Woodland Slope

8/10/2019 Woodland Slope

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Are you, as a woodland owner, expectedto per orm certain engineering unctionstypically per ormed by engineers when theydesign roads? Te answer is, Sort o . Tis publica-tion does not pretend to turn you into a pro essionalengineer, but it does provide a basis or understand-ing the process o designing woodland roads. Yourintimate knowledge o your property enables you tocontribute special expertise to road design, such as

in planning the route and locating control points.Understanding the process o designing roads helpsyou identi y whether you need pro essional servicesand prepares you to supervise any contractors youmay hire.

Designing woodland roads involves two elements:developing the specications or constructing theroad, and setting the eld layout and location thatguide the construction. Te degree to which youbecome involved in road design depends on yourinterest and background, and the complexity o thetask. Some woodland owners design and build theirown roads when the project is small-scale with asimple design.

You can reduce the cost o road constructionthrough effective design. Te cost o road design,even when done by contracted pro essionals, is smallin relation to the cost o construction.

ReconnaissanceRoad reconnaissance involves observing your

property with a road plan in mind. You know yourproperty as well as anyone and, with some training,you can identi y where roads should or should notbe built.

Revised by Steve Bowers, Extension forestry agent, OregonState University. Original author: John J. Garland, Extensiontimber harvesting specialist emeritus, Oregon State University.

Steve Bowers

EC 1137 R e v i s e d June 2012

Designing Woodland Roads

Be ore doing any on-the-ground reconnaissance,inspect aerial photographs, maps, soil surveyin ormation, or even a simple sketch o yourproperty to identi y a possible route location. Teseactivities help ensure the proposed road ts theoverall plan or providing access to the property.Regardless o the size and scope o the road design, itmust t the overall plan.

Control pointsA major reconnaissance activity is to locate

control points or the road. Control points arespecial areas on your property where its eitherdesirable to build or wise to avoid building a road.Te ollowing are control points that deserve care ulconsideration:

Landings. Potential landing areas are locationsalong the route where logs removed rom aharvest unit are loaded onto trucks. In cablelogging, this is the location o the yardingmachine. With ground-based logging, logs areskidded to a landing location that minimizesthe skidding distances.

Contents Reconnaissance . . . . . . . . . . . . . . . . . . . 1

Road geometry . . . . . . . . . . . . . . . . . . . . 4

Design specications . . . . . . . . . . . . . . . . 7

Road structures . . . . . . . . . . . . . . . . . . . 11

Drainage planning . . . . . . . . . . . . . . . . .12

Field location and layout . . . . . . . . . . . . . 14

Summary . . . . . . . . . . . . . . . . . . . . . . .21

For more information . . . . . . . . . . . . . . .21


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Saddles. Ridgetop roads almost always passthrough saddles (low points along the top o aridge). When roads are located in saddles, youhave access to both sides o the ridge system.Tis makes saddles good landing sites.

Benches. Benches are natural breaks betweenslopes where easy road construction and goodlanding locations ofen are available. Teselocations should be used whenever possible.

Figure 1. Indicators of slides and slumps

Top: Debris avalanches and ows typically occur on steep slopes with shallow soils overlying animpermeable layer. Indicators include areas of previous slides; steep areas lacking vegetation; andgranular, low-cohesion soils that have a low to moderate clay content.

Bottom: Slumps and earthows frequently occur together, creating such landform featuresas sag ponds, tension cracks, and headwall scarps. Indicators include tipped, jackstrawed, orpistol-butt-shaped trees; poor drainage in deep, clay-rich soils; hummocky topography; and areas ofpast failures.

Bedrock

Weatheredbedrock,soil, etc.

Zone ofweathered

bedrock andsoil

Bedrock

Debris avalancheAlluvium

Stream channel

Toe Tension cracks

Slip surface

S a g p o

n d

E a r t h

o w

S l u m p

s


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Steep hillsides and rockoutcrops. Generally, it isdifficult and expensive to con-struct roads on steep hillsideswith rock outcrops. However,excavating a road through anoutcrop can be benecial whenthe outcrop provides sur acingmaterial.

Slumps and slides. Roads onunstable terrain are difficult todeal with during constructionand can lead to more extensiveproblems with slope stability.Indicators o slumps and slideareas are listed in Figures 1(page 2) and 2.

Wet spots, swamps, andsprings. I possible, avoidroad locations that exposesubsur ace water or that crosswetlands. Tese areas presentuture maintenance problems.

Potential stream crossings.Suitable locations or streamcrossings depend on the typeo crossing and the ease oconstructing it. A ord requires

a shallow streambed with asolid bottom, whereas a bridgerequires a narrow channel withstable stream banks. You should consult withyour Oregon Department o Forestry (ODF)stewardship orester when con ronted withsprings and stream crossings.

