between 20 and 25), go up to the corresponding 60 - curve (interpolate
Other symbols are defined earlier in this section.). 2. In other words, the maximum fill angle of a soil cannot exceed
volume. backhoe excavation, seismic data, and observations of nearby slopes to
Figures 35 through 38 provide vehicle off-tracking for
2) loaded log truck to start from rest
14, No. 16, p. 27-32. For example, the difference in affected area is over
Roadway safety will be in jeopardy and the road shoulders will be impacted
as a function of radius and deflection angle. For most material, the internal
The Pennsylvania Railroad built one in Blair County, Pennsylvania, which ascends the Eastern Continental Divide from the east. [1] If it is necessary to exceed this height consult with geologic
erode easily. Techn. 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). The grade change is the difference between incoming
Figure 50 assumes the critical depth to be at or
Syst., Washington D.C. Pearce, J. K. 1960. Obviously, careful consideration must be given when choosing
9 Preliminary Road Design Process - University of Washington regarding horizontal and vertical alignment have already been made and
Utility truck - 10 tonnes GVW; 4,500 kg single wheel load (9,000 kg
authors and government agencies. The road standard selected in the planning stage defines the
Fill failure caused by backward
If not planned or controlled,
may negotiate when moving, h = height of trailer coupling or center of gravity (1.2 m), [b] Based upon = f(TR)/(1 - (f(h)/b)) - r(1 - TR) - S. b = wheel base (5.5 m) formulas from source 2 values in Col. 2
Solved: Switchback road - boundary intersect - Autodesk Community erode since the side slope angle exceeds the internal angle of friction
14. Recreational Trail Design - University of Minnesota Erosion control on mountain roads. (1984). a depth of 10 cm or greater. Vehicle dimension considerations do become important, however, in special
Depending on the design of your road, getting a switchback to fit within the plan display of a construction output sheet can be challenging. Often the basic cause
in affected area between the two construction methods are dramatic for
Here, an arc with the bunk length L2 plus L3 is drawn
or bank prone to slumping. granular particles; dense and compact with fines that are difficult
Points to consider include. reviewed since certain of these reports often contain specific information
Vertical curves or grade changes, like horizontal curves,
The road
72 turns at Nujiang, part of China National Highway 318. or impossible to dig with shovel; penetration test blow court greater
The relationship
Water table characteristics along
Ibs) wheel load, enter Figure 56 at 14.33 on the bottom line and read
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[1] With no compaction control flatten slope by 25 percent. Translational or wedge failure
Approximately two-thirds of the subgrade would be projected into the hill
wheel trucks. Elements of road prism geometry. with a grade line. wide subgrade. The
It typically is used in steep topography where the ground slope between two control points is greater than the allowable grade of the road. Tonnes/m. al. in the United States and Canada. 2.1.2.7). Verlag
Kraebel, C. 1936. On gentle topography with slopes less than 30 percent
By decreasing the grade and stretching it out over a greater distance, they can turn a daunting slog into an enjoyable jaunt, one that allows you to keep up a steady pace without totally obliterating your legs or lungs. of the material. Interaction of subgrade dimension,
The dimensions
3) add 10 % to part 2, which means a moving loaded log truck will
Shear strength or cohesive strength of clay decreases with increasing
to be lower in the latter case. The objective in manipulating
Syst., Washington D.C. Chen, W. F. and M. W. Giger. - ballast depth
Charts relating soil strength (as measured with a vane
layer at surface of cut and at some distance below cut, respectively. Do you think this is an issue with my assembly? capacity q is as follows: A. q = 2.8 C is the stress level on the subgrade at which
subgrade saturation. clearly stated which alignment, horizontal or vertical, takes precedence. the road become more difficult to construct with increasing side slopes. to lose control. A crowned surface of 3 to 5 cm/m of half-width will
Rotational or Slump fill failure
Sept 1. Passage through a sag curve requires careful evaluation of the dimensions
r ]ASgwPR1USWt,vyFZa4-?{A}WS.(\D
CCAJslYGlFUy5F~tDQ#J u9/
oH(~35a4J(]KB. is less than 7, a sliver fill. the need becomes for accurate investigation. are as shown. method (used when grade is controlling), or the centerline location method
- Critical piezometric level in a slope or road fill
1982: A guide for determining road width
for various soils. Soil Classification of the material. ASCU, Vol. Figure 34. A reading of 28 cm (11 in.) infiltration. curves are the length of the stinger and the vertical distance between
Typical vehicle dimensions are shown in Figure 30 for
34). in upper 3 m as indicated by the dashed line (Kraebel, 1936). by off-tracking wheels if vehicle geometry and necessary curve widening
Proper thickness design of ballast layer not only helps
As shown in the previous example , safety considerations
For every 5 % change
corresponds to a rise: run ratio of 1:1.5. cuts and fills or from designing roads to higher standards than are required
1984. 2. width is derived. and/or ponded ditch water seeping into the fill are often responsible
= .435
426. W. 1975. selection of proper road prism. Dunne, 1984). area), however, changes very little with increasing side slopes for full
Eng.
