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For a road to be kept in first class travelling condition it must be well constructed and well maintained. The amount of maintenance necessary after construction can be reduced by a high standard of construction. However, a road constructed to a high standard but neglected after construction will soon fall into disrepair. Maintenance, to be successful, must be planned and organised.
Many factors influence the management of road maintenance and thus make it a complex operation. Funds available for maintenance never seem to be sufficient and are always subject to conflicting demands.
Maintenance can be divided into three types according to the mode of management:
This is maintenance which cannot be predicted or planned in detail but which is assessed on the basis of accepted levels of service. It includes such things as pothole repair, grading gravel or earth shoulders, controlling vegetation, washing or renewing signs, and painting road linemarking.
Special maintenance can be predicted and planned and is therefore able to be subjected to rigorous planning. Typical examples of special maintenance are asphalt overlaying, bitumen resealing, and shoulder resheeting.
Restoration work seeks to repair damage caused by events beyond the control of the road authority. Typical examples are restoration of roads and bridges after scouring by floods, removal of fallen trees after wind or lightening storms, and replacement of road furniture after bushfires.
Routine maintenance and the routine component of special maintenance are usually organised and performed by permanent maintenance gangs or patrols, whereas the specialised tasks in special maintenance and restoration will usually be done by specialist gangs. Permanent maintenance gangs consist of 3 or 4 men equipped with a truck and hand tools. They operate over a defined length of road, or area of road network. The system is largely self managing with the pride of the gang in the condition of its stretch of road being very important.
Maintenance planning, to ensure best value for the limited funds available, involves a number of steps.
Step 1. Establishing Standards
Quality standards need to be defined which indicate the level of road defects at which maintenance action is justified. Standards need to define the severity levels for road defects at which either maintenance action is justified or at which rehabilitation is warranted, i.e. the levels at which intervention is necessary. The severity of deficiencies which can be tolerated is influenced by various factors such as road classification, climatic conditions, soil type, form of construction, and the volume and type of traffic using the road. It is therefore not practical to adopt one universal standard which applies to all road types and conditions.
Step 2. Assessing the Condition of the Road Network
This is generally done on a regular basis. The condition of each road, or section of road, is evaluated against the standards established in (1), and required maintenance action is determined. For the establishment of annual programmed maintenance works, inspection may be carried out at twelve month intervals. However, the need for routine maintenance action (e.g. repair of potholes) can arise fairly quickly, and more frequent inspection is needed to ascertain the requirements for this type of work.
Step 3. Planning and Budgeting
From the data gathered in the assessment of the road network, priorities for maintenance work can be established and maintenance plans prepared. An annual plan is usually required, although a longer planning period can be used (e.g. 5 years) incorporating annual reviews.
Step 4. Executing Maintenance Work
Road maintenance work may be carried out by day labour forces or by contract.
Step 5. Measuring and Recording Work Done
This provides data for future work, planning and expenditure monitoring. Data is required on work carried out, road conditions prior to and after maintenance intervention, materials used workmanship, costs, etc.
The drainage system is a most important part of any road. Its functions include:
It is a principle of good drainage practice that the concentration of water should be increased as little as possible. When, because of road works, increased concentration is unavoidable the flow should be so controlled that it does not cause scouring or other damage. As a general rule it is good practice to interfere as little a possible with the natural flow of water. Water flowing towards a road formation should be allowed to return to its natural course as soon as possible after being passed under the road.
Bituminous and Concrete Pavements
Bituminous and concrete pavements are relatively impervious to water so that drainage is carried out by providing the surface of the pavement with a crossfall normal to the centreline of the road. Most pavements have crossfalls of 2 to 3 percent. The surface should be maintained in a waterproof condition by the prompt repair of any cracks in the surface and by filling minor depressions that would hold surface water.
Gravel Surfaces
As gravel surfaces are not waterproof the crossfall is usually increased to 4 or 5 percent. Shoulders should be steeper depending upon the nature of the shoulder material. Ponding of water in depressions in the pavement can have serious results because of the consequent weakening of the pavement material and its displacement under wheel loading. To prevent serious damage from water and to maintain unsealed surfaces in reasonable condition for traffic, scours and depressions must be promptly filled and the whole surface kept in a smooth and self-draining condition by frequent grading.
Unpaved Surfaces
As with sealed pavements the principal means of draining an unpaved formation is to provide a crossfall normal to the centre line that will remove surface water as quickly as possible. Grading to restore the crossfall and to fill potholes and ruts is the major activity to maintain riding conditions and surface drainage efficiency.
Drainage Structures
The function of a table drain is to collect water that has fallen on the carriageway or the batters of a cutting and flowed to the edge of the formation. Table drains are essential wherever the road is in cutting and often desirable along the shoulders of embankments. Table drains require frequent maintenance, such as grading of unlined drains to remove silt and other debris that may easily block the flow, and to restore the original shape. Scours in table drains need prompt attention to prevent serious damage that may lead to undermining of the drain lining, the carriageway, or the cutting batters.