Sharp ridges and V draws. Constructionproblems are likely to occur when sharpridges require heavy excavation to create astable roadbed. Crossing V shaped draws alsocan cause problems i the excavated materialbecomes unstable and slides away underneaththe roadway.

Areas for surplus excavation. In additionto other control points, its use ul to identi ybenches or other stable, at areas where youcan dump excess excavation.

Te next step in road reconnaissance is to connectthe desirable control points with trial ribbon lines.

Tese are lines o ribbons hung in trees and shrubsat the approximate location o the road. In simplesituations, you can build roads rom these ribbonlines. For more complex situations, however, thetrial location provides a rough guide or collectingdetailed in ormation to use in calculating theroads nal design. rial locations may be subject torevisions and modications, even afer you beginconstruction. I you encounter problems (e.g.,

hidden rock), its ar better to revise the road locationthan incur high costs o drilling and excavating theserock sites or initiate environmental problems.

Te major reason or conducting a thoroughreconnaissance is to minimize construction costby implementing designs that avoid environmentalproblems. For example, roads that are too close tostreams may trigger land ailures; such ailures arethe result o a poor reconnaissance effort. Once youestablish a trial location, it can be help ul to contact

Before failure

After failure

Potential failuresurface

Figure 2. The e ects of improper road location on a slump area

Original ground surface


Ground surface after slump

Failure surface


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the ODF orest practices orester or advice onenvironmental questions and requirements o theOregon Forest Practices Act.

Road geometryYou can build roads in a variety o shapes. Teir

sur ace shapes and characteristics depend onmanagement objectives and the terrain. Figures 3, 4,and 5 show some road shapes.

Crowned roads

Roads with the center elevated to drain water offhal the road to the outside and hal the road to aninside ditch are called crowned roads (Figure 3). Teslope o the crown needs to be sufficient to quicklydrain water off the road or to the ditchline. Tisdesign is the most common road sur ace becausethe running sur ace, i properly maintained, quicklydrains water off the road.

In crowned roads, a system o ditches and cross-drains maintains the greatest degree o controlover the water. Cross-drains should be spaced at arequency that minimizes erosion o the ditch andadequately handles water during periods o requentand intense rains. Proper maintenance o the roadsur ace, ditches, and cross-drains is critical to theireffectiveness.

Inslope roadsRoads that have a slope across the running

sur ace toward the cutbank and do not have aconstructed ditch are called inslope roads. Use these

road sections when its impractical to maintain aditch. Build cross-drains or inslope roads usingrolling dips or rubber water bars (see Figures 4, page5, and 18, page 14) so that the entire sur ace o theroad handles the rain all.

On roads with steep grades10 to 15 percentthe inslope must be 1 to 3 percent higher than thetravel grade, or the water will drain down the roadsur ace rather than to the inside. Inslope roads onsteep grades may present traction problems whencombined with the slope across the sur ace. Insloperoads are more effective on gentle grades.

In inslope roads, the spacing o cross drains needsto be close enough to handle the runoff, but notso close that they create issues with erosion on thedownside o the road. Tey must be large enough todirect water across the road to the outside, but not so

large that they present obstacles to vehicles.Outslope roads

Roads that drain water to the outside acrosstheir entire sur ace are called outslope roads (seeFigure 5, page 5). Because water is not collectedand controlled, the outslope grade across the roadmust be sufficient to keep the runoff draining tothe outside. It is imperative you maintain the roadsur ace because no cross drains are available.

Ridgetops with gentle grades are good candidatesor outslope roads. Tese roads, i maintainedbe ore snow all, may be more effective in snowareas because they can handle the snowmelt. Onsteep grades, outslope roads have the same kinds otraction problems as inslope roads.

Ditch width 3' Surface width 12'

Sustained ow of water

should not be higher thanbottom of rock layer Centerline

3 % 3 %

Rock

Subgrade

Figure 3. Crowned road cross-section


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Figure 4. Inslope road cross-section

Surface width 12'

Centerline

3%

Rolling dip feature

1'2' drop

Inslope

Inslope

Water ow

20' 40'

Figure 5. Outslope road cross-section

Surface width 12'

Centerline

3% surfacecross-section slope for drainage


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Full-bench roads and balancedroads

Depending on terrain conditions,woodland roads are mixtures o cut-and-ll construction (see Figures 6,7, 8, and 9, page 7). You can excavate

the road sur ace rom undisturbed,stable soil or build it entirely rom llmaterial.

Full-bench roads are usually builton slopes over 65 percent. Te entirerunning sur ace is on previouslyundisturbed (and presumably stable)soil.

