Understanding Road Cross SectionEveryone involved in gravel road main-tenance must understand the correctshape of the entire area within theroad’s right-of-way. Figure 1 shows atypical cross section of a gravel road.If states have minimum standards orpolicies for low-volume roads, theymust be followed.

In order to maintain a gravel road prop-erly, operators must clearly understandthe need for three basic items: acrowned driving surface, a shoulderarea that slopes directly away from the edge of the driving surface, and aditch. The shoulder area and the ditch of many gravel roads may be minimal.This is particularly true in regions withvery narrow or confined right-of-ways.Regardless of the location, the basicshape of the cross section must be correct or a gravel road will not performwell, even under very low traffic.

Paved roads are usually designed andthen constructed with careful consider-ation given to correct shape of the crosssection. Once paving is finished, the

roadway keeps its shape for an indefi-nite period of time. Gravel roads arequite different. Unfortunately, many ofthem are not constructed well initially.In addition, gravel roads tend to rutmore easily in wet weather. Traffic alsotends to displace gravel from the sur-face to the shoulder area and even tothe ditch during dry weather. Managersand equipment operators have the con-tinual responsibility of keeping theroadway properly shaped. The shape of the road surface and the shoulderarea is the equipment operator’sresponsibility and is classified as routine maintenance.

Keeping the foreslope and ditch estab-lished and shaped is often the mainte-nance operator’s responsibility as well.Obviously, the whole idea here is tokeep water drained away from theroadway. Standing water at any placewithin the cross section (including theditch) is one of the major reasons fordistress and failure of a gravel road.There is sometimes a need for special-ized equipment to do major reshapingof the cross section,especially in verywet conditions. However, the operatorof routine maintenance equipment mustdo everything possible to take care of

Section I:Routine Maintenanceand Rehabilitation

Figure 1: The components of the roadway cross section.

Section I: Routine Maintenance and Rehabilitation 1

2 Understanding Road Cross Section

This road, located in Poland, has very poor cross section with no ditches. Consequently, water drains down the roadway itself and after many years of erosion,the roadway is several feet lower than its original elevation. (Courtesy of Mary O’Neill,Office of Remote Sensing, South Dakota State University)

This well-traveled road in Ecuador performs well in a region that receives approximately

200 inches average annual rainfall.(Courtesy of Ron Anderson, Tensar

Earth Technologies, Inc.,USA)

the roadway since budgets often do notallow for the use of extra equipmentand manpower on gravel roads.

The recommended shape of each part of the cross section will be discussed indetail later in this manual.When a gravel road is maintained properly, itwill serve low volume traffic well.Unfortunately, most gravel roads willfail when exposed to heavy hauls evenwhen shaped properly. This is due toweak subgrade strength and marginalgravel depths which are often problemswith gravel roads. The low volume ofnormal traffic does not warrant recon-struction to a higher standard. However,improper maintenance can also lead to very quick deterioration of a gravelroad, especially in wet weather. Themaintenance equipment operators mustalways work at maintaining the propercrown and shape.

An example of a well shaped gravel road shoulder that slopes away from the driving surfaceand drains water to the inslope and ditch.

Example of a gravel road with good shape of cross section. Notice crown in driving surface andproper shape of shoulder and ditch.

Understanding Road Cross Section 3

moisture, material, and subgrade stab-ility vary; therefore, the maximum speedfor good maintenance can vary.

However, in virtually any condition, it isdifficult to exceed 5 mph and still do agood job.

Moldboard AngleThe angle of the moldboard is also criti-cal to good maintenance. This angle isfixed on some grading devices, but onmotorgraders it can be easily adjusted.It is important to keep the angle some-where between 30 and 45 degrees. It isa challenge to recover loose aggregate

The primary focus of this section will be the use of the motorgrader

for gravel road maintenance. However,there are other devices used for the job that can work well. Front or rearmounted grading attachments for tractors, road rakes, and other devicesof various designs are used in someareas of the country. The principles ofshaping are the same no matter whatmachine is used.

Operating SpeedOperating speed in blading operationsmust not be excessive. This has causedproblems on many roads. It is virtuallyimpossible to do good work above atop speed of 3 to 5 mph.When themachine begins to “lope” or bounce,it will cut depressions and leave ridgesin the road surface. Conditions including

Routine Shaping Principles

Grader operator cleaning a ditch and restoringshape to the foreslope and backslope.

The distortion that was cut into this road surface is the result of operating a motorgradertoo fast.The angle of the depressions whichmatch the angle of the moldboard reveal this.This is not the same as “washboarding,” whichhas different causes.

4 Routine Shaping Principles

This is an example of poor use of the grader.The moldboard is pitched back too far and is not angled enough.Notice the gravel builds upand does not fall forward to give a good mixingaction.Also, the loss of material from the toe of the moldboard will create a high shoulder,which destroys good drainage across the shoulder to the ditch.

