Encyclopedia of Anchoring (CA06114E)

If a hard stratum at an oblique angle to the anchor’s path is the problem, change the anchor batter so that the angle is closer to 90 degrees if possible, or stop down pressuring the anchor as it reaches the stratum and allow it to auger a “pocket” which will counteract the tendency to lead off. In obstruction-laden soil, be prepared to remove the anchor, move over, and try again if the anchor starts leading off.

B

In the absence of engagement problems, the appearance of the shaft fracture surface is not of much significance.

The fractures shown (above right) are typical for solid shafts anchors like the SS (above). Contrary to common belief, there is no practical difference in these two types of fractures; more specifically, the Type A fracture (the above right) is not necessarily indicative of brittle shaft material. In fact, we have never seen such a fracture that was due to brittle shaft material. It is true that, for pure torsion, the Type A fracture would be typical for a brittle material while a Type B fracture (above right) would be typical for a ductile material. However, without engagement problems, virtually all shafts fracture close to a helix where stress conditions in such areas include the non-axisymmetric structure (helix projecting from one side of shaft) and non-homogeneous material (shaft parent metal, weld filler metal, helix parent metal, zones of intermixing, and heat-affected zone). End restraint effects from wrench engagement and bending moments resulting from failure to maintain alignment or the anchor’s striking obstructions in the ground may also affect the stress conditions. The result is that the stress conditions causing fracture are triaxial, not torsional and Type A fractures are neither unusual nor indicative of brittle material. It has been claimed that a helical-end wrench which engages the anchor shaft along the upper helix surface increases the torsional capacity of the anchor by forcing it into a Type A fracture which

naturally has a larger fracture surface area than a Type B fracture. Actually, such wrenches offer little practical advantage because most of the time they merely force anchors to fracture the way they would have done anyway. If you are able to rule out wrench engagement problems, there are still a couple of possibilities left. If the anchor seems to be encountering obstructions, or the operator does not seem

to maintain alignment, impact loading or excessive bending moments may cause the anchor to fracture at reduced torque. Try the same type and size anchor again but with slower rotation speed and additional operator care. If on the other hand the Type A Type B

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