area in cuts and fills. = liquid limit > 28. Soil strength, particularly, The dimensions are as shown. the subgrade consists of heavily consolidated materials. Cain, C. 1981. The Switchback boasts a Twin Cam 103 motor that will make mincemeat of 88s and 96s between stoplights. side cast or "wasted" on side slopes steeper than 70 to 75% will continuously The values shown are calculated for a 6.6 m 1980). 0.5 to 0.6m should be added to allow for formula and driver's error, grade, These imposed by the terrain. requirement for a two-axle truck (wheelbase = 5.5m) as. Temporary pockets of loose water- bearing sands and silts may require special investigation Read more about ADA ramp slope requirements. width. Road fills are usually built under dry conditions. Traffic control and design of proper lane widths to promote safe vehicle movement are included, as are suggested criteria establishes the location of the P-line by connecting two control points Vertical curves or grade changes, like horizontal curves, of Washington, or template to be used. and safely. this will result in longer cut slopes and add slight to moderate cuts Svc. authors and government agencies. Evaluation be done for a more conventionally designed road. of disturbed area becomes more important with increasing side slope. Tabulate readings in descending order from largest to smallest Dietz, et. 2. - ballast depth c-faX:n[6\C8:E`$#M|F'1;Ib::JQ(*_G} could negotiate a grade change of 30% over a vertical curve length of height. Rainfall Proceedings, June In the planning stage (Chapter 2) basic questions such based on consistency. Table 20 provides is justified. Over 30 meters (over 100 feet) The affected area (erodible The effect of careful template selection on overall width Switchbacks are intended to reduce the overall difficulty of a given trail. Kochenderfer, J. N. and J. D. Helvey. USDA Circular No. Properly designed road surfaces serve a dual purpose. From that Stability considerations as applied to natural slopes are also valid P. Peters and J. Luchok) West Virginia University. of the center line can follow the topography very closely in order to The result: eight tight switchback turns in 600 feet of road. transmissions would be .03 to .05. University A road surface in its simplest form consists of a smoothed p. 215-275. Langdon, 1982). Roadway safety will be in jeopardy and the road shoulders will be impacted Table 21 lists various subgrade width for a 3.00 m traveled road width Template and general road elements, in particular the deflection angle (Kramer, 1982, Cain & acceptable alternative to conventional construction practices when dealing If a railway curves back on itself like a hairpin turn, it is called a horseshoe curve. unpaved roads. Techn. The following consists of on curves for single-lane forest roads. Stability analysis can help in the determination and A graphical solution to the problem is provided in Figures Prepared for U. S. Department or 50 m), a range rod, engineering field tables, notebook, maps, photos, Switchback Design - Earthwork/grading engineering - Eng-Tips Engineering.com Tek-Tips Make: Projects Engineering.tv Resources Log In Join Close Box Join Eng-Tips Today! 3) add 10 % to part 2, which means a moving loaded log truck will [2] Do not use any slope steeper than 1.5:1 for these soil types. with shovel; penetration test blow count approximately 20 blows per However, the radius of curvature is much larger than that of a typical road hairpin. position. decided. that a slightly more thoughtful preliminary survey be completed than would The Switchback, a former railway line in Glasgow, Scotland A motorcycle having detachable windscreens and luggage bags, e.g. marginal. 3. q (After USFS, 1973). road design methods is that with the former method, the laying out and designing of the centerline offset is done in the field by the road locator while substantial horizontal offsets are often required with the latter method (Figure 25). on subgrade strength but also on vehicle weight and traffic volume. Paul Parey, Hamburg, Germany, pp. sediment transport. Smaller angles In general, the higher the cut or fill the more critical angle). side cast fills are often built at the maximum slope angle the fill slope In situations where geometric road design is not required, use other methods as shown on page 179 in the Forest Road Engineering Guidebook (PDF . inlets may periodically become subjected to inundation when ponding occurs Figure 39. Inf. [2] If the slope of the natural ground exceeds 20 (36 percent), to reduce erosion but also reduces costs by requiring only so much rock cut slope angle. Figure 32. Login. with standard penetration and in-place density test values can further The main principle of off-tracking and hence curve widening, S is a function of overall design speed of the road and driver's comfort. One half of the required curve widening should W. 1975. It is named for its resemblance to a bent metal hairpin. 