This is the other extreme of pitching the moldboard too far forward.The material will notroll across the face of the moldboard and doesnot mix.In addition to this, the cutting edge willnot easily penetrate a hard surface, making ithard to trim out even light depressions in theroad surface. It simply tends to skip along thesurface with no real benefit.

Moldboard pitch or “tilt” refers to how much themoldboard is tipped forward or backward.The

right pitch ranges from aggressive cutting (1), tospreading (2),to light blading or dragging action

(3) for maintenance of gravel roads.

Routine Shaping Principles 5

1

2 3

Notice these examples of good pitch and angle. The gravelfalls forward and moves across the moldboard very well.

The cutting edge is close to vertical from the road surface,which makes a nice light trimming action for routine

maintenance, and the angle is good,not allowing material to spill from the toe of the moldboard.

from the shoulder of the roadway with-out spilling material around the leadingedge (toe) of the moldboard. Operatingwithout enough angle is a primarycause of this spilling.

Moldboard PitchAlong with correct angle, it is importantto understand proper pitch or “tilt” of amoldboard. If the moldboard is pitchedback too far, the material will tend tobuild up in front of the moldboard andwill not fall forward and move along tothe discharge end of the blade. This alsocauses excess material loss from the toeof the moldboard.It also reduces themixing action that is desirable when

recovering material from the shoulderand moving it across the roadway, level-ing and smoothing it in the process. Thismixing action is part of routine mainte-nance. Traffic tends to loosen materialfrom the road surface and displace it tothe shoulder area as well as betweenthe wheel tracks. The stone will tend to

separate from the sand and the fine-sized material.At the same time, smallpotholes and an uneven surface willdevelop. It is the job of the maintenanceoperator to recover the material, mix itagain as it rolls along the face of themoldboard and restore good surfaceshape.

6 Routine Shaping Principles

Routine Shaping Principles 7

Figure 2:Illustration of an articulated motorgrader. (An illustration showing additional components of a motorgrader and recommended walk-around checks is shown in Appendix E.)

Motorgrader StabilityIt can sometimes be hard to keep amachine stable, especially while carry-ing a light load of material. Counter-acting machine bounce or “loping”requires experience in knowing thecause and then finding a solution.If a motorgrader begins to rock from sideto side — often called “duck walking”in the field — it is usually caused byblade angle that closely matches theangle from corner to corner of the tireson the rear tandems. The solution isgenerally to stop, change angle slightlyon the moldboard and slowly resumeblading. Simply reducing speed willoften eliminate the loping effect of amachine. Experimenting with differenttire inflation pressures can also helpstabilize a machine as well as leaningthe front wheels in the direction thatmaterial is being moved. Filling tireswith liquid ballast to about 70%

capacity is sometimes done to increasetraction, weight and stability of thegrader. The ballast often used is a solution of calcium chloride and water.Stability problems that are constant andsevere should be brought to the atten-tion of your equipment dealer and/ortire supplier.

ArticulationVirtually all modern motorgraders areequipped with frame articulation. It canbe an advantage to slightly articulatethe machine to stabilize it even in acommon maintenance operation.

If a maintenance windrow is allowed by policy and used, try to keep it as

light as possible. These examples show a light windrow being placed at the edge of the roadway and anobviously excessive windrow being

left at the roadside. In the latter case,multiple passes should have been made to work out the vegetation and spread more of the material

on the roadway, or perhaps some mechanical means of breaking up

the lumps of sod such as a disk should have been used to allow

more of the material to be spread on the roadway.

8 Routine Shaping Principles

accepted practice in some regions. Inothers, it is disapproved of and depart-ments may even have policies forbid-ding windrows. This is often true inregions with narrow right-of-ways andnarrow driving surfaces. Operatorsshould follow department policy at alltimes. For those who allow the use ofwindrows, it is very important to keepthem to a minimum. It can be very diffi -

WindrowsIn some areas of the country, particular-ly arid or semiarid regions, it is commonto leave a small maintenance windrow,sometimes referred to as an inventorywindrow. This leaves a small amount ofmaterial to be picked up next time andworked back across the road for fillingsmall depressions. This is a commonly

cult to define what is acceptable andwhat is an excessive windrow. Thewindrow should also be placed near theedge of the roadway to allow as great a width for travel as possible. In theabsence of a policy on this matter, beaware of the commonly accepted prac-tices in your region and try to deviate as little as possible.

Establishing proper crown in the gravel surface probably generates

more controversy than any other aspectof good maintenance. How much crownis enough? Can one get too much?What is a recommended crown? Theseare frequently asked questions by localofficials, the traveling public, and equip-ment operators.

First of all,problems develop quicklywhen a gravel road has no crown.Water will quickly collect on the roadsurface during a rain and will soften thecrust. This will lead to rutting which canbecome severe if the subgrade alsobegins to soften. Even if the subgraderemains firm, traffic will quickly poundout smaller depressions in the roadwhere water collects and the road willdevelop potholes. A properly drainedgravel road should have crown.

