This presentation provides details on the construction process of a mat foundation. It discusses when mat foundations are required, such as for buildings with large footprints or poor soil conditions. The 13 step construction process is then outlined, including soil testing, excavation with shoring and bracing, placing reinforcement meshes and concrete in layers, vibrating, and curing. Advantages of mat foundations include reducing differential settlement and accommodating poor soils, while disadvantages include higher costs and potential for trapped heat or water seepage.

1. Welcome to
Our
presentation

2. Ahsanullah university of science and technology
Department of civil engineering
CE 200
Details of Construction
Presented By:-
Group 03
Salma Afia Mim (16.02.03.015)
Mehedi Hassan Shuvo (16.02.03.016)
Abir Mahmud (16.01.03.052)

3. Visited Sites
Malibagh,Hazipara,DIT Road.
Tejgaon Industrial Area,Roads and
Highways Department.

4. MAT FOUNDATION

5. What is Mat Foundation ?
It is a type of shallow foundation(depth≤width).
Generally used in heavy industrial plant,official and commercial
buildings and sometimes in residential buildings where
basement is needed.
Mat foundation is a large,thick,usually reinforced concrete mat
which transfers load from a number of columns, or walls to the
underlying rock or soil. Also known as Raft Foundation.

6. When Mat Foundation is required ?
Where differential settlement is suspected.
If foundation area covers 50-60% of the total plot area.
It is required where soils have low bearing capacity and have to
support heavy structural loads.
When the expenses of deep foundation is higher than mat
foundation.

7. Procedure Flow Chart
Centering &
Leveling
Polythene
& CC Layer
Leveling of
Soil
Vibrating
Placing
Reinforcement
Concreting
Leveling
Shoring
Soil Excavation
Shuttering &
Bracing
Placing CC
Block
Soil Test

8. Details Construction Process of Mat Foundation

9. Step 01- Soil Test
 Bearing capacity of soil;
 Soil classification;
 Ground water level;
 Moisture content;
 Appropriation & depth of Mat.

10. Step 02- Centering & Leveling
 To provide an accurate network of height.
 To get the accurate position of excavation.
Figure:- Centering & Leveling

11. Step 03- Shoring
 Support the load of the surrounding structures during construction.
 Prevents the surrounding soil from breaking during construction.
 Prevents the collapsing of the existing structure.
 Protects from vibration.
 Can be of three types: Concrete pile shore, Steel pile shore, Timber
shore.
Figure:- Timber Shoring.

12. Figure:- Steel pile shoring. Figure:- Shore Pile.

13. TIE BEAM
 Tie beam is constructed mainly to join the piles of border line.
Figure:- Tie Beam.

14. KING POST
 The vertical member to support the bracing and struts is called king
post.
 Generally hollow steel piles are used as king post.
 After the end of the construction, the king posts are removed and the
vacuum space in the basement slab is filled in with rich concrete.
King Post

15. Step 04- Soil Excavation
 Partial and full excavation is required before further construction.
 The soil was not excavated fully at once rather it was done step wise for
depth basis bracing.
 Excavation can be done in two ways:- ⅰ) Manually, ⅱ) By using machine.
Figure:- Machine Excavation.

16. Step 05- Providing strutting
& Bracing
 Generally made of steel sheet.
 In order to support the shore piles bracing are provided.
 The horizontal members placed in between the bracings are the struts.
 Its requirement depends on the depth of the foundation.
Bracing
Strut

17. Step 06- Compaction & Leveling
of Soil
 After excavation, soil compaction is needed to obtain a
uniform surface for the placement of BFS and other layers.
Figure:- Soil Leveling

18. Step 07- Provide Polythene,
BFS & CC Layer
 First one layer of BFS is placed over the area.
 After that, CC layer of 2”-3” thickness is provided.
 After that, polythene is placed as damp proof course (DPC).
 After that, another cc layer is provided.
 Bricks should be placed alternately so that there remains no weak
position on the layer and the friction is developed evenly.
 Polythene sheets are used as damp proofing membrane as polythene is
impermeable to water.
 Finally a theodolite is used to check the degree of leveling.

