Tips for Choosing and Installing Fill Dirt for Underneath Pavement

Posted on: 15 March 2016

Fill dirt is incredibly useful for changing the pitch or elevation of your property, but if you are putting fill dirt under a footpath, a driveway or any other type of concrete slab, you need to choose your fill dirt carefully. Here's what to keep in mind as you select your fill dirt and prepare to pour your concrete:

1. Avoid fill dirt with lots of clay.

If possible, avoid fill dirt that has lots of clay in it. Clay absorbs water, and when your fill dirt has more water in it, its tendency to expand and contract in freezing temperatures increases. As the soil grows and shrinks, it can destabilise the pavement above it, causing shifting and potential damage.

2. Look for fill dirt with lots of sand or gravel.

In most cases, dirt either has clay or sand in it or a combination of both of these elements. As indicated above, you want to avoid too much clay, but you also want to look for fill dirt that has plenty of sand or even gravel in it.

When you have a piece of pavement resting on a bunch of fill dirt, it presses down on the dirt. If the dirt has a lot of clay, it will be prone to compression. Once the dirt has compressed, air bubbles or gaps may appear.

Dirt with lots of rocks is harder to compact or consolidate than dirt with lots of clay. It holds its position better and provides more support to your pavement. If you cannot find fill dirt with rocks in it, take what you can find and mix in some pea gravel.

3. Tamp down your dirt before pouring the concrete.

In addition to choosing the right fill dirt, you need to compress it. Before laying your slab of pavement, tamp down the soil. If it's loosely packed, it will compact and create air gaps or sinkholes.

To tamp it, run a vibratory plate compactor over the dirt before pouring the concrete. A vibratory plate compactor is about the size of a large push mower. You can hire them at many construction supply shops, and to use them, you simply push them over the dirt making repeated passes until it seems to be firmly compacted.

4. Shape the fill dirt to avoid erosion.

Finally, before you pour the concrete, look at the slope of your fill dirt. Ideally, you want a slight slope that will help to carry water away from your pavement. If the slope of the fill dirt allows water to pool right next to your pavement or if it encourages rainwater to flow toward the pavement, that can cause erosion and ultimately damage your pavement.

For more information, contact Eastern Plant Hire or a similar company.