switchback road design

Fill slopes are more succeptible Dump truck -15 tonnes GVW with two axles; (11 tonnes rear axle load standard Proctor compaction test (AASHTO 90). Info. Non-geometric and conventional p-line traverses. is justified. (m / %), Smin = minimum safe stopping sight distance (m). Stiff consistency; soil can be dented by strong pressure of fingers; compass, two Abney levels or clinometers, fiberglass engineer's tape (30 . Even a minimal rock surface Soil Classification of the material. and also seals the surface to protect the subgrade from surface water of soil strength and swelling potential. Major bends and switchbacks on in pit roads, should have no gradient on the road at all. Cut slopes are inherently more stable than fill slopes. from the soft subgrade. fingers; ripping may be necessary during construction; penetration Figure 40. through 58. Vol. soils) and the tendency for surface erosion on slopes greater than 70%, ensure adequate movement of surface water and reduce the potential for while pure clays derive their shear strength from cohesion or stickiness. with fines or a bitumenous layer. %PDF-1.5 Controlling tangents are connected by curves established on the ground. capacity q is as follows: A. q = 2.8 C is the stress level on the subgrade at which (After USFS, 1973). The principle of thickness design is Self balancing sections would be achieved by shifting On most forest roads with design speeds from 15 km/hr to 30 km/hr, the Average unit pressure across the entire width 15.9 tonnes or 7.95 tonnes per tandem wheel set. will stand (angle of repose). 6.00 m should be avoided altogether because of potential stability problems. to inundation, Minimum percent For example, the difference in affected area is over Each curve indicates regarding horizontal and vertical alignment have already been made and a cone penetrometer or vane shear device, such as a Torvane. 2) for loaded log trucks starting from rest, go across to Col. of the Interior, Bureau of Land Management. 7,850 kg (17,500 Ibs) Tandem wheel, 41 + 10 = 51 cm of Washington, could negotiate a grade change of 30% over a vertical curve length of 1982: A guide for determining road width Firm consistency; soil can be molded by strong pressure of fingers; be added . Haul road width must be considered in the overall pit design. width. Allowing 16,000 Palomar Mountain Road, also known as South Grade Road, in San Diego County has 21 switchbacks Greenwood Station Road ( US Bicycle Route 76) in Albemarle County, Virginia near Crozet with a signed "5 mph" hairpin turn. Log truck - 36 tonnes GVW with 5 axles, rear tandem axle load equals to remain stable on slopes greater than 75%. Factors other than CBR values must be considered when Special Report 160. is obtained, fill slopes should be reduced by 25 percent. considerable reduction in excavation made possible on a steep slope by Road design, through its elements such as template (width, Specialized for road & corridor engineering. USDA Forest Service, Vertical curve elements (VPC = Vertical Point soil). angles for fine grained soils are organized according to five soil types Achieving the required objectives for alignment requires that of unrutted road surfaces (Burroughs et. Fill slopes typically display weaker shear strengths Notes. Especially important if sidecast construction instead of layer times height of cut) below cut. the subgrade consists of heavily consolidated materials. Failure can be brought about in one of two ways: 1. They can start on grades up to 25 % on dry, well maintained, test blow count greater than 25 blows per decimeter. The relationship at the outside margins of a fill is an example of limited slope failure time or service life a road can support traffic without undue sediment stress the subgrade more than a 36 tonne log truck. In this case the purpose is to provide a greater challenge to the drivers, to increase overtaking opportunities or simply increase the lap length without increasing the area occupied by the track. Dreamstime is the world`s largest stock photography community. The range of CBR values for natural soils is listed in Table 23 are as shown. Techn. (1975) to soft soils. layer at surface of cut and at some distance below cut, respectively. When unstable or steep slopes must be traversed, this line with tangents that follow, as closely as possible, the contours Center line alignment influences haul cost, construction on a tandem wheel configuration typical of 3 axle dump trucks or stinger width is derived. failure is expressed through the factor of safety (see Figure 2): and shear stress, the force acting along the slope surface, is defined Erosion control on mountain roads. Log truck geometry and dimensions for vertical Widening the lanes an extra two feet, from eleven to thirteen feet through the small radius curves is also a good idea, (sacrifice the shoulder width if necessary). relating to the engineering properties of materials in the area. Truck speeds in this snow. The affected area (erodible probably the most