How to Fill Materials in Foundations, Trenches, Plinth, and Flooring? [PDF]

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A filling refers to a quantity of earthen material such as murrum, soil, rock, aggregate, shingle, and sand that is placed and compacted in trenches, foundation, and under floors for the purpose of filling in a hole or depression.

In this article, we discuss the type of materials used in filling and how to do filling in different kinds of works such as trenches, plinth, and flooring.

Types of Filling Materials

1. Soil or Earth

The soil used for the filling in a different type of works shall be from salts, organic, or other harmful matter. Black cotton soil is not recommended for use unless so specified due to its property of high expansion.

The selected soil for filling borrow pits and surplus earth from excavation, if any, shall be directly used for filling, and double handling of soil shall be avoided. All clods of earth exceeding 50 mm shall be broken or removed.

2. Murrum

The murrum shall be obtained from approved pits and quarries of disintegrated rocks, which contain silicon material, and a natural mixture of clay of calcareous origin. The standard size of murrum material shall vary from dust to a 40 mm gauge.

3. Sand

The sand which is used for filling shall be clean, free from dust, organic, and other extraneous matter.  It shall not contain more than 5% of clay/silt.

4. Shingle

The shingle shall be clean and free from foreign matter and obtained from river or canal beds. The shingle of all in size ranging from 40 mm down to 4.75 mm gauge shall contain a sufficient proportion of fine material to fill all interstices and ensure binding when consolidated.

How to do Filling in Foundation?

1. Once the work in the foundation has been completed the space around the foundation masonry in trenches shall be cleared of all debris, brickbats,  etc.,
2. The cleaned foundation trenches shall be filled with earth in layers not exceeding 250 mm, each layer being watered, rammed, and compacted before the succeeding one is laid.
3. Earth shall be rammed with iron rammer where feasible and with the butt ends of crowbar where rammer cannot be used.

How to do Filling in Trenches of Pipes, Drains, Cables, etc.?

1. The filling material selected for filling shall be free from salts, organic, or other harmful matter. 
2. All clods of the filling material exceeding 50 mm shall be broken or removed.
3. Unless otherwise indicated, where the excavated material is mostly rock, the rock fragment shall be broken into pieces not bigger than 150 mm size and mixed with fine material, to fill up the voids.
4. The filling process in trenches for pipes and drains shall be commenced only after the joints of pipes and drains have been tested.
5. Generally, the excavated material is recommended for the filling of trenches on both sides simultaneously and on top of pipes in layers not exceeding 250 mm thick.
6. Each layer is watered, rammed, and compacted. It must be made sure that no damage is caused to the pipe below.
7. When the available filling material is rock, the filling up to a depth of 300 mm above the crown of pipe shall be done with fine material such as earth, murrum, or pulverized decomposed rock according to the availability at the site.
8. The remaining filling can be done with rock fragments mixed with fine material as available to fill up the voids, watered, rammed, and compacted, in layers not exceeding 250mm thick.
9. Special care shall be taken in backfilling to avoid future troubles from bursts and leakage due to differential settlement.

How to do Filling in Plinth, flooring, and Hard Standings?

1. The filling in plinth shall be started from the lowest level in regular horizontal layers, each not exceeding 250 mm in depth.
2. Each layer of the filling shall be compacted by ramming with rammers of 7 to 10 kg weight.
3. The filling shall be adequately watered for achieving maximum compaction.
4. The top surface of the filling shall be neatly dressed level or to a slope or grade as desired.
5. For filling in large floors, like factory floors, hangars, etc. compaction is carried out by mechanical means such as sheep-foot roller or by hand roller or by power roller to 90 to 95 percent of standard Proctor’s density under optimum moisture conditions.

How to Carry out Measurement of Filling?

The methodology used for recording the measurement of filling may vary depending upon the country rules and methods. General measurement recording method is described below-

1. The length and breadth of filling shall be measured with a steel tape correct to the nearest centimeter or millimeter.
2. The depth of cutting or height of filling shall be measured, correct to 5mm, by recording levels before the start of the work and after the completion of the work.
3. The cubical contents shall be worked out to the nearest two places of decimal in cubic meters.
4. In case of borrow pits, diagonal ridges, cross ridges, or dead-men, the position of which shall be fixed by the engineer, shall be left by the contractor to permit accurate measurements being taken with steel tape on the completion of the work.
5. Deduction of such ridges and dead men shall be made from the measurements unless the same are required to be removed later on and earth so removed is utilized in the work.
6. In the case where ordinary and hard rock are mixed and used as filling material, two kinds of rock shall be stacked separately and measured in stacks.
7. A deduction of 50% is applied to allow for voids in stacks.
8. In the case, where the measurement of the depth of cutting is not feasible or reliable, the actual measurements of the fill shall be calculated by taking levels of the original ground before the start of the work after site clearance and after compaction of the filling material.

FAQs

Read More:
1. Backfilling Procedure in Basement
2. Backfilling of Sewer-Sanitary Trench -Compaction and Equipments
3. Excavation and Backfilling of Soil – Work Sequence and Procedure
4. Backfilling in Foundation: Types and Procedure