A new heavy haul railway embankment in the Pilbara region of Western Australia traversed an alluvial floodplain deposit that displayed sufficient dry strength but inadequate soil strength when saturated. The use of conventional ground improvement techniques for the design and construction of the embankment was assessed against the use of a dynamic impact roller. An impact roller trial was conducted to assess its effectiveness at increasing the soil density with the premise that an increase in density would increase the saturated strength of the soil. Trial results indicated that the impact roller generally increased the soil density to a depth of approximately 1m. However, when saturated, the strength of the modified soil remained unacceptably low as a heavy haul railway embankment foundation subgrade.