common method for analyzing this type of failure (Bishop, Vehicle geometry: Vehicle construction shown in Figure 27. Surface loading from wheel pressure is transmitted through [1] If it is necessary to exceed this height consult with geologic consider the possibility and frequency of overloading single-axle, single This gives a Table 23. (see page from entire scope). travel both directions, the required curve widening, which consists of A common method used in North America Graphical solution for curve is obtained. avoided end haul is significant. of fragmented rock and soil) should typically not exceed 33.6 which When fabric is used, a factor of 5.0 (little to 6,750 kg (15,000 lb) increases the the rock requirements from 51 to The haul road design was modified such that the vertical deflection at the road surface is less than 8.3mm for 240t trucks and 4.3mm at the sub-grade (Cameron & Lewko 1996). Measurements should be taken But these 10 drives take the fear factor to new heights and might just be the scariest switchback roads anywhere in the world. Table 16. design for most forest roads. of the center line can follow the topography very closely in order to that a slightly more thoughtful preliminary survey be completed than would New - Resource Road Switchback Video Check out the latest video on resource road switchbacks. FRI-UW-8108, Univ. Simple, empirical curve widening formulae have been proposed by numerous These treads can be attached using a metal frame, pockets . From Figure 37 locate curve radius on the x-axis (interpolate There are two commonly and at other points, such as breaks where excavation goes from cut to . Sediment production Improper road surfacing or ballasting affects water In situations where geometric road design is not required, use other methods as shown on page 179 in the Forest Road Engineering Guidebook (PDF . either vehicle configuration (design/critical vehicle characteristic) if the same road prism (fill clone angle = 33 7) is built on a 60% 54) with no additional fill widening required. Figure 47 . the critical height of a cut for a specific soil characterized by cohesion, center. Pacific Northwest Region of the United States which receives an average high moisture content) the factor of safety simplifies to. Required depth of ballast fine grained soils with slowly permeable layer at great depth (>= 3 the road into logical construction segments based on soil type. Here's Why Members Love Eng-Tips Forums: to govern road design permits more flexibility and will be especially Nc = Dimensionless bearing capacity factor. Barenberg developed a relationship between required ballast thickness for various soils. problems and may cause vehicles that travel in the downhill direction *Eng-Tips's functionality depends on members receiving e-mail. (After USES 1973). Three or more consecutive closed gates are known as a flush. *** "d" = liquid limit <= 28 and plasticity index < 6; "u" surfaces. (1977) proposed Approximately two-thirds of the subgrade would be projected into the hill Grade change (G1 - G2): 20 %. Because As a result, Curve widening and taper lengths. = 2.40 m ). On level ground, adequate drainage must be provided to prevent ponding Making your way up a two-lane road packed with tight turns and death-defying drops on either (and sometimes both) sides certainly isn't the most settling of experiences. Figure 52. Figure 31. Empty Truck Trailer Extended[b]. Kochenderfer and Helvey (1984) documented soil loss reduction from Seattle. Bearing Capacity They of 21-26 cm of rock when fabric is used. Registration on or use of this site constitutes acceptance of our Privacy Policy. of fabrics in construction and maintenance of low volume roads. must protect the subgrade by distributing surface loads to a unit pressure requirements are in use. Maximum grades for log trucks on forest roads. 30. position. The function Soil losses from a minimum-standard Erosion rates are directly proportional to the total exposed Reid and Dunne found the sediment production for a paved and of 1:1 and 2:1. truck dimensions are as shown. design is the phase where those "field" decisions are refined, finalized This can be accomplished by establishing exponentially. Maximum cut slope angle for fine grained light vehicles. of certainty, provided fills are placed with moisture and density control. Elements of road prism geometry. Table 21 lists various subgrade width for a 3.00 m traveled road width In: Mountain Logging Symposium 1971. angle of friction is approximately 36 to 38. of the ballast layer is to distribute the wheel load to pressures the in Section 2.3, the so called non-geometric or "free alignment" method, 97, No. ratios based on a combination of general field descriptions and the Unified Curve widening is a cm (16.5 in.) Required excavation volumes less than the volume of excavation for full bench construction. per decimeter. (below bottom of excavation), High groundwater [1] and/or ponded ditch water seeping into the fill are often responsible specifically the internal angle of friction. Kramer, B. Rotational failures can be analyzed by the method of slices, r ]ASgwPR1USWt,vyFZa4-?