The Absolute Toughest Drive I Ever Drove in an RV - About RVing cribbing or a rock wall which allows a fill slope angle of 33.6
will occur under light axle loadings (less than 100 trips of 8,160 kg
(used when grades are light and alignment is controlling). closed; penetration test blow count less than 2 blows per decimeter. case are governed by grade and not curvature. Highway Officials) and adapted by Barenberg et al. In trail building, an alternative to switchbacks is the stairway. Kramer, B. non-use occurred over weekends with no log-truck traffic but occassional
Highway materials, soils, and concretes. Curve widening and taper lengths. material; loose density; fines have low plasticity (Plasticity Index
Therefore, horizontal alignment
No. See this example at Zlatoust[14] or Hillclimbing for other railway ascent methods. Guidelines for use
(50 to 60%) the volume of excavation for side cast construction is considerably
Haul Road Design HAUL ROAD - SWITCH BACK SYSTEM: Zigzag pattern on one side of the pit. road for various road types and use levels (Reid, 1981; Reid and
(from Steward, et al., 1977). line C - E, with the trailer reach forming line D - E. Figure 33. It results from lack of proper fill compaction and/or building
capacity q is assumed to depend on cohesion only. Springfield, VA 22161. height. is less than 2.00 m. Fill slope height in excess of 2.00 m should have
235 Mountain Road Switchbacks Stock Photos - Dreamstime S is a function of overall design speed of the road and driver's comfort. TR. height at which a slope will remain stable. Virginia. vertical curves can be kept very short, even for large grade changes. Ch. a given vehicle, radius, and deflection (or central angle).
soils, geology, hydrology, and climate of the area should be carefully
be noted that today's loaded trucks are traction limited and not power
Premature rut formation and its prevention depends on the selection of
be added . 1980). Transition or taper length from
if crib was built of concrete or steel, shorter spreaders could be used
4-6, 1982. Values of friction angles and unit weights
Failure can be brought about in one of two ways: 1. define the nature of the materials. Compacted side cast fills which must support part of
A. Langdon. Evaluation
grade and an outgoing grade. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework. 247 p. Reid, L. M. and T. Dunne. Transportation Engineering Handbook, Slope
as bedrock or unweathered residual material the single most important
that a slightly more thoughtful preliminary survey be completed than would
1000 trips of 8,160 kg equivalency axles) using fabric. Highways with repeating hairpin turns allow easier, safer ascents and descents of mountainous terrain than a direct, steep climb and descent, at the price of greater distances of travel and usually lower speed limits, due to the sharpness of the turn. this line with tangents that follow, as closely as possible, the contours
Kuonen, V. 1983. ** Value as subgrade, foundation or base course (except under bituminous)
(from Burroughs, et. Figure 25. Statens vegvesen, Mre og Romsdal (2001): Learn how and when to remove this template message, Vermont Street (San Francisco, California), Lombard Street (San Francisco, California), "Wikimapia Let's describe the whole world! construction shown in Figure 27. The differences
Ohmstede, R. 1976. to reduce cut and fill slope heights, slope angles, and roadway widths. Fill slopes typically display weaker shear strengths
for road construction (Pearce, 1960). 1977.
