Wok Method statement for Excavation and Backfilling

Srinivasan

Administrator
Sep 7, 2017
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mumbai
Wok Method statement for Excavation and Backfilling

SCOPE :
Covers clearing of area, excavation, backfilling, grading and testing.


CODES / SPECIFICATION :
Technical Specification
IS 2720 Part VIII, IS 2720 Part 28, IS 2720 Part 29


RESPONSIBILITIES :
Responsibilities of all concerned is clearly mentioned with respect to overall administration and implementation in the approved Organogram.


MATERIALS TO BE USED :
As per the requirement and the direction of project manager.


SAFETY REQUIREMENT :
  • Care shall be taken not to dump the excavated material near the excavation area and follow the safety norms.
  • Barricading shall be provided around excavated area and signal light shall be provided at night hours.
  • Excavated material shall not be dumped alongside the pit excavated. Excavated earth shall be disposed off to designated locations as mentioned in contract. Some quantity of excavated earth shall be retained for backfilling if specified so. Excavation pit shall be kept free from water by suitable means of dewatering as and when required
  • In case of mechanized excavator with excavators. Work shall be continued till about 150mm above final level. Levelling and dressing shall be done manually with light compaction, either manually or with plate compactor, as instructed by Project Manager.
  • All persons engaged in job shall wear PPE and the equipments deployed will be checked by HSE Officer.

DEPLOYMENT OF EQUIPMENT :
Excavation

Theodolite / Total Station, Leveling Instrument, Excavator, Rock breaker, dumper, Dozer, Grader, Roller and dewatering pump, etc.


DEPLOYMENT OF LABOUR :
As per the requirement and the direction of project manager.


IMPLEMENTATION

Preparatory works
Spot levels with 5 meter x 5 meter grids shall to be jointly recorded at the ground levels and at rock level after soil excavation is over.
Ensure availability of transverse survey pillars, immediate grid pillars and temporary bench mark pillars.


Pre-checks
  • Permission required before start of the work :
  • From statutory authority like BMC / MMRDA / SRA etc; as applicable.
  • From competent authority like RIL/MTNL/TATA POWER etc; as applicable.
  • To check whether services are crossing the plot boundary, excavate the drain of size 500mm wide and 1500mm depth along the breadth and width of the available area in one direction only.
  • Marking excavation areas with lime powder.

Clearing :
Clearing of all materials including bushes, trees, vegetation, obstruction and rubbish disposed off.


Stripping
All top soil shall be stripped as shown in the GFC drawings and technical specification.


EXCAVATION
  • Excavation in Soil means excavation of any material which can be removed by the ordinary application of picks or by any mechanical equipment without breaking.
  • Excavation in Rock means excavation in a material, which cannot be removed by application of pickaxe or crowbars but can only be removed by Rock breaker or other machinery or blasting or by application of chisel and hammer, or by mechanical equipment such as jackhammer / excavator etc as approved.
  • Excavation up to formation level as per GFC drawings.
  • Sufficient working space of 1000mm all around as per site requirement.
  • In firm soil, sides of the excavation shall be kept vertical up to a depth of 2 meter from bottom, for greater depth steps of 500mm width shall be provided for every 2 meter depth from the bottom of the pit.
  • In case of loose soil, sides of the excavation shall be suitably sloped to avoid collapse.
  • Arrangement of shoring/strutting, dewatering to be ensured.
  • Excavated earth shall be disposed off to designated locations.Some quantity of excavated earth shall be retained for backfilling if directed.
  • If excavation has gone deeper than the required level, extra depth shall be brought to the level by backfilling using approved filling material with proper compaction.
  • If earthwork involves mass excavation, the same shall be carried out in a well-planned manner with pre determined sequence using plant & machinery.
  • After completion of excavation final level shall be taken and recorded and check list for excavation work approval shall be prepared jointly.

BACKFILLING
SCOPE/PURPOSE

This work procedure describes the method to be adopted for: Backfilling the areas around and over foundations, trenches, plinth and under grade slabs of various structures with the filling material duly approved.
Controlled backfilling in the areas as specified in the relevant drawings and when instructed by the engineer

CODES/SPECIFICATION
  • Tender Specification
  • IS 2720-Part VII
RESPONSIBILITY
Responsibilities of all concerned is clearly mentioned with respect to overall administration and implementation in the approved Organogram.