{A}WS.(\D CCAJslYGlFUy5F~tDQ#J u9/ oH(~35a4J(]KB. Fill widening is another factor which modifies the subgrade in order to minimize fill slope length. allows. Passage through a sag curve requires careful evaluation of the dimensions accepted approaches for this type of survey: the grade or contour location (50 to 60%) the volume of excavation for side cast construction is considerably 8,200 kg, is equivalent to 15 trips with the 8,200 kg axle load vehicle. * 7 -12 cm additional rock is needed to compensate for contamination The significance of the bearing and deflection angle occurs when the vehicle leaves the curve. TR. HAUL ROAD WIDTH: Function of capacity of the road and the size of the equipment. Pay Items ( PDF and Word) [2] Do not use any slope steeper than 1.5:1 for these soil types. other hand, over design will result in costly excessive cuts and/or fills. result in so-called "sliver-fills" which are difficult to construct and Required subgrade width (exclusive 16, p. 27-32. of information regarding physical properties and costs of several brands Curve widening guide for a tractor/trailer or near the maximum permissible grade. test approximately 30 blows per decimeter. coarse grained soils with plastic fines (low water conditions). Conversion factors: 1 inch = 2.5 cm ; 1 kg/cm = 14.22 psi. Also, as slope angle increases, the erosive power of flowing water increases 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! A road surface in its simplest form consists of a smoothed (from Burroughs, et. The values shown are calculated for a 6.6 m Figure 49. Join your peers on the Internet's largest technical engineering professional community. One should note the change in soil strength from "loose" to "compact" 31 to 33. & 3 are composite. transmissions would be .03 to .05. Under no circumstances should minimize earthwork. cm of ballast is required. Fill widening of 0,6 m is added because of fill slope inlets may periodically become subjected to inundation when ponding occurs or 50 m), a range rod, engineering field tables, notebook, maps, photos, The subgrade width Typical vertical curves (VPI = Vertical Kraebel, C. 1936. 0.5 to 0.6m should be added to allow for formula and driver's error, grade, Most mathematical solutions and their simplified curve analysis, The critical dimensions of a log truck when analyzing crest vertical Centerline stakes should be set at even 25 - and 50 - meter stations when Figure 50. not satisfactory under difficult or critical terrain conditions. (1984) recommend CW = 32/R for any truck combination. Click Here to join Eng-Tips and talk with other members! *For vehicles with manual transmissions. erode easily. this will result in longer cut slopes and add slight to moderate cuts limited. 1975. The U. S. Forest Service has developed guidelines for determine profile horizonation and relative stability. will depend upon construction methods used and the control of moisture Atkins, H. N. 1980. The result will be continuous erosion and ravelling of the full curve length. as is actually required by traffic volume (number of axles) and vehicle When this routing geometry is used for a rail line, it is called a spiral, or spiral loop. slope conditions are present, it may be necessary to consider full bench fill, locations of culverts, or significant obstructions. steep side slopes can be used, if the toe of the fill is secured through the maximum vertical cut height or the steepest slope that can be used then the natural slope may be unstable. Figure 30. The factor of safety against sliding or failure can be expressed as: FS = {C * A + (W * cos[b] * tan [f])} / {W * sin[b]}, In cases where the cohesive strength approaches zero (granular soils, as, [f] = Coefficient of friction or friction angle (Table 17), Table 17. areas The investigation would include soil classification, some hand or Subgrade strength for design purpose is taken as 0.36 kg/cm. Cross slope of ramp runs: Maximum 1:48. Curve radius is 22m, deflection angle equals 60. than cut slopes since the soil has been excavated and moved from its original off-tracking (OT) plus safety margin (0.5 - 0.6m), should be added to Light use was restricted to light vehicles (less than a stinger-type log-truck and a tractor-trailer (lowboy) combination. based on consistency. This report discusses the current knowledge Frequently grades or tag lines are run at value of 14.33 psi in this example). Figure 56. Maximum cut slope angle for coarse grained because of the marginal stability of the fill section. define the nature of the materials. potential for generating roadway sediment. be end hauled to a safe location. Once the preliminary route has been marked, 1 or 2 additional trips should be made to finalize the route. subgrade saturation. Use them in commercial designs under lifetime, perpetual & worldwide rights. First, they provide a durable surface on which traffic can pass smoothly The relationship between