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.
M25 GRADE CONCRETE
The ratio is 1:1:2... so 1 bag of cement is used..ie; cement:sand:aggregate....
25 denotes the COMPRESSIVE STRENGTH of the mixture. It means 25
IS 456-2000 has designated the concrete mixes into a number of grades as M10, M15,
M20, M25, M30, M35 and M40. In this designation the letter M refers to the mix and
the number to the specified 28 day cube strength of mix in N/mm2. The mixes of grades
M10, M15, M20 and M25 correspond approximately to the mix proportions (1:3:6),
(1:2:4), (1:1.5:3) and (1:1:2) respectively.
SCOPE OF WORK :
The work covered under this specification includes all type of
soling work either by bricks or by rubble stones laid
under floors/foundations, hand packed, complete as per under
mentioned specification and applicable drawings.
Preparation of Surface : The bed on which rubble soling is to be laid shall be
cleared of all loose
materials, levelled, watered and compacted and got approved by the Engineer-inCharge before laying rubble
soling. Cable or pipe trenches if shown in the drawing and as required by the
Engineer-in-Charge shall be got done
before the soling is started.
Storage of aggregates : All coarse and fine aggregates shall be stacked
separately in stock piles in the material
yard near the work site in bins properly constructed to avoid inter mixing of
different aggregates. Contamination with
foreign materials and earth during storage and while heaping the materials
shall be avoided.
Aggregates having a specific gravity below 2.6 (saturated surface dry
basis) shall not be
used without special permission of the Engineer-in-Charge.
DESIGN MIX CONCRETE :
All reinforced concrete in the works shall be “Design Mix Concrete” as defined in
Mix Design :
This is to investigate the grading of aggregates, water cement ratio, workability
and the quantity of cement required to give works cubes of the characteristic
strength specified. The proportions of the mix shall be determined by weight.
Adjustment of aggregate proportions due to moisture present in the aggregate
shall be made.
GRADES OF CONCRETE : The concrete shall be in grades designated as below.
Specified Characteristic compressive strength of
150 mm cube at 28 days (N/mm2)
M 10 10
M 15 15
M 20 20
Standard Concrete M 25 25
M 30 30
M 35 35
M 40 40
M 45 45
M 50 50
M 55 55
High strength concrete M 60 60
M 65 65
M 70 70
M 75 75
M 80 80
Precautions during Excavation of Foundation Work
The depth of the foundation should not be less than 1 meter in case the
design is not available.
2. The length, width and depth of excavation should be checked with the
help of center line and level marked on the burjis.
3. The excavated material/ earth should be dumped at a distance of 1
meter from the edges.
4. Work should be done on dry soil.
5. Arrangement of water pump should be made for pumping out rain
6. The bottom layer of the foundation should be compacted.
7. There should be no soft places in foundation due to roots etc.
8.Any soft/ defective spots should be dug out and be filled with concrete/
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.
Precautions while designing 'Foundation‘
1. A foundation should be designed to transmit combined dead.
2.Net loading intensity of pressure coming on the soil should not
exceed the safe bearing capacity.
3. 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.
4. Whole design of the foundation, super structure and
characteristics of the ground should be studied to obtain economy
in construction work.
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.