Rock anchors have been used in the United States since the early 1960s as temporary tie backs and permanently in dams since 1968. Permanent anchors are designed to last up to 100 years with sophisticated corrosion protection systems. There are various types of permanent anchors including multi-strand systems with up to 27 strands and over 4000 kN of tension capacity, as well as permanent stressbar anchors and rock bolts used in infrastructure retention. Proper corrosion protection involving encapsulation and sheathing is necessary for permanent anchors to achieve their long design life.

1. http://www.cpi-team.com

4. http://www.youtube.com/watch?v=8qUuQbi4ocQ
http://www.youtube.com/watch?v=eICMSgr-x14&feature=related

5. ROCK
ANCHORS
• Ground anchors had been
used in the U.S. since the
early 1960’s primarily as
temporary “tie backs” and
as permanent installations
for dams since 1968.

6. ROCK
ANCHORS
•How long will the anchors
last?
•What is the cost?
ROCK
ANCHORS
• Database of over 400 dam
anchor projects completed in
North America from 1968 to
2004

7. Rock Anchor Components (PCI,
1974).
(Note the lack of protection to the
steel other than grout.)

8. ROCK
ANCHORS
• 1996. Permanence is now defined as
a minimum of 24 months in a
completely revise set of
Recommendations.
ROCK
ANCHORS
• A wider spectrum of issues than
simple chemistry now have to be
considered when selecting
corrosion protection principles.

9. A major breakthrough was to
identify two classes of protection
(Class I and II) for permanent
anchors
It replaced the poorly defined
“double” and “single” corrosion
protection systems offered by
various tendon manufacturers.
ROCK
ANCHORS

10. The details are summarized
inTable 1 and a “decision
tree” (Figure 2) was
provided for the guidance
of designers.

12. Figure 2. Corrosion Protection
DecisionTree (PTI, 1996).

13. 2004
 The existing Recommendations
were revalidated while it is stated
that, for permanent anchors,
“aggressive conditions shall be
assumed if the aggressively of the
ground has not been quantified by
testing.”

14.  Table 1 was revised, as shown inTable
1R, mainly to clarify the Class I status of
epoxy protected steel in a “water
proofed hole.”
 The sophistication of contemporary
tendons is shown in Figure 3 and 4. A
long supplement is devoted to epoxy
protected strand.

20. Between 1974 and 2006
(i) Extremely sophisticated corrosion
protection systems were developed and
(ii) (ii) the latitude offered to designers relative
to choice of corrosion protection intensity
and details was severely restricted: to install
a permanent anchor in a dam without Class I
protection is now not only impermissible,
but unthinkable.

24. Permanent Anchors
 Permanent anchors come in many
different shapes, sizes and types.
 (supply of all materials,
fabrication, installation, grouting,
testing, tensioning, lift-off
testing).

27.  Multi-strand system ranges from a
single strand of working load 150 kN to
27-strands that accommodate over 4000
kN (400 ton force +) of tension capacity.
 With typical permanent anchors double-
encapsulated and sheathed in sinusoidal
HDPE, design lives can stretch to 100
years.

29.  Permanent Stressbar Anchors are high-strength,
1000 MPa grade threaded bar, used mainly in Civil &
Infrastructure retention and construction works.
 As with the multi-strand anchors, the stressbar is
encapsulated in a sinusoidal sheathing providing a
design life of up to 100 years.
 Standard thread bar sizes allow for a safe working
load of up to 660 kN, but non-standard sizes allow
for a far greater load.

31.  Similar to permanent stressbar anchors, rock
bolts are a lesser grade – 500 MPa – of
threaded and are more common.
 Ranging in size from 20 to 40mm in diameter,
rock bolts are most commonly found in
Infrastructure retention systems and can be
both actively or passively (nominally)
tensioned, usually against, or encapsulated-
in, shotcrete walls.

34.  Unbonded Length
 Bond Length
A.UnbondedLength
B.BondLength

35. 1. Wedge
2. Wedge Plate
3. Bearing Plate
4. Greased & PE or PP Extruded
Strand in Unbonded Length
5. Spacers along Bond Length
6. Bare Strand in Bond Length
7. Centralizer

37.  Grout Filled Bond Length Encapsulated
 Greased & PE Extruded Unbonded Length
1. Cover Cap
2. Wedge
3. Wedge Plate
4. Bearing Plate
5. Trumpet
6. Greased & PE or PP Extruded Strand in Unbonded
Length
7. Corrugated Sheathing
8. Spacers along Bond Length
9. Bare Strand in Bond Length
10. Centralizer
11. End Cap