We specialize in low impact house sites, roads and installation. From
the most technical to the simplest foundations and footings, we really enjoy
taking your site from preparation to finish grading, and then move immediately
into the hard scape development, and finishing with a complete landscape.
However, working with other grading crews works just as well..
A foundation is a structure that transfers loads to the earth. Foundations
are generally broken into two categories: shallow foundations and deep
foundations.
Shallow Foundations
Shallow foundations are usually embedded a meter or so into soil. One
common type is the spread footing which consists of strips or pads of concrete
(or other materials) which extend below the frost line and transfer the weight
from walls and columns to the soil or bedrock. Another common type is the
slab-on-grade foundation where the weight of the building is transferred to the
soil through a concrete slab placed at the surface.
Deep Foundations
Deep foundations are used to transfer a load from a structure through
an upper weak layer of soil to a stronger deeper layer of soil. There are
different types of deep foundations including helical piles, impact driven
piles, drilled shafts, caissons, piers, and earth stabilized columns. The naming
conventions for different types of foundations vary between different engineers.
Historically, piles were wood, later steel, reinforced concrete, and
pre-tensioned concrete.
Earthquake-protective foundations
Earthquake-protective foundation, also known as seismic or base
isolation system, is a collection of structural elements which should
substantially decouple a superstructure from its substructure resting on a
shaking ground thus protecting a building or non-building structure's integrity.
It is believed to be the most powerful tool of the earthquake engineering
pertaining to the passive structural vibration control technologies.
Design
Foundations are designed to have an adequate load capacity with limited
settlement by a geotechnical engineer, and the foundation itself is designed
structurally by a structural engineer.
The primary design concerns are settlement and bearing capacity. When
considering settlement, total settlement and differential settlement is normally
considered. Differential settlement is when one part of a foundation settles
more than another part. This can cause problems to the structure the foundation
is supporting. It is necessary that a foundation is not loaded beyond its
bearing capacity or the foundation will "fail".
Other design considerations include scour and frost heave. Scour is when flowing
water removes supporting soil from around a foundation (like a pier supporting a
bridge over a river). Frost heave occurs when water in the ground freezes to
form ice lenses.
Changes in soil moisture can cause expansive clay to swell and shrink. This
swelling can vary across the footing due to seasonal changes or the effects of
vegetation removing moisture. The variation in swell can cause the soil to
distort, cracking the structure over it. This is a particular problem for house
footings in semi-arid climates such as South Australia, Southwestern US, Turkey,
Israel, Iran and South Africa where wet winters are followed by hot dry summers.
Raft slabs with inherent stiffness have been developed in Australia with
capabilities to resist this movement.
When structures are built in areas of permafrost, special consideration must be
given to the thermal effect the structure will have on the permafrost.
Generally, the structure is designed in a way that tries to prevent the
permafrost from melting.
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