Building Temporary Roads
From farmers field to supportive road & back in 5 easy steps
Phase 1: Any field anywhere in the UK
Phase 2: Top 10 cm of grass and roots for area of road is
removed and put to one side.
Phase 3: RoadCem/cement is rotavated into the remaining
250mm of topsoil
Phase 4: To remove the temporary road just rotavate it again
Phase 5: Replace the the 10 cm of grass sod
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In Phase 1 we have a farmers field with a well cultivated 1-2 metres of good organic soil, topped by grass or crops.
In Phase 2 the top 10 cm of grass & soil has been removed from the area where the roadwill be built. This grass sod can be put aside to be put back in place if required when the temporary road has been removed.
In Phase 3 rotavating/mixing of the top 250 mm of organic site soil will take place with the addition of the RoadCem and cement.The easiest way to do this is by a Soil Stabiliser plant (machines like a Wirtgen WR2500 ora tractor pulled Wirtgen WS220 or WS 250 which are available for hire) followed by a final roller compaction.
In Phase 4 rotavation/remediation of the 250 mm of stabilised soil has been carried out to make it a loose inert soil ready again for crop growing or grazing. This can be done with the same mixing machines and will result in a nice loose soil structure.
In Phase 5 the old top grass sod has been placed on top of this rotavated material (phase 4), basically no visible nor ecological traces will be left of the temporary road.
The traditionally alternative method for the building a temporary road of the same specification would be put down 300 mm of stone, over Terram.
As an example for the building of a 900 metre road using our unique new technology the job could be completed for half the price and in one third of the time. It would also save 180 lorry deliveries of stone to the site.
Plus of course if the road has to be removed the trucks would have to be used again to remove the stone (which is now classified as waste) from the site. At a cost very similar to that of laying the road. In this application it definetly pays to be green.
Temporary Roads on Construction Sites
During the past decades construction projects have become more complex, larger and higher. Increasingly heavier machinery and transport vehicles are being used to build these projects.
This heavy machinery needs to be able to get on to the construction site and move about on it. In large parts of the UK the sub-grade is weak with not enough stability and bearing capacity to support the construction activities
Therefore construction sites are made construction ready first. This process includes the construction of temporary roads to make the sites better accessible for construction traffic.
Temporary roads on construction sites are similar throughout the UK.
Five main reasons can be named for this:
Firstly, the UK has one of the highest construction densities in the world, leading to more traffic load on the roads creating the need for temporary roads.
Secondly, in many countries no distinction is made between the utilisation and construction stage.In this case the permanent road serves also as temporary road.
Thirdly, a small element pavement is fast becoming the preferred permanent pavement in the UK where asphalt is the preferred pavement in many other countries.
Small element pavements are not suited for temporary roads.
Fourthly, the public roads in the UK are relatively small in the utilisation phase of the project (sometimes only 4,5 metre while at least 5,5 metre is required), creating the need for wider temporary roads.
Finally, buildings in the UK are constructed using heavier construction materials (i.e. concrete) then other countries (i.e. wood in Scandinavia), leading to heavier loads.
There are three key differences between temporary and permanent roads:
Firstly, the weight of the vehicles during the construction process is much higher during construction than during the utilisation phase.
Secondly, the traffic volume on a temporary road is lower then on the permanent road.
Thirdly, the temporary road’s lifespan is much shorter then the permanent road. Sensibly there is a preference for constructing temporary roads on the same route as the permanent roads are going to be built.
Therefore an integral approach for the temporary and the permanent road can lead to a reduction in project costs and the opportunity to significantly minimise the carbon footprint of the project.
Currently, temporary roads are mainly designed on previous build methods involving the import to site of quantities of sand and virgin stone, because there is seldom any real attempt to estimate the future traffic loads on temporary roads, nor to identify opportunities to reuse existing site materials
This can result in over or under dimensioned and specified roads and the unnecessary trucking to site of large quantities of aggregate materials, leading to additional project costs or bad working conditions on construction sites.
