Every construction project requires specific care so that the final result is compatible with what you wanted to achieve. In mining, there are many miners that believe the only purpose of haul roads is to connect two points. But is it really?

Roads that make up these sectors are part of a critical and important component of the production process. Roads in poor condition whether due to lack of maintenance or lack of construction quality, result in impacts on productivity, the safety of workers, and equipment life cycle.

A good haul road design is that one with an integrated design approach of sizing, building and maintenance to ensure the safety and quality in the field. The design requires an analysis of several components that meet a set of criteria where the absence or the deficiency of one can harm the others. Key design considerations are discussed below:

How important is Road Geometry?

A good geometric design allows for safety, reduction in fuel consumption and agility in operation.

The geometry of a haul road must present a horizontal alignment that enables a line of sight distance, which must be greater than the stopping distance to allow the driver see the potential hazards ahead, such as intersections, parked or broken down vehicles, or debris.

Curves of geometric designs must meet criteria in a way that facilitates the transport operation. Curves with a very small radius, require vehicles to slow down and obviously increase the time and costs of operation, although this must be balanced against available space onsite.

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The vertical geometry design must provide smooth ramps with a constant grade for better trafficability of mining vehicles. Ramps with greater inclinations make it difficult for the vehicles to reach operating speeds and can result in loss of material during transportation or unnecessarily increasing fuel consumption. Again, this must be balanced against site constraints with the view of optimising the outcome.


How important are Crossfall and Drainage?

Another important component of the designing of haul road is road crossfall and drainage. Drainage elements to consider are surface (tied to crossfall), longitudinal, and subsurface using pipes or culverts. Water results in several defects that may influence mining operations, such as damaging the wearing coarse layer or pavement structure. Constructing and then maintaining the road with a crossfall of 2% to 3% is required to avoid the accumulation of water on the surface, and thus to minimize the damage to surface layers and the percolation through to lower layers.

Adequate longitudinal drainage in the form of v-drains (ditches) to remove/intercept this water is required, and ties into the vertical geometry of the road alignment. Provision to bleed this water off through safety bunds or into subsurface pipes must also be considered – as does the need to control erosion at the outlet.

Subsurface drainage is rare in many mines, due to the short-term nature of many roads. However, it should be better considered, particularly where roads cross natural flow paths of concentrated flows. Even in dry environments, water from steep catchments can cause catastrophic damage when not designed for.

How important is Pavement?

Pavement design aims to decrease stresses on the subgrade, which the resistance is typically measured by California Bearing Ratio (CBR) test. Low resistance values of the subgrade require higher thicknesses to meet designing criteria and thus can be divided into layers with different resistances. When the resistance criterion is not met, the pavement begins to present permanent displacements and can lead to accumulation of water, delayed operation or collapse of the pavement structure.

Haul road pavement must be functional, that is, it requires adequate values of rolling resistance and adhesion. In this way, crushed stones with good quality are recommended for wearing course to ensure good operation performance, safety and to avoid defects such as potholes. Engineering input is required to find this material onsite, source this material from offsite, or if completely unavailable – to make the best of a bad situation.

A good engineer should be a master of optimisation.

Proper compaction of road embankment and then the pavement itself is another critical factor often missed. This is worse in road maintenance practice. Whilst nearly all mines will have graders running continually, it is extremely rare for rollers to be utilised onsite.

How important is Maintenance?

In addition to construction criteria, haul roads require careful operation and maintenance. During hauling of the mined materials, haul roads will fatigue and may present other problems such as corrugation, rutting, and potholes due to loss of in situ materials, displacements/settlement, and weather events. Engineering oversight of maintenance processes must take into account the need to maintain the intent of the original design, for the life of the road.

However, despite all of this, haul roads may still present problems caused by impacts outside of the geometric, drainage or structure design. For example, road generated dust is a problem that can compromise operation and safety.

GRT can assist you to optimise haul road design, construction and maintenance.

Read Part 3: Materials Optimisation & GRT Products for Haul Road Pavements

Read Part 1: Productivity On Haul Roads Suffers From a Lack of Road Engineering Input

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