Yet an operator can also build too muchcrown into the road surface. This canlead to an unsafe condition in whichthe driving public does not feel comfort-able staying “in their lane”or simplystaying on the right side of the road.Because of the excessive crown,driversbegin to feel a slight loss of control ofthe vehicle as it wants to slide towardsthe shoulder. There is additional risk driving on gravel roads with excessivecrown in regions that experience snowand ice cover. For these reasons driverswill tend to drive right down the middleof the road regardless of how wide it is.

Crown

A road that lacks good crown.There is also centerline corrugation (washboarding),a problemthat will grow worse when there is inadequate crown.

A gravel road with a 26-foot driving surface, yet everyone drives in the middle. The primary rea-son is excessive crown.

Crown 9

Problems from center wear in cutting edge.

This road located in New Zealand does not have adequate crown to drain water to the roadside.Consequently, potholes form. (Courtesy of Ken Skorseth,SD LTAP)

10 Crown

What then is recommended crown?Recommendations from supervisors and skilled operators across the countryindicate that at least 1/2 inch of crownper foot (approximately 4%) on thecross slope is ideal. It is also recognizedthat it is virtually impossible for anyoperator to maintain an absolutely uniform crown. However, try to deviateas little as possible. There are crowngauges available which can be used todetermine existing crown. There are also very sophisticated electronic slopecontrols available for graders. These are found more often in constructionoperations than in maintenance, butcertainly can be used for maintenance.

There is one further problem with crown that needs to be discussed.The ideal shape is a straight line fromthe shoulder up to the centerline of the road. This gives the road the sameshape as the roof of a house, oftenreferred to as a flat “A” shape. However,this shape can sometimes becomerounded. The engineering term for thisis “parabolic crown.” This is virtuallyalways a problem. The middle portion of the road will have considerably lesscrown than the outer edges. Water willnot drain from the middle and potholesand ruts will form. The greatest cause of parabolic crown is excess wear at the center of the cutting edge. This isnormal wear and will vary with types of gravel, width of road, wheel pathlocation and other factors. A good operator will make an effort to avoidthe parabolic shape on a roadway bykeeping the cutting edge straight.

Roadway with parabolic crown.The outer edge of the road slopes too much. Gouging causeshigh shoulder, and center 1/3 of the road tends to be flat.

This road in New Zealand performs remarkably well because of good crown and good gravelquality in a region that receives nearly 150 inches of moisture a year! (Courtesy of Ken Skorseth,SD LTAP)

Crown 11

A simple method is to use a cuttingtorch and straighten the cutting edgewhenever 1/2 to 3/4 inch or more of center wear exists. Another method is to use a thicker, harder section of cutting edge in the middle of the moldboard to resist wear. This willretard excess center wear, but generally will not eliminate it.

Another option is to use the moderncarbide-tipped bits on the cutting edge. These are extremely wear-resistant and dramatically reduce center wear. There are also carbideinsert or carbide-faced cutting edgesthat are very wear-resistant.

In summary, the recommended crown is a straight line from the shoulder to the centerline that risesapproximately 1/2 inch per foot (or approximately 4%).

The photos above and below show good examples of gravel shoulders that match the edge ofthe roadway very well and drain water to the ditch.

12 Road Shoulder

The road shoulder serves severalessential functions. It is there to

support the edge of the traveled portionof the roadway. But another importantfunction is to provide a safety area fordrivers to regain control of vehicles ifforced to leave the road surface. Yetanother important function is to carrywater further away from the road surface to the foreslope and ditch.

In order for the shoulder to perform all of these functions, its shape is critical. First of all, the shoulder shouldmeet the edge of the roadway at thesame elevation. In other words, theshoulder should be no higher or nolower than the edge of the roadway.By maintaining this shape, the lowshoulder or drop-off is eliminated which is a safety hazard and alsoreduces roadway edge support.But the other extreme, which is a high shoulder, should also be avoided.This will be discussed later.

It is also recognized that gravel roads in some regions, particularly those withvery narrow right-of-ways, have very little shoulder area. In some cases, theedge of roadway is actually the begin-ning of the foreslope down to the ditch.But here again, it is important thatthere is not a steep drop-off or a ridgeof soil to block drainage. Maintainingshoulders is a critical part of gravel road maintenance.

Road Shoulder

High Shoulders(Secondary Ditches)This problem can be seen along gravel roads almost anywhere people travel. There are many slangterms used in the field such as “berms”or “curbs.” The engineering term for this condition is “secondary ditch” andit is a good description of the condition.When a gravel road develops a highshoulder, it destroys the drainage ofwater directly from the surface to thereal ditch. This causes several problems.In relatively level terrain,the water collects here and seeps into the sub-grade, often causing the whole roadwayto soften. In rolling and rugged terrain,the water quickly flows downhill alongthe secondary ditch,often eroding awaya large amount of gravel and even

eroding into the subgrade. This also creates a serious safety hazard. Thereare many reasons to work hard to eliminate secondary ditches.

