Specifications of rcc foundation
- 2. 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. M25 GRADE CONCRETE The ratio is 1:1:2... so 1 bag of cement is used..i.e.; cement:sand:aggregate.... 25 denotes the COMPRESSIVE STRENGTH of the mixture. It means 25 N/mm2
- 3. 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.
- 4. 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-in-Charge 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.
- 5. 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.
- 6. GRADES OF CONCRETE : The concrete shall be in grades designated as below. Group Grade Designation Specified Characteristic compressive strength of 150 mm cube at 28 days (N/mm2) Ordinary concrete 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
- 7. Specification for excavation: The excavation for the foundation trenches shall be carried out in all sorts of soils as per plan and lining approved at site. The sides of the foundation trenches shall be truly vertical and bottom shall be uniformly levelled. The excavated material shall be stacked away from the sides of the trenches of the excavation by at least 2 meters. The excavated material shall be spread out uniformly up to a lead of 100 meters. All the existing services such as water pipes, sewers, electric cables, etc. which are met with in foundation trenches shall be carefully supported and protected by the contractor as per instruction of the engineer. The excavation shall be measured as per exact length and width of the lowest step of footings according to drawings or the engineer’s instructions. The depth of the trenches shall be measured vertically from the average ground level taken at site before starting the work. The rate of excavation includes all timbering and other supports which are necessary for securing the sides of the trenches and the contractor shall be responsible for their safety. No extra amount shall be paid to the contractor for the excavation of the working space. The materials or valuables found during excavation shall be the property of the owner.
- 8. 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 Precautions during Excavation of Foundation:
- 10. 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. Depth of Foundation
- 11. Specification for removal of water from foundations: The contractor shall provide necessary pumps and other equipment to keep the foundation trenches clear of water. All the water getting admission to the trenches shall be pumped out so as to keep the trenches dry. No consideration shall be given to the source of water from where it is coming. The sumps shall be arranged in positions which are approved by the engineer. The sumps shall be arranged in such a way that water clear of sand is pumped out. The operations of removal of water from foundation trenches shall be so conducted by the contractor that there is no danger to the foundations or stability of the adjoining structure.
- 12. Specification for damp proof course: •DPC: Proportion -1 part of cement, 2 parts of sands and 4 parts of coarse aggregates / 1 part of cement , 1 ½ parts of sand and 3 parts of coarse aggregate by volume. Thickness - 25 mm to 40 mm. •Coarse aggregate : Clean, hard, dense and free from organic impurities (earth ,coal, dust etc). Size varies from 12 mm to 6mm. •Fine aggregate( sand ): clean , coarse and free from organic impurities – average size 5 mm •Cement -fresh and shall comply with the standard requirements. The water-proofing compound used shall be of standard specifications. Water used shall be clean and fresh. •The mixing of all the materials in their required proportion by volume shall be done on a clean and solid platform. Dry coarse aggregates shall be stacked evenly on the platform. Sand and cement in their required proportion shall be mixed dry till of uniform colour and then this mixture shall be spread over the stacked coarse aggregate. The materials shall be turned over once without adding water and shall be turned over for at least three times after adding required quantity of water gradually and slowly to give a uniform concrete. Water-proofing compound in proportion as specified shall then be added and mixed with concrete to make it water proof.
- 13. •The base where damp proof course is to be laid shall be constructed with bricks on edge or with frogs of the bricks down. The top of the plinth bed over which damp proof course is to be placed shall be thoroughly cleaned with a steel brush, washed and wetted before laying damp proof course. The wooden straight edges shall be fixed on plinth wall having the same inner width as that the required thickness of damp proof course. • Damp proof course shall be laid to the full width of the plinth or of the superstructure as mentioned in the drawings or tender. It shall be laid to the specified thickness over the plinth wall flush with the floor surface and shall not be carried across the doorways or such other openings. It shall be properly consolidated by temping and leveled horizontally as well as vertically. Laying of damp proof course shall be completed on the same day. The joints shall be given at the openings. The concrete surface shall be roughened and chequered when air dry to impart proper bondage with brickwork above. •The work shall be kept well-watered for at least 7 days after laying, if there is no commencement for further brickwork. In no case, brickwork shall be commenced unless the fresh work has been flooded with water for at least 48 hours.
- 15. 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.
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