Foundation is the lowest part of a structure which provides a base for the super-structure. This term includes the portion of the structure below the ground level as well as the artificial arrangement of concrete block, piles, raft, grillage, etc. provided to transmit the load on the structure including the dead weight of the structure itself to the soil below.

1. Foundation
Foundation is the lowest part of a structure which provides a base for the super-structure. This
term includes the portion of the structure below the ground level as well as the artificial
arrangement of concrete block, piles, raft, grillage, etc. provided to transmit the load on the
structure including the dead weight of the structure itself to the soil below.
Figure: Foundation of a building
Purpose of Foundation
 To prevent the lateral movement of supporting materials.
 To attain a level and firm bed for building operations.
 To increase the stability of the structure as a hole.
 It is often misunderstood that the foundation is provided to support the load of the
structure.
 To distribute the weight of structure over a large area without stressing the soil beyond
its capacity.
 To load the sub-stratum evenly and prevent unequal settlement or differential
settlement.
 To provide a level surface that facilitates subsequent construction works.
 To take the structure deep into the ground and thus increase its stability by preventing
overturning.
Site Exploration
It means the inspection of the site and study of topography to get a proper information about
the soil and ground water condition.
The designer should have adequate information regarding the type and nature of soil available
at different depths at the site for designing safe, sound and economical foundation for a
structure. The aimis to get as much information about the physicalproperties and characteristics

2. of the underlying material at site as well as details of other geological features of the area. All
these attempts and activities are termed, in a broader sense, as Site Exploration.
Figure: A soil scientist advances a Giddings Probe direct push soil sampler.
Purposes of Site Exploration
The purpose of site exploration is to determine the existing soil profiles and engineering
characteristics of the subsurface conditions at the site and to provide the designer with
comments on the following:
 To fix the value of the safe bearing capacity of soil.
 To select an economical yet safe type of foundation.
 To fix the depth up to which the foundation must be taken inside the ground.
 To predict the likely settlement of the selected foundation and to make allowance for the
same in the design.
 To know the underground water level and if needed, to decide upon the method to be
adopted to solve the ground water problem.
 To forecast the difficulties which are likely to be encountered due to nature of the sub-
soil during construction and to take advance actions in this regard.
Methods of Site Exploration
The methods commonly adopted for site exploration are:
 Test pits
 Probing
 Sub-surface sounding
 Boring
 Geo-physical method


3. Test Pits
The commonly used method to find the nature of the subsoil strata is to dig a hole and see. The
holes which are large enough to permit the entry of persons for inspection are called Test Pits.
 The best way to ascertain the nature of the sub-soil strata is to dig a hole and see.
 Pits are square in plane and are dug by hand or by excavating equipment.
 In cohesion less soils the sides of the test pit are sharply sloped.
 In cohesive soils, at depth below 3m, bracing is required to keep the sides of the pit
vertical.
 Comparatively expensive thus used for structure having shallow foundations (up to 3
meters).
Figure: Test Pits
Boring
The type of boring methods commonly adopted for soil exploration are as under:
 Auger boring
 Shell and Auger boring
 Wash boring
 Percussion boring
 Rotary boring
Auger Boring
The examination of the sub-soil conditions for simple buildings to be erected in clayey or sandy
soil can be best performed by a post hole auger. The auger is held vertically and is driven into the
ground by rotating its handle by applying leverage. The auger is pressed down during the process
of rotation.
 At every 30 cm of depth penetrated, the auger is taken out.

4.  This method can be conveniently used for soil penetration up to 15m.
 For deeper holes or in grounds where gravel, boulders or comp act material is present,
this method is not adopted.
Figure: Different types of Auger
Wash Boring
For test boring over 3 meter in depth, this method can be conveniently used. This method can be
adopted in soft to stiff cohesive soils and fine sand.
Figure: Installation for wash boring

5. Step 01: Three legged pipe derrick is placed
Step 02: Centering and Placing of Augur
Step 03: Temporary casing is placed

6. Step 04: Provision for water supply by hose pipe
Step 05: Using bentonite
Types of Foundation
Foundation
Shallow
Strip Individual Mat
Deep
Pile Caisson Cofferdam

7. Wall Footing
Figure: Wall footing
 Consists of several courses of bricks.
 Lowest course usually twice the breadth of wall.
 CC and BFS are not part of foundation.
 Where the walls are subjected to heavy loading and the bearing capacity of soil is low,
reinforced concrete footing below the wall should be provided
 R.C. footing may be stepped or single
Single Footing
 Step 01: Excavation of Trench

8.  Step 02: Leveling and Dressing
 Step 03: Brick Flat Soling (BFS), 3”- Size of brick 10x5x3 (9.5x4.5x2.75)
 Step 04: Cement Concrete (CC), 3” – C:FA:CA = 1:2:4/1:3:6
 Step05: Shuttering/ Formwork (must be leak proof)
 Step 06: C.C. block (to maintain clear cover)
 Step 07: Rebar Placement

9.  Step 08: Casting of Concrete, C:FA:CA=1:1.5:3/1:2:4, w/c ratio=0.42-0.5
 Step 09: Compaction (to avoid segregation)
 Step10: Removal of shuttering
 Step 11: Curing (usually 21 days for foundation)
 Step 12: Backfilling