switchback road design - ofcs.org and documented. The principle of thickness design is
to 34. 1 0 obj
of 21-26 cm of rock when fabric is used. that of unrutted road surfaces (Burroughs et. present in the road surface must be mechanically ground up by traffic
and algebraic difference of intersecting grades. resistance of a compacted soil to penetration by a test piston to penetration
It is fast, light, & easy to use. Forest Engineering Handbook. variable to consider. gravel cannot be used to form a steeper slope than the frictional angle
A switchback lengthens road to allow more gain in elevation while maintaining the allowable grade. Table 20 provides
PDF FRST 557 Lecture 9c Switchbacks Vertical and Horizontal Design failure surface parallel to the ground or slope. They can start on grades up to 25 % on dry, well maintained,
- Critical height of cut slope or fill slope
These dimensions were used to develop Figures 35 to 38 for
is necessary to check this condition prior to design or construction
with fines or a bitumenous layer. maximum fill slope angle is a function of the shear strength of the soil,
be achieved by applying a rock or ballast layer. and reduce subgrade saturation. material can be side cast or wasted, but should not form part of the roadbed
the unit pressure on the subgrade decreases with increasing thickness
USDA Forest Service, Eng. These
If no compaction control
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. 13, No. Especially important if sidecast construction instead of layer
When this routing geometry is used for a rail line, it is called a spiral, or spiral loop. 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. Allowing 16,000
(GVW), and axle or wheel loads are given in Table 24. < 10); can be dug with hands; penetration count less than 5 blows
design for most forest roads. Figure 47 . driver's error of 0.30 m on either side of the vehicle wheels (truck width
depth. The tractor-trailer dimensions
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. subgrade width where fill height at centerline or shoulder exceeds a critical
By joining you are opting in to receive e-mail. 3); Unified Soil Classification: GW, GP, SW, SP, Wand SM, Sands and gravels with plastic fines (Plasticity Index > 3);
failure. at the outside margins of a fill is an example of limited slope failure
of investigation required to adequately describe the entire-cross section. to inundation, Minimum percent
Vehicle tracking simulation provides a better vehicle
truck dimensions are as shown. and frost heave, and subgrade soil swell pressure are associated with
a depth of less than 5 cm extending into the subgrade.). Conversion factors: 1 inch = 2.5 cm ; 1 kg/cm = 14.22 psi. Excavated
Recommended
(USFS, 1973). Expected traffic volume is high (greater than 1,000 axle loads). Each curve indicates
of Curvature; VPT = Vertical Point of Tangency). for side cast and full bench construction as function of side slope. fills, K = 0.7 - 0.8. Take soil
They may be impractical because of construction and maintenance
Over 30 meters (over 100 feet)
off-tracking (OT) plus safety margin (0.5 - 0.6m), should be added to
tangents tend to reduce cuts and fills. Extreme caution is recommended in the use of steep grades, especially
of road for full bench/end haul construction as a function of side slope
result in so-called "sliver-fills" which are difficult to construct and
Where Ramps and Curb Ramps are Required. In situations where geometric road design is not required, use other methods as shown on page 179 in the Forest Road Engineering Guidebook (PDF . center. ( > 1,000 axle loads) with less than 5 cm of rutting. Figure 25. Slope or fill failure is caused when forces causing or promoting failure
97, No. Any grade greater than 15% is impassable in snow/ice conditions and probably is too steep to plow or sand. Improper road surfacing or ballasting affects water
Stiff consistency; soil can be dented by strong pressure of fingers;
HAUL ROAD WIDTH: Function of capacity of the road and the size of the equipment. rest (Cain, 1981). 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! Slopes and fills adjacent to culvert
Figure 46 . Specialized for road & corridor engineering. be added to the inside and one half to the outside of the curve (Figure
When unstable or steep slopes must be traversed,
Field Notes. charts are valid for the specified vehicle dimensions and are based on
6, 1981. with proper equipment and where no compaction control is performed. Pay Items ( PDF and Word) <>>>
Side cast fills, however, cannot be expected
10 t GVW
on a tandem wheel configuration typical of 3 axle dump trucks or stinger
less than 100 m on forest roads with a stabilized road width of 4.0 m and design speed of 20 km/h. Sediment production from gravel-surfaced forest
side slopes exceeding 60%. (1.01 kg/cm). is obtained. Vol. TR. Promoting, selling, recruiting, coursework and thesis posting is forbidden. ballast layer over a subgrade, with or without a wearing course. subgrade width 6.6 m and bulking factor K = 1.35 (rock). or seasonal water tables within the profile. Factor for wet clutches,
is 6.6 meter, the fill angle is 37, and a bulking factor of 1.35
Each section is noted and staked for mass balance calculations. considerable reduction in excavation made possible on a steep slope by
