Foundation Design – Traditional
Traditional Foundation Design Solutions
Ashby Consulting Engineering are local foundation design experts.
With almost two decades of experience with the unique soils of the Canterbury area we can advise and design the best and most cost effective foundation design solution for your building project.
Driven Timber Piles / Driven Concrete Piles
Driven timber piles can provide a very economical foundation system for light timber framed dwellings with timber floor, provided the site is reasonably flat and floor level is not too far above ground.
Driving rigs for the timer piles can be anything from a tractor mounted rig used by your local fencing contractor to the more specialised driving rigs owned by specialist contractors.
Driven piles (timber or concrete) are also commonly used to underpin foundations where ground conditions are soft, i.e. soft clay or when building on peat country.
Reinforced Concrete Piles (Bored)
Reinforced concrete piles are typically required for heavily loaded foundation systems like those found in high rise construction, commercial and industrial applications.
Although less common in domestic construction, they are often specified on “geotechnically challenged” sites. They are especially helpful on the steeper grounds of Cashmere and the Port Hills.
The piles take foundation loads down to more solid ground where they are less likely to exacerbate any slope instability.
Reinforced Concrete Strip Footings and Pad Footings
Reinforced concrete strip footings and pad footings are a versatile foundation system suitable for most applications where ground conditions are favourable.
Founding depth is dependent on the nature of the soil in which they are founded. The more expansive the soil, the deeper the foundations required to reduce the effect of the seasonal ground shrinking and swelling.
Pipe Bridging (Reinforced Concrete Ground Beams)
Pipe bridging is often required where stormwater and sewer pipes are located on a site beneath the proposed building.
Foundations are then designed to take loads away from the zone of influence for any pipe work. These foundations are similar to reinforced concrete strip footings, but with additional steel reinforcing: both longitudinal (bars) and transverse (stirrups).
Isolated Timber Piles
Isolated timber pile foundations can be found under most timber framed buildings with timber floors. They are generally regarded as both economical and versatile.
Dwelling piles typically consist of a 125 x 125 H5 treated timber pile cast in a concrete foundation 450mm to 900mm deep. Piles can be designed to provide sub-floor bracing by their cantilever action, provided the floor is not too high above ground.
In NZS3604 these are termed “Anchor Piles”. Isolated timber piles to which diagonal timber braces are attached are generally more robust built because they need to resist uplift and lateral loads from the attached braces.
Pole House / Pole Platform Footings
Similar in principle to isolated timber piles, pole house footings are generally deeper. They typically utilise round H5 treated timber poles rather than 125 x 125 square piles. They are generally spread farther apart to minimise the number of piles necessary. Pole house footings are usually specified on steeper sites which carry geotechnical difficulties.
Cantilevered Retaining Wall Footings
There are generally two types of cantilevered retaining wall footings: timber pole and reinforced concrete or masonry.
Cantilever action can be resisted by embedding piles in the ground sufficiently deep to resist overturning forces. This is the principle of the timber pole wall.
Alternatively, the cantilever action can be mitigated by providing a wide footing which essentially relies on the self weight of the wall and footing. This becomes a lever arm between the “centroid of bearing” and “centroid of mass of wall” to resist overturning forces from the lateral earth pressure behind the wall.
The wide footing is typically used for reinforced concrete and reinforced masonry retaining walls.
Please contact Ashby Consulting Engineering to discuss your foundation requirements. Phone us now on 03 383 0514 or send us an email regarding any foundation questions you may have.