z/(0.5B)
D(m)
o
Nq
Predicted qc
(MPa)
G50
Fqc
Measured qc
(MPa)
Comparison of qc between centrifuge and variable – 
analysis (accounting for compressibility) (Gui &
Muhunthan, 2002)
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, Rs” as compared with the relative
density, Dr, used in the conventional practice.
Normalized pile capacity tends to decrease with
increasing Rs or increasing depth.
Normalized pile capacity tends to converge or
remain constant when the in situ soil state nears
critical state or Rs converges to unity.
Constant Rs, 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
pa
Rs 
pc
Rs < 1 - dilative behavior
Rs >1 - contractive behavior
Summary

NEED TO INTERPRET
Single, Group, Network effects based on
STATE BASED SOIL MECHANICS
 Soil parameters (Capacity, stiffness) as
functions of Rs
