RCC FONDATION

FoundationFoundation 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 CONCRETEThe 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 N/mm2

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 laidunder 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 loosematerials, levelled, watered and compacted and got approved by the Engineer-in-Charge before laying rubblesoling. Cable or pipe trenches if shown in the drawing and as required by the Engineer-in-Charge shall be got donebefore the soling is started.

Storage of aggregates : All coarse and fine aggregates shall be stacked separately in stock piles in the materialyard near the work site in bins properly constructed to avoid inter mixing of different aggregates. Contamination withforeign 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 beused 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 I.S. 456-2000.

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.Group GradeDesignationSpecified Characteristic compressive strength of150 mm cube at 28 days (N/mm2)Ordinary concrete M 10 10M 15 15M 20 20Standard Concrete M 25 25M 30 30M 35 35M 40 40M 45 45M 50 50M 55 55High strength concrete M 60 60M 65 65M 70 70M 75 75M 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 water. 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/ hard material

Depth of FoundationDepth 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 CapacityDry coarse and well graded dense sand have maximum shear resistance and maximum bearing capacity. In general submerged soil and clay have less bearing capacity.