Pavement Management Systems for Highways, Unsealed Road Networks and Suburban Roads

Asphalt road surfacing is the most important part of a road; it provides protection to vehicles, road users and the long time sustainability.


Asphalt is found as one of the products of crude petroleum or as a natural deposit found all over the world. In the Australia the world asphalt is used for the makeup of the asphalt and the aggregate that it is mixed with.

Asphalt comes in many different qualities and can be applied in many different ways. Due to the versatility of asphalt, there also become many problems that can be associated. Many problems associated with asphalt surfacing are not due to the properties and quality but the design or the way it is constructed.

There are five different ways BP Bitumen describe that asphalt surfaces can fail and many with different causes and ways in which this can happen and many different ways in which they can be rectified.

1. Deformation

Deformation results in the vertical or horizontal movement of the asphalt layer from inadequate strength, pavement thickness, compaction of the surface or base and many other defects mainly from the incorrect design of the asphalt layer.

2. Cracking

Cracking can form in many different ways, each with its own causes. Many causes of asphalt cracking is due to under layers, stressing the asphalt to cracking point. This can include, swelling of the base layers, cracking of the underlying concrete layer or the introduction of tree roots.

3. Surface texture deficiencies

Surface texture deficiencies are a great problem for grip and skip resistance of an asphalt layer. This is most commonly caused from incorrect design of the asphalt surface, and includes surface flushing, ravelling, stripping, delamination, polishing or a combination of these problems.

4. Edge defects

Edge defects occur in many regional roads where roads are thin and do not have side protection for cost savings. These defects are usually caused by traffic wearing the edges and removing the outside layer.

5. Potholes

Potholes are caused due to the top layer peeling off locally or moisture penetration causing weekness. Potholes usually occur on rural roads where road surfaces are reduced for cost savings, and usually treated by filling in with additional asphalt.


Remedies for correcting problems with road surfaces can be extremely expensive, depending on the problem.

For problems where the asphalt layer has been permanently altered and on a large scale, the usual remedy is to replace the whole layer with a new design in place. Yet for localised problems, the most common remedy is to locally replace the outside layer for a short term fix.

Many remedies for road surfaces consider many different aspects, including the cost and long term use of the road. Investigations of asphalt failure are extensive throughout the world; these investigations are very important in finding the correct remedy for the problem. In many cases problems with the asphalt is the design, and therefore the initial designs of road surfaces need to be concise due to the long time affect on the roads.

When designing pavements, long term loadings need to be taken into account. For instance a rural road may only currently take a small loading, yet what will the load be in a years time or five years time.

Geotextiles and geosynthetic clay liners are used in landfills to create a barrier between waste material and the environment. The use of these liners is varied throughout different countries and different practices around the world, yet the way in which they act in these situations is the same.

Geotextiles

Geotextiles are fabrics that have the ability to provide a permeable soil barrier for use in geotechnical applications. There are many different types and forms of geotextiles used throughout the world; yet in general fall into one of three catergories;

Each different category of geotextile can be made of many different materials, yet most of the time made of some sort of polypropylene or polyester.

Geosynthetic Clay Liners

Geosynthetic clay liners come in many forms and there are many companies which make different products. Basically a geosynthetic clay liner is a layer of clay bounded by two layers geotextiles. These liners are used in landfills to provide a non permeable boundary to protect the environment from leakage of harmful materials.

The picture above shows a geosynthetic clay liner produced by one company, displaying the general three layer construction.

Landfill Lining System

There are many different ways of lining landfills, each with the same goals in mind;

- Provide boundary from environment

- Allow drainage of leachate

- Long time storage

A typical lining system is shown below;

Australian Standards also outline regulations in the way waste is stored depending on the type being stored. The following diagram shows the classes of wastes outlined by Australian Standards.

Recent Landfill Operations

Recently an upgrade of the Red Hill Waste Management Facility, Red Hill, Western Australia was undertaken. This facility has been upgraded to hold both class III and class IV waste; the class III storage cell holds approximately 1.1 million cubic metres of commercial and municipal waste and is engineered with geosynthetic clay liner and 2mm High Density Polyethylene (HDPE) liner. The geosynethetic clay liner used in the construction is made of Kaolinitic clay found from the site. The class IV cell storage is more harmful and therefore higher safety is required for the construction; the Red Hill Facility is built using two lining systems each with leachate collection systems, geosynthetic clay liners and HDPE. This storage is also highly controlled and monitored to alert any signs of leachate leaking through the two layers. The following diagram shows this situation.

As seen above the layers allow for leachate to be monitored through the coarse material layer.

