Foundations types and selection of suitable foundation.
The purpose of foundations is to transfer loads on columns or bearing walls in building to the soil below.
The design o foundations often required special care and
precaution, unlike other structure elements such as beams and slabs , as any
error in their design can be easily remedied and rectified except for errors in
the design of foundations as this leads to the collapse of a part or all of the
structure if it is completed. Take care and make necessary reservations both in
design and implementing foundations.
It should be noted that it is also not like the design of
all structure elements above the surface of the land, where the design is done
by the knowledge of the structure engineer, but in the design of foundations
requires joint efforts between both geotechnical and structure engineer.
Where geotechnical
engineer conducts studies and soil research and provides recommendations for
the type, depth, and level of foundation as well as the net soil effort allowed
at the foundation level.
While the structure engineer is entrusted with designing
the fundamentals through structural calculation on the columns at the level of
the ground surface, thus determining the concrete dimensions of the
foundations, as well as, the quantity and details of the reinforcing steel and
the views of these design of these elements.
-Types of foundations.
There are many types of foundations and choosing the appropriate
type for a structure or building that is desired depends on several factors including:
- The depth of foundation or the depth of the layer that will be loaded on, measured from the surface of the natural ground.
- The capacity and bearing capacity of the soil at the foundation level or the value of the permissible net breeding effort at the foundation position.
- The value of the loads on the columns and transported to the soil and counting the floor of the building.
- The level of groundwater in relation to the land surface and foundations.
- The nature of the loads transferred to the soil, are they vertical forces, lateral pressure, bending moments, or both.
Foundations can be divided according to the level and depth
of foundation relative to the natural surface of the land into two types:
- Shallow foundation
- Deep foundation
- Shallow foundation.
There are the common and well-known foundations, which includes:
- Isolated footings.
- Wall footing.
- Combined footings.
- Strip footing.
- Raft footing.
- Deep foundations.
It includes:
- Piled footings.
- Caisons foundation.
In the follow articles, we will explain each type of
foundation and how they design and construct.
- Good foundation and factors affecting selection of suitable foundation.
A good foundation is the foundation that resists the
different loading conditions that it may
be exposed to represented by the weight of the structure in addition to other
load exposed to the structure such as live load, wind loads. Earthquakes, or
any loads.
Other especially depending on the type and use of the
structure.
Foundation resistance is here by providing reactions
distributed in the soil, weighting with the loads of structure and located on
the foundation which cause the generation of stresses in the soil that do not
exceed the safe and permissible stresses, the ability of soil bearing under
this type of conditions.
It should be noted that in addition to this, adequate
protection must be available for the foundations against the infiltration of
groundwater into it and inside the structure which in turn affects its uses and
its lifespan.
- The factors that leads to choosing the type of foundation.
1- Structure requirements.
It includes:
- Sensitivity of structure to relative or uneven subsidence.
- Structure lifespan.
- Foundation level and ground structure level.
- Various factors.
2- Foundation load.
It includes:
- Value of dead and live loads.
- Negative lateral friction in case of deep foundations.
- The type and nature of loads (axial and non-axial load, vertical or lateral loads, static or dynamic loads, etc.)
- How to distribute loads.
3- Soil and groundwater conditions.
It includes:
- How loads transfer from structure to foundation then to the soil under foundation.
- Soil resistance under the foundation and its compressibility.
- Troubled soil such as expansive soils (shrink and swell).
- The presence of layers of fill and the problems that result from (subsidence, iron rust, deterioration and attacking the foundation, etc.)
- Groundwater level and the extent of its fluctuations.
- The impact of rust and chemical agents.
- The presence of defects in the subsoil such as sewage lines, caves, or voids caused by drawings water from wells.
4- Site and environmental condition.
It includes:
- Topography of the site (balanced of natural tendencies of the soil, back-filling, etc.)
- The presence of drains, canals, or farms and the exposure of the soil to erosion.
- The level of neighboring building, the type and nature of their foundation and the depth established level.
- The effect of groundwater drainage.
- The thermal and frost effects.
- The impact of earthquakes and natural disasters.
5- Construction requirements.
It includes:
- The duration and time required to implement the project.
- The permissible area for the implementation of the project.
- Feasibility study for some works such as drilling and back-filling the side of drilling, drainage of groundwater, etc.
6- Economic consideration and miscellaneous.
It includes:
- The cost of construction and how to estimate.
- The degree of confidence in the proposed foundation system.
- Quality controlling of the site.