Micropile Bond Strength to
Concrete
Fundamental Full Scale Test Program
Preliminary Results
Allen Cadden, P.E.
Jesus Gomez, Ph.D., P.E.
Schnabel Engineering, Inc.
A Privately Funded Research
Project – Phase 1
Footing Connection
What do you use for the bond stress?
Can you prove it?
Are you being conservative or
unconservative?
Test Summary
•Tested Steel Bar
•Tested Steel Casing
•Tested Casing with Weld Beads
•Hole Drilled with DHH
•Type I grout w:c=.45±
Test Setup
4”
Block Summary
Block Summary
Hole
1
Diameter
(nom.)
Block
1
Drill
Length
2
Pile
Length
(nom.)
Diameter
cast
Drill
Length
3
Pile
Length
(nom.)
Diameter
cast
Drill
Length
Pile
Length
(nom.)
cast
2
4.5
29.75
18
4.5
30
24
4.5
35.5
36*
3
5
32
18
5
31.75
24
5
38.25
36
4
6
28
24
6
39.25
36
5
8
38
36
8
27?
24
6
6
38
36
6
26.5
24
7
8
23
18
6
21+
18
dimensions in inches
block drilled for strain gage wires
All dimensions in inches. 1 inch = 25.4 mm
Comments
Shear Ring Welds
Construction
Testing
Preliminary Results
Preliminary
Stress At Hole Perimeter
Stress At Reinforcing
-0.01
-0.01
B1P1
B1P1
1 mm
B2P2
B2P3
B3P1
Bar
0.09
8 inch hole
B3P2
2.3 mm
B3P3
B4P1
Weld bead
B4P2
B5P1
3.5 mm
0.14
Deflection (in)
Deflection (in)
0.04
B1P3
B1P3
B2P2
1 mm
0.04
B2P3
B3P1
Bar
0.09
B3P2
Weld bead
B3P3
B4P1
8 inch hole
0.14
B4P2
3.5 mm
B5P1
B5P2
B5P2
B6P1
B6P1
B6P2
0
200
(1.4 MPa)
400
600
Stress (psi)
800
(5.5 MPa)
4.8 mm
0.19
4.8 mm
0.19
1000
0
300
(2.1 MPa)
600
900
Stress (psi)
1200
(8.3 MPa)
B6P2
1500
Summary Data
Preliminary
Strain
Stress
6.0%
16.0
5.0%
Strain at Failure (%)
12.0
10.0
8.0
6.0
4.0
3.5
4.0%
3
2.5
3.0%
2
2.0%
1.5
1
1.0%
0.5
2.0
0.0%
0.0
3
53
103
153
203
253
0
0
50
Steel Perimeter
150
200
250
Hole Diameter (mm)
Hole Diameter (mm)
Hole Perimeter
100
Linear (Hole Perimeter)
% of Hole Diameter
% of Steel Diameter
Deformation vs Hole Diam.
Deformation at Failure (mm)
4
14.0
Stress (psi)
4.5
Conclusions and Request
Good bond can be achieved with normal
grout
Use of 200 psi allowable bond value in typical
situations is reasonable.
Greater stress and strain to failure was
observed with deformed steel surface.
Shrinkage may be a concern with larger
annulus space.
Please provide comparative data if you have
any.