You can transport the excavatedmaterial to an area needing llmaterial or to a disposal (waste)area. I the amounts o excavatedmaterial are small, relative to thetotal excavated material, you cansidecast the material along the edgeo the road. However, i this practiceis abused, landslides and sidecastailures can result, making largeland areas unproductive and causingpossible environmental issues i theroad is adjacent to nearby streams.

A common practice on gentleslopes is to build part o the roadwayon a stable bench and use theexcavated material to build a portiono the running sur ace. You cando this by removing all debris andwoody material rom the side slopesand depositing the clean ll materialto minimize road ailures.

It is possible to calculate theamount o ll material needed and

excavate only the amount or a roadcross-section (see Figure 8). Includean allowance or shrinkage thatprovides additional material.

When the excavated materialmatches the required ll, the cross-section is balanced. On gentle slopes,balanced sections minimize theamount o earthwork excavation andmaterials handling.

Figure 6. Full-bench road cross-section

Excavated volumeremoved

Centerline

Undisturbed soil

Original ground

Excavation = all volume removed from site

Figure 7. Road cross-section with partial ll

Excavated Centerline

Original groundline

Remove vegetation and debris fromoriginal surface (potential slippage zone)

Excavation = par tial volume removed + partial volume for ll

Fill

Figure 8. Balanced road cross-section on gentle slope

Centerline

Excavation = ll needed + amount to compensate for ll shrinkage

Excavated

Fill


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Balanced excavation also describes the lengtho road where excavated materials must beaccumulated or a ll section (see Figure 9). Roaddesign procedures estimate the excess excavationneeded on both sides o a ll section to providematerial or the ll.

Te extra excavation depends on the amount oshrinkage. Also, ll sections ofen are compacted inlayers to develop road strength; thus, the amounto excavation also depends on the degree ocompaction o the ll.

Design specicationsContractors and landowners who build their

own roads need design specications. Depending

on the size o the job, specications (or specs, asthey sometimes are called) can be a simple list orpages o contract provisions. Te most commonspecications are discussed here, along with criteriaor deciding which are needed or woodlandproperties.

Road width

Most landowners want roads as narrow aspossible to minimize the cost o construction andthe amount o land area removed rom production.A 12- oot running sur ace is usually needed orlog truck traffic. I you plan to gravel the road, thesubgrade (width o the roadway including ditch)should be at least 14 eet. Curves and two-way traffic

Section

S e c t i o

n

Cut slopeCut slope

Exploded cross-section views

CenterlineCulvert

Compact soil in12" layers

Centerline

Extra excavationneeded for llmaterial

Figure 9. Fill cross-section with extra excavation for ll material


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may require widening the road sur acein designated segments.

Some large mechanized loggingequipment requires a minimumrunning sur ace o 14 eet (16- ootsubgrade). Also, i you plan to use theroad as a landing area, you may needwider sections to allow traffic to pass.Designate landings in advance andwiden them during road construction.

Alignment

Alignment is the degree ocurvature in the road. Roads shouldbe as straight as possible; however,there are always tradeoffs. I roadconstruction is made easier byadjusting alignment to t the terrain,the road will have curves. However,there are limits on how sharp thecurves can be and still allow log truck traffic.

Measure curves by the radius o curvature. Aminimum radius o 50 eet is needed or log trucks(see Figure 10). Another way to measure curvesis by using the middle-ordinate method, whichrequires you make measurements in the middle othe roadway rather than rom the center o the circle(see Figure 24, page 19).

Although you can calculate limits o curvatureduring design, the real test is whether a log truck canpass the curves. I you plan to harvest poles or utilizechip trucks on the property, the curves will need toaccommodate the added vehicle length.

Curves in draws or around ridges or switchbacks(horseshoe turns) on a slope are especially critical.You can improve these trouble spots by curvewidening, in other words, providing extra roadwidth at critical points along the curve to allowlonger trucks (such as those carrying poles) orlogging equipment to pass (see Figure 11, page 9).

Road intersections are another element oalignment. Design intersections so that loadedtrucks can make the turn easily. Te State HighwayDivision district engineer must approve intersectionswith public highways. Other considerations includesight distance (clear eld o vision or oncomingtraffic), distance to other intersections, andintersection width.

Grades

Te slope (grade) o roads is either adverse oravorable. Favorable grades are downhill slopes orloaded trucks and adverse grades are uphill slopesor loaded trucks.

Favorable grades may reach 12 to 15 percent orshort distances, while grades o less than 10 percentare recommended or adverse grades. For mostroad designs, steeper grades are possible underspecial circumstances, such as terrain conditionswhere construction and excavation costs becomeprohibitive. Sharp curves require moderate grades,not greater than 7 percent.

