Designing a Foundation | | | |
Foundation
Foundation is the part of structure below plinth level up to the soil. It is in direct contact of soil and transmits load of super structure to soil. Generally it is below the ground level. If some part of foundation is above ground level, it is also covered with earth filling. This portion of structure is not in contact of air, light etc, or to say that it is the hidden part of the structure.
Depth of Foundation
Depth of foundation depends on following factors.
1. Availability of adequate bearing capacity
2. Depth of shrinkage and swelling in case of clayey soils, due to seasonal changes which may cause appreciable movements.
3. Depth of frost penetration in case of fine sand and silt.
4. Possibility of excavation close by
5. Depth of ground water table
6. Practical minimum depth of foundation should not be less than 50 cm. to allow removal of top soil and variations in ground level.
7. Hence the best recommended depth of foundation is from 1.00 meter to 1.5 meter from original ground level.
Footing
Footing is a structure constructed in brick work, masonry or concrete under the base of a wall or column for distributing the load over a large area.
Width of Foundation/Footings
The width of footings should be laid according to structural design. For light loaded buildings such as houses, flats, school buildings etc having not more than two storeys, the width of foundation is given below.
1. The width of footing should not be less than 75 cm for one brick thick wall.
2. The width of footing should not be less than 1 meter for one and half brick wall.
Different Processes in Foundation Work
The processes executed in the foundation works are given below.
1. Excavation of earth work in trenches for foundation.
2. Laying out cement concrete.
3. Laying the footing in case of raft or column construction.
4. Laying Anti termite treatment.
5. Laying Brick work up to plinth level.
6. Laying Damp proof course on the walls.
7. Refilling of earth around the walls
8. Refilling of earth in the building portion up to the required height according to plinth level.
Precautions while designing 'Foundation'
- A foundation should be designed to transmit combined dead load, imposed load and wind load to the ground.
- Net loading intensity of pressure coming on the soil should not exceed the safe bearing capacity.
- Foundation should be designed in such a way that settlement to the ground is limited and uniform under whole of the building to avoid damage to the structure.
- Whole design of the foundation, super structure and characteristics of the ground should be studied to obtain economy in construction work.
Ratio of Cement Concrete and Mortar for Foundation
- The cement concrete 1:8:16 is generally used in the foundation of walls in construction work.
- In case of column raft cement concrete 1:4:8 is the best recommended ratio for it in the foundation.
- For brick masonry cement mortar 1:4 to 1:6 is used as loading condition.
In case of column and raft footings up to plinth level cement concrete 1:2:4 or 1:1.5:3 are used.
Soil having Safe Bearing Capacity
Dry coarse and well graded dense sand have maximum shear resistance and maximum bearing capacity. In general submerged soil and clay have less bearing capacity.
Precautions during Excavation of Foundation Work
The depth and width of foundation should be according to structural design.
- The depth of the foundation should not be less than 1 meter in case the design is not available.
- The length, width and depth of excavation should be checked with the help of center line and level marked on the burjis.
- The excavated material/ earth should be dumped at a distance of 1 meter from the edges.
- Work should be done on dry soil.
- Arrangement of water pump should be made for pumping out rain water.
- The bottom layer of the foundation should be compacted.
- There should be no soft places in foundation due to roots etc.
- Any soft/ defective spots should be dug out and be filled with concrete/ hard material
BR>
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| Related tips | -
If excavation is made deeper than the adjacent building
then proper support should be planned for the old building before starting the
work.
- In case of shuttering for even small bridges & culvert work the shuttering cribs or iron girders should be used.
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| 100 Comment(s) |
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| | By Anonymous - On 4/22/2013 10:09:26 PM | | I feel that Mr. S L Gupta (Civil Engg)is right and in case the level of the floor is to be raised than additional beam i.e. strap beam shall be used. |
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| | By Anonymous - On 4/5/2013 5:12:19 PM | | Very interesting and helpful information provided. KEEP IT UP |
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| | By cosntruction novice - On 4/1/2013 4:11:25 PM | | For foundation and columns, I have been advised to use "dust" rather than "ghagger sand" -- which my contractor is using. ANy thoughts? How do I differentiate dust from what is being used right now.. |
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| | By sam (Civil Engg) - On 4/1/2013 4:11:25 PM | | Hi I am designer, i am offering if any one want to design their home (Structural design, architectural design, vaastu, , plans, 3d views) call me +919810636565 |
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| | By trsvijith - On 4/1/2013 3:41:15 PM | | this part is very critical stage of a dream home, so the article is vey helpful |
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| | By S L Gupta (Civil Engg) - On 4/1/2013 11:33:29 AM | Dear Murthy Lay or construct plinth beam at plinth level i.e. at floor level. |
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| | By GVS Murthy - On 4/1/2013 10:46:47 AM | I would like to construct my new house one and half feet above the road level. Should the plinth beam be at ground level and raise a brick wall up to required level then go for filling or raise the level of the ground by filling up to required level then go for plinth beam, which one you suggest for the good strength of my house with four levels. Thanks & Regards |
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| | By Anonymous - On 2/14/2013 10:44:20 AM | | Sir, Can i get full design of single storeyed house(structurel) |
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| | By Anonymous - On 2/7/2013 8:35:30 PM | | The information given is very important for civil engineer.realy good details |
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| | By Anonymous - On 1/5/2013 8:51:36 PM | | SIRCan u guide me How to design corner rcc foundation for long span 6m and show me the diagram CHRISTOPHER |
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| | By Anonymous - On 1/2/2013 1:48:16 PM | | it include the best and good information. it is very helpfull . |
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| | By samarendra nath das - On 12/1/2012 12:42:26 PM | | I have a plot north facing 60mt distance from railwaytrac.the plot is about 6ft down from road level.I have made a self design of house plan of G(Parking)+3floor of 1000sqft area for each floor.But do not know how to make the design of foundation ,pillar, beam etc.Please help me for giving the design and advice.Than Q |
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| | By Prabhat Kumar - On 11/3/2012 1:40:18 PM | | plzzz explain the exact mean of plinth & plinth level...??? n give with a suitable diagram.. plzz..??? |
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| | By Anonymous - On 10/8/2012 10:36:16 PM | | Thank you.I find your article very helpful.However, concrete mix of 1:8:16in foundation as depicted in the figure above is too weak.I would suggest 1:2:4.Thank you |
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| | By Anonymous - On 9/29/2012 2:12:55 PM | | This informaation is very helpfull . But i have one quetion "what points should kept in mind while designing foundation on black cotton soil" |
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| | By Dipankar Gharami - On 8/17/2012 12:23:50 PM | | I like it and i am interest about foundation |
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| | By DEBASISH SARKAR - On 7/21/2012 5:43:32 PM | | hi every body,this is debasish here.i am going to construct my o3 story house.i want to make all wall load bearing 230mm thick.The site is at nadia,West Bengal(delta of Ganga). please guide me for foundation.what should be the depth,what should be width of first layer of brick?i want to use fly ash bricks. |
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| | By lovysta - On 6/13/2012 11:32:10 AM | | hello! in short i lack words to say, becuz everything i xpected, i found it here. please keep up, you're doing perfect. Good day |
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| | By rajneesh - On 5/27/2012 7:27:57 PM | | construct in nagpur |
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| | By Anonymous - On 5/5/2012 6:48:44 PM | | Wow! It is very very interesting and helpful to me. I am B-tech (Hons) in Architecture from Nigeria. Thanks |
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