Backfill Sand for Tank Foundation 1

[D27]

Hi!, we are doing tank foundation (for Demi water, fresh water, etc) using concrete ringwall ... and we are using backfill sand on top of soil backfill, im in need of specification for backfill sand, is there any specific code or standard for backfill sand? please help ... thanks!

d27

 

[bimr]

8.3.2 There are several different materials that can be used for the grade or surface on which the tank bottom will rest. To min­imize future corrosion problems and maximize the effect of corrosion prevention systems such as cathodic protection, the material in contact with the tank bottom should be fine and uniform. Gravel or large particles shall be avoided. Clean washed sand 75 mm- 100 mm (3 in.- 4 in.) deep is recommended as a final layer because it can be readily shaped to the bottom contour of the tank to provide maximum contact area and will protect the tank bottom from coming into contact with large particles and debris. Large foreign objects or point contact by gravel or rocks could cause corrosion cells that will cause pitting and premature tank bottom failure.

During construction, the movement of equipment and materials across the grade will mar the graded surface. These irregularities should be corrected before bottom plates are placed for welding. Adequate provisions, such as making size gradients in sublayers progressively smaller from bottom to top, should be made to pre­ vent the fine material from leaching down into the larger material, thus negating the effect of using the fine material as a final layer. This is particularly important for the top of a crushed rock ringwall.

Note: For more information on tank bottom corrosion and corrosion prevention that relates to the foundation of a tank, see API RP 651.

https://law.resource.org/pub/us/cfr/ibr/002/api.650.2007.pdf

 

[oldestguy]

Check with local geotech firm for testing and specify that all fill must meet 95 percent of Modified Proctor Density.

 

[BigH]

Similar to another post in another forum . . . we typically used crushed (3/8") fines for the finishing layer against the tank bottom.

 

[emmgjld]

If the lower fill is coarse grained or may allow downward migration of fines, it is useful to place a geo-fabric for separation purposes immediately below the final/upper layer. Judicious use of fabric for separation may allow the use of readily available, less costly lower fill materials, as long as they can be properly compacted to control total/differential settlement. Like oldestguy, I am a big fan of the Modified Proctor.

 

[Ron]

Clean fine to medium sand with less than 10% fines, compacted to 95% of the maximum dry density as determined by the Modified Procter Method.

If you have a water table issue where water will be present at or near the bottom of the ring wall, add a 6" layer of medium to coarse sand having a fineness modulus of 2.75 or greater to act as a capillary barrier.

 

[BigH]

Caveat on my use of the 3/8" crushings . . . beneath would be a well graded sand and gravel - similar to a subbase or base course. -