Different types of footing and foundation

- Isolated Footing
- Combined Footing
- Mat or Raft Foundation
- Pile Foundation
- Piled Raft Foundation
- Shore Pile or Sheet Pile Protection System

1. Presentation On Isolated Footing Combined Footing Mat or Raft Foundation Pile Foundation Piled Raft Foundation Shore Pile or Sheet Pile Protection System Submitted By: Farhan Sadek Efaz Student ID: 1601124 Department of Civil Engineering Chittagong University of Eng. & Tech. Submitted To: Ms. Nafisa Tabassum Subah Lecturer, Department of Civil Engineering Chittagong University of Eng. & Tech.

2. Isolated Footing Isolated footing is defined as the footing, which is provided beneath the column to distribute the loads safely to the bed soil. This kind of footing is used to support single-columns and when the columns are arranged relatively at long distance. This the most inexpensive kind of footing.

3. Isolated Footing Fig: Section of an Isolated Footing Fig: Various Types of Isolated Footing

4. Isolated Footing Advantages of Isolated footing: ( i ) Isolated Footing is cost effective. ( ii) Construction is easy. ( iii) Material used is concrete. ( iv) Does not require skilled labors for construction.

5. Isolated Footing Disadvantages of Isolated footing: ( i ) It will have settlement. ( ii) It has limited capacity. ( iii) It can be subjected to torsion or tension forces easily.

6. Combined Footing

7. Combined Footing Whenever two or more columns in a straight line are carried on a single spread footing, it is called a combined footing. A combined footing is usually used to support two columns of unequal loads. In such a case , the resultant of the applied loads would not coincide  with the centroid of the footing , and the consequent the soil pressure would not be uniform .

8. Combined Footing Combined footings are provided only when it is absolutely necessary, as 1 . When two columns are close together, causing overlap of adjacent isolated footings 2. Where soil bearing capacity is low, causing overlap of adjacent isolated footings 3. Proximity of building line or existing building or sewer, adjacent to a building column. Fig.: Section of a Combined Footing

9. Raft Foundatio n Raft foundations (sometimes known as Mat Foundations ) are a large concrete slab which can support a number of columns and walls.The slab is spread out under the entire building or at least a large part of it which lowers the contact pressure compared to the traditionally used strip or trench footings.Because of the speed and volume of houses required after the second world war, the raft foundation was widely used. The raft foundation was cheaper, easier to install and most importantly, did not require as much excavation as the usual strip foundations.When the Building Regulations were introduced in 1965 there were no generic rules for raft foundations as there were for strip foundations.This meant that to use a raft foundation, it had to be designed and approved by Building Control. This made the entire operation much more difficult and time consuming so raft foundations became less widely used almost overnight.

10. Raft Foundatio n Fig: Layout of Raft Foundation

11. Raft Foundatio n When Are Raft Foundations Used Rafts are most often used these days when the strata is unstable or (because of this) a normal strip foundation would cover more tha n 50% of the ground area beneath the building. There are also situations (usually in areas where mining has occurred) where there may be areas of movement in the strata. They are much more commonly used in the construction of commercial building in the UK that they are for domestic homes, but can be used very successful in both situations. To understand when it is better to use raft foundations, you need to understand how they work. Fig: Section of a raft foundation

12. Raft Foundatio n Advantages and Disadvantages of Raft Foundations Raft foundations tend to be cheaper and quicker to use than traditional footings. There are a number of reasons why this is the case: - The foundation and floor slab is combined, which saves time and materials - Less excavation is required - Other reasons that make raft foundations preferable to footings are due to their engineering benefits. They are ideal for poor ground condition where normal footings would not cope well as they cannot spread the load as effectively.

13. Raft Foundation Advantages and Disadvantages of Raft Foundations Related to this is that raft foundations can reduce differential settlement, where settlement occurs at different rates across the ground surface of the building, which reduces cracking and other more serious problems . The main disadvantage is that they can prone to edge erosion if they are not treated properly. They are not effective is the load of the building is going to be focused on a single point, although this is rare in domestic construction, so this isn’t generally of concern. Fig: Construction of Raft Foundation

14. Pile Foundation A pile is basically a long cylinder of a strong material such as concrete that is pushed into the ground to act as a steady support for structures built on top of it.

15. Pile Foundation Pile foundations are used in the following situations: # When there is a layer of weak soil at the surface. This layer cannot support the weight of the building, so the loads of the building have to bypass this layer and be transferred to the layer of stronger soil or rock that is below the weak layer. # When a building has very heavy, concentrated loads, such as in a high rise structure, bridge, or water tank. # Pile foundations are capable of taking higher loads than spread footings.

16. Pile Foundation There are two fundamental types of pile foundations (based on structural behaviour ), each of which works in its own way. End Bearing Piles In end bearing piles, the bottom end of the pile rests on a layer of especially strong soil or rock. The load of the building is transferred through the pile onto the strong layer. In a sense, this pile acts like a column. The key principle is that the bottom end rests on the surface which is the intersection of a weak and strong layer. The load therefore bypasses the weak layer and is safely transferred to the strong layer.

17. Pile Foundation Friction Piles Friction piles work on a different principle. The pile transfers the load of the building to the soil across the full height of the pile, by friction. In other words, the entire surface of the pile, which is cylindrical in shape, works to transfer the forces to the soil. To visualise how this works, imagine you are pushing a solid metal rod of say 4mm diameter into a tub of frozen ice cream. Once you have pushed it in, it is strong enough to support some load. The greater the embedment depth in the ice cream, the more load it can support. This is very similar to how a friction pile works. In a friction pile, the amount of load a pile can support is directly proportionate to its length.

18. Pile Foundation Fig: Different Types Of Piles

19. Pile Foundation Fig: Steps of Pile Foundation

20. Piled Raft Foundation A piled raft foundation combines two foundation-building techniques into a hybrid design suitable for specialized circumstances. The raft, or spread, foundation spreads the load of the building across the ground. Think of it as a raft floating on the ground supporting a structure. Piles are columns extending below the ground surface that connect at the top of the building. A piled raft foundation uses both methods to support the building.

21. Piled Raft Foundation When a Piled Raft Foundation Is Used Builders use piled raft foundations when the stability of the material that anchors the piles is questionable or when stable material does not extend under the entire building. The piled raft foundation offers the floating foundation partially anchored for support.

22. Shore Pile Or Sheet Pile Protection System

23. Shore Pile Or Sheet Pile Protection System

24. Shore Pile Or Sheet Pile Protection System Sheet piles are  sections  of sheet  materials  with interlocking edges that are driven into the  ground  to provide earth  retention  and  excavation  support. Sheet piles are most commonly made of  steel , but can also be formed of  timber  or  reinforced concrete . Sheet piles are commonly used for  retaining walls ,  land reclamation , underground  structures such as car parks and  basements , in marine  locations  for riverbank protection,  seawalls ,  cofferdams , and so on. The selection of  sheet piling  is dependent on factors, such as: - The type of  work , for example. whether it is permanent or temporary. - Site   conditions . - The required depth of  piles . - The   bending moments  involved. - The nature of the  structure . - The type of protection required.

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