Quick Sand Formation/Condition

Quick Sand Formation/Condition

Quick sand formation/condition is not a soil type. Quick sand formation/condition is created in saturated thick layers of loose fine sandy soils when disturbed either due to vibration such as from pile driving in the near by locality or due to the presence of flowing water. The particles in trying to achieve a closer packing will force the pore water upwards and out at the surface and if this has sufficient velocity to cause a flotation or boiling up of the particles, the sand particles begin to move horizontally and get lifted up, the bottom sand rising up and its space is occupied by the adjoining particles, thus making a regular movement. The finer the sand the more readily it is affected by a current of water, especially if it contains a little clay. A particular form of this known as piping is met within coffer dam failures. Under such conditions the material may be carried off from under a structure, which can result in the settlement of buildings at a considerable distance. Even if a full flow is not created, the stability of the soil is lessened due to the upward seepage pressure. The condition can be corrected by lowering head of water by underground drainage.

Quick Sand Formation/Condition

lf there is any chance of excavation or pumping on adjoining sites causing a “loss of ground” beneath the structure by releasing a  layer of running sand. this layer should be effectively confined by  sheet piling.

Running sand:   Sand below the natural ground water level. which is carried into the trenches, trial pits or boreholes by the flow of  ground water as excavation proceeds.

Test for Sand – Fine Aggregate

Test for Sand – Fine Aggregate

The required test for sand are as follows,

1. Take a glass of water and add some quantity of sand in it. Then it is vigorously shaken and allowed to settle. If clay is present in sand,its distinct layer is formed at top of sand.

2. For detecting organic impurities in sand, take a container add some quantity of sodium hydroxide or caustic soda and also add small quantity of fine aggregate/sand stir the container. If the color of the solution changes to brown it indicates the presence of organic matter.

3. To find the presence of salts in sand, the sand is actually tasted.

4. Take a heap of sand and it is rubbed against fingers, in case if the fingers get stained then it clearly indicates the presence of earthy matter.

5. The color of sand will indicate the purity of sand, the grain sharpness and size can be observed by naked eye.

Other test for sand such as void ratio, durability are carried out by mechanical analysis.

Bulking of Sand

Bulking of Sand

The increase in moisture of sand increases the volume of sand. The reason is that moisture causes film of water around sand particles which results in the increase of volume of sand. For a moisture content percentage of 5 to 8 there will be an increase in volume up to 20 to 40 percent depending upon sand. If the sand is more fine there will be more increase in volume. This is known as bulking of sand.

Graphical representation of bulking of sand is shown below.

Bulking of sand

When the moisture content of sand is increased by adding more water, the sand particles pack near each other and the amount of bulking of sand is decreased. Thus it helps in determining the actual volume of sand, the dry sand and the sand completely filled with water will have the exact volume.

The volumetric proportioning of sand is greatly affected by bulking of sand to a greater extent. The affected volume will be great for fine sand and will be less for coarse sand.If proper allowance is not made for the bulking of sand, the cost of concrete and mortar increases and it results into under-sanded mixes which are harsh and difficult for working and placing.

To calculate the percentage of bulking of sand, the following test procedure can be used.

1. A simple container is taken and it is filled with 2/3 of the sand to be tested.

2. The height of sand is measured, for example say 200 mm.

3. Now, the  sand is taken out of container. Care should be taken to see that there is no remains of sand should be there in the container during this transition .

Bulking of sand

4. Now the same container is filled with water.

5. Pour the sand in to the container filled with water and stir the sand with a rod.

6. Again, the height of sand is measured, say 160 mm.

Bulking of sand is calculated as,  = (200-160)/160 = 40/160 = 1/4 (or) 25%.

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Classification of Sand

Classification of Sand

Classification of sand is as follows,

The sand is classified according to the size of grains, the sand are classified as fine, coarse and gravelly.

The sand which is passing through a screen with clear openings of 1.5875 mm is known as the fine sand. It is mainly used for plastering jobs.

The sand which is passing through a screen with clear openings of 3.175 mm is known as the coarse sand. It is generally used for brick masonry work.

The sand passing through a screen with clear openings of 7.62 mm is known as the gravelly sand. It is generally used for concrete work.

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