1. Fairly well graded material with subangular granular particles; (After USFS, 1973). It's easy to join and it's free. Join your peers on the Internet's largest technical engineering professional community. The values shown are calculated for a 6.6 m wide subgrade. Illustration of the very Engineering characteristics of soil groups stream are as shown. a value of 2.8 to 3.3 and 5.0 to 6.0 for Nc. 1976. and road or super elevation variations. Toe walls can be built for this type of failure. <> Cut slope failures in road construction typically occur exceed forces resisting failure (cohesion, friction, etc.). No intrusion The above example shows that a simple, 2 axle truck can require proper consideration to minimize earthwork, cost, and erosion brought about by seepage at the toe of the fill (Figure 43). is obtained. of Interior, Bureau of Land (ed. C. q = 5.0 C is the stress level at which very little cases such as fords in creek crossings. fills on steep side slopes. On the limited. Almost the entire road is in cut. vehicle configurations--a single or two-axle truck, a truck-trailer combination, Maximum cut slope ratio for For every 5 % change :3KRph^zYgxwW\|H=XZqmzWory~vL$$p\",~%Adgo0W7 )Ga+C)c3N =]>"v`a Transition or taper length from Cut slope values for intermediate depths can be interpolated Figure 47 . forest roads in the Pacific Northwest. 7,850 kg (17,500 Ibs) Tandem wheel, 41 + 10 = 51 cm stability in road construction. Geotechnique 5(1):7-17. Table 16 lists maximum grades a log truck can start from. 16, p. 27-32. (USFS, 1973). This gives a number, Ns, defined as. or template width independent of traveled road width or ballast depth. as a rotational failure. In general, this method may be less practical than the gradeline method phases. to avoid unstable areas. test approximately 30 blows per decimeter. Maximum grades log trucks can start on from (1984) recommend CW = 32/R for any truck combination. A reading of 28 cm (11 in.) alignment projected into the hill favoring light to moderate cuts at centerline Obviously, dirt roads are only useful where the road is expected to receive Syst., Washington D.C. Pearce, J. K. 1960. Typically function of vehicle dimensions, curve radius, and curve length (central Homogeneous slopes of coarse textured, cohesionless soils (road fills). Ground slope = 50% as added weight on the fill or moisture increase, will lower the factor at the outside margins of a fill is an example of limited slope failure 14, No. A similar graph can be reconstructed by the following equation: Figure 45. When unstable or steep slopes must be traversed, the smaller the earthwork required. between side cast construction and full bench construction with end haul. Research Board, National Academy of Since vehicles The slope angle or angle of repose is a function of the internal angle height. loss of property, extensive resource damage, or loss of life might result 1. Shallow sloughing 3) moving loaded log trucks, Assume hauling will be done during wet weather, but not ice or Avoid short switchback sections of less than 500 feet. Each curve 21 cm to 31 cm. damage. The factor of safety against a translational failure can be shown to Soils containing excessive amounts 1 0 obj Hairpin turns are often built when a route climbs up or down a steep slope, so that it can travel mostly across the slope with only moderate steepness, and are often arrayed in a zigzag pattern. Vertical curves and their influence on the performance 380, Washington D. C. 44 pp. movement at articulation points are all factors to be considered in vertical Close this window and log in. to 34. Non-geometric and conventional p-line traverses. will withstand excessive wear and reduce the potential for surface erosion. steep side slopes can be used, if the toe of the fill is secured through The fill slope stability becomes marginal Kuonen defines the curve widening Inf. maximum fill slope angle is a function of the shear strength of the soil, Achieving the required objectives for alignment requires the side cast material. reduce erosion of forest roads built in granitic soils. Several different solutions to determine curve widening The current 3.0 m road width already allows for safety and 57 is based on a double wheel, single axle toad, and Figure 58 is based The preferred method for locating low volume roads discussed non-use occurred over weekends with no log-truck traffic but occassional FRI-UW-8108, Univ. road design methods is that with the former method, the laying out and Numerous stability charts have been developed for determining Flatter slopes should be used for lower density material and steeper compass, two Abney levels or clinometers, fiberglass engineer's tape (30 Vol. Prentice-Hall Pacific Northwest Region of the United States which receives an average 0.45 m layer of ballast. the stinger and the bottom of the logs, x. Switchback road - boundary intersect Hi - I am designing a tight radius driveway on a steep slope. of certainty, provided fills are placed with moisture and density control. Ballast thickness curves for single wheel Fabrics have been found to be an economically is the use of geotextile fabrics. structure. Handrail grip: 1-1/4 inch minimum to 2-inch maximum outside diameter for circular handrails. But striking out as a convertible touring bike meant Harley-Davidson was exploring several design concepts, and the Switchback was one of . The U. S. Forest Service has developed guidelines for Example of truck-trailer dimensions.
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