“If the sand being tested contains any amount of clay or organic material, it would require
analysis, otherwise the individual
washing and drying prior to sieve
grains would stick together giving a false ‘coarser’ result”
plants may also include: magnetic separation, sand attrition or even hot acid leaching.
Particle size distribution
Sieve grading, or particle size distribution, is carried out using laboratory analysis. Standard procedures must be followed at each stage, from initial sampling through to sample reduction and final testing. The first stage is to obtain a
representative sample from the stockpile. This large sample then has to be reduced in size. It is this smaller, dried sample, of around 100g, which is then mechanically shaken through a set of sieves for a predetermined length of time, usually fifteen minutes. Various sieve mesh sizes are used depending on the grain size distribution of sand being tested. If the sand being tested contains any amount of clay or organic material, it would require washing and drying prior to sieve analysis, otherwise the individual grains would stick together, giving a false ‘coarser’ result. For sportsturf, the majority of sand grains should fall between the sizes of 0.125mm and 1.0mm. Even when the majority of sand grains fall between these sizes, we still need to identify what percentage of sand grains fall within individual categories, e.g. coarse sand (0.500-1.000mm), medium sand (0.250- 0.500mm), fine sand (0.125-0.250mm). We can use the information obtained
from a particle size distribution (PSD) analysis in a number of ways. One is to calculate the Average Grain Size (AGS), which is normally quoted in microns.
Whilst this information is helpful, it does not give an indication as to the spread of particle sizes present. A more useful method is to calculate
“D Values” from the cumulate percent passing curve. Any given D value is the particle size diameter at which a given cumulative percentage of material is indicated to pass. For example, if the D90 Value was shown as 650 microns, this would indicate that 90% of material is smaller than 650 microns. D Values can be used to show the potential for interpacking by calculating the D90/D10 ratio (Gradation Index). They are also used to ascertain whether drainage gravels are compatible with the rootzone layer (bridging factor).
Grain shape
This refers to two attributes: one being the grain surface texture or angularity, and the other being grain roundness or sphericity. Grain shape is influenced by nature, and is entirely dependent on the weathering and erosion subjected to each grain at the time when they were formed and/or deposited. Glacial deposits and some river “alluvial” sand deposits tend to have a more rounded grain surface, whereas carboniferous sandstone deposits would typically have a more angular grain surface.
Sands having an angular or sub- angular grain surface are preferred when used in golf bunkers, as this gives greater stability and less ball plugging due to greater frictional resistance, whereas rounded sands are preferred for use in synthetic turf infill due to them being less abrasive to the carpet.
Saturated hydraulic conductivity
Sometimes referred to as Perc rate or Ksat. This is one of the most critical tests where sands are used in sports turf. The main reason for using sand is to achieve adequate water movement from the surface through to the drainage below. This test is used to give an indication as to the amount of water that would percolate through a material, whilst at field capacity, for a given depth when placed above a gravel drainage layer. This test should not be confused with infiltration rate. Whilst the two are certainly connected, they are carried out using completely different test apparatus and procedures. Results of any sand tested for saturated hydraulic conductivity should be quoted, as the amount of water passing through the sample at a given depth of material. The result would be in the form of 1050mm/hr at 30cm tension. It is crucial that the quoted result indicates the tension (or simulated depth). In general, testing the same sand at greater tension (depth) will give a higher result so, if the information quoted does not show the tension (depth), the results cannot be relied upon.
Total porosity
This measures the void space between the grains when compacted. Total porosity, as the term suggests, measures the total available pore space. Typically, values are around 38%-45%
Capillary porosity (water filled porosity)
This is the percentage of total porosity which contains water at or near the
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