Foundations are broadly classified into shallow and deep foundations.
In areas which have already been developed, advantage shall be taken of existing local knowledge, records of trial pits, bore holes, etc., in the vicinity, and the behavior of existing structures, particularly those of a nature similar to that of the proposed structure. In such cases, exploration may be limited to checking that the expected soil conditions are those as in the neighborhood.
If the existing information is not sufficient or is inconclusive the site shall be explored in detail in accordance with the principles set in IS: 1892 so as to obtain the knowledge of the type, uniformity, consistency, thickness, sequence and dip of the strata and of the ground water conditions.
The shallow foundation shall be of three types:
Generally building foundations are constructed with stone masonry or concrete. The quality aspects of materials are given in sections of concrete and masonry.
Where the bearing soil is either loose or soft, the load from the structure has to be transferred to deeper firm strata. These foundations are classified as deep foundations. Pile foundation is the most commonly used deep foundation for buildings.
1. Pile foundation
1.1 Bored cast-in-situ piles
For construction of piles, guidance shall be taken from relevant Part/Section of IS:2911. The following points shall be kept in mind while bored cast-in-situ piles are installed.
1.2 Under-reamed piles
Casting Tolerance above cut-off level for piles
Cut-off distance below commencing surface (H)
Casting tolerance above cut-off level in metres
|0.15 m to 10 m||0.3 + H/12 + C/8|
g. For piles cast under water or drilling fluid, the pile heads shall be cast to a level above the specified cut-off so that, after trimming to remove all debris and contaminated concrete, a sound concrete connection with the pile can be made. The casting level shall be within the tolerance above the cut-off level shown in table above, but shall not be above the commencing surface level. Cut-off levels may be specified below the standing groundwater level, and where this condition applies, the bore hole fluid level shall not be reduced below the standing groundwater level until the concrete has set.
TESTING OF PILES
The testing shall be done as per the procedure laid down in IS: 2911- Part4.
The number of tests may generally be 0.5% of the total number of piles required. The number of the test may be increased up to 2% in a particular case depending upon nature, type of structure and strata condition. However in the case of sandy or clayey strata at least one pile shall be tested.
1. IS:1080-Design and construction of shallow foundations in soils. (Other than raft, ring and shell)
2. IS: 1888-Method of load test on soils.
3. IS: 1904-Design and construction of foundations in soils: General requirements.
4. IS: 2911-Design and construction of pile foundation.
(Part 1/Sec.1) Driven cast-in-situ concrete piles.
(Part 1/Sec.2 Bored cast-in-situ concrete piles.
(Part 1/Sec.3) Driven cast-in-situ concrete piles.
(Part 1/Sec.4) Bored precast concrete piles.
(Part 4)Load test on piles.
5. IS:2950-Design and construction of raft foundation.
6. IS:6403-Determination of bearing capacity of shallow foundations.
7. IS: 8009-Calculation of settlement of foundations.
(Part 1)-Shallow foundations subjected to static symmetrical vertical loads.
(Part 2)-Deep foundation subjected to static symmetrical vertical loads.
8. IS: 9456-Design and construction of conical and hyperbolic. Paraboloidal types of Shell foundations.
9. IS: 9527-Design and construction of caissons.
10. IS: 9556-Design and construction of diaphragm wall.
11. IS: 11089-Design and construction of ring foundation.
12. IS: 13094-Selection of ground improvement techniques for foundation in weak soils - guidelines.
13. IS: 14893-Non-destructive integrity testing of piles (NDT) - Guidelines.
14. IS: 15284-Design and construction for ground improvement- guidelines.
(Part 1)-Stone columns.
(Part 2)-Vertical drains