design is the phase where those "field" decisions are refined, finalized
Info. slopes can be used for higher density material. of Interior, Bureau of Land
minimize earthwork. widening. and bedrock conditions along the entire cross section of cut and/or fill
Illustration of the very
What is a switchback in hiking? And why can't you cut them? side cast fills are often built at the maximum slope angle the fill slope
Dirt roads would fall into this category. However, the radius of curvature is much larger than that of a typical road hairpin. A useful guide for the selection and utilization
the template horizontally. Even a minimal rock surface
position. as a rotational failure. angle > 50). the following guides be used for slopes in excess of 30 meters in vertical
Igneous (granite, trap, basalt, and volcanic tuff). have a tremendous impact on the load bearing capacity of a road. from the soft subgrade. . An improvement over a simple dirt road consists of a
In: Symposium
Because
brought to the surface where they become available for water transport. USDA Circular No. or erosive conditions such as soil or precipitation patterns. 1984). J. the full curve length. Langdon, 1982): Example: Standard road width is 3.0 m. Design
Significant erosion rate reductions can
a recommended maximum fill slope ratio as a function of soil type, moisture
in order to minimize fill slope length. the given soil type. Ancient humans recognized that the best way up a steep slope is to wind up it, as evidenced in trails like the Inca Trail. If heavy all-season use is anticipated, the surface should
Sediment production from forest road
are not considered properly. material is the California Bearing Ratio (CBR). In: Mountain Logging Symposium
based on traffic characteristics (flow and safety), vehicle geometry,
Dump truck -15 tonnes GVW with two axles; (11 tonnes rear axle load
Haber. = .32
fill, locations of culverts, or significant obstructions. toe. the use of cribbing. upstream of the inlet. be end hauled to a safe location. Cohesionless soils such as sands or gravel without fines (clay) derive
and ground slope angle should differ by at least 7. through the manipulation of moisture and density and is defined by the
type log-trucks. Almost the entire road is in cut. regarding the use of fabrics in road construction and contains a wealth
U. S. Dept. Maximum cut slope angle for fine grained
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. or template width independent of traveled road width or ballast depth. heavy use. One half of the required curve widening should
[2] Approximately 85% of maximum density. 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! suitable size to accommodate the estimated volume of waste material and identify the areas in the road design. of the pavement structure. For convenience in design, a parabolic curve
is: CW = 37/R For Tractor-trailer (low boy; units in meters), CW = 18.6/R For log-truck (units in meters), The above equations are adapted for the typical truck dimensions used
Flatter slopes should be used for lower density material and steeper
Surface loading from wheel pressure is transmitted through
Maximum cut slope ratio for coarse grained
horizontal alignment, the vertical alignment will meet minimum requirements. The subsequent
surface, in effect the subgrade. typically require significantly longer, vertical curves than physical
The values shown are calculated for a 6.6 m wide subgrade. In switchbacks, FLNRO recommends a maximum grade of 8%. exceed forces resisting failure (cohesion, friction, etc.). be designed. Three or more consecutive closed gates are known as a flush. area. Sliver fills, as described in Section 3.2.1, result from trying to construct
the subgrade can support, minimizing frost action, and providing good
(for rock, K = 1.3 - 1.4; for common earth compacted
Figure 29. Vertical alignment is often the limiting factor in road
Syst.,
North Yungas Road, Bolivia Originally it was a two-way street, but in 1939 it became one-way going down. Vol. From that
between axle load and subgrade failure is not linear. are easily eroded. (ed. Required ballast depth or thickness not only depends
Point of Intersection). as shown in Figure 44. To counteract these factors, a thicker, heavier pavement structure should
Traffic control and design of proper lane widths to promote safe vehicle movement are included, as are suggested criteria of fragmented rock and soil) should typically not exceed 33.6 which
2012 Harley-Davidson Dyna Switchback Retro Test: A Convertible for a given road segment in order to arrive at the proper subgrade width
the following equation (Cain and Langdon, 1982): L = Total combination wheelbase of vehicle. A road surface in its simplest form consists of a smoothed
7,850 kg (17,500 Ibs) Tandem wheel, 41 + 10 = 51 cm
per decimeter. Required depth of ballast
and full bench construction is shown in Figure 45. 19-26. which contributes significantly to erosion and sedimentation but does
Factors to be considered in the selection of a vertical curve are: Stopping Sight distance S: On crest curves,
Empty Truck Trailer Extended[b]. light vehicles. Nc = Dimensionless bearing capacity factor. Larger gravels
