I am not knowledgeable about this particular field, but this is how I would parse the sentence:
A power function can fit as (the relation between UCS and (porosity (n) of cemented soil specimens as voids) / (volumetric cement content ratio (n/Cv) parameter that has been investigated by several researchers))
Functions are typically described like "the relation between X and Y", so I would assume X here is UCS, and Y is .. the rest of it.
If we interpret "/" as a division sign, then Y would be
(porosity / volumetric cement content ratio), where
volumetric cement content ratio is given in units of n/Cv, and has been investigated by several researchers .
I would rewrite it something like:
This can be fit by a power function relating UCS to the porosity (n) of cemented soil divided by volumetric cement content ratio (n/Cv) parameter, which has been investigated by several researchers [1, 2, 3].
- Explicitly stating "divided" instead of "/", which is ambiguous and (at least in papers I've read) inappropriate to include in text. (Too informal to use as shorthand for "or", and math equations should be math equations.)
- "which" instead of "that": "parameter" can (presumably) be understood without the clause about being investigated, so it is a nonessential clause and should be used with "which".
- Adding citations: that way the reader can verify exactly which part of the equation those researchers were investigating, and it's clear what reference goes with what.
Of course, I would also include the equation nearby, so the reader can correlate the description with the actual math!