References

1. Geofabrics, Australasia, http://www.clay-liner.com/wawcs0131042/idDetails=172/Our-GCL%27S-are-manufactured-to-the-highest-international-standards.html, viewed 08/09/2009

2. Landfill Waste Classification and Waste Definitions 1996, Department of Environment, http://www.dec.wa.gov.au/component/option,com_docman/gid,1316/task,doc_download/, viewed 10/09/2009

3. The Eastern Metropolitan Regional Council, www.emrc.org.au/news-pg-617.asp, viewed 10/09/2009

Coursework Interpretation

Geotechnical Engineering has become a topic of keen interest for me now due to the way that everything learnt about rock and soil has come cleanly together for a good body of knowledge and understanding for practical use.

It is interesting that originally the first thoughts of retaining soil was something that I thought was not calculated but just estimated, yet this course and ones previously have taught me that there are much greater forces that apply within the ground than earlier anticipated.

I feel that the coursework is interesting and I enjoy what I am learning, if there is anything that I could change within this field of work is the use of practical experience. Something as simple as working out the stability of a surface from start to finish as an engineer would using Australian Standards and what might be expected of us as an engineer, similar to what selected students were expected to do last semester. By doing this, i think that we could get a better indication in what areas we might want to pursue within civil engineering.

Earth Dams and Tailings Dams

Earth dams for reservoirs and ring dyke tailings dams are similar in many ways; they both provide a boundary for the retained liquid and are both of similar shape. Yet what sets them apart is the way in which they retain the fluid and the construction internally which acts in different ways.

Earth Dams

Earth dams have a very specific use; to retain water inside the boundary and provide support so that it is safe and will not fail due to the weight of the retained water. The construction of an earth dam has two distinct parts; one of which to provide a water tight layer so that water cannot pass through and the other to provide restraint. Figure 1 shows a common cross section of an earth dam.

As seen from figure 1, the earth dam contains a clay core that provides the dam with an almost impermeable layer at which water cannot pass through and a soil or rock mass to each side providing restraint. Other parts of this dam include an upstream blanket to reduce water seeping under the wall, and drainage blankets on the downstream wall for water to drain freely away.

Earth dams although can be found to be constructed in many different ways due to the size, amount of water being held back, location and availability of materials and safety factors.

The Core

Comprised of a low permeable (k=10-8, 1 0-9), low plasticity (CL & SC or SC-CL) usually high clay content. Compaction of the core is a vital part and usually compacted to a level of 95% to 98% RD. The core can be placed in many different ways throughout the dam cross section yet never downstream from centre. Different positioning of the core provides the dam with different properties and different flow paths, and is usually optimized depending on the situation.

Shoulders

Can vary in composition and usually dependent on local materials but always of higher grain size than that of the core. The shoulders provide restraint for the core from near horizontal forces applied by the water. On the outer edges of the shoulder is usually a form of rip-rap or large boulders to prevent wave action from erosion of the shoulder. Although the shoulders have a large mass and strategically placed, movement of the wall is generally expected and can be as much as 20mm per year.

Blankets

Upstream BlanketUsually located on the upstream side of the dam and usually made of a material similar to that of the core, the blanket provides another almost impermeable layer so that there is less seepage through the dam foundation. A blanket also has a good ability of increasing flow paths beneath the dam as seen in the diagrams below.

Filters

Filters are installed between materials of high grain size and materials of low grain size to prevent boundaries from mixing. Materials of these filters are of a grain size between these two materials and most commonly sand.

Tailings Dams

Tailings dams are very similar to normal earth dams for reservoirs yet precautions for failure of these structures are monitored much closer. Tailings dams are built to allow the remains from processing ores to settle out from the water that is used in the processing.
The construction of tailings dams can vary significantly and is mainly dependent on the type of tailings being stored and the topography of the storage facility. Vick, SG states that there are four main types of tailings storage, Water Retention Dam, Upstream Dam, Downstream Dam and Centreline Dam; these are displayed below.

From the types of tailings dam it can be seen that most start in the same way with the conical shape seen in a normal earth wall, yet as the amount of tailings increases the wall is also heightened in addition and in different ways depending on the design. The four types all have advantages and disadvantages depending on their construction; the following table shows some of these properties.

Monitoring of tailings dams is much more strict than that of an earth fill dam, this is due to the some time hazardous materials being held. For instance a tailings dam for a Uranium processing plant can be extremely harmful containing over a dozen radioactive nuclides including thorium, radium and radon. If not controlled properly, dust can be blown from these ponds entering food chains and bodies of water.