Difference between revisions of "Grain size analysis"

From LID SWM Planning and Design Guide
Jump to navigation Jump to search
m
 
(35 intermediate revisions by 2 users not shown)
Line 1: Line 1:
This method of determining [[design infiltration rate]] is only approved for native Clean Sand and Dune Sand (SP) with d<sub>10</sub> between 0.1 - 2.5 mm (i.e. soils to which the Hazen formula is applicable). This method is not allowed 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>.  
==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:
 
## 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 [https://www.astm.org/Standards/D422.htm ASTM D422].
 
  
==Data Analysis==
+
'''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.'''
# As the Soil Grain Size Analysis method is only approved for soils with D10 between 0.1 and 2.5 millimeters, the Hazen formula (below) may be used to calculate the soil permeability (K). Soil
 
permeability shall be considered to be the measured infiltration rate:
 
  
K = C (D10)
+
==Procedure==
2
+
# 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:
Where K is in cm/s, C = 1, and D10 is the soil particle diameter in mm for which 10% of all soil
+
#* 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.  
particles are finer (smaller) by weight.
+
#* 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.  
2. Adjust the measured infiltration rate using the correction factor described in Section 4 to
+
#* 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.  
establish the Design Infiltration Rate in inches per hour (in/hr).
+
# 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===
 +
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>f=C\cdot {\left (d_{10}\right )^{2}}</math>
 +
 
 +
{{Plainlist|1=Where:
 +
*''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)}}
 +
 
 +
{| class="wikitable"
 +
! colspan =2| 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 [[Design infiltration rate#Safety correction| a safety correction factor]] before beginning your sizing calculations==

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.