Difference between revisions of "Grain size analysis"
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<math>K=C\cdot {\left (d_{10}\right )^{2}}</math> | <math>K=C\cdot {\left (d_{10}\right )^{2}}</math> | ||
{{ | {{Plainlist|Where: | ||
''d<sub>10</sub>'' = the soil particle diameter for which 10% of all soil particles are finer (smaller) by weight (mm), | ''d<sub>10</sub>'' = the soil particle diameter for which 10% of all soil particles are finer (smaller) by weight (mm), | ||
''C'' = is a shape factor (see below), and | ''C'' = is a shape factor (see below), and | ||
Revision as of 15:10, 8 March 2018
This method of determining design infiltration rate is only approved for sandy native soils with d10 between 0.1 - 2.5 mm (i.e. soils to which the Hazen formula is applicable)[1]. This method must not be applied within areas of fill.
Procedure[edit]
- Collect soil samples for each defined soil layer below the bottom of the proposed infiltration facility. Layers must be evaluated to the following depths, depending upon facility type:
- For bioretention facilities, analyze each defined layer below the proposed facility bottom to a depth of at least 3 times the maximum ponding depth, but not less than 1 m.
- For permeable paving, analyze each defined layer below the proposed facility bottom to a depth of at least 3 times the maximum depth of water within the base course, but not less than 1 m.
- For other types of infiltration facilities serving drainage areas up to 4 Ha, analyze each defined layer below the proposed facility bottom to a depth of at least 2.5 times the maximum depth of water in the facility, but not less than 3 m.
- Submit the soil samples for laboratory testing of particle size analysis according to ASTM D422.
Data Analysis[edit]
As the Soil Grain Size Analysis method is only approved for soils with d10 between 0.1 and 2.5 millimeters, the Hazen formula [2] may be used to calculate the soil permeability. The calculated soil permeability shall be considered to be the measured infiltration rate:
| Shape factors (C) to yield K in mm/hr | |
|---|---|
| Very fine to fine sand | 144000 |
| Medium to coarse sand | 288000 |
Safety Correction Factor[edit]
Adjust it!
- ↑ San Francisco Public Utilities Commission. (2017). Determination of Design Infiltration Rates for the Sizing of Infiltration‐based Green Infrastructure Facilities. Retrieved from http://sfwater.org/modules/showdocument.aspx?documentid=9681
- ↑ Hazen, A. (1893). Some physical properties of sand and gravel with special reference to the use in filtration. 4th Annual Report, State Board of Health, Boston.