PERMEABILITY TEST OF SOIL – CONSTANT HEAD METHOD

Purpose:

The purpose of this test is to determine the permeability (hydraulic conductivity) of sandy soil by continuous top test method. There are two common types of permeability test methods that are routinely performed in the laboratory:

• Continuous head test method, and (2) falling head test method. Continuous head test method is used for permeable soil (k>10^-4 cm / s) and
• Falling head test is mainly used for less permeable soils (k<10)^-4 cm / s).

Standard Reference:

ASTM D 2434 – Standard Test Method for Permeability of Granular Soils (Standard Top) (Note: The Falling Head Test Method is not standardized)

Importance:

Permeability (or hydraulic conductivity) refers to the ease with which water can flow through a soil. This property is necessary for the calculation of seepage under the walls of earthen dams or sheet piles, the calculation of the leakage rate from waste storage facilities (landfills, ponds, etc.) and the calculation of the rate of disposal of clay soil deposits.

Device:

• Perimeter,
• Molestation,
• balance,
• Scoop,
• 1000ml graduated cylinder,
• clock (or stopwatch),
• thermometer,
• filter paper.

Testing Process:

(1) Measure the initial mass of the pan along with the dry clay (M₁,

(2) Remove the perimeter cap and upper chamber by unscrewing the pointed cap nuts and lifting them off the tie rods. Measure the inside diameter of the upper and lower chambers. Calculate the average diameter inside the perimeter (D,

(3) Place a porous stone on the inner support ring in the base of the chamber and then place a filter paper on top of the porous stone (see Photo C).

(4) Mix the soil with a sufficient amount of distilled water to prevent particle size separation during application in permetre. Enough water should be added so that the mixture can flow freely (see photo B).

(5) Using a scoop, pour the prepared soil into the lower chamber using a circular motion to fill it to a depth of 1.5 cm. An even layer should be made.

(6) Use tamping device to compact the soil layer. Use about ten rams of tamper per layer and provide uniform coverage to the soil surface. Repeat the compaction process until the soil is within 2 cm. at the top of the lower chamber section (see photo D).

(7) Replace the upper chamber section, and do not forget the rubber gasket going between the chamber sections. Be careful not to disturb the already compacted soil. Continue the placement operation until the soil level is approximately 2 cm below the rim of the upper chamber. Level the top surface of the soil and place a filter paper on it and then the top porous stone (see photo E).

(8) Place the compression spring on the porous stone and replace the chamber cap and its sealing gasket. Secure the cap firmly in place with cap nuts (see Photo F).

(9) Measure the sample length at four locations around the circumference of the centimeter and calculate the average length. Record this as the sample length.

(10) Place the pan with the remaining clay in the drying oven.

(11) Adjust the level of the funnel so that it maintains a constant water level a few inches above the top of the soil.

(12) Connect the flexible tube from the tail of the funnel to the bottom outlet of the permeter and open the valves at the top of the permeter (see photo G).

(13) Place tubing from the top outlet to the sink to collect any water (see Photo G).

(14) Open the bottom valve and allow the water to flow through the perimeter.

(15) As soon as the water starts to exit the top control (de-airing) valve, close the control valve, allow the water to exit the outlet for some time.

(16) Close the bottom outlet valve and disconnect the bottom tubing. Connect the funnel tubing to the top side port (see Photo H).

(17) Open the bottom outlet valve and raise the funnel to a convenient height to obtain a reasonably steady flow of water.

(18) Allow sufficient time for the flow pattern to stabilize (see photo I).

(19) Measure the time taken to fill a volume of 750-1000 ml using a graduated cylinder, and then measure the temperature of the water. Repeat this process three times and calculate the mean time, average volume, and average temperature. record the values ​​as Tea, Why, And Tea, respectively (see photo I).

(20) Measure the vertical distance between the funnel head level and the chamber outflow level, and record the distance as h,

(21) Repeat steps 17 and 18 with different vertical distances.

(22) Remove the pan from the drying oven and measure the final mass of the pan with the dry clay (M₂,

Analysis:

(1) Calculate the permittivity using the following equation:

K_Tea = QL/A*T*H

Where:

K_Tea = coefficient of permeability at temperature t, cm/sec.

L = length of sample in centimeters

t = time to discharge in seconds

Q = volume of discharge cm. In³ (Assume 1 ml = 1 cm³,

A = area of ​​cross-section of cm (= .) [(π D²)/4] , d = inside diameter of the parameter)

H = hydraulic head gap in length l, in cm of water; Or it is equal to the vertical distance between the fixed funnel head level and the chamber overflow level.

(2) The viscosity of water varies with temperature. As the temperature increases, the viscosity decreases and the permeability increases. The coefficient of permeability is standardized at 20 °C, and the permeability at any temperature T is related to K20 by the following ratio:

K₂₀ = k_Tea (η_Tea,₂₀,

Where:

I_Tea And₂₀ The test temperatures are T and the viscosities at 20°C respectively. Obtain viscosity from Table 1 and K. calculate₂₀,

(3) Calculate the amount of soil used: V = LA,

(4) Calculate the mass of dry soil used in cm (m) = initial mass-final mass:

m = m₁-M₂

(5) Calculate the dry density (ρ_D) Of clay

I_D = m/v

Table 1. Properties of Distilled Water (η = Absolute)

*1 poise = dyne*s/cm² = 8/cm*s

article written by

Pro. Krishna Reddy, UIC