Air Content in the Sandy soil

[BTAC888]

The sandy soil in the sand dune is dry and porous. I would like to know the air content 1 meter (3.3 ft) below the surface. How much the air is there?

[insane_alien]

depends on the fineness of the sand and its packing structure.

[cypress]

It in practice it does not depend very much on the size nor the packing but it does depend most on the size distribution of the sand particles. Our well completions depend heavily on use of sand packing for reservoir integrity maintenance and empirical data on porosity is widely available based on relative size distribution. If you can give me more information I may be able to help you.

[BTAC888]

The field condition is as follows:

1. Location - sand dune in middle east

2. Depth of the pipeline buried under the sand = 1 meter below the surface

3. Water content in the send = < 1%

4. Pipeline operation temperatures= 110 - 120 C.

5. Air content around the pipeline will have impact on the thermo - oxidation of the external pipeline coatings.

6. I would like to know the air content (oxygen content).

[cypress]

What, roughly, is the relative distribution in size of the sand particles? Depending on the distribution, porosity could vary from 5 to 30%. If you have some of the sand, you can measure the porosity with water and a scale. If you don't know and don't have any sample sand, then go with 20% as most surface sand is well sorted and mostly spherical shaped by wind and water.

[swansont]

If it's pure sand, i.e. silicon dioxide, you can compare the density of a sample to that of SiO2. The difference will tell you the mass of the air.

[michel123456]

The field condition is as follows:

1. Location - sand dune in middle east

2. Depth of the pipeline buried under the sand = 1 meter below the surface

3. Water content in the send = < 1%

4. Pipeline operation temperatures= 110 - 120 C.

5. Air content around the pipeline will have impact on the thermo - oxidation of the external pipeline coatings.

6. I would like to know the air content (oxygen content).

 

Are you sure your pipeline will remain burried all time long at the same depth? As much as I know, sand dunes are moving. IMHO you must work on 100% exposure. Maybe worse, your coating must resist the abrasive force of sand under wind, and exposure to U.V.

Edited December 28, 2010 by michel123456

[BTAC888]

Are you sure your pipeline will remain burried all time long at the same depth? As much as I know, sand dunes are moving. IMHO you must work on 100% exposure. Maybe worse, your coating must resist the abrasive force of sand under wind, and exposure to U.V.

 

The coating has very good abrasion resistance, but not to UV. Do you have any cocrete information on the sand dune movement?

 

What, roughly, is the relative distribution in size of the sand particles? Depending on the distribution, porosity could vary from 5 to 30%. If you have some of the sand, you can measure the porosity with water and a scale. If you don't know and don't have any sample sand, then go with 20% as most surface sand is well sorted and mostly spherical shaped by wind and water.

 

Thanks. Your response shed light onto my questions on the air content in the sand dune. The sand dune has 5-30% porosity. Air is in the porosity. So at the 1 meter deep air is still there. Oxygen is there too. In short, air is there at 1 meter depth of the sand dune. However, in Houston, the soil is composed of sand, clay, silt and water, there may be no air below 1 meter deep soil.

[cypress]

Thanks. Your response shed light onto my questions on the air content in the sand dune. The sand dune has 5-30% porosity. Air is in the porosity. So at the 1 meter deep air is still there. Oxygen is there too. In short, air is there at 1 meter depth of the sand dune. However, in Houston, the soil is composed of sand, clay, silt and water, there may be no air below 1 meter deep soil.

 

Below the water table, and in Houston 1 - 2 meters is normally where the water table lies, there is very little free air except near trees due to the roots and water consumption by the trees, however there is still dissolved oxygen and generally plenty of it. However for your situation in the sand you are correct.

 

One final note, dry sand that is not smooth and not compacted can have porosity significantly greater than the 20% I suggested due to inefficient packing caused by irregular shapes. In tests, porosity up to 40% is observed, but addition of small amounts of liquid provides sufficient lubrication to end this effect.

[michel123456]

I know dunes move several meters a year, according to local conditions. A paper I found on the net is here and another here and another here

 

After some search, I am amazed of how little research has been made on the subject. About speed I found here that:

"In his studies of the Kelso dunes, Sharp (1963;1966) also found that ripples move downwind at relatively fast rates. At a threshold velocity of 18 kph, ripples advanced downwind at a rate of .9cm per minute, with the rate increasing to 8 cm per minute during the strongest winds. Consequently, Sharp concluded the "adjustment in size, shape and spacing can presumably occur rapidly in response to differences in velocity" (1963, p. 631). From an initially flat surface, ripples can form a complete pattern in ten minutes (in a 48 kph wind) and can flatten out, reform or change direction as quickly. This rapid formation and movement of sand ripples also contributes to a large volume of sand movement. At one test plot, Sharp discovered that, in one hour's time, 48 kph winds could move 6000 pounds of sand across a 32-meter line."

Edited December 28, 2010 by michel123456

[BTAC888]

Below the water table, and in Houston 1 - 2 meters is normally where the water table lies, there is very little free air except near trees due to the roots and water consumption by the trees, however there is still dissolved oxygen and generally plenty of it. However for your situation in the sand you are correct.

 

One final note, dry sand that is not smooth and not compacted can have porosity significantly greater than the 20% I suggested due to inefficient packing caused by irregular shapes. In tests, porosity up to 40% is observed, but addition of small amounts of liquid provides sufficient lubrication to end this effect.

 

 

Thanks for your expert feedback. I found out more information about the san dune soil composition. It contains 95% find sand (0.05-2.0 mm), 4% clay (<0.002 mm), and 1% silt (0.002-0.05 mm). The porosity varies from 33 to 48%.