A special point of attention is water management on the construction site. If not enough attention is paid to water management, significant water logging on the construction site can occur.
The combination of low permeability soils and inadequate drainage system is the main cause for water logging on construction sites.
The height of the temporary roads surface level in comparison to the ground level can also cause water logging problems.
Temporary roads above ground level with low permeability embankments or with bad drainage systems can start acting as ditches which can lead to water logging on the build areas of the construction site.
Conversely roads that are constructed under the ground level can easily turn into muddy rivers. Soaked roads have a strongly reduced bearing capacity, which will shorten the roads lifespan.
Temporary Road Construction costs, four types of cost can be distinguished:
- construction
- maintenance costs
- upgrade
- removal
When the temporary road is not combined with the permanent road the total costs consists of construction,maintenance and removal costs.
When the temporary road is combined with the permanent road, the total cost consists of construction costs for the temporary road and the upgrade costs to the permanent road.
Traffic distribution
The traffic distribution plan for the construction site needs to be formulated before the traffic loads and routes of the temporary roads can be calculated.
Transport routes
Any resident and construction traffic should be separated as much as possible.
It is recommended to classify the temporary roads into categories. The two main categories can be distinguished on construction sites as:
- Roads that provide the main access to the complete project site.
These roads will mainly be under the supervision of the local authority.
- Roads that provide access to any separate inner site zones.
These second category of roads can be found in separated construction areas within in a zone. In most case these are constructed and operated by the construction companies themselves.
Sub-grade characteristics
Temporary roads are constructed in or on top of the existing sub-grade present at the project site.
The sub-grade has to support additional weight of the embankment, pavement and traffic load applied to it, without showing unacceptably large deformations.
Therefore, consolidation and stability of the sub-grade determines largely the design and performance of a road.
Thus it is very important to know the characteristics of the sub-grade and what consequences this has for the road design.
Drainage design
Temporary roads can not only experience damage resulting from water logging, they can also cause flooding as described in the introduction.
By installing drains in the road not only the road is drained, but also the surrounding construction site.
This will result in better conditions on the construction site.
To calculate drainage, data regarding the required drainage head (during the construction and the utilisation phase) is necessary.
There are two main locations for drainage pipes under a road: on both sides of the road or under the centre of the road.
When the drainage pipes are installed on both sides, water will flow directly into the drainage pipes.
Sited at side of the road the pipes are also more accessible in case they get clogged.
Drainage pipes can be installed on different depths in the road body.
When the drain is installed deeper this will result in larger distances between two parallel drains, and thus to cost reductions.
Installing drains below the ground water table is not recommended unless the drains can dispose their water on waterways with a lower water table.
Temporary road design
Construction and maintenance costs of temporary roads are indirect costs to a construction project.
For this reason the pavement selection, after certain preconditions are met, is largely based on the construction cost of the different pavement types and any removal costs incurred and on the ‘upgrade’ costs for a temporary road to a permanent road.
There are numerous materials available for use as a foundation in road construction.
All can be classified in one of the following three categories: unbound, bound and self-binding foundations.
Unbound foundation
Materials will have only a slightly higher (150 MPa) constructive value than sand (100 MPa).
Therefore unbound foundation materials are not recommended for use as an unpaved road or in the foundation layer.
However for temporary roads, a normal bound foundation layer can cause problems too if cables and pipes need to be laid in the roads’ body because these layers are often too strong and also expensive to restore.
The bound option will of course be difficult and expensive to remove.
Therefore bound foundation layers are also not recommended
Self binding foundations
Have been available in the UK for some time, though a relatively new product SMR stabilising binder which can be added as a powder to any existing cohesive sub grade is now proving to be the holy grail for contractors looking for strength and workability in recovering/strengthening difficult or weak site soils.
Fast curing and workable for up to seven days after mixing in most weather conditions. This newly approved product provides a cheap solution for recycling on site materials and avoiding unnecessary landfill and importing aggregates to site.
Unpaved roads
An unpaved road is a road without a top layer of asphalt, concrete, small elements or other top layer material.
