DETERMINING DEPTH OF FOUNDATION

Many factors affects the determination of depth of foundation. Calculation for foundation depth is done based on type of soil, ground water table, loads from structure, bearing capacity of soil and other factors.
General factors to be considered for determining depth of foundation are:
1. Load applied from structure to the foundation
2. Bearing capacity of soil
3. Depth of water level below the ground surface
4. Types of soil and depth of layers in case of layered soil
5. Depth of adjacent foundation
The minimum depth of foundation should be considered to ensure that the soil is having the required safe bearing capacity as assumed in the design. However, it is advised to carry out soil investigation before deciding on depth of foundation. Soil investigation report will suggest the foundation depth based on the type of structure, soil properties, depth of water table, and all other variable that should be considered. Soil investigation report provides bearing capacity of soil at different levels and at different locations.
Depth of Foundation
When the soil investigation report is not available, the depth of foundation should be selected such that it is not affected by swelling and shrinking of soil due to seasonal changes. Depth of foundation should also consider the depth of water table to prevent and scour below the ground.
For foundation near existing foundation, It must be ensured that pressure bulbs of foundations do not coincide if the depth of new foundation has to be taken below the depth of existing foundation.
The foundation should not be contracted at shallow depth considering the frost action in cold countries.
Rankine’s formula provides the guidance on minimum depth of foundation based on bearing capacity of soil.
Rankine's Formula for Depth of Foundation
Where, h = minimum depth of foundation
p= gross bearing capacity
density of soil= density of soil
Angle of repose of soil = angle of repose or internal friction of soil.
The above formula does not consider the factors discussed above and just provides the guidance on minimum foundation depth, assuming that the foundations are not affected by factors such as water table, frost action, types and properties of soil etc. as discussed above. This formula does not consider the loads from the structure on the foundation.
In the Rankine’s formula, it can be seen that foundation depth depends on the bearing capacity of soil, so, if the bearing capacity of soil increases, the depth of foundation also increases.
Foundation Depth Calculator:
Gross bearing capacity of soil= p =kN/m2
Density of soil =
density of soil

kN/m3
Angle of repose =
Angle of repose of soil

 degree
Mnimum foundation Depth= h =m

Comments

Post a Comment

Popular posts from this blog

How To Calculate or Estimate Long-span Aluminium Roofing Sheets.

Image
Aluminium roofing sheets, they come in rolls of average of 600mm to 1300mm depends on the manufacture and specifications. As stated in previous articles, the aluminium sheets comes in rolls at the factory just like toilet rolls but with different widths and thickness based on specifications. Calculating the roof required could be done by calculating the surface area in square meters of the area covered by the aluminium and for some companies it could be calculated in meter lengths ,knowing the width which is 600mm above as constant. For a simple gable roof as shown in pic 1 with length of 25.2m. First you must know the height of roof from the section. For this sample we are taken the eight to be 3meters (10 feet)to know the length of leaf “x” or “y” Remember the pythagoras theorem x2=32 +6.12 x=6.8m Hence the area of roof is (6.8 i.e x)+6.8 i.e y) multiply by length 25.2m=342.72m2 If the width of the roof comes in 600mm or 0.6m, the length of the roof ...
Read more

Post Tension Slab – Advantages and Disadvantages of Post Tension Slab

Image
Post Tension Slab Although concrete is a strong material for construction, it is not resistant to breakdown especially where longer concrete slabs are required like in a bridge or a length of a beam. For this, the concrete slab is tensioned with a process called pre-stressing and the slab of concrete which comes out after this process is known as post tension slab. This slab is much stronger as well as more durable than the normal concrete slabs. In today’s world, where the modern engineering is finding new ways to build longer, more efficient and stronger structures, post tension slab becomes one of their chief requirements. There are many advantages and disadvantages of post tensioned slabs which we will discuss in this post. Advantages of Post Tension Slab Post tension slabs are advantageous in many ways. Some of the major benefits of post tension slabs are as follows. 1. Reduced cost: Post tension slabs are excellent ways to construct stronger structures at an affordable...
Read more

How to install POP (plaster of paris) ceilling

Image
Plaster of Paris is regarded as any type of plaster containing calcined gypsum (calcium sulfate dihydrate), sand and water. When these ingredients are combined, they result in the formation of a tough, dry product; however, plaster of Paris can be sanded to achieve a variety of looks. By following some basic guidelines, you can use plaster of Paris to mend cracks, fix dents,for ceiling, in walls and even to create artworks. However in this case our focus is on ceiling. POP popularly called plaster of Paris is used for a lot of purposes because it can easily be formed to any shape and it hardens quickly and is easy to operate. To do a pop ceiling in your home, getting it done is in two ways, you can buy the materials yourself which include pop cement , yarn(sponge-like material) etc then pay the installer based on per square meter of area of coverage, or you can give it out totally as a contract. But these are the basic steps in getting pop ceiling cast-on-site done. Get cemen...
Read more