It sometimes happens that water from table drains must be discharged down the embankment batters. In such cases the slope of the invert of the drain down the batter is too steep to allow the water to flow over most natural materials because the high velocity induced would lead to serious scouring. Batter drains are, therefore, generally lined with concrete, metal, or some other hard material such as grouted stone. It is important that batter drains should be inspected frequently and immediate steps taken to make good any undermining and repair any breaks in the lining.
The primary function of a catch drain is to intercept surface water flowing towards the road cutting or formation embankment. It thus prevents the water flowing down the cut batter or along the toe of the embankment, which may cause severe scouring. Maintenance involves periodic inspection, clearing of obstructions, repairing of breached banks, and the filling of scours.
Culverts are key structures in any road drainage system and since they often provide the only passage for surface water from one side of the road to the other failure usually has serious consequences. Maintenance tasks include the constant clearing of debris and growth from the channel, particularly after forest fires, or in seasons when trees shed their leaves. The accumulation of silt or drift sand in the culvert barrel must also be removed periodically by mechanical or hydraulic means. Scour in the vicinity of culverts must be recognised in the early stages and repaired promptly before the damage becomes extensive.
The two main purposes of subsoil drains are to lower the level of the water table and to intercept or drain underground water trapped or held by impervious material. To be effective subsoil drains need to be not less than 500 mm below the subgrade level. Subsoil drains are constructed near the outside edge of the pavement parallel to the centre line of the road, but it is not uncommon for transverse drains to extend as branches from longitudinal drains to at least the centre line of the pavement. Maintenance action for buried drains consists primarily of inspection of outlets from time to time to ensure that water is seeping from them.
Underground drainage systems, which are rare in a rural situation but rather common where the road passes through urban or built-up areas, consist of both longitudinal pipes or conduits running generally parallel to the road centre line and transverse pipes passing under the road formation. Frequent inspection and cleaning of the drainage system is essential because serious damage can be caused if surface water bypasses inlets and overloads the system at other locations leading to flooding of the road or adjoining property.
Earth roads are usually regarded as suitable for dry weather use only. They may vary from wheel tracks on the natural surface to formed but unpaved roads usually constructed out of the soil occurring along the line of the road. Gravel surfaced roads may be defined as formed roads, the surfaces of which are composed of gravel won from a selected deposit, but which have not been given a bituminous surface treatment. They form a large proportion of the total length of rural roads in Australia and their adequate maintenance is of great importance to the rural community.
Grading
Grading is the most important operation in the maintenance of earth and gravel roads. The basic purpose of grading is to keep the road well drained to maintain a satisfactory running surface. The process of maintenance grading consists of bringing material in from the sides or cutting down high sections of the surface and filling the low spots with the surplus loose material.
Scarifying and Reshaping
When a gravel road has become worn to a state where the surface has hollows, potholes, and corrugations, it can sometimes be restored by loosening and reshaping. The shoulders are normally built up at the same time.
Gravel Resheeting
Gravel resheeting is the process of adding material over the full width and length of a specified section of pavement that is already gravelled. Resheeting is undertaken to restore the thickness of the pavement to give adequate support to all vehicles using the road. The steps in gravel resheeting are:
A bituminous surface is applied to a pavement to resist abrasion by traffic and to prevent penetration by moisture. Constant surveillance of the bituminous surface is an important phase of road maintenance because any failures may cause rapid deterioration of the pavement. Prompt attention to minor faults may obviate major failures with consequent costly repairs, and prevent the development of conditions likely to be hazardous or inconvenient to the road user.
If the bituminous surface of a pavement shows signs of weakness it is essential to determine whether the fault is in the surface, the pavement, or in the subgrade before any extensive repairs or resurfacing works are begun. Correct diagnosis of the cause is often difficult (especially in the early stages of distress), and it may be necessary to dig small inspection pits to examine the various layers and arrange laboratory tests of the materials. Proper investigation will guard against wrong treatment and waste of effort. Defects such as those arising from a faulty subgrade, a soft area in the pavement, faulty pavement material or poor drainage, will continue unless the cause is removed.
Many failures result from the presence of excess moisture in the pavement or subgrade, therefore, one of the most important functions of surface maintenance is to prevent water reaching or remaining in these layers.
If excavation of faulty pavement material is necessary the sides of the hole must be trimmed vertical, the depth of the hole being just sufficient to remove the poor material. Gravel or crushed rock used for backfill must be moistened to facilitate compaction and all materials should be compacted in layers not exceeding 100mm thick, preferably with mechanical equipment. The amount of material used must be chosen to ensure that the patch, when compacted, is flush with the surrounding pavement surface. On no account must a patch be left higher for traffic to compact it.
