Analytical design for mobile anchor systems

Abstract

Cable yarding systems are a common method for transporting materials in mountainous terrain in situations that do not allow for ground-based skidding, forwarding or shovel-logging. Cable yarding, although effective in steep locations, requires anchored guylines to support the skyline and operating lines. The skyline and operating lines rely on a fixed anchor, or tailhold, to provide adequate tension for effective yarding. Anchored guylines and skylines usually depend on available stumps or trees. Where these are not available, mobile anchors such as bulldozers can be used. Mobile equipment anchors have an advantage of known resisting capacity, as opposed to trees and stumps, but there are no well-defined design criteria for the application of the system. Here an analytical design solution for mobile anchor capacity is presented, based on force equilibrium analyses, and accompanied by a series of design charts. A moment equilibrium analysis involving vehicle center of gravity and anchor attachment points is used to bracket feasible designs. It is shown that when the guyline angle is relatively high, the primary factor in anchor capacity is equipment weight. At lower cable angles, the passive resistance of the soil in front of the blade can play a major role, especially with deeper embedment, stronger soils and with an uphill vehicle placement. Finally, the anchor attachment point must be kept relatively low to the ground, especially if smaller equipment is used as an anchor. The results demonstrate that use of equipment as a primary or auxiliary anchoring system can be effective when adhering to design constraints based on equipment and in-situ soil properties.