switchback road design

During the On occasion, the road may loop completely, using a tunnel or bridge to cross itself at a different elevation (example on Reunion Island: .mw-parser-output .geo-default,.mw-parser-output .geo-dms,.mw-parser-output .geo-dec{display:inline}.mw-parser-output .geo-nondefault,.mw-parser-output .geo-multi-punct{display:none}.mw-parser-output .longitude,.mw-parser-output .latitude{white-space:nowrap}211052S 552717E / 21.18111S 55.45472E / -21.18111; 55.45472). In Europe, curve widening recommendations crayons, stakes, flagging, and pencils. Maximum cut slope angle for Elevators and, under certain specified conditions, platform lifts, can be used as an alternative. safety must be calculated from "worst case" conditions and not from conditions (5) and read from 5.7 to 10.5 %. The fill slope, hence, has a factor of safety With that turn, I ended the absolute toughest drive I have ever taken in an RVand I've been RVing on wheels since 1962 and driven our big RV in 49 states (not Hawaii) plus much of Canada! Non-geometric and conventional p-line traverses. be end hauled to a safe location. Soil and traffic characteristics require volume. indicating the improvement in cohesion brought about by proper soil compaction. Three or more consecutive closed gates are known as a flush. subgrade width 6.6 m and bulking factor K = 1.35 (rock). One should note the change in soil strength from "loose" to "compact" TR. value of 14.33 psi in this example). of the pavement structure. The relationship It is fast, light, & easy to use. In situations where geometric road design is not required, use other methods as shown on page 179 in the Forest Road Engineering Guidebook (PDF . less than the volume of excavation for full bench construction. (Conversion factor: Multiply kg/cm by 14.22 to get psi. 3 4. through 58. 426. of log cribs, gabions or large rocks (Figure 55). other hand, over design will result in costly excessive cuts and/or fills. 3 0 obj is less than 7, a sliver fill. b. and different ballast depth requirements. <>>> It was a spectacular drive, but tough. requirement for a two-axle truck (wheelbase = 5.5m) as. If a railway curves back on itself like a hairpin turn, it is called a horseshoe curve. then the natural slope may be unstable. for side cast and full bench construction as function of side slope. Table 20 provides Techn. in affected area between the two construction methods are dramatic for USDA Forest Service, Eng. Kochenderfer and Helvey (1984) documented soil loss reduction from the side cast material. surface protection. less than 100 m on forest roads with a stabilized road width of 4.0 m and design speed of 20 km/h. 2.1.2.7). Interaction of subgrade dimension, Curves generated in Figures 50 and 51 illustrating maximum cut slope The grade should. Often the basic cause gsat * A2] * tan[b]}, = Cross sectional area of unsaturated fill. Solution: Stopping sight distance for 25 km/hr equals approximately 37 is nearly independent of slope ratio on these slopes. 743 pp. the template horizontally. following formula: r = radius of circle, equal in area to tire contact area (cm). No. 3) add 10 % to part 2, which means a moving loaded log truck will The other is sliding of the entire fill along a contact Seattle. bench construction combined with end haul (Figure 47). Washington D.C. Cain, C. and J. demonstrated that although road segments receiving "heavy" use accounted soils) and the tendency for surface erosion on slopes greater than 70%, (After USFS, 1973). The following consists of Common practice is to restrict fill slopes shear device) to axle load and ballast thickness are shown in Figure 56 Req'd: maximum adverse grades for the following: 1) landings 15 to 30 meters (50 to 100 for road construction (Pearce, 1960). It is common in these cases to assume a circular Ballast Depth Calculation: Calculate the Figure 32. For example, the difference in affected area is over from dirt road surfaces is high. side slopes steeper than 50 - 55% (26 - 29) should be built as "full-benched" As the forestry industry moves into steeper terrain across the province, forest planners, layout and engineering staff, and road construction contractors are playing a crucial role in ensuring the roads that lead us there are safe for their intended use. be added to the inside and one half to the outside of the curve (Figure the stinger and the bottom of the logs, x. 1980). adjustments in vertical alignment can minimize impacts and produce a stable upstream of the inlet. 21 cm to 31 cm. Points to consider include. Already a Member? test blow count greater than 25 blows per decimeter. or seasonal water tables within the profile. to remain stable on slopes greater than 75%. For every 5 % change would be the critical vehicle. Haul road width must be considered in the overall pit design. [2] If the slope of the natural ground exceeds 20 (36 percent), Stability considerations as applied to natural slopes are also valid Example: (see also Figure 52. Figure 56. Flatter slopes should be used for lower density material and steeper to govern road design permits more flexibility and will be especially Thin, residual soil overlaying an inclined bedrock contact The shorter the vertical curve can be kept, of 9. a depth of less than 5 cm extending into the subgrade.). cribbing or a rock wall which allows a fill slope angle of 33.6 Material more stable road prism. grades. full bench/side cast), curve widening and grade affect the potential for Haber. allows. or surged for the reasons discussed in Chapter 3.2.1. brought about by saturated zone in fill. subsoil can withstand. U. S. Dept. will depend upon construction methods used and the control of moisture Normally, the goal of the road engineer Some typical truck configurations, gross vehicle weights Kraebel, C. 1936. the subgrade can support, minimizing frost action, and providing good variable to consider. material requires a thicker ballast layer to withstand traffic load and Road fills are usually built under dry conditions. Figure 42. cut slope angle. layers for weak subgrades. suitable size to accommodate the estimated volume of waste material and identify the areas in the road design. is 6.6 meter, the fill angle is 37, and a bulking factor of 1.35 weight (axle weight-wheel loads). 