Helical anchors consist of an assembly of steel shafts with a series of helical steel plates attached on a pitch to create a screw anchor. These steel anchors can be screwed into the ground to create foundation support, tie back wall systems and soil nail wall systems. It is screwed into the ground until there is enough torque resistance to indicate sufficient bearing strength. The capacity of a helical anchor in compression or tension is based upon the bearing capacity of the helices against the soil in which it is embedded. Therefore the capacity increases as the area of the helices is increased and as the soil friction angle increases. During installation, the torque resistance of the anchor is monitored and provides verification when the anchor capacity is achieved. It provides working/design compression and uplift capacity on the order of 30 to 100 kips depending on the soils encountered. The benefits of this system is that they eliminate the need for grout to set up to gain capacity, and eliminates disposal of spoils, which is especially important when installed in contaminated soils.
Helical external gears are generally used when both high speeds and high horsepowers are involved. External helical gears have been built to carry as much as 45,000 kW of power on a single pinion and gear. External gears are the most common and consists of a wheel with exterior teeth. Helical gears are cylindrical in shape. However, the teeth on helical gears are set at an angle relative to the axis of rotation. It is widely used in automotive applications. It can be used in parallel in, like spur gears, or at right angles.