December 4, 2012

Trail Science 105: Other trail elements

Switchbacks (Photo credit: QuintanaRoo)
Switchbacks, climbing turns and retaining walls are common in trail construction; however, they are often relatively difficult to design and construct correctly

Switchbacks and climbing turns are used to reverse the direction of travel on hillsides and to gain elevation quickly. The difference between the two is a climbing turn is a reversal in direction that maintains the existing grade going through the turn without a constructed landing. Climbing turns have a wider turn radius than switchbacks and are used on gentle slopes, typically 15 percent grade or less. Ideally, 7-percent sideslopes are best.
Trail switchback
A switchback is also a reversal in direction, but they are usually used on steeper terrain and have a relatively level constructed landing. Switchback turns have tight corners because of the steeper grades.
A common problem with climbing turns is they are often built on too steep of terrain. The advantages of climbing turns in appropriate terrain is that a wider radius turn of 13 to 20 feet is relatively easy to construct. Climbing turns are usually less expensive than switchbacks because much less excavation is required and fill is not used.
Switchbacks are used in steep terrain with sidelsopes from 15 to 45 percent. Although switchbacks can be constructed on sideslopes of up to 55 percent, retaining structures are needed on such steep slopes. The key to successful switchback construction is adequate excavation, using appropriate structures to hold the fill in place, and building psychologically sound approaches.
Retaining structures keep dirt and rock in place. Retaining walls are useful for keeping scree slopes from sliding down and obliterating the tread, for keeping streams from eroding abutments, and for holding trail tread in place on steep sideslopes. Two common retaining structures are the rock retaining wall and the log crib wall.
Retaining wall on downslope of trail
Steps are another trail element used to gain a lot of elevation in a short distance. Steps are common on steep trails in New England and much less common on western trails.
Next: Trail Science 106: The Trail Corridor
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