The Constructor

Backfilling in Foundation : Types and Procedure

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What Is Backfilling?

In construction, backfilling is the process of replacing or reusing the soil that is removed during building construction to strengthen and support a structure’s foundation or any other structural member.

Backfilling in Foundation

Factors affecting Backfilling in Foundation

  1. Choosing the right backfill material
  2. Compacting the backfill
  3. Period of backfilling

Types of Backfilling in Foundation

Based upon the type of material used for backfilling in foundation, they can be divided into,

Course Grained Soil

Coarse-grained soils include gravelly and sandy soils and range from clayey sands through the well-graded gravels of gravel-sand mixtures  with little or no fines.

Fine-Graded Soils Of Low To Medium Plasticity

In organic clays of low to medium plasticity (gravelly, sandy, or silty clays and lean clays) and inorganic silts and very fine sands of low plasticity (silty or clayey fine sands and clayey silts) are included in this category.

Commercial By-Products

The use of commercial by-products, such as furnace slag or fly ash as backfill material, may be advantageous where such products are locally available and where suitable natural materials cannot be found. Fly ash has been used as a lightweight backfill behind a 25-foot-high wall and as an additive to highly plastic clay. The suitability of these materials will depend upon the desirable characteristics of the backfill in foundation and the engineering characteristics of the products.

CLSM (Controlled low strength material)

CLSM is a self-compacting, flowable, low-strength cementitious material used primarily as backfill, void fill and utility bedding as an alternative to compacted fill. Conventional CLSM mixtures usually consist of water, Portland cement, fly ash or other similar products, fine or coarse aggregates or both. Fly ash obtained from thermal power plant was used.

Steps involved in backfilling in foundation

  1. Before you begin the backfill process, you have to be sure that the foundation cures for at least five to seven days. There are even instances when cracks may occur when you backfill too soon.
  2. The ground over which the filling has to be done should be cleaned off all grass, loose stones, rubbish of all kinds etc. If there is water in the area, it should be pumped or bailed out.
  3. Determine the types of material you will use for foundation backfill. A mixture of various materials such as rocks, soil and stone are commonly used. Some soil can retain too much moisture that is not good for your foundation.
  4. Try to use the refilling material from the excavated earth
  5. The approved excavated material, which has been stocked, shall be cleaned of all rubbish, large size stone, vegetation etc.
  6. Begin backfilling at the corners and be sure that the distribution of the soil is even so as to provide ample lateral support for the walls of your home.
  7. Use an excavator to fill in twelve inches of mixed materials on the sides of the area. After which, compress the soil and stone using the rolling compactor. You must repeat the same backfill procedure until the entire area is completely filled.
  8. Filling should be done in layers, each layer being of 15cm to 20cm.
  9. Each layer is watered and compacted with heavy rammers of wooden logs or steel.
  10. Under no circumstances black cotton soil shall be used for filling in plinth and footing pits.
Read More : Excavation and Backfilling of Soil – Work Sequence and Procedure
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