As almost all the properties of soil depend on water content, it is very important to measure the water content very accurately.
Different methods to find water content:
Different methods to find water content:
- Oven Drying Method
Oven Drying Method is a standard laboratory method. It is a very accurate method but this method needs 24 hours for its completion so it's a lengthy method. This method is based on IS 2720 Part 2.
- A small empty container is weighed, let it be ${W}_{1}$
- The soil to be tested is filled in a small airtight container and weighed, let it be ${W}_{2}$.
- The container is then dried at a temperature of $105-110^{\circ}C$ for 24 hours in the laboratory
Above $110^{\circ}C$ water of crystallisation may be lost. It is the water in the molecular structure of soil particles.
- If the soil contains a significant amount of organic matter then the soil is dried at a temperature of $60-80^{\circ}C$.
- After 24 hours the container is cooled down to room temperature and weighed, let this weight be ${W}_{3}$
Water content, $\frac{W_{w}}{W_{s}}=\frac{W_{2}-W_{3}}{W_{3}-W_{1}}$
-
Pycnometer Method
A pycnometer is a glass jar of about 1-litre capacity and fitted with a brass conical cap. This cover has a small hole of 6 mm diameter at its apex. This method for the determination of water content can be used only if the specific gravity (G) of soil solids is known.
- Weigh the empty pycnometer, say ${W}_{1}$.
- Fill the pycnometer with moist soil and weigh it, say ${W}_{2}$.
- The remaining volume of pycnometer is gradually filled with distilled water or kerosene and weighed, say ${W}_{3}$. The entrapped air should be removed either by slight heating or vigorous shaking or by applying vacuum.
- Empty the bottle and clean it thoroughly and filled with distilled water or kerosene and weighed, say ${W}_{4}$.
Water Content, $w=\left( \frac{{{W}_{2}}-{{W}_{1}}}{{{W}_{3}}-{{W}_{4}}} \right)\left( \frac{G-1}{G}-1 \right)$
This method is not suitable for cohesive soil because removal of entrapped air in case of cohesive soil is difficult.
-
Sand Bath Method
Sand bath method is a rapid field method but it is not accurate. A Sand bath is a large open vessel containing sand filled to a depth of 3 cm or more. This method is based on IS 2720 Part 2.
- Crumble the soil to be tested and place loosely in a tray. Place a few pieces of white papers on it and weighed the whole assembly.
- Place the tray on the sand bath and heat it over a stove. Drying will take about 20 to 60 m.inutes, depending upon the type of soil.
- Turn the soil specimen with a palette knife.
Overheating of the sample should be avoided and overheating is occur when white paper turns brown.
The drying should be continued until the sample attains a constant mass.
- When drying is complete, remove the tray from the sand bath, cooled and weighed.
Water Content, $w=\frac{{{W}_{final}}-{{W}_{initial}}}{{{W}_{final}}-{{W}_{tray}}}$
-
Calcium Carbide Method
When water reacts with calcium carbide it produces acetylene gas. The water content of the soil is determined indirectly from the pressure of the acetylene gas formed. The instrument used is known as moisture tester. This method is based on IS 2720 Part 2.
$Ca{{C}_{2}}+2{{H}_{2}}O\to {{C}_{2}}{{H}_{2}}+Ca{{(OH)}_{2}}$
The instrument used is known as moisture tester.
The pressure of the acetylene gas produced acts on the diaphragm of the moisture tester. The quantity of the gas is indicated on a pressure gauge. The water content $({w}_{t})$ based on the total mass is determined from the calibrated scale of the pressure gauge.
The water content based on the dry mass is determined by, $w=\frac{{{w}_{t}}}{1-{{w}_{t}}}$
-
Radiation Method
In this method, Radio-active isotopes are used to determine the water content. A device containing a radio-active isotopes materials, such as cobalt-60, is placed in a capsule. It is then lowered in a steel casing A. The steel casing has a small opening on its side through which rays can come out. A detector is placed inside another steel casing B.
Neutrons are emitted by the radioactive isotope. When these neutrons strike with the hydrogen atom of water, they lose energy and this loss of energy is proportional to the quantity of water present in the soil. The detector is calibrated to give directly the water content.
Oven Drying Method is a standard laboratory method. It is a very accurate method but this method needs 24 hours for its completion so it's a lengthy method. This method is based on IS 2720 Part 2.
- A small empty container is weighed, let it be ${W}_{1}$
- The soil to be tested is filled in a small airtight container and weighed, let it be ${W}_{2}$.
- The container is then dried at a temperature of $105-110^{\circ}C$ for 24 hours in the laboratory
Above $110^{\circ}C$ water of crystallisation may be lost. It is the water in the molecular structure of soil particles. - If the soil contains a significant amount of organic matter then the soil is dried at a temperature of $60-80^{\circ}C$.
- After 24 hours the container is cooled down to room temperature and weighed, let this weight be ${W}_{3}$
Water content, $\frac{W_{w}}{W_{s}}=\frac{W_{2}-W_{3}}{W_{3}-W_{1}}$
A pycnometer is a glass jar of about 1-litre capacity and fitted with a brass conical cap. This cover has a small hole of 6 mm diameter at its apex. This method for the determination of water content can be used only if the specific gravity (G) of soil solids is known.
- Weigh the empty pycnometer, say ${W}_{1}$.
- Fill the pycnometer with moist soil and weigh it, say ${W}_{2}$.
- The remaining volume of pycnometer is gradually filled with distilled water or kerosene and weighed, say ${W}_{3}$. The entrapped air should be removed either by slight heating or vigorous shaking or by applying vacuum.
- Empty the bottle and clean it thoroughly and filled with distilled water or kerosene and weighed, say ${W}_{4}$.
Sand bath method is a rapid field method but it is not accurate. A Sand bath is a large open vessel containing sand filled to a depth of 3 cm or more. This method is based on IS 2720 Part 2.
- Crumble the soil to be tested and place loosely in a tray. Place a few pieces of white papers on it and weighed the whole assembly.
- Place the tray on the sand bath and heat it over a stove. Drying will take about 20 to 60 m.inutes, depending upon the type of soil.
- Turn the soil specimen with a palette knife.
Overheating of the sample should be avoided and overheating is occur when white paper turns brown.
The drying should be continued until the sample attains a constant mass. - When drying is complete, remove the tray from the sand bath, cooled and weighed.
When water reacts with calcium carbide it produces acetylene gas. The water content of the soil is determined indirectly from the pressure of the acetylene gas formed. The instrument used is known as moisture tester. This method is based on IS 2720 Part 2.
The instrument used is known as moisture tester.
The pressure of the acetylene gas produced acts on the diaphragm of the moisture tester. The quantity of the gas is indicated on a pressure gauge. The water content $({w}_{t})$ based on the total mass is determined from the calibrated scale of the pressure gauge.
The water content based on the dry mass is determined by, $w=\frac{{{w}_{t}}}{1-{{w}_{t}}}$
In this method, Radio-active isotopes are used to determine the water content. A device containing a radio-active isotopes materials, such as cobalt-60, is placed in a capsule. It is then lowered in a steel casing A. The steel casing has a small opening on its side through which rays can come out. A detector is placed inside another steel casing B.
Neutrons are emitted by the radioactive isotope. When these neutrons strike with the hydrogen atom of water, they lose energy and this loss of energy is proportional to the quantity of water present in the soil. The detector is calibrated to give directly the water content.
No comments:
Post a Comment