Before applying the final bituminous surface the patched area must be swept clean of dust and loose stones. The surfacing is then applied using materials similar to those in the original surface. Premix may be used for patching in some circumstances. Premix, made by mixing aggregate (preferably dried) with fluxed and/or cutback bitumen by hand or in a mixing plant, may be stored for several weeks or even months depending upon the amount and type of flux and cutter used. A bitumen emulsion of a suitable type may be used as the binder. Where available, hot mix is preferable to cold mix provided it can be used satisfactorily before it sets.
Ravelled Surface
Ravelling is a condition in which plant mix or penetration macadam becomes rough in texture due to a loss of aggregate. The causes could include insufficient or aged binder, excessively open-graded mix, poor compatibility of aggregate and binder, or fracturing of aggregate. Ravelled surfaces will require binder to be added, the rate of application depending upon the amount and condition of the existing binder. If ravelling has not developed too far the condition can be corrected by a seal, slurry seal, enrichment seal, or fogcoat made by spraying a very light application of binder with or without fine cover aggregate. Otherwise resurfacing with plant mix will be necessary.
Stripped Surface
Stripping is a condition in which aggregate is lost from a spray seal due to one or more of the following reasons:
If stripping is occurring due to aged and hardened binder it should be treated without delay to avoid further loss of aggregate. If there has been loss of scattered individual stones only the condition may be corrected by an enrichment seal with or without fine cover aggregate. If stripping has occurred over large isolated areas a reseal will be necessary but care must be taken in selecting an aggregate similar to the existing.
Fatty or Slick Surface
A fatty surface is due to surplus binder on the surface. Fatty surfaces become soft in hot weather (bleeding) and slippery in wet or frosty weather. Slick surfaces are hard, smooth, and slippery. They result from:
The successful treatment of this condition is difficult. Possible methods of treatment are resurfacing with open-graded plant mix, resealing, incorporation of additional aggregate into the existing binder, and burning-off .
Polished Aggregate Surface
Exposed stones may become polished under the action of traffic causing slippery conditions when wet even though the surface is generally not smooth. A polished aggregate surface must be resurfaced with either plant mix, sprayed seal, or slurry seal.
Shoving
Shoving is a fairly regular waviness (somewhat resembling corrugations in a gravel road) which may develop in bituminous surfaces due to movement under traffic. The deformations are usually shallow and are not likely to be confused with larger depressions resulting from weaknesses in the pavement or the subgrade. If the bituminous material has been compacted by traffic to a stable condition it will be practicable to fill in the depressions with premix. If it remains unstable it will be necessary to remove the unsound material and replace it with a stable premix.
Rutting
Rutting usually takes the form of depressions in the wheel tracks. If the transverse deformation is accompanied by adjacent bulging of the pavement or shoulder surface it may be a sign of excessive subgrade movement or weak pavement. The treatment is the same as that described for shoving provided there is no subgrade movement. Any faulty subgrade material must be replaced by suitable material.
Cracks
A bituminous surfacing may crack for a variety of reasons and often, in the early stages, the crack pattern can indicate the cause. When the cracks have developed over a large area and become sufficiently wide and numerous to allow the entry of surface water or disturbance of the surfacing by traffic it can be very difficult to determine the original cause of the trouble. Cracks wide enough to be treated should be filled with a binder having a viscosity low enough to enable it to be poured or worked into the cracks. Wider cracks should be filled with fine premix or bituminous slurry. Large areas with fine cracks should be spray sealed, slurry sealed, or resurfaced with plant mix.
Pot Holes
Pot holes not accompanied by distortion of the adjacent surface are usually due to a cracked bituminous surface allowing moisture to enter the pavement. The repair of pot holes will involve the vertical trimming of edges and removal of loose material prior to reinstatement.
Edge Failures
Fretting or breaking of the edge of a bituminous surface may be caused by worn shoulders , inadequate strength at the edge of the pavement, or entry of water through the shoulder. The failed area should be boxed out and both pavement and shoulder material replaced.
Large Depressions
Large depressions occur in the pavement surface when a fill has been inadequately compacted, for instance at bridge abutments. Depressions caused by failure to compact the fill may continue to increase in size and depth and deep seated correction may be necessary.
The road shoulder is that portion of the road adjacent to the pavement. The net width of shoulder is that width available to traffic inside guide posts or guard fencing or the edge of a table drain or fill slope measured from the edge of the pavement.
Shoulders may be constructed of earth, gravel, or bituminous concrete with surfaces unsealed, grassed, stabilised, or sealed. A shoulder should have a smooth running surface, a minimum of loose material, an adequate slope for drainage, sufficient strength to support wheel loads and a surface flush with the pavement edge.
Maintenance of earth and gravel shoulders will normally involve one or more of the following operations:
Grass shoulders must be mown regularly.
Page last modified 24June 2002.