I two grades join on the road, you will need a vertical curve to smooth the transition (Figure 12,page 10). Failure to plan or these transitions canresult in truck bind, caused by the limited verticalmovement o loaded trucks.

Intersections also are areas where grades are

critical. In a location where one road leaves another,you must continue with the original grade or at least100 eet to make a smooth transition. I the trafficmust stop or slow down at an intersection, make theavorable grade low so the vehicle can come to a stopand make the adverse grade low so the vehicle canstart out again.

Landing grades must be just steep enough todrain off water. When loaded log trucks leave the

Figure 10. Log truck on a curve with a 50foot radius

5 0 ' r a

d i u s5 0 ' r a d i u s


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landing, the grade must be low enough to get themstarted.

On gentle terrain, road grades may alternate rom2 to 3 percent (where conditions are avorable oradverse) without affecting truck efficiency. Rollinggrades (alternate segments o avorable and adversegrades) can help drainage because water velocitydoes not build up be ore it drains across the road.On inslope and outslope roads, rolling grades areessential or controlling sur ace runoff.

Clearing limits

Clearing limits, or right-o -ways, are well-dened

areas to be logged be ore road construction. Teseareas vary in width and extend about 5 eet beyondthe edge o cut slopes or lls. A 30- oot clearing limitis considered a minimum width. Remove vegetationrom between the clearing limits and dispose o itoutside the roadway, or pile and burn it. Dig stumpsout instead o leaving them to rot in the road.

Excavation

Because most orest road construction consists o

excavation, the road design must speci y how muchearth to remove at the centerline o the road andhow steep to make the cut slope and ll slopes.

You measure cut slopes opposite the way youmeasure grades (Figure 13, page 11). For a :1 cutslope, the elevation difference is one vertical unit orevery unit o horizontal distance.

Cut slopes are designed to match the soil typesability to hold the slopes steepness. Steep hillsideslopes o hardpan soils that are high in clay can hold

a :1 cut slope, while gentle slopes with loose, non-cohesive soils need a 1:1 cut slope. (Rock can be cut vertically.)

On some steep slopes, a 1:1 cut slope may not beas steep as the adjacent ground slope. However, thecut slope will ail i it is too steep or the soil to hold(Figure 14, page 12).

Cut slope

Cut slope

Curve widening

Extra excavation or extra ll

8 0 ' r a d

i u s

T o m i l l

Figure 11. Curve widening to permit truck passage on sharp curves


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Figure 12. Vertical curves

G r a d e

( g 1 ) =

8 % ( a d

v e r s e )

D = 2.5'

G r a d e ( g 2 ) = + 1 2 % ( f a v o r a b l e )

T o m i l l

Length of vertical curveL = 100' horizontal distance

R o a d s u

r f a c e

R o a d s u r f a c e

D = 1.1'

T o m i l l

g 2 = 3 % ( f a v o r a b l e )

g 1 = + 1 2 % ( f a v o r a b l e )

Length of vertical curveL = 100' horizontal distance

D = di erence from grade intersection to form vertical curveg 1, g2 = grades in percent

Sample amounts of excavationdi erences needed for smoothvertical curves

(g2g 1) L

800D =

g 2g 1 D

20% 2.5 ft 15% 1.9 ft

10% 1.3 ft 5% 0.6 ft


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VerticalD

C

B

A

1

1

1

1

1

3 4

1 2

1 4

Centerline

DesignCut slopes measurement

A 1:1 B 3 4:1 C 1 2:1

D 1 4:1

Fill slopes also depend on terrain steepness andsoil types, but to a lesser degree than cut slopes. Fillsusually are designed to have a 1:1 slope (Figure 15,page 13) because this is the steepness that will holdnon-compacted or loose earth. Te stability o llson sloped terrain depends on the original groundssteepness. Fills on slopes that are more than 65 percent

will not catch (attach to the original ground) orprovide support; material will ravel (slide away)down the hillside (Figure 16, page 13).

Speci y where to dump excess excavation in yourroad design. Waste areas need to be at and stable.Occasionally, material needed or a ll is unavailableor o poor quality. o compensate, you can includeborrow pits (excavations outside the constructionarea that provide soil and aggregate or both) in yourroad design.

End hauling is the process o removing materialrom its excavation site or transporting it to a ll areawith a dump truck. While the machines typicallyused in road construction can move material200 to 300 eet, its usually more economical to loadthe material in dump trucks or hauling. Good roaddesign eliminates or minimizes end hauling.

Occasionally, you can anticipate road sur aceproblems and speci y solutions in the road design.

