Hi, everyone

Soil investigation, soil profile is very important. what is the determine boundary between major soil layers and sublayer based on? Based on boring log, moisture content, unit weight, liquid limit, particle-size analysis , etc...I don't understand to divide soil layers and sublayer in soil profile. Everyone can help me!

YP

I put down a borehole and I find white marbles in the first 2.5 m.  Then, all of a sudden, I find black marbles for the next 5 m and underlying is green marbles - but blocky and then not marbles at all - but solid.  Obviously, the white marbles are a different major soil layer than the black marbles and underlying green ones which may represent rock.  The white marbles would be characterized by physical description, routine classification testing, maybe by the packing (thin layers of smaller marbles).  Similarly the black would be characterized by the physical and routine classification tests; etc. for the green.  Strength and compression testing would be used for determining the properties of each of the layers based on experience/judgment and engineering acumen. As you are likely a student, pick up any good geotechnical textbook (such as Terzaghi, Peck and Mesri - the the 1967 edition of Terzaghi and Peck) and read the chapters at the beginning.  

document everything in all the borings, then look for trends.  Use the trends to characterize the strata.  As BigH says if you have funny brown dirt with red flecks overlain by funny red dirt with brown flecks and they both are silty sand, it's important to anticipate that these may be different layers.

Consider SM (silty sand):  One may be fine to coarse and the other fine grained. One may have elastic silt fines and the other non-plactic fines. They'd be different layers, eh?

Alternatly you may have silty sand with 49 percent passing the #200 sieve and elastic silt fines and another sample of sandy fat clay with 51 percent passing, just on the other side of the "A" line. The laboratory would give these two differnt classifications, but the geology would indicate that they are really both from the same layer.

There is no universal answer.

f-d

¡papá gordo ain't no madre flaca!