All soil is rock. Looking at this from a geotechnical perspective rather than agrarian or geologically will clarify why.
Rock consists of up to 50% metal and that is mostly aluminium, calcium, silicon and a few other light metals in the earth's lithosphere. Rock weathers either mechanically or chemically. The processes that cause weathering are wind, rain, thermal variation and kinetic erosion due to gravity and solar energy.
Some rocks are almost devoid of metal in their composition because they are mostly carbon, hydrogen and oxygen compounds with a metal atom bond. As rock decomposes due to oxidation its density changes.
Igneous rocks create very dense, dark soils and often are highly metallic. Black granite, basalt and gabbro are good examples of such rock. These rocks decompose to metal rich souls which can be very heavy and highly compacted to produce surfaces "as hard as rock" because they are made from rock. The finer the soil particles, the greater the compaction and if treated with chemicals, they may bond together like rock and behave like bedrock structurally. To say compaction is as strong as rock is accurate but soil integrity to resist penetrative pressure requires lateral strength only available from extreme heat that made the parent material to begin with: in excess of 1750°C
In summation, so can only achieve the strength of the rock from which it consists less the pore content and frictional factors of the grains. These some may reduce structural load-bearing strength by a much as 60%. When water is added to the mix, then it may reach liquefaction and behave as a fluid instead of a solid at ambient temperatures. However, as permafrost it is another animal. Technically it is theoretically possible but in practice not. 95% compaction is considered safe in engineering applications but any more than that raises economic issues without the mechanical properties being greatly improved.
Hope this helps