Work Procedure of Excavation Back Filling and Anti-Termite Work

[Srinivasan]

Work Procedure of Excavation Back Filling and Anti-Termite Work

EXCAVATION FOR BASEMENT AND FOOTING

1. Establish Temporary Bench Marks (TBM) all round the site. Locations are decided based on visibility and permanency of TBMs. Write the Reduced Levels (RL) on the TBM. TBM should be related to an OBM (Ordinance Bench Mark) taken from the Survey of India authorities.
2. Take grid levels at 5-meter interval before the start of mass excavation. If the terrain is sloping or rolling, closer grids of 3m may be required for greater accuracy.
3. Excavate in a phased manner after proper setting out of works.
4. Keep de-watering pumps available and discharge point accessible. Keep necessary information regarding water table, periods of rainfall and flooding of site and so on.
5. Shore slopes or step cut the sides as you excavate below 1.2 meters to ensure stability of sides.
6. The combination of machinery used in terms of output and efficiency should be matched. This will ensure minimum idling time of equipment.
7. Avoid excavation after sunset. Due to poor visibility errors may occur, even under artificial lights. Again it is not safe to work under poor lighting conditions.
8. Depth of excavation is to be constantly monitored with dumpy level in relation to the TBM located around the site.
9. Plan your works to balance cutting and filling. Re-handling of excavated earth is costly and should be minimized.
10. Structural consultant should inspect the site after the required depth of excavation is achieved i.e., the bearing stratum is exposed. Immediately after inspection the bottom level of excavation is sealed with blinding.
11. Hard rock removal can be done by compressed air jackhammer, wedging, chiseling etc. Do not resort to blasting as much as possible.
12. If blasting is necessary the work should be entrusted to a certified, license holding contractor. All necessary statutory clearances should be obtained. Controlled blasting should be resorted to. Put up adequate precautionary signage during the period of blasting. All blasting works should be completed before commencing RCC works.
13. Proper arrangement for de-watering should be made whenever the excavation crosses the existing water table level.
14. Ascertain location of permanent main services like UG cable OFC, water supply, telecom lines, sewage etc. Maintain and protect these lines throughout the phase of excavation and back filling.

FILLING AND COMPACTION

1. Approved material shall be used for backfilling. Soil with liquid limit exceeding 65% and plasticity index exceeding 35% cannot be used. High clay soil is not preferred for backfilling.
2. Imported fill shall be selected - graded hard granular fill with 100% free stones larger than 100 mm, up to 50% passing 5 mm mesh and not more than 20% passing a 75 micron sieve.
3. Compaction is done in layers of 150 mm. Choose the compaction equipment based on the nature of soil
4. Soil with organic material, construction debris, susceptible for spontaneous combustion, soft clay, and moisture content greater than optimum value to be avoided as backfill material.
5. Insitu field densities of compacted material should be 95% of maximum dry density or as specified by the consultant. Test should be conducted 10m center-to-center and before the anti-termite treatment is done. Sand replacement method can be used to ascertain insitu field density.
6. If removal and replacement of the weak strata with strong compact material is necessary, check the compatibility of the proposed fill material with the existing chemical ground conditions.
7. The checks that need to be made before work starts include the stability and levels of the original ground or foundations at the base or top of embankments, selection of suitable fill material and the stability and profiles of side slopes.
8. The stability of slopes to cuttings and embankments (in all weather conditions) is critical to safety on site. If in doubt, the Project-in-charge must be consulted and the decisions taken to be recorded.
9. Know your soil conditions before starting any large-scale earth-moving operations.
10. Unit of measurement of backfill material should be clear before the work starts.
11. For volumetric calculations cater for 30% quantity more of loose backfill to compacted volume.

ANTI-TERMITE TREATMENT

1. It is the treatment to structures to protect against attack by sub-terranian termites by suitable chemical measures. The work shall be carried out by specialist pest control agency and a guarantee for satisfactory performance of treatment for a minimum of 10 years.
2. Treatment shall be carried out according to the stipulations laid down by IS 6313 part II.
3. The chemical to be used is Chloropyriphos 20% EC with ISI certification.
4. Dilute one part of Chloropyriphos 20% EC with 20 parts of water to get 1% emulsion.
5. Trained personnel should handle the chemical and proper safety precautions like face-mask, hand gloves, goggles, rubber boots etc. should be used. Check the wind direction before spraying. Do not face the wind and spray.
6. For horizontal and vertical surface, the dosage rate is 7.5 litre/m2.
7. For along the perimeter of building insert rod at intervals of 150 mm and depth 300 mm and pour the chemical directly into the hole.
8. The general idea is to give continuous barrier all along the building coming in contact with soil irrespective of the material i.e. PCC, RCC or stone masonry of concrete block or bricks.

TOOLS TO BE USED BY TRADESMEN
Required tools must be available at site to ensure correct work
BASIC TOOLS OF THE MARKING GANG ARE:

1. Theodolite
2. Dumpy levels
3. Staff and ranging rods
4. Steel Measuring tape – 3 & 30 m
5. Plumb bobs
6. Trowels
7. Masonry nails
8. Timber pegs
9. Spirit Levels
10. Wax marking crayons
11. Linen (Fibron) tape – 30m
12. Paint and brushes
13. Optical square

BASIC TOOLS OF THE EARTHWORK GANG ARE:

1. Trowels
2. Pick axe
3. Line dori
4. Plumb bobs
5. Measurement Tape
6. Pencils
7. Spade
8. Hammers
9. Brushes and buckets
10. Right angles

INSPECTION METHODOLOGY FOR QUALITY ASSURANCE

1. First check if the approved site plan exists.
2. The checks that need to be made before work starts include the stability and levels of the original ground or foundations at the base or top of embankments, selection of suitable fill material and the stability and profiles of side slopes.
3. Marking in conformance as per drawings. The center line should be checked and certified by a marking supervisor from another site.
4. Ensure that correct area is excavated properly including the depth, length and breadth of the site using dumpy levels as per drawings. Checking of levels (random) using a dumpy level.
5. Wherever the depth of the trench is more than a meter, barricading all around the excavated site at a distance of one meter from the circumference.
6. If the slope of the excavated earth has a gradient more than 60 degrees, then ensure that the stepping /terracing is done to avoid any caving in of earth due to landslides.
7. Check up if the ground has been chemically treated for termites, or not.
8. All access routes to the sites have to be free and approachable at any point of time.
9. Visual examination of site and check for water table report. Check whether de-watering procedures have been applied on site.
10. If water table is high ensure retaining wall has been planned and the necessary waterproofing agent applied properly. The waterproofing supervision job card should be attached.
11. The detailed instructions should bear the signature of the consultant.

TOOLS TO BE USED FOR QUALITY INSPECTION
Theodolite
Dumpy levels
Spirit levels 3 m
Rolled measuring tapes (minimum 2 meters)
Measuring tape (minimum 50 m)
Calculators
Writing pads
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