Fill Sand in Construction: A Comprehensive Guide

Fill sand is used for filling, levelling, and providing a solid foundation for site works, foundations, floors, and paving. Fill sand should possess characteristics such as proper grading, low contamination, and compaction.

This guide will discuss the various types of fill sand, selection criteria, and some guidelines for the use of fill sand in construction projects.

What Is Fill Sand and Its Role in Construction?

Fill sand is a loose, fine-grained material used to occupy voids and create a compacted layer beneath or around construction elements. It is primarily used to provide uniform support below uneven ground, excavation, or formation below the required level.

Fill sand in the construction industry is used in the following applications:

• Raising ground levels.
• Trenching and filling in low-lying areas.
• Making bases for slabs on grade.
• Backfilling of a foundation.
• Assisting with paving and landscaping jobs.
• Enhancing drainage where appropriate, granular material is specified.

Types of Fill Sand Used in Construction

There are three major types of construction fill sand: coarse, fine, and utility sand. Each type has different particle sizes, drainage, and compaction.

The following are the common types of fill sand used in construction:

Read our guide on types of sand used in construction to compare various sands for different construction applications.

Choosing the Right Fill Sand for Your Project

Choose fill sand in accordance with the use, compaction, drainage, and situation of the site. The material should be solid for support and fulfill the project requirements.

The key points to review:

• Project requirements: Use sand that matches foundation filling, trenches, floors, or landscaping.
• Grading: Choose suitable particle distribution for compaction and support.
• Compaction: Make sure the sand can achieve the desired density in the field.
• Drainage: Use free-draining sand where water movement is important.
• Quality: Minimise the amount of silt, clay, organic matter, and debris.
• Budget: Consider material and handling, transport, testing, and wastage.
• Site conditions: Review groundwater, rainfall, soil, and equipment access.

Choose fill sand always according to the specification of the project, not only according to the price and manufacturer description.

Calculating the Quantity of Sand Needed

The volume of sand to be filled (sand fill volume) is calculated by multiplying the area to be filled with the depth of fill. For rectangular areas, use this formula:

Length × Width × Depth = Volume of fill sand

Follow the steps below to calculate the quantity:

1. Measure the length and width: Record length and width in metres.
2. Measure the fill depth: Change the depth into metres and then calculate. For example, 300 mm = 0.30 m.
3. Calculate the volume: Volume = Length × Width × Depth. Example: 10 m × 5 m × 0.30 m = 15 m³.
4. Add allowance for compaction and wastage: Loose sand will shrink when compacted. The allowance is to be determined from the project specification.
5. Check irregular areas separately: Divide irregular areas into smaller rectangles or simple shapes and calculate each volume, then sum up the volumes.

Testing and Ensuring Sand Quality

Before use, check the density, moisture content, silt and grading of the fill sand, and for any visible contamination. These tests will provide a guarantee that the sand can compact properly and will provide stability over the long term.

These are the key tests to be performed:

• Field Density Test: Test to determine the density of compacted fill sand in place. It is useful to verify that the compaction level required on site has been attained.
• Moisture Content Test: This test is used to find out how much water is in the sand. Moisture content during compaction can affect compaction.
• Silt Content Test: This test is conducted to find out the percentage of fine silt present in the sand. If the silt content is too high, it can negatively affect the material's quality and performance.
• Grading Test: This test is used to determine the particle size distribution of the sand. The correct grading will help to achieve uniform support and compaction.
• Visual Quality Check: Check the sand for unwanted materials such as clay, organic matter, rubbish, roots, etc.

Avoiding Common Mistakes with Fill Sand

Common mistakes with fill sand include choosing the wrong material, ignoring moisture, placing thick layers, and skipping proper compaction. The avoidance of these errors can minimise settlement issues, drainage issues, and rework.

The following are the common errors that should be avoided:

• Choosing fill sand only based on price.
• Using the wrong sand type for the application.
• Ignoring moisture content.
• Placing fill sand in very thick layers.
• Skipping proper compaction.
• Using sand with excessive silt or debris.

Read our materials required for house construction guide to understand where sand and other materials are required at different stages of a building project.

Next Steps: Practical Tips for Using Fill Sand Effectively

Proper choice of sand material, moisture control, and compaction of each layer are crucial factors when using fill sand. Good site practices will lead to better support, less settling, and no rework.

Here are some tips for effective use of fill sand:

• Store fill sand on a clean and firm surface.
• Keep the sand free from soil and debris.
• Keep excess rainwater away from the stockpile.
• Apply fill sand graduated in layers.
• Ensure adequate moisture when compaction is being done.
• Obey project specifications.
• Use field testing where compaction needs verification.

Frequently Asked Questions

How to calculate sand for filling?

Fill sand is calculated by multiplying the length, width, and depth. For example, an area of 10 m x 5 m with a fill depth of 0.30 m needs 15 m³ of sand, before adding an allowance for compaction and wastage.

What is sand fill used for?

Sand fill is used for the following applications: levelling grounds, filling trenches, raising plinth levels, and preparation under floors and paving.

What is bulking of sand in construction?

The apparent volume of sand increased by moisture around the sand particles is called bulking of sand.

How does bulking of sand affect concrete mix ratios?

If the wet sand is measured by loose volume, bulking can cause a lesser amount of sand to be added than required. This can disturb the intended proportions of the concrete mix and impact the workability and consistency of the concrete.

How can you check the quality of sand for construction?

Determine the quality of sand by conducting a grading test, moisture test, silt test, density test, and a visual test for contamination. Use proper field and/or lab tests for important construction work rather than appearance alone.