Geo Technical Engineering and Foundation Engineering
Geotechnical engineering is the branch of civil engineering concerned with the engineering behavior of earth materials. Geotechnical engineering is important in civil engineering, but also has applications in military, mining, petroleum and other engineering disciplines that are concerned with construction occurring on the surface or within the ground. Geotechnical engineering uses principles of soil mechanics and rock mechanics to investigate subsurface conditions and materials; determine the relevant physical/mechanical and chemical properties of these materials; evaluate stability of natural slopes and man-made soil deposits; assess risks posed by site conditions; design earthworks and structure foundations; and monitor site conditions, earthwork and foundation construction.
A foundation is defined as that part of the structure that supports the weight of the structure and transmits the load to underlying soil or rock. Foundation engineering applies the knowledge of soil mechanics, rock mechanics, geology, and structural engineering to the design and construction of foundations for buildings and other structures. The most basic aspect of foundation engineering deals with the selection of the type of foundation, such as using a shallow or deep foundation system. Another important aspect of foundation engineering involves the development of design parameters, such as the bearing capacity of the foundation.
Aims of Foundation Engineering study
To be able to calculate the bearing capacity of shallow and deep foundations
Part of the structure which is above ground level
It is the lowest part of the structure which supports the structure by distributing its load on the soil and keeping it less than the bearing capacity of soil. Usually factor of safety in foundation is 2.5 - 3.0. Foundation can also be said to as the interface between the super structure and the soil.
If foundation is not provided the stress on the soil due to the building may exceed the bearing capacity of the soil and will fail. Thus, the foundation keeps the load on the soil in allowable range by distributing it on a vast calculated area.
Who is a foundation Engineer???
The one who has enough knowledge and experience to design the foundation. A foundation engineer must have:
|Primary duty of a foundation engineer is safety and economy
- Enough knowledge of scientific principles
- It comes by taking specialized courses e.g. Geology, Soil Mechanics, Foundation Engineering, Structural Engineering etc.
- Experience and courage to take engineering judgments
- It comes by working with seniors, attending seminars and workshops etc.
Requirements of a foundation
The foundation must be stable and safe in the first place. Safety of a foundation is ensured:
- By keeping a factor of safety.
- By avoiding structural failure of foundation itself.
- By avoiding the excessive settlements (Total settlement + Differential settlement)
- Depth should be such that foundation is below seasonal volumetric changes caused by freezing and thawing.
- Depth of foundation should be up to a point where changes of moisture do not occur frequently and abundantly. Erosion should also be prevented and any loose soil should not be underneath foundation e.g. Peat
When laying a foundation the surrounding (already existing foundations of adjacent buildings) should also be considered and the new foundation should be built at a distance from it so that the previous one is not affected by digging or excavation.
Economy and functionality:
The project of foundation designing must be economical and should fulfill all the requirements, necessities and standards.
Design Soil Parameters
Steps in designing foundation
The type, quantity and amount of loads that the structure is subjected to. These loads are sorted out to the foundation engineer by a structural engineer working on the same project, by the client or he may have to estimate them himself.
The foundation engineer must visit the site and should observe the topographical and geological features of the area where foundation is to be built. Drainage system of the area and water table information should also be studied. By observing the buildings previously built in the area, the engineer can come to know about the log term effects of soil on the buildings.
Sampling and Testing:
Samples of soil should be collected from the area and should be tested for all the required properties and parameters that are required.
Design of foundation:
At the end, now, foundation is designed with consultance with the client, structural engineer of the same project, contractor and architect.
- Shallow Foundations
- Spread footing foundation
- Strip foundation
- Combined footing
- Rectangular footing
- Trapezoidal footing
- Strap footing
- Matt footing
- Deep Foundations
Ultimate bearing capacity:
It is the least pressure that would cause shear failure of soil underneath the footing. Denoted by qult
Allowable Bearing capacity:
It is the maximum pressure that would ensure factor of safety i.e 2.5 - 3 of soil and limiting settlement to tolerable amount. Bearing capacity of shallow foundation can be found by
In correlation with field test
In situ determination