Road authorities must switch focus to pavement maintenance
04 April 2013
The maintenance of roads involves the co-ordination of a wide range of seemingly unrelated activities. In practice, to achieve a good standard of effective maintenance, it is essential that different aspects of the work should integrate smoothly. The task facing the engineer in road maintenance is to maintain a network of roads within available budgets.
This is made difficult by the amounts of road that are built to inadequate standards and the increase in both the volumes of traffic and in axle loadings, combined with decreasing budgets and the expectation of further cuts in public expenditure. In rural areas, the intensification and diversification of agricultural production has resulted in minor roads of minimal pavement construction having to accommodate relatively large volumes of traffic and, more particularly, commercial vehicles that sometimes barely fit onto the road. In urban areas, the growth of towns and cities has incorporated areas serviced by minor roads but now carrying heavy volumes of traffic.
Of these, the majority of national primary roads and some national secondary roads have been realigned to modern design standards, but those that remain are old, pre-automobile tracks. These received an overlay of gravel and surface dressing during the 1950/’60s, with subsequent granular overlays and surface dressing.
Due to the dispersed settlement pattern in Ireland, we have a proportionately long road network for our population. The maintenance of these roads will continue to be an ongoing problem, as resources will not allow for complete structural overlays or realignment of a significant proportion of these roads.
During the past decade and a half, funding has been available to allow a higher expenditure on road maintenance than was previously available, resulting in significant improvements in the standard of road pavements through the country. The challenge for engineers over the next few years will be to maintain the road network to an acceptable level with less resources than have been previously available.
ROAD PAVEMENT DETERIORATION
The structural design of road pavement is determined by the estimated traffic-volume over the design life of the pavement as well as the ground conditions, giving a depth of layered construction to provide for a 20-year life. Road pavements designed and constructed in the last 30 years have been designed and constructed according to this approach. Pavement overlays are designed on the basis of strength testing and the relevant depth of construction is added to the road structure.
In recent winters, the country experienced heavy rainfall during November and December, followed by severe frost in January and into spring. This resulted in severe damage to many sections of roads throughout the country, noticeably on old portions of road and not on newly constructed, strengthened or surface-dressed roads. Why is this? What can road maintenance engineers do to prevent road damage in future?
The road network in Ireland consists of approximately 2,739km of national primary roads, some 2,676km of national secondary roads and 89,000km of regional, county and urban roads. This article will concentrate on basic routine operations that can significantly increase the life of the road pavement.
All our roads are founded on natural soils, which, with the exception of organic material such as peat, are treated by geotechnical engineers as granular materials – as are the non-bitumen bound layers in the road structure. The strength of such materials is at its maximum at optimum moisture content. During construction, these materials are tested and checked to ensure this moisture content is achieved.
Granular materials that are saturated with water will lose 90% of their strength, resulting in pavement failures. If this is to be avoided, two things are necessary: the road must have adequate drainage and its surface must be sealed against the ingress of water.
The most effective action that can be taken by a road engineer to maintain the road pavement and prolong its life is to ensure that the pavement is adequately drained and that water does not pool on the road surface. There should be no such thing as a flat road; roads are built to falls, with either camber or super elevation to assist in draining the water to the road edge.
When water has reached the road edge, there must be a drainage system in place to remove the water from the pavement. This can be a piped system with gullies in urban areas, stoned drains on large roads and motorways and water cuts, possibly with side drains on rural roads.
Over time, silt and grit from the road is washed into these systems, rendering them ineffective unless they are regularly cleaned: a drainage system is useless unless it can accept the water coming to it. There should be a regular system of checking drainage outlets and cleaning them to ensure they function properly. Problem areas can be easily identified by driving the road on a wet day and then carrying out investigations or remedial works in dry conditions.
Localised ponding is often a result of an accumulation of silt and debris in gullies and water cuts, which can be easily cleaned. Equally, the openings of bridges, culverts and pipes passing under the road should be checked for blockages during conditions of low flow.
Water cuts consist of channels at right angles to the road, which allow water to flow into adjacent fields. Traditionally, these were maintained by gangs of workers, manually using shovels. As the labour force available to road authorities has fallen over the last twenty years, this work can in general no longer be carried out manually.
A commonly used alternate method is to use a backhoe (JCB) with a wide (1.2-1.5m) bucket, which can open and clean the water cuts quickly and efficiently, while the machine is parked parallel to the road. Various devices have also been designed for use on agricultural tractors that will perform this task but without the flexibility of a wheeled loader/backhoe.
Roadside drains were in the past also cleaned manually, but now must be cleaned by machine. This can be a tedious and awkward task, as there is no excavator that will comfortably clean narrow drains parallel to the road edge without considerable manoeuvring, leading to low outputs. There is definitely an opening for a machine geared specifically for this purpose.
With increasing traffic on rural roads, problems have arisen with these often-narrow drains being closed by the pressure of the wheels of truck and agricultural machinery. In many instances, it has proved necessary to replace them with piped drainage systems.
Piped drainage systems can be sealed or open, with water entering through gullies or via a permeable medium. In either case, the drain must be capable of taking the flows of water and the water must be able to reach the drain. Piped drainage systems must be regularly checked to ensure that conduits are not blocked and that in the case of French drains, the water can soak to the drain.
Recent developments include the use of plastics to replace concrete pipes in French drains and the use of pipes that can be ploughed into place at a lower cost than traditional systems.
URBAN ROAD DRAINAGE
In general, drainage is achieved by the use of a piped drainage system accessed by means of road gullies. Such a system will only work effectively if pipes are clear and gullies are not blocked with litter or debris. Road sweeping operations should include a check of all road gullies and cleaning of these as a matter of routine while mechanical sweepers are sweeping the road.
It makes very good sense to survey and map all road gullies and their outlets, and set up a routine inspection programme to ensure the drainage system is adequately maintained.
Many drainage systems are inadequate to meet the demands at present placed upon them; in many cases, substantial resources are necessary to provide new drainage systems. It is part of the function of the road maintenance engineer to identify the necessary modifications, or to establish the need for new systems, while ensuring that the existing system is capable of operating at its maximum efficiency.
Often in problem areas, a thorough investigation will produce simple solutions. In many cases, there may well be disused drainage systems which have been abandoned by neglect – with minor modifications, they can be used to remedy localised drainage problems.
NEW DEVELOPMENT PROPOSALS
When projects are at planning permission stage, the possible effects on the drainage system should be established and catered for, existing drainage systems should be protected by condition and any new systems required must be included in the submitted proposals. Developments on or near floodplains should be subject to rigorous scrutiny, similarly downstream drainage systems should be checked for their capacity to accept the accelerated runoff from paved areas.
Information on flood risk is available from the Office of Public Works, but local knowledge is also very relevant. If an area has flooded once, it will most probably do so again, unless there has been some change in circumstances since the previous flood event.
Having stressed the importance of road drainage, it is necessary to consider the importance of providing an impermeable seal across the entire road surface to protect the underlying layers of the pavement. We will look at the issue of surface dressing to seal pavements in the next article in this two-part series.http://www.engineersjournal.ie/2013/04/04/road-authorities-must-switch-focus-to-pavement-maintenance/http://www.engineersjournal.ie/wp-content/uploads/2013/03/Slide10.jpghttp://www.engineersjournal.ie/wp-content/uploads/2013/03/Slide10-300x300.jpgCivilinfrastructure,roads,water