Calculating the Unit Weight of In-Situ Soils
Calculating the Unit Weight of In-Situ Soils
(OP)
Can anyone out there give me insite on current testing methods for calculating the In-situ unit weight of soils? We are constructing a gravity sewer and would like to calculate the specific gravity of the material we are excavating, so we can backfill with a similar weight material. Any help would be greatly appreciated! :) Thank you!





RE: Calculating the Unit Weight of In-Situ Soils
the sand cone is basically a method to dig out the in-situ soil (and weight it), then fill the hole back with a known specific type of sand to get the volume of soil removed. So density = weight/volume. In balloon method, you fill the void created by digging using a rubber ballon filled with water. Volume of water in the balloon can be easily calculated (specific gravity of water = 1)
I don't think you are going to check the specific gravity of the soil.... just the unit weight or in-situ density. Specific gravity test is a different test... it is in a way similar to a measure of weight/volume of the actual mineral aggregates/soil, excluding the voids, etc.
Soil labs usually do the in-situ density tests for you. To check whether the backfill material has good density (good compaction)... or to compare it with the density of the original materials.
Regards
RE: Calculating the Unit Weight of In-Situ Soils
RE: Calculating the Unit Weight of In-Situ Soils
((1+w)(gamaw))/(w + 1/G) where G= specific gravity
gamaw =unit weight of water
w= water content of soil
If the soils to be excavated are cohesive, you can push Shelby tubes into the soil and determine the unit weight of the soil in the laboratory. There are correlations between the standard penetration resistance and soil unit weight in the literature--you may want to look in any basic soil mechanics textbook for these correlations.
RE: Calculating the Unit Weight of In-Situ Soils
RE: Calculating the Unit Weight of In-Situ Soils
RE: Calculating the Unit Weight of In-Situ Soils
The difference is actually that density is mass over volume, and unit weight is weight over volume. Since we are always going to be considering gravity, density will have to take it into account, also.
All ASTMs that deal with density are actually dealing in unit weight. Trust me! This is true. If you look at the proctor test, nuke test or the sand-cone test, all use WEIGHT over volume, and not mass over volume. So if you are looking at it from the angle of an ASTM, they are going to be the same there, too.