Drilling Rock Anchor Bolts

Manufacturer of quality IBO drill rods
2016-12-20
Highway Tunnel Self Drilling IBO Rock Bolts
Application of big diameter IBO
2017-01-12
Drilling Rock Anchor Bolts

Drilling Rock Anchor Bolts

Abstract:

There are many kinds of roof/rib support & rock reinforcement methods in the engineering. Such as mechanical rock anchors, grouted bonded rock & soil anchors, polyester resin chemical rock anchors, etc.

This article is mainly telling the difference between these anchor bolts.

Difference between Rock Anchor Bolts

Mechanical Rock Anchors

Mechanical Rock Anchors

Mechanical Rock Anchors

Advantages of mechanical rock anchors:

  1. No bond zone, so less drilling is necessary to develop the same shear cone as the bonded anchor system. What’s more, less grout is needed since the less volume of the drilling hole.
  2. The installer can pre-stress and grout the anchor bolt in the same day.
  3. There is no cracking of the grout column, since the installer is pre-stressing the anchor bolt before grouting.
  4. The oversized drill hole provides for excellent grout coverage.

Disadvantages:

  1. The mechanical rock anchor bolt should only be used in competent rock.
  2. The maximum working load for the largest mechanical anchor, utilizing a 2:1 safety factor from the ultimate tensile steel capacity, is 1,241 Mpa.

Grout Bonded Rock & Soil Anchors

Grout Bonded Rock & Soil Anchors

Grout Bonded Rock & Soil Anchors

Advantages of grout bonded rock & soil anchors:

  1. Grout bonded anchors can be used in virtually all rock conditions and also in most soils.
  2. The maximum working load with a single anchor bar or multi-strand tendon can exceed 6,895 Mpa.

Disadvantages:

  1. The installer must wait for adequate compressive strength of the grout to be reached before pre-stressing the anchor.
  2. A bon zone must be established, so deeper drilling is required to develop the design load in comparison to a mechanical anchor.
  3. In the weak rock or soils, a test program or sample borings should be used to determine drill hole diameter and anchor lengths.

Mechanical Soil Anchors

friction anchor rod

friction anchor rod

Advantages of mechanical soil anchor rods:

  1. Problems associated with drilling anchor holes are eliminated because the anchor is driven into the soil.
  2. All anchors are tested during installation and provide immediate anchorage. Actual holding capacity is determined during pull testing.
  3. Time and expense associated with mixing and dispensing grout is eliminated.

Disadvantages:

  1. The anchors are designed to hold no more than a 345 Mpa maximum working load. Holding capacity can be limited by the bearing strength of the soil.
  2. Corrosion protection is limited.
  3. Rocks or other obstructions in the installation path can prevent adequate embedment.

Polyester Resin Rock Anchors

Polyester Resin Rock Anchors

Polyester Resin Rock Anchors

Advantages of polyester resin rock anchors:

  1. Pre-stressing can be accomplished within minutes of the installation.
  2. Resin bonded anchor bolts are one of the most economical temporary rock anchor systems available.
  3. Resin anchoring is successful in most rock types.

Disadvantages:

  1. Resin anchors are difficult to protect against corrosion. They require tight drill holes for proper mixing of cartridges, resulting in only a thin resin cover. In addition, resin anchors cannot be centered in the drill hole, which allows the bolt to rest on the bottom or side of the hole.Resin is placed into the drill hole in a pre-measured amount which does not account for resin loss into rock seam sand cracks. Loss of resin creates unprotected gaps along the anchor, essentially reducing the safety factor of the system.
  2. Resin anchors with lengths over 7.5 meters are difficult to install because resin gel time often requires speedy installations.

    Couplings cannot be used with full column resin anchors because their outer diameter is too large relative to the drill hole diameter.

  3. Water presence can greatly reduce the holding capacity of the anchor or cause the anchors to be susceptible to creep.
  4. Temperature affects set and cure times of the resin.