Foundation Design
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Foundation Design - Traditional
Traditional Foundation Solutions Ashby Consulting Engineering are local foundation design experts. With almost two decades of experience in the unique soils of the upper North Island we can advise and design the best and most cost effective foundation 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 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 under-pin foundations where ground conditions are soft such as soft clay or when building on peat country such as the Omaha Flats. Reinforced Concrete Piles (Bored) Reinforced concrete piles are typically required for heavily loaded foundation systems, such as is found in high rise construction, commercial and industrial applications. Although less common in domestic construction they are often specified on “geotechnically challenged” sites especially the steeper grounds of the Kaipara District. The piles take foundation loads down to more solid ground, where they are less likely to exacerbate 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 dependant 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 seasonal shrinking and swelling ground movements so common in Rodney. 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 pipes work. These foundations are generally 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 economical and versatile. Typically dwelling piles consist of a 125 x 125 H5 treated timber pile cast in a concrete foundation typically 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 ti mber braces are attached are generally more robust as they need to resist uplift and lateral loads from the braces.
Pole House / Pole Platform Footings Similar in principle to isolated timber piles, pole house footings are generally deeper, and typically utilise round H5 treated timber poles rather than 125 x 125 square piles. They are generally spread further apart to minimise the number of piles necessary, as they are usually specified on steeper sites which carry unique geotechical difficilties. Cantilevered Retaining Wall Footings There are generally two types of cantilevered retaining wall footings Timber Pole or Reinforced Concrete or Masonry. Cantilever action can be resisted by embedding piles in the ground sufficiently deep to resist overturning forces. This is the pricipal 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.
Foundation Design - Raft Slab
Stiffened Raft Foundation Raft Foundations or Waffle Slabs as they are sometimes called were developed in the 1980’s, as a response to more traditional strip footing foundation failures in expansive clays. Expansive clay soils shrink and swell significantly throughout the year in response to moisture levels and are common in Northern New Zealand. This shrink / swell cycle puts large pressures on in-ground foundations and is responsible for foundation cracking and movement which can cause damage brick facades and internal plaster board walls.
The raft foundation avoids many of these issues by sitting on top of the ground and having a lattice of steel reinforced concrete ribs and beams to provide support and stiffness. Because they do not require excavation and are specifically designed for each building they can be more robust, quicker to build and often less expensive than traditional foundations. As they are specifically engineered for each structure it is not “one size fits all”. Accurate numerical loading calculations and rib placement are critical. Ashby Consulting Engineering has spent time developing the tools and expertise to design strong, cost effective stiffened raft foundations for domestic and commercial projects.
Traditional Foundation Solutions Ashby Consulting Engineering are local foundation design experts. With almost two decades of experience in the unique soils of the upper North Island we can advise and design the best and most cost effective foundation 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 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 under-pin foundations where ground conditions are soft such as soft clay or when building on peat country such as the Omaha Flats. Reinforced Concrete Piles (Bored) Reinforced concrete piles are typically required for heavily loaded foundation systems, such as is found in high rise construction, commercial and industrial applications. Although less common in domestic construction they are often specified on “geotechnically challenged” sites especially the steeper grounds of the Kaipara District. The piles take foundation loads down to more solid ground, where they are less likely to exacerbate 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 dependant 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 seasonal shrinking and swelling ground movements so common in Rodney. 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 pipes work. These foundations are generally 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 economical and versatile. Typically dwelling piles consist of a 125 x 125 H5 treated timber pile cast in a concrete foundation typically 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 ti mber braces are attached are generally more robust as they need to resist uplift and lateral loads from the braces.
Pole House / Pole Platform Footings Similar in principle to isolated timber piles, pole house footings are generally deeper, and typically utilise round H5 treated timber poles rather than 125 x 125 square piles. They are generally spread further apart to minimise the number of piles necessary, as they are usually specified on steeper sites which carry unique geotechical difficilties. Cantilevered Retaining Wall Footings There are generally two types of cantilevered retaining wall footings Timber Pole or Reinforced Concrete or Masonry. Cantilever action can be resisted by embedding piles in the ground sufficiently deep to resist overturning forces. This is the pricipal 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.
Foundation Design - Raft Slab
Stiffened Raft Foundation Raft Foundations or Waffle Slabs as they are sometimes called were developed in the 1980’s, as a response to more traditional strip footing foundation failures in expansive clays. Expansive clay soils shrink and swell significantly throughout the year in response to moisture levels and are common in Northern New Zealand. This shrink / swell cycle puts large pressures on in-ground foundations and is responsible for foundation cracking and movement which can cause damage brick facades and internal plaster board walls.
The raft foundation avoids many of these issues by sitting on top of the ground and having a lattice of steel reinforced concrete ribs and beams to provide support and stiffness. Because they do not require excavation and are specifically designed for each building they can be more robust, quicker to build and often less expensive than traditional foundations. As they are specifically engineered for each structure it is not “one size fits all”. Accurate numerical loading calculations and rib placement are critical. Ashby Consulting Engineering has spent time developing the tools and expertise to design strong, cost effective stiffened raft foundations for domestic and commercial projects.