A common condition along the edge of manygravel roads:the secondary ditch.

Secondary ditch over six inches deep.

Road Shoulder 13

Here, water has run down a secondary ditchor high shoulder and then eroded throughthe shoulder material at the bottom of a hill.This creates a hazardous condition.

vegetation on the shoulder, simplyextend the moldboard out into theshoulder material and begin to pull itonto the roadway. If the amount ofmaterial is light, you may be able to dothis in one pass. The material recoveredis often good gravel that needs to bereturned to the roadway surface.

14 Road Shoulder

Causes of High ShouldersWhat causes secondary ditches to form?There are several causes. They candevelop from improper maintenancesuch as losing material from the toe ofa grader’s moldboard,which builds up ahigh shoulder, or from cutting too deepat the shoulder line with the toe of themoldboard. This is a particular problemwhen the cutting edge is not kept reasonably straight. But there are othercauses, such as excessive “whip-off” ofloose material from fast traffic,whichtends to build up along the shoulderline. Also, heavy loads on gravel roadswith weak subgrades can cause this.When heavy vehicles have to travelnear the shoulder while meeting othervehicles, the roadway can rut while the shoulder area shoves upward. Yetanother cause is the buildup of sand innorthern regions where winter ice/snowcontrol requires some winter sandingoperations on gravel roads. An expert in the field once made this statement:“It is difficult to completely eliminatesecondary ditches, but it pays to workhard to keep them to an absolute minimum.” This is excellent advice.The time spent in dealing with a highshoulder (secondary ditch) will result in a road that is easier to maintainafterwards. But the real challenge isgetting the job done.

Recovering and Spreading on RoadwayIf a motorgrader is the only piece ofequipment used on the job, generallymore than one pass will be required torecover material from high shoulders.It is wise to place standard MUTCDwarning signs such as “Road WorkAhead” since this is more than routinemaintenance. If there is little or no

Using grader to recover material from a highshoulder and restore correct shape to theshoulder.

A commercially manufactured rock rake,normally used in farming operations.

Breaking up Sod and Vegetation inRecovered MaterialQuite often, the material pulled outonto the roadway from the shoulder isvery hard to spread because of the veg-etative material in it. It will require mul-tiple passes with the grader to get thejob done. Many agencies are turning toother mechanical means of breaking upthe material to make the road safe fortraffic. This can range from somethingas simple as a disk or drag to sophisti-cated pulverizing equipment.

Windrow pulverizer fabricatedby the Hyde County HighwayDepartment of Highmore,South Dakota.

Road Shoulder 15

A commercially manufactured pulverizer.

A small rear-mounted tandem disk on a mower tractor.

material loose, pull it onto the roadwayand then load and remove it. However,this can be very expensive. It is some-times acceptable to pull the materialand cover it. In several areas of thecountry, a method called “sweeping it

16 Road Shoulder

under the carpet”is used. The followingphoto sequence shows how “sweepingit under the carpet”is done.

Make sure that the soils are suitable to be used as base material under theedge of roadway and shoulder beforedoing this. If you’re not absolutely sure,try this on a test section of 1000 ft.or less to see how it performs. Thismethod works best when there is a lotof sandy soil both in the subgrade ofthe roadway and also in the materialrecovered from the high shoulder. Thesand will be unsuitable to recover andspread onto the roadway, but will bereasonably easy to cut and place underthe gravel that will be placed back over it. If the road is scheduled to beregraveled, it is an excellent time to do shoulder work to get the roadwayback into good shape.

Again, this is much more than routinemaintenance and signs should beplaced to warn motorists of roadworkbeing done. A better option would be to close the section of road beingworked on if possible.

The existing secondary ditch isthen cut slightlydeeper and thematerial is placedin the ro a d w a y.

The windrowed gravel is then brought backover the recovered material and the roadwayis restored to proper crown and shape. Thehigh shoulder has been eliminated.

The material from the high shoulder is then pulled into the cut that has just been made.G e n e ra l l y, this material will have to be worked several times with the grader to break it upenough to spread evenly.

The existing surfaceg ravel is cut looseand windrowed to

the opposite side of the ro a d .

Pulling Shouldersand CoveringThe material from a high shoulder is not always suitable to be reused on the roadway. It may be best to cut the

Notice the dramatic difference in the road shoulders shown above and below. It becomes somuch easier to recover gravel that has drifted to the edge of the roadway when the vegetationhas been cut cleanly. It is particularly important to get rid of the vegetation prior to a shoulder-pulling operation.

Road Shoulder 17

Benefit of MowingAny of the procedures discussed fordealing with high shoulders are mucheasier to accomplish if a good job ofmowing is done in advance. This is trueeven in routine maintenance operations.When grass or other vegetation growshigh along the edge of the roadway, itbecomes difficult to maintain a clean,uniform shoulder line. In a survey ofoperators in the state of Iowa, mowingthe shoulders on gravel roads ranked asone of four primary functions needed tomaintain a good gravel road! (Keepingproper shape, drainage, and straightcutting edges were the other three.)