19. Figure:- BFS. Figure:- Provide polythene.

20. Figure:- CC Layer & a theodolite

21. Step 08- Placing CC Block
 CC blocks are placed beneath bottom layer reinforcement to maintain
3” clear cover.
CC Block

22. Step 09- Placing Reinforcement
Placing of
Bottom mesh
Column rod
placement
Chair placement
over bottom
mesh
Upper mesh
placement

23. Placing of Bottom mesh
 At first some reinforcements are placed at regular intervals along the
short distance of the site.
 Then a few more rods are placed on them along the long distance.
 At the junctions, the rods are tied with G.I. (galvanized iron) wires.
Figure:- Bottom mesh

24. Column rod placement
Figure:- Column rods
 In bottom mesh extra bars are placed beneath the positions of column
rods.
 Then the reinforcements of the columns are erected and tied.

25. Chair placement over bottom mesh
 There is a special type of bar used in between the top and bottom layer
reinforcement of mat foundation called the chair.
 The chairs are placed to provide support to the upper layer
reinforcement.
 Distance between two chair was 4’.
Figure:- A Chair
Figure:-Placing of chairs and
checking their alignment.

26. Upper mesh placement
 After that the top layer reinforcements are placed according to the
design.
 In the top layer, extra bars are provided in between the columns to resist
the punching shear.
Figure:- Upper mesh.

27. Important Factors
Reinforcement Selection
60~72.5 Graded
12 mm ~25 mm
Rod cutter
Rod bending
Hook right angled
(90° or 135° )
Tie bar

28. Formwork or Shuttering
 Shuttering or formwork is a sort of temporary construction provide for
laying concrete to required shape.
 Steel plate, Wooden plate is used for shuttering purpose.
Figure:- Formwork.

29. Step 10- Concreting
 Concreting is the process of pouring concrete in the reinforcement mesh.
 Casting was done in layers.
 The ratio of cement: sand: aggregate was 1:2:4
 Water: Cement ratio was 0.45.
Figure:- Concreting.

30. Step 11- Vibrating
 Concreting and vibrating both are does simultaneously.
 By using vibrating machine this work is done.
 Vibrating is necessary to distribute the concrete uniformly and to remove
the void.
Figure:- Vibrating.

31. Step 12- Leveling
 After casting the whole mat area levelling is essential to be ensured that
the thickness of the mash slab is same all over the area.
Figure:- Leveling.

32. Step 13- Curing
 Curing is the process of keeping the set concrete continuously damp for
some days in order to enable the concrete gain more strength.
 It is very important to continue curing for 28 days so that hydration is
completed and the concrete is hardened properly.
Figure:- Curing.

33. Advantages and Disadvantages
Advantages
 Where differential settlement needs to be reduced.
 Can cope up with poor soil condition.
 It gives greater space which is needed for basement.
 Loads are spread over greater area.
Disadvantages
 Shore protection is needed.
 Cost is high.
 As the raft thickness is high, heat may trap inside.
 Water may seep inside the basement.
 While constructing, water level may rise that might cause the lose of
contact with the soil.

34. Some special observations
 Hanger: This is a small ‘U’ shaped reinforcement provided in the slab of
the mat while casting. This is used to support the rods that keep the
column reinforcements erect.
Figure:- Hanger

35.  Sewerage pipes: Provision for passing of sewerage pipes may be
present on the raft slab.
Figure:- Sewerage pipes provided on mat foundation.
Some special observations

36. Figure:- Failure of shuttering wall.
Some special observations
 Failure of shuttering wall: On the site we observed that after heavy
rainfall, shuttering wall collapsed due to pressure of water. The shuttering
wall was built again and necessary provisions were made so that in
future such type of failure did not occur.

37. Figure:- Bracing.
Some special observations
 Bracing: Bracing to keep the column or retaining wall reinforcement
align.

38. Figure:- Retaining Wall.
Some special observations
Retaining Wall:
 RCC wall is constructed around the mat foundation.
 It is constructed to resist the lateral load of soil.

39. Completed Mat Foundation

40. MAT FOUNDATION