Compaction of soil materials on site

Sufficient compaction of the soil material constitutes a key prerequisite in avoiding premature settlement and other negative consequences. Sufficient compaction is ensured by applying necessary compaction energy at optimum, or almost optimum, moisture content. The application of the necessary compaction energy is obtained with the use of appropriate compaction plants applying a sufficient number of passes. 

The thickness of the layer to be compacted constitutes another key factor for effective and uniform compaction with respect to depth. It is again related to the type of compaction plant used as well as the type of soil material. Vibratory rollers are able to compact thicker layers than static rollers. Pneumatic tyre rollers are not suitable for uniformly graded granular materials (single sized) or silty cohesive materials. 

Rolling velocity and tyre pressure, in case of pneumatic tyre rollers, constitute additional factors affecting compaction. With respect to the velocity, it should not be higher than 3 km/h, in all cases. As for the tyre pressure, it is determined by the manufacturer and should not fluctuate during compaction. 

The engineer, before compaction, for a given thickness and type of soil material, should determine the number of passes, so that sufficient compaction is achieved by using the 

Adequacy or acceptability of compaction may also be based on MCV determined in situ (Highways Agency 2009b Matheson and Winter 1997). 

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