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Table 8.7
→Common Methods for Surface Infiltration Rate Testing
===Common Methods for Surface Infiltration Rate Testing===
===Common Methods for Surface Infiltration Rate Testing===
{| class="wikitable" style="width: 900px;"
|+'''Description of common methods for surface infiltration rate testing'''
|-
!<br>'''Method'''
!<br>'''Description'''
|-
|'''Double Ring Infiltrometer''' (constant head)
|
*The double-ring infiltrometer is made of two concentric tubes typically of thin metal or hard plastic, that are both continuously filled with water such that a constant water level is maintained as water infiltrates into the soil (ASTM International, 2005). The rate at which water is added to the centre tube is measured to determine the infiltration rate. For detailed guidance on how to perform the testing, refer to ASTM D3385-09 Standard Test Method for Infiltration Rate of Soils in Field Using Double-Ring Infiltrometer (ASTM International, 2009) and ASTM D5093-15 Standard Test Method for Infiltration Rate of Soils in Field Using Double-Ring Infiltrometer with Sealed-Inner Ring.
*Accuracy is only moderate relative to permeameter methods (ASTM International, 2010) and results tend to be biased towards higher values due to lateral flow. Potentially requires large volume of water and significant length of time for each measurement to reach steady state.
|-
|'''Single Ring Infiltrometer''' (constant or falling head)
|
*Similar to the double-ring infiltrometer, except with only one ring. Can be used to measure the vertical movement of water through a soil or permeable pavement. The standard design is a ring that is 30 cm in diameter and 20 cm tall, driven 5 cm into the soil or sealed to the surface of a permeable pavement and filled with water (Klute, 1986). For detailed guidance on how to perform the testing on permeable interlocking pavers, follow the procedure provided by ASTM C1781_C1781M – 15 (ASTM International, 2015). For pervious concrete or porous asphalt, follow the procedure provided by ASTM C1701_C1701M – 09 (ASTM International, 2009).
*Accuracy for soil testing is only moderate relative to permeameter methods (ASTM International, 2010) and results tend to be biased towards higher values due to lateral flow. Potentially requires large volume of water and significant length of time for each measurement to reach steady state when used for soil testing.
|-
|'''Modified Philip Dunne Infiltrometer''' (falling head)
|
*The Modified Philip-Dunne infiltrometer is falling head test device made of an open ended 50 cm long clear plastic cylinder with 2 mm thick walls, a 10 cm inner diameter and graduations, inserted into a machined metal base. Unlike the Philip-Dunne permeameter, which requires digging a borehole (i.e., not a surface infiltration test method), it is inserted 5 cm into the surface of the soil without the need for removing vegetation cover. Water level measurements in the tube can be obtained using the graduations on the side of the cylinder and a stopwatch, or continuously recorded through use of a data logger and pressure transducer installed in a piezometer tube.
*Measurements of soil moisture (e.g., using a handheld soil moisture probe) are needed before and after each test. Using relationships established by Ahmed and Gulliver (2011), the observed infiltration rate and initial and final soil moisture measurements are used to calculate a value for saturated hydraulic conductivity. A quicker test to perform than constant head tests. Superior to the single-ring infiltrometer falling head test as lateral flow is incorporated into the calculations.
|-
|'''Guelph Permeameter with Tension Disk''' (constant head)
|
*The Guelph permeameter is another test device for measuring saturated hydraulic conductivity of a soil surface when used with a tension disc attachment. The method is similar to a Tension infiltrometer, but with water being directed to the tension disc from an inner or outer Mariotte reservoir, giving it the capacity to test low and high permeability soils (Soil Moisture Equipment Corp. 1986). Infiltration rates are calculated from monitoring the water level drop in the reservoir until a steady state is approached.
*Like the Tension infiltrometer method, tests are run with two applied tensions. Steady state infiltration rates from the two applied tensions are used to calculate a value for saturated hydraulic conductivity. Potentially requires large volume of water and significant length of time for each measurement to reach steady state.
|-
|'''Tension Infiltrometer''' (constant or falling head)
|
*This test involves a porous disc of 10 or 20 cm diameter that is connected to a Marriotte bottle (water reservoir) and a bubbling tower where a negative pressure or tension is set (Figure 8.19). The porous disc must be placed in contact with the soil surface which usually requires removal of any vegetation and debris. In many cases it is necessary to place a thin layer of fine sand onto the soil surface to provide good contact between the disc and the soil.
*Infiltration rates are measured based on the water level drop in the water reservoir. The steady state infiltration rate into the soil is measured for two applied water pressures. To estimate saturated hydraulic conductivity the pressures need to be slightly negative (i.e., tensions) and it is recommended that successive pressures of -5 cm and -1 cm be used (Erickson et al., 2013). The measured steady state infiltration rates are used in equations derived by Reynolds and Elrick (1991) to calculate a value for saturated hydraulic conductivity.
*For detailed guidance on how to perform the testing, refer to Reynolds and Elrick (1991). The Mini-disc Tension infiltrometer (4.5 cm porous disc) uses a falling head method developed by Zhang (1997) to estimate saturated hydraulic conductivity. It is a quicker test to perform than the constant head method but potentially more difficult to achieve adequate contact with the soil surface.
|}
===Standard Equipment Used===
===Standard Equipment Used===