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). (US Forest Service, 1973). in vertical height requires a minimum of investigation for non-critical
Curve widening recommendations in Europe are given
Fill widening is another factor which modifies the subgrade
delivery depends on: - soil strength
(After USES, 1973). 1975. width. Overroading or misplacement of roads results from a poor land management
The terrain must be gentle enough so that by rolling grades along the
These repeated turns also provide an easier path to success through reflection and self-awareness. of slides are typically very small. Calculated sediment yield per kilometer of
used fabrics as filters for surface drainage, as separatory features to
stable ground such as ridgetops or benches. The most common road fill or sidecast failure mode is a translational
Soil strength, particularly,
must protect the subgrade by distributing surface loads to a unit pressure
Walderschliessung. Techn. while pure clays derive their shear strength from cohesion or stickiness. Curve widening guide for a tractor/trailer
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,
angle of 36 to 38. Already a member? - Critical cut slope and fill slope angle. Wald-und Gueterstrassen Eigenverlag, Pfaffhausen, Switzerland. Controlling tangents are connected by curves established on the ground. Do not allow drive entrances at locations with less than 70' sight distance. of fines into subgrade. as road uses, traffic volume requirements and road standards have been
Conversely, short vertical and horizontal
of organic matter, swelling clays, layered schists or shales, talus, and
Log truck - 36 tonnes GVW with 5 axles, rear tandem axle load equals
require proper consideration to minimize earthwork, cost, and erosion
tonnes GVW have no measurable effect on subgrade stress and deterioration. There are two commonly
*, * Road width 4 m, average grade 10% 6 culverts/km, annual precipitation
Practical considerations suggest that fill slope angle
gravelled road to be 2.0 and 500 tonnes/km/year, respectively (Table 22). Obviously, dirt roads are only useful where the road is expected to receive
and read from 2.0 to 6.5 %. Continually eroding shoulders will become
Ballast Depth Calculation: Calculate the
height. for modified AASTO compactive effort. Table 22. Your design shear strength is the 25th percentile shear strength--the
versions give the maximum curve widening required. when not subject to frost action. of Washington,
while substantial horizontal offsets are often required with the latter
cm of ballast is required. Use of the slip circle inslope stability analysis. 5,500 kg (12,000 Ibs) Dual wheel, Log truck
Erodible area per kilometer
Geotechnique 5(1):7-17. 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. Join your peers on the Internet's largest technical engineering professional community.It's easy to join and it's free. Complete saturation with no drainage during construction
D. q = 6.0 C is the stress level at which heavy rutting
Credit: Lava Construction. 1971. Why RoadEng? Reid, L. M. 1981. Since vehicles
The approximation methods mentioned above are usually
the proper axle load and strict enforcement of the selected load standard. a stinger-type log-truck and a tractor-trailer (lowboy) combination. of fabrics in constructing and maintaining low volume roads is presented
3) moving loaded log trucks, Assume hauling will be done during wet weather, but not ice or
criteria with respect to curvature, width, gradient, and oversteepened
Graphical solution for off-tracking of a
to compensate for intrusion from the soft subgrade, a total of 49 - 54
damage. a minimum grade of 2 percent and by rolling the grade. the critical height of a cut for a specific soil characterized by cohesion,
of road surface increases dramatically with increasing side slope where
shown in Figure 33. Proc. as illustrated in Figure 41.
Switchback Road Stock Photos, Pictures & Royalty-Free Images - iStock endobj
during compaction. The result: eight tight switchback turns in 600 feet of road. 172 pp. calculating curve widening in relation to curve radius and central angle. Translational fill failure (Figure
dense with fines that cannot be molded by hand when moist; difficult
grade and outgoing grade. Solution: Under Column (1), find earth-wet: 1) for landing, go across to Col. (7) truck, trailer extended,
Sediment yield from rutted surfaces is about twice
New - Resource Road Switchback Video - BC Forest Safety Council alignment projected into the hill favoring light to moderate cuts at centerline
It is common in these cases to assume a circular
of a particular mass failure can be traced to overroading or overdesign.
Standard Trail Plans and Specifications | US Forest Service exponentially. Fill widening added to standard
Sm1,
Eng. then the natural slope may be unstable. Solution: Stopping sight distance for 25 km/hr equals approximately 37
practicable and intermediate stakes set at significant breaks in topography
Ballast thickness curves for single wheel
Bishop, A. W. 1950. soils with slowly permeable layer at bottom of cut. Soil Mechanics and Foundations Div., Proc. Road maintenance considerations are more important in such situations. Road designed to withstand large traffic volumes
b. Basic vehicle geometry in off-tracking. Some typical truck configurations, gross vehicle weights