Wet spots are likely to cause problems. You mayuse special abrics or dig out the wet material andreplace it with rock or better material (e.g., replacingblue clays with sandy soils).

Compaction benets road subgrades, especiallylls. It is common to speci y that lls be built up in12 inch lifs (layers) and compacted each time by theroad-building machine. You may need compactionmachines i the ll is large or i the soil strength is very low. Consider compacting the entire subgradei you have to sur ace the road immediately aferconstruction.

Road structuresYou need specications or all structures that you

build into orest roads. Tis includes bridges andcomplicated support structures, as well as the ofen-overlooked culverts and earth-constructed items,such as water bars and dips.

Slope stabilization structures

Under special circumstances, woodland roadsmay need to cross unstable slopes. You can usestructures such as bin walls, sheet piling, rockbuttresses, and hal bridges, but they likely willrequire pro essional assistance in planning and

Figure 13. Cut slopes at common steepnesses


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constructing. Although these structures may costas much as a bridge, you should be aware that theyexist to solve particular slope stability problems, andyou should only consider them afer exhausting allother options.

Drainage planningA road that is properly designed and constructed

to control water will avoid most maintenanceproblems. Tere ore, the key requirement o a goodplan is drainage, drainage, drainage! You will need todesign requent cross drains and stream crossings tocontrol water during storms ( able 1).

Cross drains

Several structures are available or draining wateracross the road. Tese range rom simple earthworkstructures like water bars and rolling dips to open-top, wooden culverts and pipe culverts o variousmaterials. Figures 18, 19, 20, and 21(pages 14-15)illustrate these options.

When designing cross drain structures, considerwhere the water will most effectively and efficientlydrain across the road. Use out all protection

measures such as rock riprap (rocks used as armor),culvert hal rounds, and water discharged on stablelocations to prevent erosion and road undermining.When installing pipe culverts, proper design mayeliminate poor- unctioning crossings. (continued onpage 14)

Failed cut slope

O r i g i n a l g r o u n d s l o p e

Centerline

1

3 4

1 4

13 4:1

1 4:1

Preferred cut slope

Figure 14. Cut slopes that are too steep may fail.

Table 1. Water bar spacing guide 1

Soil type

Roadgrade

(%)

Graniticor sandy

(ft)

Shale orgravel

(ft) Clay (ft)

2 900 1,000 1,000

4 600 1,000 800

6 500 1,000 600

8 400 900 50010 300 800 400

12 200 700 400

15 150 500 300

20 150 300 200

25+ 100 200 1501Distances are approximate only; vary them to takeadvantage of natural features. From: Forest Road Design.September 2006. Salem: Oregon Department of Forestry.


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Centerline 1

11 2

When ll does not catch (attach to originalground), it may slide away.

Figure 16. Fill slopes will not catch on steep slopes.


Centerline

Centerline


1

11 2

1

2

1

2

Figure 15. Partial lls at 1 1 2:1 (top) and 2:1 (bottom) ll slopes


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For example, a single larger pipe may be amore effective culvert than several small pipescombined (Figure 17).

Stream crossings

You can use culverts made rom steel,aluminum, concrete, or plastic to cross smallstreams. Te size you need depends on localconditions (i.e., rain all, drainage area, thestreams sh-bearing status, etc.), but anacceptable starting point is to have the areao the culvert opening equal to the area o thestream channel at the historical high water level.

o construct a stream crossing, you need awritten plan and consultation with the OregonDepartment o Forestry (ODF) in accordancewith the rules o the Oregon Forest PracticesAct. A Stewardship Forester will assist you indetermining whether the stream is sh-bearing.Note: the presence o sh does not determinewhether it is labeled a sh-bearing stream.Do not attempt to install a culvert in a streamwithout proper notication to officials!

In sh bearing streams, culvert designmust plan how sh will get into and out o theculvert, as well as the maximum water velocityin the culvert. Such determinations can only bemade with pro essional advice rom the Oregon

Department o Forestry.Under some circumstances, you might

consider a design that uses pipe arches,bridges, ords, or temporary crossings insteado culverts. Less costly approaches may savemoney in the short run, but their long-termeffectiveness, both environmentally andeconomically, is the true measure o theirsuccess.

Field location and layoutRibbons, wooden stakes, and metal tagsguide the construction o the planned roadway.While there is no single standard or markingsystem, the in ormation provided in thispublication is common to all road construction.

You have to mark the road in a way thatthe machine operator can understand. I theoperator doesnt understand the necessary(continued on page 17)

Figure 18. Water bar cross-section and placement (used oninactive roads)

5'

12"

12"

R o a d s u

r f a c e

(Used on inactive roads)

45

Figure 17. A comparison of three pipes to a single culvert

12" pipe culvertArea = 0.78 square feet

12"

3 irrigation pipes used as culvertArea = 0.59 square feet

6"

6" 6"

Note: Small, inexpensive pipes used as a culvert may carry lesswater and plug with debris more easily than a larger single culvert.


