Road Assets

Indicators of Urban Salinity Home

Damage to roads and pavements caused by salinity and waterlogging occurs primarily as a result of saturation of the different layers within the structure. There are several forms of road deterioration and pavement distress resulting from salinity and waterlogging as described below (from McRobert & Foley, 1999)

Rutting:

• caused by trafficking on a weakened pavement
• principally affects subgrade and weaker marginal pavement materials.

Major patching:

• due to base failure caused by moisture weakening large sections of the subgrade.

Bleeding and flushing of sprayed seals:

• softening of basecourse by increased moisture levels
• embedding of stone chippings into base.

Ravelling and potholes:

• abrading effect of traffic removes surface stone chippings on moisture weakened seals and granular base materials

Loss of seal and potholing:

• caused by high levels of salt in base layer causing debonding of bituminous surface
• most likely use of highly saline water during construction, rather than from capillary action of groundwater
• except where groundwater salinities are very high.

Fig. 7: Road pavement cracking	Fig. 8: Damaged road situated in a salt affected area
Fig. 9: Road pavement that is cracked and potholed as a result of being affected by waterlogging and salinity.	Fig. 10: Close-up of cracked road pavement affected by salinity and waterlogging.

Figures 7 - 10 show examples of damage caused by salinity and/or waterlogging to roads in Bendigo.

The most common types of damage to road assets in the Northern region according to Houghton et al (2002) and O'Flaherty (2003) are:

• base failure,
• shape loss,
• potholing,
• pavement shoving, and
• seals deteriorating (particularly in regions with saline groundwater).

Houghton et al (2002) and O'Flaherty (2003) provide useful information and guidelines for salinity management for road asset managers.

It is not always easy to determine the precise impacts of a high watertable and salinity on road assets since there are a number of inter-related processes that can contribute to a damaged road pavement.

There are, however, several general clues that you can look for: Topographically low areas within areas known to have salinity problems will be the most likely sections of road to be vulnerable to salinity. Vegetation on road verges may also show signs of being affected (see Figure 11) The presence of several salt indicator plants (eg spiny rush, sea barley grass, buck's horn plantain, etc) Bare, patchy growth or scalding White salt crystals forming on the ground surface.

Fig. 11: Cracked and potholed road in the foreground and salt tolerant vegetation and scalding in the background.

References

McRobert, J. & Foley, G (1999) The impacts of waterlogging and salinity on road assets: a Western Australian case study. Special Report 57, ARRB Transport Research Ltd. Sth Vermont, Vic.

Houghton, N, McRobert, J & Styles, E (2002) Salinity and rising water tables - risks for road assets. Austroads Project No. BS.A.N.523. Austroads Inc, Sydney

O'Flaherty, K (2003) Roads and salinity. NSW Department of Infrastructure, Planning and Natural Resources.

Page Top