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Rock anchors are used primarily for resisting uplift forces. On the contrary, rock sockets serve three main purposes:
(i) Rock socket friction and end bearing to resist vertical load.
(ii) Passive resistance of rock sockets contribute to resistance of lateral load.
(iii) Socket shaft friction is also used for resisting uplifting forces. But only70% of this capacity should be used because of the effect of negative Poisson ratio.
Note: Rock anchors, which may consist of a high tensile bar or a stranded cable, are provided for tension piles when there are insufficient soil covers to develop the required uplifting resistance.
A rock anchor system is designed mostly empirically .different grouts, grout pressures and rock system result in different bond resistances which when multiplied by the surface area of the anchor in question give the theoretical anchor loads.
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Rock anchors are used primarily for resisting uplift forces. On the contrary, rock sockets serve three main purpose
(i) Rock socket friction and end bearing to resist vertical load
(ii) Passive resistance of rock sockets contribute to resistance of lateral load.
(iii) Socket shaft friction is also used for resisting uplifting forces. But only70% of this capacity should be used because of the effect of negative Poisson ratio.
Rock Anchors
Advantages
Less drilling is necessary to develop the same shear cone as the bonded anchor system. Also, less grout is needed since there is less hole volume. The installer can pre-stress and grout the anchor in the same day. There is no cracking of the grout column, since the installer is pre-stressing the anchor before grouting. The oversized drill hole provides for excellent grout coverageDisadvantages The mechanical rock anchor should only be used in competent rock. The maximum working load for Williams largest mechanical anchor, utilizing a2:1 safety factor from the ultimate tensile steel capacity, is180 kips.