The frequency of mowing depends onthe region of the country and the cli-mate. However, the cost of mowing isoften offset by reduced costs of othermaintenance as well as safer roads.In northern plains regions, there is yet another great benefit to mowing.By removing the standing vegetation,drifting snow will not be trapped on the roadway and snow removal costscan be drastically reduced. The bestequipment for this is rotary or flailmowers, which do a good job of shredding the vegetation and are not as easily damaged or plugged by roadside trash.

Gravel roads are generally main-tained by routine blading and

adding gravel as needed either by “spot graveling”or regraveling entiresections. However, almost any gravelroad will gradually begin to show dis-tress that requires more than routinemaintenance to correct. The most com-mon problems that develop are“berms” or secondary ditches that buildup along the shoulder line and the shift-ing of material from the surface to theshoulder area and even onto the inslopeof the grade. This comes from gravelbeing displaced by traffic, winter plow-ing operations, erosion of material dur-ing heavy rain and sometimes frompoor routine blading techniques. Thisoften causes major problems withdrainage. At certain intervals, virtuallyevery gravel road requires some majorrehabilitation. (35, 36)

Reshaping Surfaceand Shoulder These can usually be corrected with the motorgrader alone. Spring is thebest time for this as there is minimalvegetative growth and moisture is present. The reshaping of the drivingsurface and the road shoulder can bedone by cutting material with themotorgrader and relaying it to the proper shape and crown.If possible,the use of a roller for compaction willgreatly improve the finished surface.This will leave a denser, stronger,smoother surface that will be easier to maintain.

Reshaping EntireCross SectionSevere rutting,loss of crown, gravel loss and deep secondary ditches — a combination of any two or more ofthese calls for a major reshaping. Thisrequires a much greater effort.It oftenoccurs after a gravel road has been subjected to an unusually heavy haul.This will be worse if a heavy haul occurs during wet weather.

Major reshaping often has to be doneon the entire cross section and it mayhave to be done immediately regardlessof the vegetative growth. Motorgraders,disks, pulverizers/mixers and rollers areoften needed. These are not always

available, but certainly make the jobeasier. The field supervisor’s knowledgeand the operator’s skill in knowing howto rebuild the cross section becomesvery important. These projects seldomhave the benefit of much planning ortechnical assistance. There is seldomany surveying or staking done. But it isvery important to rebuild a uniformcross section and pay attention torestoring good drainage. Only after thisis done — and done correctly — shouldgood surface gravel be replaced.

Gravel Road Rehabilitation

This gravel road shows severe distress after being subjected to a heavy haul from trucks haulingwheat to a grain elevator. The problem was made worse by an unusually wet season.

18 Gravel Road Rehabilitation

Gravel Road Rehabilitation 19

Erosion ControlHaving discussed the importance of reshaping a gravel road, there is another issue that must be addressed.When major reshaping is done out-side of the traveled way, vegetation and ground cover will obviously be disturbed. This can lead to erosion ofsoil. The problem will vary depending on the region. In arid and semi-aridareas, the problem is small or non-existent.Areas which receive frequentrains, have rolling or rugged terrain,and have highly erodible soils, are particularly vulnerable. When vegetativecover is disturbed,there are problemsthat can arise. While trying to eliminateproblems, new ones can be createdsuch as clogged culverts and blocked

ditches, pollution of streams and lakes,and eroded slopes which can shortenthe life of improvements. You may befound in violation of state and federalregulations. Damage claims and law-suits may be filed.

The solution to this issue is not to cancel plans for gravel road improve-ment,but to plan your work carefullyand use methods of reducing or eliminating erosion. Here are somethings to consider:

• Some regions have certain times in the year when frequent and heavy rainfall can be expected. Try to avoid major reshape work during those periods of time.

• Keep disturbed areas small. The more earth you disturb, the greater will be the risk of soil erosion. Set work boundaries and don’t let work crews get outside of them.

• Consider stabilization of disturbed areas. Silt fences, mulching, erosion control blankets and other means should be considered.

• Keep water velocity low. Removing vegetative cover and topsoil generally increases the amount and speed of runoff. Keep slopes as shallow or gentle as possible. Keep ditch slope as gentle as possible. Shorten drainage runs and work to get vegetative cover reestablished as soon as possible after work is finished.

• Keep sediment within work bound-aries. Sediment can be retained by filtering water as it flows (as through a silt fence), and ditch checks will retain dirty runoff water for a period of time until the soil particles settle out.

• Inspect recent work. This is vital to make sure channels haven’t formed in ditch bottoms or on slopes, oraround and under controls that were used. Be particularly vigilant after heavy rains.

The same road as shown on the previous page approximately three months after the heavy haulwas finished.The road was restored to remarkably good shape simply with the use of motor-graders doing a complete reshaping of the inslope, shoulder and surface with a small amount of surface gravel added.