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Rolling dip feature

12' drop Water ow

Inslope

Inslope

20' 40'

Figure 19. Use a rolling dip to drain surface runo .

4x4 running boards

6"8" diameter logs Ditch water ow

Ditchplug

30

Riprap

Figure 20. Wooden or steel opentop culvert

Ditch plugto keep waterfrom bypassingculvert

30

Riprap foroutfall protection

Figure 21. Pipe culvert installation

Culvert materials available Concrete Steel Aluminum Plastic

Ensure upslopeis free of debris


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1 0 0 ' V

. C .

D =

2 . 3

'

C u t

9 5 a t r i

d g e

P l a n n e

d r o a

d s u r f a c e

E x i s t

i n g g r o u n

d p r o

l e

+ 6 % ( f

a v o r

a b l e

)

F i l l 7 0

2 4 " c u

l v e r t

( 1 1 +

0 0 ) +

8 % ( f

a v o r a b

l e )

+ 2 %

( f a v o r a b

l e )

L a n

d i n g

1 2 " c u

l v e r t

( 1 2 +

3 0 )

1 0 0 ' V

. C .

D =

0 . 8

'

1 2 " c u

l v e r t

( 6 +

4 0 )

1 0 0 ' V

. C .

D =

2 '

1 0 %

( a d v e r s

e )

+ 8 %

( f a v o

r a b l e )

1 2 " c u

l v e r t

( 2 +

5 0 )

1 2 " c u

l v e r t

( 0 +

7 0 )

1 0 0 ' v e r t

i c a

l c u r v e

( V . C . )

D =

0 . 5

'

I n t e r s e c t

i o n

w i t h e x i s t

i n g

r o a

d

+ 4 %

( f a v

o r a b

l e )

0

1

2

3

4

5

6

7

8

9

1 0

1 1

1

2

1 3

1 4

5 2 0

5 4 0

5 6 0

5 8 0

E l e v a t i o n ( f t )

S t a t i o n s

( 1 0 0 ' h o r i z o n t a

l d i s t a n c e

)

F i g u r e

2 2

. R o a

d p r o

l e f o r c o n s t r u c t i o n


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in ormation, you or the contractor have to explainit. You or the contractor must also monitor thesite and replace the construction stakes (and othermarkers) that are damaged or destroyed during theconstruction process. A care ul pre-operation reviewis essential, and construction supervision must berequent to avoid problems.

Communicating operator information

Establish the right-o -way or clearing limits withribbons, colored paper tags, or stakes.

Stake the centerline o the roadthis is especiallycritical on curves, switchbacks, and intersections.Te operator needs to know where to begin cuttingand the slope o the back cut. Tis in ormationis given on a slope stake, a stake marking thepoint where the outer limit o a cut or ll meetsthe original ground. When the operator has thisin ormation, cutting or lling can begin at the slopestake, and the proper road width will be achieved at

the same time the road reaches the planned gradeelevation.

Te machine operator also needs to know how touse the excavated material. A road prole showingground levels and proposed grades is very use ul,i available (Figure 22, page 16). Te prole showswhere cut and ll sections are located along the road.

You also can use proles to obtain in ormationon stream crossings, culverts, road cross-drains,and other vital elements o road construction. I aprole is not available rom engineering in ormation,a sketchthough less accurateprovides a writtenorm o communication.

Te construction crew can avoid uture problemswith culverts and cross drains through properinstallation. Figures 18, 19, 20, and 21 (pages14-15) are some examples that you can includein specications or use to communicate with theconstruction crew.

Desired location ofcurve center

End of curve

Anglebetweentangents

1 21 2

Beginning of curve

R o a d t a n g e n t s

Trial curve #1

Trial curve #2

#3#2

#1

Select curve that goesthrough desired locationof curve center

R o a d t a

n g e n t s

Compass for drawing curves

Figure 23. Trial curves with the center of the curve located


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Curve layout on woodland roads

wo simple approaches to curve layout aredescribed here, and while they may be adequateor many circumstances (including compound andreverse curves), you may require more involvedtechniques and pro essional assistance or complex

situations.

