Difference between revisions of "Grain size analysis"

From LID SWM Planning and Design Guide
Jump to navigation Jump to search
 
(15 intermediate revisions by 2 users not shown)
Line 1: Line 1:
This method of determining [[design infiltration rate]] is only approved for sandy native soils with d<sub>10</sub> between 0.1 - 2.5 mm (i.e. soils to which the Hazen formula is applicable)<ref>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</ref>. This method must not be applied within areas of fill.
This method of determining [[design infiltration rate]] is only suitable for coarse-textured native soils with d<sub>10</sub> between 0.1 - 2.5 mm (i.e. soils to which the Hazen formula is applicable)<ref>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</ref>.  
 
'''This method shall not be applied within areas of fill or in regions where hydraulic conductivity is controlled by vertical fractures in the soil matrix.'''


==Procedure==
==Procedure==
# 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:
# 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 [[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 [[permeable pavements]], 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.  
#* 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 water storage reservoir depth, but not less than 3 m.  
# Submit the soil samples for laboratory testing of particle size analysis according to [https://www.astm.org/Standards/D422.htm ASTM D422].
# Submit the soil samples to a certified soil testing laboratory for grain-size, or particle-size distribution analysis according to [https://www.astm.org/Standards/D422.htm ASTM D422] Standard Test Method for Particle-size Analysis of Soils.


===Data Analysis===
===Data Analysis===
As the Soil Grain Size Analysis method is only approved for soils with d<sub>10</sub> between 0.1 and 2.5 millimeters, the Hazen formula <ref>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.</ref> may be used to calculate the soil permeability. The calculated soil permeability shall be considered to be the measured infiltration rate:
NB:  The Hazen formula method of estimating soil permeability based on grain size distribution analysis is only suitable for coarse-textured soils with d<sub>10</sub> between 0.1 and 2.5 millimeters <ref>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.</ref>. The soil permeability value estimated using the Hazen method can be considered to be the measured infiltration rate of the soil, f, in mm/h
<math>K=C\cdot {\left (d_{10}\right )^{2}}</math>
:<math>f=C\cdot {\left (d_{10}\right )^{2}}</math>


{{Plainlist|1=Where:
{{Plainlist|1=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), median value of all samples tested.
*''C'' = is a shape factor (see below), and
*''C'' = is a shape factor (see below)}}
*''K'' = permeability (mm/hr)}}


{| class="wikitable"
{| class="wikitable"
! colspan =2| Shape factors (C) to yield K in mm/hr
! colspan =2| Shape factors (C) to yield f in mm/h
|-  
|-  
|Very fine to fine sand
|Very fine to fine sand
Line 27: Line 28:
|}
|}


==Corrections==
==Don't forget to apply [[Design infiltration rate#Safety correction| a safety correction factor]] before beginning your sizing calculations==
Adjust it!
 
----

Latest revision as of 18:37, 6 August 2020

This method of determining design infiltration rate is only suitable for coarse-textured native soils with d10 between 0.1 - 2.5 mm (i.e. soils to which the Hazen formula is applicable)[1].

This method shall not be applied within areas of fill or in regions where hydraulic conductivity is controlled by vertical fractures in the soil matrix.

Procedure[edit]

  1. 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 pavements, 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 water storage reservoir depth, but not less than 3 m.  
  2. Submit the soil samples to a certified soil testing laboratory for grain-size, or particle-size distribution analysis according to ASTM D422 Standard Test Method for Particle-size Analysis of Soils.

Data Analysis[edit]

NB: The Hazen formula method of estimating soil permeability based on grain size distribution analysis is only suitable for coarse-textured soils with d10 between 0.1 and 2.5 millimeters [2]. The soil permeability value estimated using the Hazen method can be considered to be the measured infiltration rate of the soil, f, in mm/h

Where:

  • d10 = the soil particle diameter for which 10% of all soil particles are finer (smaller) by weight (mm), median value of all samples tested.
  • C = is a shape factor (see below)
Shape factors (C) to yield f in mm/h
Very fine to fine sand 144000
Medium to coarse sand 288000

Don't forget to apply a safety correction factor before beginning your sizing calculations[edit]

  1. 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
  2. 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.