Granulometers
Introduction
It is called granulometric classification or granulometry, the measurement and grading that is carried out of the grains of a sedimentary formation, of the sedimentary materials, as well as of the soils, for the purposes of analysis, both of their origin and their mechanical properties, and the calculation of the abundance of those corresponding to each of the sizes provided by a granulometric scale.
A granulometric soil test is carried out to determine and separate a soil test by size and thus give it a classification in the SUCS.
Granulometric determination method
The size of a grain, clast or particle is not always easy to determine when they are irregular; it is usually defined as the diameter of a sphere of the same volume, and is expressed in millimeters. For larger edges, the average of the three maximum orthogonal measurements is usually taken, even if they do not intersect at the same point.[1].
The simplest granulometric determination method is to pass the particles through a series of meshes of different lattice widths (like strainers) that act as filters for the grains, which is commonly called a "sieve column"). But for a more exact measurement, a laser granulometer is used, whose beam diffracts the particles to determine their size. Or obs gamma rays can also be used.
Sieving test
To carry it out, a series of sieves with different diameters are used that are assembled in a column. At the top, where the largest diameter sieve is located, the original material (soil or mixed sediment) is added and the column of sieves is subjected to vibration and intense rotary movements in a special machine. After a few minutes, the sieves are removed and disassembled, taking separately the weights of material retained in each of them and which, in their sum, must correspond to the total weight of the material that was initially placed in the column of sieves (Mass Conservation").
Each sieve consists of a seamless cylindrical frame, retaining tabs and a special wire woven mesh. The metallic materials used to manufacture the sieve must be resistant to corrosion. The assembly between the frame and the mesh must guarantee the elimination of waves in the mesh and the joint between both must be sealed with an epoxy tape, in such a way that a uniformly firm tension of the mesh is obtained, preserving the measurements of its grids, to ensure the precision of the granulometric distribution of the soils. Each sieve must have an identification plate indicating the sieve number, the equivalent Tyler Scale designation, the standard it meets, and the serial number of the certificate of conformity.