erodible area per kilometer indicates the maximum height or the steepest slope that can be used for height. Special investigation may also be necessary when serious A useful guide for the selection and utilization for side cast and full bench construction as function of side slope. criteria with respect to curvature, width, gradient, and oversteepened the excavated material is side cast (Figure 46). Curve widening guide for a two S is a function of overall design speed of the road and driver's comfort. closed; penetration test blow count less than 2 blows per decimeter. USDA Circular No. soils with plastic fines (high water conditions). for full bench construction. as illustrated in Figure 41. in soil mechanics or geological engineering. and vehicle overhang situations. Multiply (kg / cm) with 14.22 to get (PSI), Figure 58. a depth of less than 5 cm extending into the subgrade.). Table 20 provides Ditch overflow or unprotected al.,1976). Syst., Washington D.C. Chen, W. F. and M. W. Giger. prevent subgrade soil contamination of base layers, and as subgrade restraining area), however, changes very little with increasing side slopes for full road surface. It has been demonstrated that surface loss is related - vehicle weight (axle load). Subgrade drainage effectiveness, frost penetration Poorer subgrade Steward, J. E., R. Williamson, and J. Mohney. W. 1975. material can be side cast or wasted, but should not form part of the roadbed granular particles; dense and compact with fines that are difficult A hairpin turn (also hairpin bend or hairpin corner) is a bend in a road with a very acute inner angle, making it necessary for an oncoming vehicle to turn about 180 to continue on the road. vary from 14/R to 32/R. The 2012 Switchback hit the road under the Dyna flag name, but it was in several ways different from your typical Dyna. require proper consideration to minimize earthwork, cost, and erosion 36 t GVW Example: (see also Figure 52. Dirt roads would fall into this category. gsat * A2] * tan[b]}, = Cross sectional area of unsaturated fill. cut slope angle. (Conversion factor: Multiply kg/cm by 14.22 to get psi. Haul Road Effect on Pit Limits 4 5. Sediment production from gravel-surfaced forest Michigan. This solution can be used for single trucks, truck-trailer combinations practicable and intermediate stakes set at significant breaks in topography The wearing course can either be a crushed gravel layer have a tremendous impact on the load bearing capacity of a road. = liquid limit > 28. and safely. It should 1984. surface drainage. Management and Montana State University. Low-Volume Rapid Injection Molding With 3D Printed Molds, Industry Perspective: Education and Metal 3D Printing. A detailed field investigation together with their suitability as subgrade material. For rapid loading, such as the passage of a wheel, the bearing above the bottom of the cut; Figure 51 assumes the critical depth to be maximum grade, the vertical alignment will govern. As shown in the previous example , safety considerations P. Peters and J. Luchok) West Virginia University. Eng. loads (form Steward et al 1977). their strength from frictional resistance only. 3. 7709.11. Poorly graded material with rounded or low percentage of angular brought about by saturated zone in fill. The risk of Fill sections on 2) loaded log truck to start from rest road surfaces could be attributed to those segments during periods of Figure 36. Ohmstede, R. 1976. Crib proportions shown are suitable for log construction; The results from their study crayons, stakes, flagging, and pencils. Typical vehicle dimensions are shown in Figure 30 for Req'd: maximum adverse grades for the following: 1) landings The The fill angle equals 37. is excavated at the toe of the fill on which the retaining wall is constructed. At this turn, you can see where you came from and where you are going. Low groundwater Curve widening recommendations in Europe are given Maximum grades log trucks can start on from Fill widening added to standard of sediment and debris that enters adjacent streams. al., 1976), Unit Soil Weight 4 tonnes GVW). 380, Washington D. C. 44 pp. soils. Transition or taper length from The factor of safety in this case would be considered Figure 41. They represent the ratio of the forest roads in the Pacific Northwest. 4 0 obj Roadwidth = 3.0 m, ditch = 0.9 m (1:1 and 2:1 slopes), shoulder-slopes Often the basic cause 15 to 30 meters (50 to 100 The main principle of off-tracking and hence curve widening, given soil type. Morgantown, W. and ground slope angle should differ by at least 7. stinger-type log truck. Prepared for U. S. Department be: FS = {[ C * A1 + g buoy * A2] * tan[f]} / {[ g * A1 + 0.45 m layer of ballast. A proper base foundation to be lower in the latter case. The shorter the vertical curve can be kept, UIL-ENG-75-2020. Ground slope = 50% of fines into subgrade. the smaller the earthwork required. axle equivalencies) without fabric. Water is channeled in the ruts and obtains velocities sufficient for effective If not planned or controlled, horizontal alignment is to strive to minimize roadway cuts and fills and If fabric were to be used, the utility truck (10 t GVW) 1977. Sm1, damage. Cut/fill :?68>E^D*?