002ROCK

ANCHORS

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Science Art Religion Politics Scholarly Articles For Mathematics and Productivity http://www.twitlonger.com/show/n_1sp9pjo?new_post=true …Dr f Dejahang BSc CEng, BSc (Hons) Construction Mgmt, MSc, PhD 

ROCK ANCHORS

Rock Anchor-Excavator mounted drill rig for soil nailing - YouTube.htm

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Corrosion Protection and Anchor Longevity

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•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.

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•How long will the anchors last?

•What is the cost?

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•Database of over 400 dam anchor projects completed in North America from 1968 to 2004

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

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•1996. Permanence is now defined as a minimum of 24 months in a completely revise set of Recommendations.

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•A wider spectrum of issues than simple chemistry now have to be considered when selecting corrosion protection principles.

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

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

Table 1. Corrosion Protection Requirements (PTI, 1996).

Figure 2. Corrosion Protection Decision Tree (PTI, 1996).

ROCK ANCHORS2004 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.”

ROCK ANCHORSTable 1 was revised, as shown in

Table 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.

Table 1R. Corrosion Protection Requirements (PTI, 2004).

Figure 3. Class I Protection – Encapsulated Strand Anchor (PTI, 2004). Figure 4.

Figure 4. Class I Protection – Epoxy Coated Strand Anchor (PTI, 2004).

ROCK ANCHORSBetween 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.

Full Length (Corrugated and Smooth) Encapsulation (Franklin Falls Dam, NH, 1980)

Full Length Corrugated Protection (Dolby Dam, ME, 1995).

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Permanent AnchorsPermanent anchors come in many different shapes, sizes and types.

(supply of all materials, fabrication, installation, grouting, testing, tensioning, lift-off testing). 

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Tested system for multi-strand permanent anchor

ROCK ANCHORSMulti-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.

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Permanent Stressbar Anchors

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.

 

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Permanent Rock Bolts

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.

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12 tonne Excavation Drill Rig

ROCK ANCHORS Unbonded Length Bond Length

A. Unbonded Length B. Bond Length

Typical Uses:  Temporary Applications with a service life of <= 24 Month

1. Wedge2. Wedge Plate3. Bearing Plate4. Greased & PE or PP Extruded

Strand in Unbonded Length5. Spacers along Bond Length6. Bare Strand in Bond Length7. Centralizer

Anchor with Double Corrosion Protection (PTI-Class I)

ROCK ANCHORS Grout Filled Bond Length Encapsulated Greased & PE Extruded Unbonded Length1. Cover Cap2. Wedge3. Wedge Plate4. Bearing Plate5. Trumpet6. Greased & PE or PP Extruded Strand in Unbonded Length7. Corrugated Sheathing8. Spacers along Bond Length9. Bare Strand in Bond Length10. Centralizer11. End Cap