A commonly used road on construction sites is the mixed aggregate/stone road.
Unpaved roads are much cheaper to construct than paved roads, but require more maintenance, especially on weak sub-grades (due to rutting), in case high traffic loads can be expected or in dry (dust prevention) and wet (damage to the top layer) times.
Unpaved roads require the regular addition of aggregate, grading and shaping in wet times.
The construction and maintenance costs increase as traffic load increases, stiffness of the sub-grade decreases and this type of temporary road depends strongly on the weather conditions.
Prefabricated concrete plate pavement
Prefabricated concrete plates are easy to install and being easy to remove are being proffered as a green option, they can resist heavy traffic, require hardly any maintenance and can be re-used multiple times.
There use however would add to the construction miles tally of each site as they are heavy and bulky to truck.
A commonly used size for a prefabricated concrete plate used in temporary roads is 2 by 2 meters, or the less fashionable sleeper size and both are available in different thickness
.
Prefabricated plates are available with or without steel edging for extra strength.
However, if the steel edging is broken it can cause flat tires.
It is recommended to chose plates that can handle heavy axle loads up to 200 kN without steel edging because sometimes trucks are over-loaded on construction sites.
As prefabricated concrete plates are installed using a fork lift truck, it will be a requirement for the existing sub grade to be strong enough to support the use fork lift trucks.
The concrete plates are laid on a 10 cm thick bedding sand layer.
The embankment layer alongside the plates has to be well compacted to a minimum depth of one metre.
However if this the embankment becomes impervious, this will cause water accumulation in the embankment layer. Causing damage to the road because of ‘pumping’ under the plates.
A better solution, which is mostly used when concrete plates are used as or in temporary roads, is a sand embankment.
In places with a high ground water table extra drainage might be required.
Prefabricated concrete plates are not only applicable as pavement but also as protection for lead-up services or as reinforcement in unpaved roads.
Lead-up services under prefabricated concrete plates are easily accessible.
Unpaved roads cannot handle torsion forces applied by the wheels of the trucks in corners and connections to existing infrastructure.
This will quickly lead to damage on the unpaved road surface.
Prefabricated concrete plates can handle these forces very well.
Just applying these plates in corners and on connections to existing unpaved roads can increase the lifespan of the roads.
This can result in a temporary road partly paved with concrete plates and partly with another pavement material or even unpaved.
Finally, prefabricated concrete plates can also be used to widen a small existing road.
Geosynthetic materials
A road construction is only stable when the maximum load capacity of the sub-grade is not reached.
Good load spreading in the road is necessary to prevent the road from showing displacements or other forms of damage.
On weak soils this often results in extra thick foundations and/or embankment layers being necessary.
Geotextiles are permeable fabrics, which have the ability to separate, filter, reinforce, protect, or drain and can be used to improve the road characteristics.
The costs for geotextiles can be estimated at £1.00per m2. This corresponds with a mixed granule layer with a thickness of 135 mm.
This is within the set limit for the maximum reduction of 120 mm.
Therefore it can be cost neutral to construct a geosynthetic layer under the foundation layer.
Applying geosynthetic layer can also result in better maintainability and thus in longer lifespan of the road.
However, geotextiles are also used to increase or control the road drainage capacity therefore it has additional positive effects.
Permanent road design
Wherever possible it is preferable to construct temporary roads on the same path as any future permanent road.
An integral approach for temporary and permanent roads can lead to a significant increase in the quality of the temporary road and a big reduction in project costs.
There are some additional design requirements present when a temporary road is upgraded to a permanent road.
The most obvious one is that the temporary road dimensions and routes should be the same.
Besides this aspect there, are three other aspects:
Firstly, it has to be structural possible to combine the permanent road with the temporary road.
Secondly, it should be checked that the drainage requirements for the utilisation phase is met.
Thirdly, the frost penetration criteria has to be met.
The Future
Several companies are developing artificial textiles with flexible fibreglass tissues, which can detect moisture and damage/deformation by monitoring changes in spectrums. This type of system could easily be installed under temporary roads and could stay a long time for monitoring changes due to traffic intensity on temporary roads.