There are special situations in gravelroad maintenance that should be

addressed. These are common to nearlyall gravel roads and it is important tounderstand how to deal with them.These concerns are unique to gravelroads and practical solutions are recommended for each of these.

Dealing with Corrugation

The technical term is corrugation, butvirtually everyone in the field refers tothe problem as washboarding. Thisproblem can bring more complaintsthan any other. It is very annoying tothe driver and, when it becomes severe,can lead to loss of vehicle control.

It is impossible to deal effectively withthis problem if you do not understandthe causes. Motorgraders are oftenblamed, but in reality, they seldomcause the problem.

There are three primary causes: the driving habits of people, lack of mois-ture, and poor quality of gravel. Drivinghabits are clearly evident when youobserve washboarding at intersections,going up or down steep hills, leadinginto or out of sharp curves and some-times even near driveways. These are allplaces where drivers tend to acceleratehard or brake aggressively. This is amajor cause of washboarding. (24,33,35, 36)

Lack of moisture will encourage wash-board formation and prolonged dryweather can really aggravate the problem. This is because the crust that

Areas of Concern

This type of corrugation,“washboarding,” is caused by lack of moisture, hard acceleration,aggressive braking, and poor quality gravel.

This type of washboarding appears at an angle across the roadway with ridges and depressionstwo to three feet apart.It is caused by excess grader speed.

20 Areas of Concern

Areas of Concern 21

It is a good practice to loosen,mix, reshape gravel in a washboard-prone area while it is moist.

Another washboard-prone area is at the transition from paved to gravel sections as shown inthis photo.

An effective tool for dealing with washboard areas is the front dozer equipped with carbide bits.

forms on the surface of a good gravelroad will tend to loosen in dry weather.This allows the stone and sand-sizedparticles of gravel to “float” and thematerial can easily align itself into the washboard pattern under traffic.

The two causes just mentioned arecompletely out of the control of gravelmaintenance operators and managers.The third primary cause — the qualityof the gravel — is the cause we needto concentrate on. Good quality sur-face gravel is thoroughly discussed in Section II of this manual. Simply put, good gravel must have the rightblend of stone, sand, and fines. Thestone should be fractured and the fine-sized particles should have a binding characteristic, technically called “plasticity.” This type of gravelresists washboarding. However, themaintenance operators also must dotheir part.

Virtually any gravel will develop somewashboard areas under traffic. The keyfor the maintenance operator is tostrive to keep the material blended.In dry conditions, the operator can only smooth the road temporarily.When moisture is present, it pays to quickly get out and rework theseareas. The material should be cut to a depth of one inch or more below the depressions, mixed and relayed tothe proper shape. If time allows, usingthe machine to apply wheel compactionto material will help reform the crust.If possible, use of a roller will improvethe compaction.

With the best of maintenance, wash-boarding can never be completely elimi-nated.However, the key to reducing it is

to work hard at obtaining quality gravelwith a good binding characteristic. Theoperator can then reshape trouble spotswhen moisture is present and mostroads will perform quite well.

If a motorgrader causes washboarding,it is almost always the result of runningat too great a speed. The ridges anddepressions will be spaced furtherapart.

The solution to the problem is simple — reduce grading speed! Another problem can be improper tire inflationpressure or defective tires. This willcause a motorgrader to bounce or oth-erwise operate in an unstable manner.

IntersectionsThere is one important thing to under-stand in knowing how to shape a gravelintersection: is it a controlled or uncon-trolled intersection? This means: doestraffic have to stop or yield from sideroads? If so, it is a controlled intersec-tion as shown in Figure 3. The primaryroad on which traffic passes throughshould retain its crown and the inter-secting roads should have crown gradu-ally eliminated beginning approximately100 feet before the intersection.At thepoint of intersection, the side roads arevirtually flat to match the primary road.When the intersection is uncontrolled as shown in Figure 4,the roads shouldall have the crown gradually eliminatedbeginning approximately 100 feet fromthe intersection. The intersection itselfbecomes virtually flat, allowing vehiclesto pass through without feeling anoticeable hump or dip from any direction. Be careful not to makethe intersection lower so that water collects there.

Figure 3: Proper shape of a controlled intersection.Notice through-road retainscrown;side roads whichhave stop or yield signs are shaped to match the edge of through road.

Figure 4: Proper shape of an uncontrolled intersection.Eliminate crown from all directions approaching the intersection.

22 Areas of Concern

Areas of Concern 23

Intersections with Paved Roads

The rule for shaping these intersections is always the same. Begin to eliminate crown on the gravel road approximately 100 feet from the edge of the pavement.At the intersecting point, the gravelshould match the paved surface. This requires continual attention since pot-holes can easily develop at the edge of pavement. However, be careful not to push gravel out onto the pavement since this causes a dangerous loss of skid resistance on the pavement.(35,36) The technique of “backdragging” is useful in these operations. In order to fill a pothole at the edge of pavement,extra material may spill onto the pave-ment. Simply pick up the moldboard and set it down in front of the material, thenback up and spread the excess back on the gravel road.

