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National Standard of the People's Republic of China
Determination of forest soil permeability
Determination of forest soil permeability This standard applies to the determination of forest soil permeability. 1 Penetration cylinder method
1.1 Key points of the method
UDC 634.0.114
GB 7838—87
In soil saturated with water, the soil permeability coefficient is based on Darcy's law and is expressed as follows: K
Where: K Permeability coefficient, cm/s
-Flow rate, that is, the amount of water that penetrates through a certain cross-sectional area S (cm2), ml-Thickness of saturated soil layer, that is, the distance penetrated, cm, S
-Cross-sectional area of the penetration cylinder, cm2
-Time required for water to penetrate through the amount Q, Sh
-Thickness of the water layer in the experiment, that is, the water head (water level difference), cm. (1)
The permeability coefficient is related to the number of soil pores, soil texture, structure, salt content, water content and temperature. The dimension of the permeability coefficient K is cm/s, or mm/min, or cm/h, or m/d. From the above formula, it can be seen that the amount of water passing through the soil layer is proportional to its cross-sectional area, time and water layer thickness (water head), and inversely proportional to the distance of infiltration (saturated layer thickness). QK.sth/1
Therefore, the saturated permeability coefficient can be said to be a constant unique to soil fill. 1.2 Main instruments
Permeability cylinder (as shown in the figure), measuring cylinder (500ml), beaker, funnel: stopwatch, thermometer, etc. 1.3 Measurement steps
(2)
1.3.1 Determination depth: Determination is carried out according to the soil occurrence layer (A, B, C layer), and each layer is repeated for no less than 5 times. The A layer measurement is mainly used to design measures to prevent soil erosion and formulate irrigation systems. The B layer measurement is used to design measures to prevent soil erosion and predict the possibility of temporary stagnation of soil moisture in this layer, identify the firmness and alkalinity of this layer, and identify whether this layer is suitable for temporary irrigation and fixed irrigation channels. The C room measurement results can provide soil water retention and identify whether it can be used as a large irrigation channel or channel. Approved by the National Bureau of Standards on June 4, 1987
Implementation on January 1, 1988
GB 7838-87
Schematic diagram of the infiltration tube
1.3.2 On the selected test site, use the infiltration tube to collect the original soil, the soil sampling depth is 10cm, cover the bottom screen with filter paper, and bring it back to the room for measurement.
1.3.3 Immerse the infiltration tube in water, and be careful not to let the water surface exceed the soil column. Generally, sandy soil is soaked for 4 to 6 hours, loam is soaked for 8 to 12 hours, and clay is soaked for 24 hours.
Take out the infiltration tube at the scheduled time and hang it in a proper position. After the gravity water drips, install the funnel and place a beaker under the funnel. 1.3.5 Add a 5cm deep water layer on the top of the infiltration tube (mark it), start timing when the first drop of water drips from the bottom of the funnel, and replace the beaker under the funnel every 1, 2, 3, 5, 10·ti…tnmin (the length of the interval depends on the speed of infiltration, and pay attention to maintaining a certain pressure gradient), and measure the infiltration water volume Q1, Q2, Q3, Qs, Q0Q.Qn respectively. Each time the beaker is replaced, quickly add the water layer above the infiltration tube to a depth of 5cm and record the water temperature (℃). 1.3.6 Depending on the different types of soil, the test generally begins to stabilize in 30min to 1h. If it is unstable, it should be extended until the amount of water seepage per unit time is equal. 1.3.7 At the same time, measure the temperature of the water in the infiltration tube (℃). 1. 4 Calculation of results
1.4.1 Total amount of seepage water
Where: Q1, Q2, Q3....Q.-
Infiltration rate
Where: tn
Q(mm) =-(01 +Q2 +03 +0.) ×10S
-Amount of seepage water each time, ml, i.e. cm2,
Cross-sectional area of the infiltration tube, cm23
Multiples converted from cm to mm.
(mm/min):
Time between each infiltration, min.
1.4.3 Permeability coefficientbzxZ.net
K, (mm/min):
Wherein: Kt--
10×Qn
10×Qn×1
tn×Sx(h+ /)
-permeability coefficient at temperature t℃), mm/min, h+!
（5）
soil layer thickness, cm,
h -water layer thickness, cm.
GB 7838-87
1.4.4In order to facilitate the comparison of K values measured at different temperatures, they should be converted into permeability coefficient (K) at 10℃. K1o(mm/min) =
: Ki0--
0.7 +0.03t°
Permeability coefficient at 10℃, mm/min, r°Water temperature during measurement, ℃.
1.4.5 Soil permeability measurement record sheet (see table) Example Permeability tube area (S): 78.54cm2,
Test soil layer thickness (1): 10cm,
Water layer thickness (h): 5cm3
Water temperature (°): 15.2℃.
Infiltration time
After the start
t,....+*.
Period of time
Water seepage
Record of soil permeability measurement
Total amount of water seepage per unit area
(Q+ + 02.-Q.) × 10
Calculation example of soil permeability measurement result
Total amount of seepage water Q
Infiltration velocity V
Permeability coefficient K,
(Q + Q2 + Q3...Q.) × 10
= 210.98mm
10×Qn
10×On
Permeability coefficient Kto at 10℃:
2-ring knife method
2.1 Key points of the method
10×157
Penetration rate
mm/min
10×Qn
Permeability coefficient
(190 + 177 + ..... + 157) × 1078.54
= 9.99mm/min
0.7 +0.03t°
10 + 5
5.76mm/min
0.7 + 0. 03 × 15.2
=6.66mm/min
Same as 1.1.
GB 7838—87
2.2 Main instruments
Ring knife (volume 100 or 200cm2); measuring cylinder (100ml, 10ml), beaker (100ml), funnel, funnel stand and stopwatch, etc. 2.3 Determination steps
2.3.1 Take the original soil with a ring knife outdoors, the same as the water-physical property sampling, bring it back indoors and immerse it in water for 41. ... Generally, sandy soil is soaked for 4 to 6 hours, loam is soaked for 8 to 12 hours, and clay is soaked for 24 hours. When immersing in water, keep the water surface flush with the upper edge of the ring knife, and do not let the water flood the soil surface at the upper edge of the ring knife. 2.3.2 At the scheduled time, take out the knife ring, remove the cover, and put an empty knife ring on it. Seal the joint with adhesive tape first, and then glue it with melted wax to prevent water leakage from the joint. Then put the joint knife ring on the funnel, and the funnel is supported by a beaker. 2.3.3 Add water to the empty knife ring above. The water level is 1mm lower than the knife ring mouth, that is, the water layer is 5cm thick. 2.3.4 After adding water, start timing when the first drop of water drips from the bottom of the funnel. After that, change the beaker under the funnel every 1, 2, 3, 5, 10, 15nmin, and measure the seepage water volume Q1, Q2, Q3, Qs, Q1...Q...Qn respectively. Each time the beaker is changed, the water level of the knife ring above should be added to the original height, and the water temperature (℃) should be recorded at the same time. 2.3.5 The test usually lasts for about 1h before it starts to stabilize. If it is still unstable after 1h, it is necessary to measure until the seepage water volume per unit time is equal.
2.4 Calculation of results
Same as 1.4.
This method should be repeated four times and the arithmetic mean should be taken. Additional remarks:
This standard is proposed by the Ministry of Forestry of the People's Republic of China and is under the jurisdiction of the Forestry Research Institute of the Chinese Academy of Forestry. This standard is drafted by the Forest Soil Research Office of the Forestry Research Institute of the Chinese Academy of Forestry. 133
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