Besides the pavement types mentioned there are other, innovative pavements in development.
A good example for this is the use of lime and or cement to stabilise the natural sub-grade which in some circumstances can be as effective as engineered products like SMR.
But will need careful analysis of ground and weather conditions before being used.
The application of steel and rubber plates as temporary road is also being investigated.
Sustainable construction
The first initiative for sustainable construction began in the late eighties.
Sustainable construction can be described as “the use of design and construction methods and materials that are resource efficient and that will not compromise the health of the environment or the associated health of the building occupants, builders, the general public or future generations”.
There is an increasing demand, in both the private and public sectors, to understand sustainable construction practices.
This demand is driven by a realisation that sustainable practices make sense to both owners and operators.
The practices not only help the environment, but also can improve economic profitability and improve relationships with stakeholders. Road construction is especially suited to apply recycled and recovered waste and even contaminated materials.
Different types of recycled aggregate and slag are frequently used as materials for unbound road bases.
Recycling old asphalt and other tar bearing materials is now possible with recently improved techniques and will be an influence or possibility for use in construction of temporary roads in the future, and temporary roads are well suited for the application of re-cycled materials because the requirement set for this type of road are often lower then for other roads.
Summary
It will always be necessary to know the functions of a temporary road to satisfy the participants of a project.
The construction and maintenance costs of temporary roads are indirect project costs, which mean they have no direct added value to the project but are necessary to build to project.
Therefore costs for the temporary roads will be minimised, irrespective of any environmental concerns or aspirations.
When the temporary road and permanent road are combined in an integral design this does lead to cost reductions and improved road quality and improved conditions on the construction site.
Conclusion
Comparing the construction costs and the additional costs if the road has to be removed after construction is finished for the different pavement types.
As explained above, costs for temporary roads have no direct added value to a project.
Therefore the most expensive types of pavement are usually not applied in a project if they are not required.
The cheapest solution for temporary roads is considered to be the unpaved road, utilising imported aggregates and stone.
However, these roads cannot handle heavy traffic loads and they generate a lot of dust in dry times and mud in wet times, and require a lot of maintenance.
For these reasons and where planning restrictions on importing aggregates are in place an unpaved road cannot always be used. The second cheapest solution is to install prefabricated concrete plates on the road.
These plates are however, compared to other pavement types, expensive to lay and remove.
Concrete roads are seldom used as a pavement for temporary roads, simply because they are too expensive. Another reason it is expensive and time consuming to lay cables and tubes through this type of road, which is often necessary in the construction phase.
Concrete pavements are therefore not an option.
Asphalt pavements will provide the very best solution, but are the costliest option to install and unless they can be laid in the correct position and dimension of a future permanent road, they are expensive to remove.
The low carbon most environmentally friendly option and the cheapest where a cohesive sub-grade already exists on the site is to avoid land filling and trucking new aggregate to site and working with the pre existing site materials to produce an engineered or stabilised platform or sub base product. In town centres and environmentally sensitive sites this type of operation may soon be the only option available under forthcoming planning consents.
Recommendations:
- A good Type1 Recycled Aggregate is recommended as foundation or unpaved road material.
- Design the temporary road above ground level and ensure a good permeable embankment, preferably with horizontal drainage in the road.
- Design unpaved roads at least 250mm thick with a maximum of 500mm. Keep in mind that the road will loose around 5 centimetre thickness due to dust and flushing away by water.
- Asphalt roads are more expensive but do not require maintenance and provide better conditions on the construction site.
- On lower order roads a minimum width of 4,5m is recommended (to allow a truck and a car to pass by each other). On higher category roads with more traffic, a minimum of 5,5m width is recommended (to allow two trucks to pass by each other).
- Create enough parking spaces to prevent parking on the roads.
- Prefabricated plates can be used to protect underlying services and to reinforce corners and connections to other roads in unpaved roads.
- Before making any commitment/ road decision check or get advice on whether the soil already on site is suitable for stabilisation into a bound product.