Curves requently connect two straight sections,or tangents, o road. On gentle terrain you canroughly stake these tangents in advance. Te linebisecting the angle between the tangents is the linealong which the curve will be centered (Figure 23,page 17). When you select the place the road willcross this bisecting line, you can locate the center o(continued on page 20)

Table 2. Conversions of slope percentage readings and slope distance to verticaland horizontal distances

*Read table cells as:

Verticaldistance (ft)

Horizontaldistance (ft)

0.510.0

Slope Distance (ft)

Slope(%)

10' 15' 20' 25' 30' 35' 40' 45' 50'

5 0.5* 0.7 1.0 1.2 1.5 1.7 2.0 2.2 2.5

10.0* 15.0 20.0 25.0 30.0 35.0 40.0 44.9 49.97 0.7 1.0 1.4 1.7 2.1 2.4 2.8 3.1 3.5

10.0 15.0 20.0 24.9 29.9 34.9 39.9 44.9 49.9

10 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

10.0 14.9 19.9 24.9 29.9 34.8 39.8 44.8 49.8

12 1.2 1.8 2.4 3.0 3.6 4.2 4.8 5.4 6.0

9.9 14.9 19.9 24.8 29.8 34.8 39.7 44.7 49.6

15 1.5 2.2 3.0 3.7 4.5 5.2 5.9 6.7 7.4

9.9 14.8 19.8 24.7 29.7 34.6 39.6 44.5 49.4

20 2.0 2.9 3.9 4.9 5.9 6.9 7.8 8.8 9.8

9.8 14.7 19.6 24.5 29.4 34.3 39.2 44.1 49.0

25 2.4 3.6 4.9 6.1 7.3 8.5 9.7 10.9 12.1

9.7 14.6 19.4 24.3 29.1 34.0 38.8 43.7 48.530 2.9 4.3 5.7 7.2 8.6 10.1 11.5 12.9 14.4

9.6 14.4 19.2 23.9 28.7 33.5 38.3 43.1 47.9

35 3.3 5.0 6.6 8.3 9.9 11.6 13.2 14.9 16.5

9.4 14.2 18.9 23.6 28.3 33.0 37.8 42.5 47.2

40 3.7 5.6 7.4 9.3 11.1 13.0 14.9 16.7 18.6

9.3 13.9 18.6 23.2 27.9 32.5 37.1 41.8 46.4

45 4.1 6.2 8.2 10.3 12.3 14.4 16.4 18.5 20.5

9.1 13.7 18.2 22.8 27.4 31.9 36.5 41.0 45.6

50 4.5 6.7 8.9 11.2 13.4 15.7 17.9 20.1 22.4

8.9 13.4 17.9 22.4 26.8 31.3 35.8 40.2 44.7

55 4.8 7.2 9.6 12.0 14.5 16.9 19.5 21.7 24.1

8.8 13.1 17.5 21.9 26.3 30.7 35.0 39.4 43.8

60 5.1 7.7 10.3 12.9 15.4 18.0 20.6 23.2 25.7

8.6 12.9 17.1 21.4 25.7 30.0 34.3 38.6 42.9


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19

Follow the steps below to lay out a curve using the middle-ordinate (stick-length) method. Assign letters to the stakes you use for layout. Once acurve ts a given location, mark the stations on the stakes starting from thebeginning of the curve (for example, if stake A = station 12+10, and stakes areused every 25 feet, then stake C would be marked 12+35; stake E, 12+60; andso forth). All distances are horizontal measurements (they are not on the slope).

1. Select the desired radius curve and the corresponding stick length to use.

2. From stake A, measure 25 feet to B, extending the tangent line at thebeginning of the curve. At right angles to the tangent, set stake C onestick length from the tangent. You now have the rst stake on the curve.

3. At C, measure off the stick length toward the center of the curve and settemporary stake D. From A, sight through D and measure off 25 feet fromD to set stake E (another stake on the curve).

4. At E, measure a stick length toward the center of the curve and setemporary stake F. From C, sight through F and measure off 25 feeF to set stake G on the curve.

5. Repeat these steps until you approach the tangent for the end of thcurve.

6. If the curve does not t on the rst trial, you have several options the curve.

Change the stick length (and thus the curve radius). A longer stimakes a sharper curve; a shorter stick makes a curve of larger ra

Start the curve earlier than stake A or later (at B) to t the topog Try combinations of various starting points and stick lengths.

Temporary stake

Stake on curve

2 5 '

T a n g e n t

Beginning of curve

2 5 ' B

A

C

D

EF

G

Stick length

End of curve

T a n g e n t

Curve Stickradius length

(ft) (ft) 157 2

106 3

80 4

65 5

55 6

2 5 '

2 5 '

Figure 24. The middleordinate curvelocation method


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20

the curve by trial and error. Te correct radius curvewill just touch the centerline o each tangent and willcurve through the area you want the road to cross.For practice, try this on paper with a compass.

