Judging Concrete Foundation Depth

Residential home construction site in New ZealandA home’s foundation can spell the difference between success and disaster. After all, it’s the one that keeps the structure upright. Without a solid foundation, a home (or any building, for that matter) wouldn’t even be standing. This is why it’s important to never, ever skimp on preparing a structure’s foundation at all costs.

Suppose you’re about to dig the foundation for your project. It’s not enough to just deploy an excavator courtesy of a firm such as Hire Direct Ltd. and start digging. Your foremost concern is the foundation’s depth. Various factors affect the recommended foundation depth, so take note.

Ground Quality

Before judging how deep, you must know if the ground is actually suitable to hold the weight of an entire structure. New Zealand’s official standards define ‘good ground’ as any soil or rock that can permanently withstand a bearing capacity of 300 kPa. But this soil should exclude anything compressible, including soft soils such as topsoil and clay, as well as non-compact gravel.

Digging Proper

If the ground fits the criteria, it’s time to dig. Keep in mind that recommended depths vary depending on soil type. For instance, clay-like soils (soft ones) require penetration to be below the area where seasonal shrinkage and swelling can cause the soil to shift. Fine sand and silt-laced soil require penetration below the zone where frost can form, and that all soil types must have penetration below the topsoil layer.

Two types of foundations come into play: shallow or deep. The former is good if the soil is stable and level enough. A patch of land with severe sloping or drainage issues is the worst place to place a shallow foundation on. Obviously, a deep foundation is recommended for areas with sub-par soil stability and severe sloping. In locales such as this, a shallow foundation is vulnerable to tilting or slipping. Most of the time, deep foundations are deep enough to reach into the bedrock.

Consider these things when digging a structure’s foundation, for even a minor slip-up can turn the project into a costly failure.