Figure 5: Illustration of a gravel road inter-secting a paved road. Gradually eliminate the crown on the gravel road to match the edge of the pavement.

Hand work with a shovel is necessary at times to complement grader work.

The grader must fill potholes and depressionsformed near the bridge approach.

Nice job of blade work to shape road to matchbridge deck.

The technique of backdraggingcan save time.

Bridge ApproachesOnce again, the rule for shaping abridge approach is always the same.Approximately 100 feet from the bridge,begin to gradually take the crown outof the gravel road so that you canmatch the bridge deck as closely aspossible. Potholes can easily form at the edge of the deck. Keep them filled,but don’t push gravel onto the deck.(35, 36)

24 Areas of Concern

Areas of Concern 25

Superelevation at CurvesThis is one of the biggest challenges ingravel road maintenance and a situa-tion that is not understood very well bymany operators. This is sometimescalled “banking a curve” in the field.The outer edge of the roadway is higherthan the inside edge and the road sur-face is shaped straight from the upperto the lower edge.

Once again, as the operator approachesa curve, adjustments should be madewith the blade to take out the normalcrown and begin to transition into astraight, superelevated surface. Thisshape should be maintained uniformlythroughout the curve. A gentle transi-tion is then made made at the otherend back to a normal crowned road surface when you are once again on

This photo shows lack of superelevation which can lead to accidents.

Figure 6: Illustration of the transition from a normal crown to the superelevatedshape needed in a curve.

a straight section of road. This requiresconstant attention during each mainte-nance pass over the road. Traffic willtend to displace the gravel towards theupper end of the road and the inside ofthe curve will become lower. Curves canvery easily go out of proper shape. (1, 5,7, 21, 24, 29, 36)

This superelevated road section makes driving safer.

This road in Ecuador hasexcellent superelevation inthe curve. It also has goodshoulder drainage and ditch-es on both sides of the road.(Courtesy of Ron Anderson,Tensar Earth Technologies,Inc.,USA)

The correct amount of slope or “bank-ing” of a curve can only be determinedby engineering analysis. There is also a device available for determining the safe speed of a curve called a ball bank indicator. If you are unsure of correct shape on a curve, get pro-fessional advice if at all possible.

26 Areas of Concern

Areas of Concern 27

Railroad CrossingsMaintaining a road that intersects a rail crossing is very similar to bridgeapproaches or intersections with pavedroads. Always begin to eliminate crownapproximately 100 feet away and shapethe road to match the crossing.A spe-cial consideration is to be extremelycareful about keeping gravel out of theflangeways along the rails. This cancause a derailment — particularly whenit combines with snowpack in northernregions of the country. Also, be extreme-ly careful not to strike the rails them-selves. In some cases, this could slightlydisplace the rails and again could causea major disaster. If you snag or strikea rail with your equipment, report itimmediately to your supervisor and the railroad. (35, 36)

DrivewaysThe public road should always retain itsnormal crowned shape while passingdriveways. Too often the gravel buildsup on the road at a driveway entranceas shown in Figure 7. This changes theshape of the roadway itself, which cancause loss of control of vehicles. Thesesituations need to be reshaped. The driveway entrance should always matchthe edge of the public road as shown in Figure 8. (35, 36)

In heavily populated areas with gravelroads, poor installation of drivewayscan be a real problem. To reduce main-tenance problems, implement a permit-ting process. It should address the proper control of grade to match roadedge, adequate width, and drainage.

The solution to the problem shown inFigure 8 is demonstrated in a simplethree-step operation which is shown on the next page.

Grader working at a rural railroad crossing. The material that has been pushed into the flange-way should be removed.

Figure 8: Proper matching of driveway and road edge

Figure 7: Improper matching of driveway and road edge

Step 1. The operator restores the crownon the public road by removing excessive

material extended from the driveway.Note the drop off created by

this operation.

Step 2. The operator proceedsto correct the drop off at theend of the driveway by cuttingthe material loose and spreadingit back on the driveway.

Step 3. The above two steps result in a well-shaped driveway that matches

the edge of the public road.

28 Areas of Concern

Areas of Concern 29

Cattle GuardsA simple structure called a cattle guardis common in parts of the high plainsand mountain west in the US. Thesedevices are commonly found on lowvolume roads in national forests and onpublic lands where cattle or other live-stock are allowed to graze on openrange. The cattle guard allows traffic topass from one parcel of land to anotherwithout opening and closing gates. Thecattle guard is a series of heavy ironbars or pipes placed across the road-way, that generally appear like a heavygrate. There is a cavity below the barsor pipes that is generally twelve toeighteen inches deep. These structuresconfine cattle and other livestock since,by instinct, they will not cross them forfear of falling through the grate.