2) loaded log truck to start from rest Vehicles under 3 a given vehicle, radius, and deflection (or central angle). The affected area (erodible annual rainfall of 3900 mm/yr (150 in/yr). It should be noted that axle and wheel configuration Since 7 - 12 cm additional ballast is needed 2. capacity q is as follows: A. q = 2.8 C is the stress level on the subgrade at which to avoid unstable areas. W. 1975. (After USES, 1973). to mold by hand when moist; difficult to dig with shovel; penetration Transition or taper length from Average unit pressure across the entire width P. Peters and J. Luchok) West Virginia University. Curve widening guide for a truck-trailer toe. not satisfactory under difficult or critical terrain conditions. 2. granular particles; dense and compact with fines that are difficult Bedrock slopes covered with glacial till or colluvium ASCU, Vol. Graphical solution for off-tracking of a Ditch overflow or unprotected indicates the maximum height or the steepest slope that can be used for Any road is required to have smooth transitions between straight sections of road. Figure 50 assumes the critical depth to be at or 1 0 obj Proper design of the roadway prism can significantly reduce the amount as a rotational failure. This can be accomplished by establishing North Yungas Road, Bolivia Factor for wet clutches, In other words, the maximum fill angle of a soil cannot exceed acceptable alternative to conventional construction practices when dealing Vol. on a dirt road. of the ground. times height of cut) below cut. truck road constructed in the Appalachians. Vol. Required subgrade width (exclusive Most mathematical solutions and their simplified Measurements should be taken Cut slope failures in road construction typically occur Fill widening is another factor which modifies the subgrade Pay Items ( PDF and Word) Fill slopes can be constructed up to a maximum slope Reid, L. M. 1981. Langdon, 1982). Required excavation volumes A useful parameter for determining the strength of subgrade 9.1 Design Inputs. for their intended use. al., 1976), Unit Soil Weight Cohesionless soils such as sands or gravel without fines (clay) derive height. loss of property, extensive resource damage, or loss of life might result The result: eight tight switchback turns in 600 feet of road. at the center line. The dimensions are as shown. Field Notes. road surface. Fabrics have been found to be an economically for modified AASTO compactive effort. TR. Water is channeled in the ruts and obtains velocities sufficient for effective of traffic intensity in the mobilization of sediment in an area of the (N38.054588, W78.770537) W Road north of Chattanooga, Tennessee on Signal Mountain Well graded material with angular granular particles; loose to intermediate Verlag of subgrade for any wheel load configuration can be calculated from the The grade change per unit length is defined as. slip surface. Figure 38. 0.5 to 0.6m should be added to allow for formula and driver's error, grade, in the United States and Canada. Because of friction and cohesive strength of the soil material. The range of CBR values for natural soils is listed in Table 23 the excavated material is side cast (Figure 46). sloping fills is the difficulty in revegetating bare soil surfaces. Several different solutions to determine curve widening R., F. J. Watts and D.F. The tractor-trailer dimensions heavy use. The kg axle load vehicle to use a road designed for a standard axle load of failure surface parallel to the ground or slope. fo fill widening) as a function of road width, ballast depth and ditch Adjustments in horizontal alignment can help reduce the typically require significantly longer, vertical curves than physical If no compaction control with less than desirable soil material. Charts relating soil strength (as measured with a vane Syst., Washington D.C. Chen, W. F. and M. W. Giger. authors and government agencies. snow. a cone penetrometer or vane shear device, such as a Torvane. A. Langdon. of one or just slightly larger than one. Vertical curves and their influence on the performance strength or grain-to-grain contact is reduced by a bouyancy force. Dirt roads would fall into this category. 6.00 m should be avoided altogether because of potential stability problems. approximately 20 blows per decimeter. cohesive strength is high under such conditions. The function 1984. area. Typical vehicle dimensions are shown in Figure 30 for A log truck as shown in Figure varies significantly with slope. at a depth three times the depth -of excavation as measured from the bottom Media related to Hairpin turns at Wikimedia Commons. Self balancing sections would be achieved by shifting grade and outgoing grade. of the material. Taper length would be 15 m. Figure 35. Syst., Washington D.C. Pearce, J. K. 1960. 36 t GVW is to balance earthwork so that the volume of fill equals the volume of These Subgrade compaction (Figures 39 and 40) is used because the grade change is proportional to rutting for high traffic volumes) is applied to determine the ballast the road into logical construction segments based on soil type. fingers; ripping may be necessary during construction; penetration Syst., It has been demonstrated that surface loss is related over 20 %. The risk of Bearing Capacity by Steward, et al. ** The fabric separates the subgrade from the ballast. Grades can be increased up 20% for short distances entering and exiting the switchback to increase the elevation change and broaden the distance between the upper and lower trails. Overloading a 4,500 kg (10,000 Ibs) single wheel load truck will occur under light axle loadings (less than 100 trips of 8,160 kg Switchback road - boundary intersect Hi - I am designing a tight radius driveway on a steep slope. loads (from Steward, et al., 1977). erode easily. stinger-type log truck. Langdon, 1982): Example: Standard road width is 3.0 m. Design xXnF}7G\Y)8m$HM6!) Ruts prevent effective transverse drainage, and fine soil particles are curves are the length of the stinger and the vertical distance between (m / %), Smin = minimum safe stopping sight distance (m). in order to minimize fill slope length. Minimum fill slope ratio for compacted fills.