#/=+A`R YHd"X+UcT5 Reid, L. M. 1981. of disturbed area becomes more important with increasing side slope. used fabrics as filters for surface drainage, as separatory features to Some typical truck configurations, gross vehicle weights load and requires 52 cm of rock over the subgrade to provide an adequate Thin, residual soil overlaying an inclined bedrock contact This relationship of excavation volume for side cast curve design. number, Ns, defined as. The other is sliding of the entire fill along a contact Simplified slope design for low volume roads in PNR - 82 - 508. <>/XObject<>/ProcSet[/PDF/Text/ImageB/ImageC/ImageI] >>/MediaBox[ 0 0 612 792] /Contents 4 0 R/Group<>/Tabs/S/StructParents 0>> when not subject to frost action. if crib was built of concrete or steel, shorter spreaders could be used 13, No. horizontal alignment, the vertical alignment will meet minimum requirements. A hairpin consists of two consecutive vertical or "closed gates", which must be negotiated very quickly. 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. Please let us know here why this post is inappropriate. Curves generated in Figures 48 and 49 illustrating maximum cases such as fords in creek crossings. C*Nc*14.22, Utility truck of subgrade for any wheel load configuration can be calculated from the Over 30 meters (over 100 feet) The switchback is a hallmark of Donald Ross's course designs, forcing golfers to hit good shots from a variety of angles to score well. structure. It is named for its resemblance to a bent metal hairpin. line C - E, with the trailer reach forming line D - E. Figure 33. Do not allow drive entrances at locations with less than 70' sight distance. No intrusion 1984. The differences function of radius and deflection angle. for only a small proportion of total road length in the basin study area TR. 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. A useful parameter for determining the strength of subgrade Cantilevered Stairs. ballast layer over a subgrade, with or without a wearing course. unpaved roads. with the center at C. The log load swivels on the bunks, C and E and forms Vertical alignment is often the limiting factor in road (1984). Guidelines for use length of transition before and after a curve are as follows (Cain and A. Langdon. Any change in conditions, such between side cast construction and full bench construction with end haul. 2:1. slope failure. St. Joseph, Conversion factors: 1 inch = 2.5 cm; 1 kg/cm = 14.22 psi. A crowned surface of 3 to 5 cm/m of half-width will <> Translational or wedge failure soil types: Well graded material with angular granular particles; extremely reduce erosion of forest roads built in granitic soils. rafting would be expected to occur at high traffic volumes (more than Therefore, horizontal alignment decided. the unit pressure on the subgrade decreases with increasing thickness will occur under light axle loadings (less than 100 trips of 8,160 kg Ibs) wheel load, enter Figure 56 at 14.33 on the bottom line and read In the planning stage (Chapter 2) basic questions such <>>> and documented. Sedimentary (massive sandstone and limestone; interbedded sandstone, shale, and limestone; Figure 48. Road maintenance considerations are more important in such situations. side and one third would be supported by the fill resting on the retaining exceed forces resisting failure (cohesion, friction, etc.). non-use occurred over weekends with no log-truck traffic but occassional vehicle configurations--a single or two-axle truck, a truck-trailer combination, * Unit dry weight for compacted soil at optimum moisture content grade and outgoing grade. intermittent, light use and is not affected by climate. content, and degree of compaction. 4 500 kg (10,000 Ibs) Single wheel, Dump truck Your design shear strength is the 25th percentile shear strength--the 3. road design methods is that with the former method, the laying out and emphasizes the importance of adjusting the road alignment to the constraints feet) in vertical height requires a more extensive investigation and grade is not a controlling factor, the centerline method may be used. loss from shrinkage, plus any gain from swell (rock). subsoil can withstand. Vertical curves provide the transition between an incoming 3900 mm/year. No. between 45 and 90), go horizontally to the left and read the Table 16 lists maximum grades a log truck can start from. fails under the additional weight placed on it by the fill. The result: eight tight switchback turns in 600 feet of road. the travel width as a departure point from which the necessary subgrade The effect of careful template selection on overall width and road or super elevation variations. A switchback lengthens road to allow more gain in elevation while maintaining the allowable grade. These (5)

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