Cattle guards are a special maintenancechallenge when installed on gravelroads. The approach to them should betreated much like blading up to a bridgedeck. Begin to eliminate normal crown50-100 feet from the guard. The roadmust then be shaped to match the cattle guard. However, gravel mustnever be spilled into the cavity belowthe grate. If this is done repeatedly, the hollow area below will be filled withgravel and cattle will simply walk out.Stop the grader two to three feet fromthe guard and backdrag loose materialaway from the structure. Then, hand-work will often have to be done at theedge of the cattle guard to maintain a smooth crossing for traffic.

Example of good workdone to reshape a roadway approaching a cattle guard andmaintaining a verysmooth crossing.

30 Areas of Concern

passes over the surface and the roaddeflects under the load.Pressure fromthe load will cause water in the sub-grade to rise to the surface and carryfine soil particles with it. This will contaminate and weaken the newmaterial very quickly and make it weak, undrainable, and unstable.A fabric prevents this by filtering

Soft and Weak SubgradeAlthough it is extremely important toremove surface and subsurface waterfrom the roadways, there are situationswhere water simply cannot be keptaway. A good example is a section ofroad that passes through swampland or wetlands which naturally occur andcannot be drained. These areas will very often have weak subgrades, whichcannot support heavy loads. Sometimesit is even hard to maintain the road forlight traffic. The road will rut and pot-holes will be formed very quickly due to very poor soil support.

This requires more than routine main-tenance and reshaping if the problem is to be fixed permanently. Generally,there are only two solutions. One is toexcavate and remove the weak, wetsoil. Occasionally, the existing roadwayis wide enough that after adding selectmaterial and shaping, the top width ofthe finished surface is adequate. In thiscase, undercutting will not be necessary.This “select material” will vary depend-ing on what is available in the region.One thing is critical: it must be cleanand drainable. It is also advisable to get engineering advice from consul-tants to make sure that materials are adequate before starting this rehabilitation challenge.

The second method is similar, except a product called a geotextile or geo-synthetic is added. These products areoften called “fabrics” and “grids” in the field. Here the procedure is virtuallythe same as described before, but a fabric and/or grid is placed over thesubgrade soil before the select materialis brought in.A woven or nonwovenfabric (geotextile) placed on the sub-grade becomes a separator between

the weak soil and the new materialplaced above it. The five photos shownon this and the next page demonstratethe proper sequence of placing geotex-tiles as explained in the following para-graphs. This prevents very fine, wet siltand clay type soils from pumping ormigrating up into the new material.The pumping action occurs when traffic

A decision was made to stabilize the above road.A road crew is shown rolling out a fabric overthe existing road surface.

This gravel road with narrow right-of-way has turned to mud during wet spring conditions. Itrepresents low-volume roads commonly found in several parts of the world.

Areas of Concern 31

A truck is shown back-dumping a select,granular material onto the fabric.

The crawler/loaderwas used to spreadthe material overthe fabric and isnow being used topull a grid roller tosmooth the surface.

The road now performs very well after the stabilization was completed.

out the fine soils while allowing water to pass through it and drain out of the clean, granular material above.

A grid can also be used either in combination with or without fabrics.Grids are very strong geosyntheticswhich, in simplest terms, confine thematerial placed on them and do notallow lateral movement or “shoving”of the material.Grids have been rolledout over swamps and roads built overthem with remarkably good results.The ability to carry and distribute thesoil and traffic load is referred to as a snowshoe effect.Grids can also beplaced within layers of select material.There are many types and variations of these products. It is wise to get goodengineering advice when dealing withdifficult soil stabilization problems.

Once the subgrade has been strength-ened, a good coat of surface gravel can be placed and the road can bemaintained as any other gravel road.The initial cost of stabilizing a weakroad section can be expensive, but itwill result in low maintenance coststhereafter, and will often make theseprojects cost effective.

Workers are shown using a combination of grid and fabric being placed over anextremely weak subgrade. This is in a regionof Ecuador that receives average annual rainfall of nearly 200 inches. Approximatelytwelve inches of select, clean sand-typematerial will be placed over the grid to serveas a base. The fabric will be wrapped overthe side of the sand layer to keep the edgefrom eroding away. Then another layer ofgrid will be placed and covered with approxi-mately ten inches of crushed surface gravelwhich will become the driving surface.

Here is the finished road which has performedremarkably well while being used to carryextremely heavy loads during construction and equipment for oil field development.It is a good example of how an extremely weak subgrade can be stabilized and a gravelroad built over it with minimum disturbance to the surrounding terrain and the environment.

(Photos on this page are courtesy of RonAnderson, Tensar Earth Techologies, Inc.,USA)

A section of the same road during construction.Select material is being

placed over the grid and fabric. Noticethe evidence of extremely weak

subgrade shown by the rut at the bottom of the photo. This rut was

left by a light vehicle which traveledbeyond the stabilized section.

Yet this road will have to carry oil field traffic when finished.

32 Areas of Concern