In the eld, once you locate the center o thecurve, you can use two tapes or measured ropesto nd the stations along the curve. On moredifficult terrain, such as sharp draws, ridges, andhillside switchbacks, it may be impossible to locate

the center o the curve. In these cases you can usethe middle-ordinate (stick length) layout system.Tis system may be easier to use than locating thecenter o the curve. Figure 24 (page 19) provides aprocedural approach; however, you should be awarethat several trials may be necessary to get the curveto t.

During the process o road construction, itsuse ul to restake the difficult curves afer completingthe right-o -way logging. Te machine operatorwill then be able to construct curves at the proper,designated locations.

Checking road construction

Te time and effort you invest in care ul roaddesign will be lost i your design is not reectedin construction practices. Tus, it is essential tocheck on road construction requently to veri y, or

example, that the road is at the planned grade, curveradii are being satised, and the centerline is in thecorrect position.

Consider this example: your road is underconstruction but is not yet ready to grade. Youcan monitor progress using two approaches. First,you can use a hand level to check the amount ocutting (or lling) completed. Or second, you canuse a clinometer (a device or measuring slope) and

convert the percent reading, along with the slopedistance, to vertical and horizontal measurements.(See able 2, page 18, to convert slope readings andslope distances to vertical and horizontal distances.)Clinometers also give direct readings on road gradesbetween two points on the road (Figure 25). Criticalplaces to check are curves (especially vertical ones),switchbacks, intersections, and steep segments.Using either o these two methods, you then canreestablish the centerline and leave a stake to tellthe operator how much more cutting (or lling) is

needed, in the event there are necessary adjustmentsin the road design.

Monitoring road construction does not meanrigid adherence to eld-location guidelines; the roadconstruction process is not exact. Grades within 1percent and excavation to the nearest oot usually areacceptable. Te most important criterion is whetherthe road will serve the intended unction.

+ 1 1 %

E y e h e i g h t t o e y

e h e i g h t

R o a d s u b g r a d e

Figure 25. Checking road grades


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2012 Oregon State University. Tis publication was produced and distributed in urtherance o the Acts o Congress o May 8 and June 30, 1914. Extensionwork is a cooperative program o Oregon State University, the U.S. Department o Agriculture, and Oregon counties. Oregon State University ExtensionService offers educational programs, activities, and materials without discrimination based on age, color, disability, gender identity or expression, maritalstatus, national origin, race, religion, sex, sexual orientation, or veterans status. Oregon State University Extension Service is an Equal Opportunity Employer.

Revised June 2012. Published July 1983.

Good construction can improve road design.However, ailing to construct portions o theroad within acceptable variances o the designspecications and ignoring the eld layout andlocation markers can result in roads that areproblems or trucking and maintenance activities.

SummaryRoad specications and eld layout and location

are the essence o road design. You may wish todesign simple and small scale road building projectsor seek out pro essional service or bigger, morecomplex projects. Te in ormation provided in thispublication will help you design your own road orsupervise those providing contract services.

For more informationTere are a number o other help ul publications

available on various topics related to themanagement o a timber sale.

OSU Extension Service publications Contracts for Woodland Owners and Christmas

Tree Growers (EC 1192) describes how todevelop a contract and includes samples oour types o agreements: timber sale, logging,temporary road use, and road easement.

Grass Seeding Forest Roads, Skid Trails, andLandings in the Inland Northwest (PNW 628)outlines strategies or establishing vegetationto stabilize erodible areas along orest roadsand skid trails.

Other publications

Managing Woodland Roads: A Field Handbook discusses the major aspects o woodland roadsrelating to their design, inspection, maintenance,and repair. (Oregon State University, 2006).
http://localhost/var/www/apps/conversion/tmp/scratch_5/ir.library.oregonstate.edu/xmlui/bitstream/handle/1957/18894/ec1192.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_5/ir.library.oregonstate.edu/xmlui/bitstream/handle/1957/18894/ec1192.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_5/ir.library.oregonstate.edu/xmlui/bitstream/handle/1957/18894/ec1192.pdfhttp://www.cals.uidaho.edu/edComm/pdf/PNW/PNW628.pdfhttp://www.cals.uidaho.edu/edComm/pdf/PNW/PNW628.pdfhttp://www.cals.uidaho.edu/edComm/pdf/PNW/PNW628.pdfhttp://www.cals.uidaho.edu/edComm/pdf/PNW/PNW628.pdfhttp://www.cals.uidaho.edu/edComm/pdf/PNW/PNW628.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_5/ir.library.oregonstate.edu/xmlui/bitstream/handle/1957/18894/ec1192.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_5/ir.library.oregonstate.edu/xmlui/bitstream/handle/1957/18894/ec1192.pdf

Woodland Slope

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