Engineers Australia

An investigation into the effect of salt water on the geotechnical properties of a residual clay

Natalie Campbell, Burt Look and Andreas NataAtmadja


During construction, water is utilised both as a dust suppressant and for modification of the water content to aid in the compaction process. With the current high level water restrictions in South East Queensland, measures that can be taken to reduce the quantity of potable water in construction are needed. In this case, the possibility of using saline water in earthworks should warrant proper consideration.

It has been known that the presence of salt affects the natural and built environment, including pavements, agriculture, reinforced concrete structures and underground services. The main issues being degradation of bituminous surfacing, impact on vegetation, attack of concrete, corrosion of steel and ground movement. However, some studies in the past indicated that salt water can be used in earthworks.

This paper presents the findings of a limited study, which looked into the effect of salt water on the geotechnical properties of a typical clay from Queensland. To investigate the effects of salt on the engineering properties of the clay, a number of laboratory tests were undertaken, these included Atterberg limits, standard compaction, electrical conductivity, dispersion, California Bearing Ratio, shear strength, soil suction and swell. Testing was carried out at three salt concentrations.

The results show that the addition of salt water, while increasing the electrical conductivity, did not greatly affect the Atterberg limits, compaction characteristics, dispersion, strength or shrinkage of the soil. The use of salt water has been found to increase the variability of testing results; this was particularly evident in the soil suction tests. There appears to be an increase in swell potential with the increase in salt content. Furthermore, salt content appears to affect the matrix suction.