MATERIALS TO BE USED
For Backfilling In Pits, Around Structures And Plinth Filling
  • For filling works wherever applicable, depending upon the contract specification, the filling earth shall be identified and approved. The filling material shall be free from lumps, clods, vegetation and other organic and deleterious matter.
  • The existing stockpile contains an assorted mixture of rock pieces varying in sizes from 40 mm to 300 mm and soil. Stone pieces of size more than 150 mm shall be removed from fill material prior to use of such material.
  • When directed by the engineer coarse river/crushed sand shall also be used as backfill material.Soils such as black cotton soil, clay and mixtures having excessive swelling characteristics shall not be used as filling material.

For Controlled Backfilling
Selected material from any one of the following shall be used for controlled backfilling. Before selecting any material for backfilling, modified proctor density tests shall be conducted on the material to determine its maximum dry density. The maximum dry density shall not be less than 1.44 gm/sq.cm.

Murrum
Murrum of approved Quality obtained from borrow pits duly approved by ADPL shall be used. Murrum shall be composed of large, Coarse, Siliceous Grains & Gritty to the touch and free from dirt and foreign material.
Murrum shall not contain lumps larger than 40 mm in size. Natural clay content shall not exceed 10 % and fine sand content (i.e. passing 75micron sieve) shall not exceed 8 %.

SAFETY REQUIREMENT
As directed by the HSE officer at site.

DEPLOYMENT OF EQUIPMENT
Compaction Equipment
Smooth Wheeled Vibratory Roller of 10t Weight
Smooth Wheeled Vibratory Roller of 2t Weight (To Be Used In Case It Is Found Difficult To Deploy 10t Roller)
Pneumatic Rammer/Plate Compactor (To Be Used In Space Congestion Where Compaction By Vibratory Roller Is Not Feasible)

Test Equipment
Proctor Density Test Apparatus Core-Cutter In-Situ Density Test Apparatus

DEPLOYMENT OF LABOUR
As per the requirement and the direction of project manager.

IMPLEMENTATION By Excavated Material
  • After completion of the foundation works, the spaces left in the pits and trenches shall be cleared of debris, brickbats, mortar droppings etc. prior to the start of backfilling.
  • For plinth filling in buildings the watering can be done manually with pipes, while in case of large area filling or other grading works the watering shall be done by means of tankers fitted with sprinklers.
  • Filling material shall be spread in layers of thickness approx. 250 mm and compacted by 4 passes of 10 t vibratory roller. Water shall be sprinkled intermittently.
  • Each layer shall be compacted before laying the succeeding layer. Surface voids in each layer shall be filled by crusher dust.
  • In case of plinth filling the backfilling as per the above procedure shall be continued upto the bottom of the plinth beam. The top surface at this stage shall be flooded with water for a minimum of 24 hrs. And defects in backfill shall be rectified and shall be trimmed to the desired level of slope, if any. Further filling within the plinth beams shall be controlled backfilling and soling as indicated in the relevant drawings.

By Sand
Sand shall be used as filling material between foundations where space for proper compaction by mechanical means is not available and when directed by the engineer-in-charge. Sand shall be spread in 300 mm thick layers, flooded with water and rammed. Top layer of sand shall be compacted by mechanical means.

Procedure For Controlled Backfilling
When instructed by the Engineer-in–Charge, Controlled Backfilling shall be done. Material shall be spread in uncompacted layers of thickness Approx. 200 mm and rolled by adequate number of passes of a 10t Vibratory Roller so as to achieve 95% of the Maximum modified proctor dry density of the fill material.
Procedure for controlled backfilling by sand shall be submitted separately.

INSPECTION AND TEST PLAN
Each compacted layer shall be cleared by for surface voids etc randomly. A record in the form of either registers or sketches for the clearance shall be maintained.

Field Quality Check of Controlled Backfilling
Each compacted layer under controlled backfilling shall be tested for degree of compaction. One test per 100 sq. m of compacted area shall be done for determining field dry density of the compacted layer. Alternate layers shall be tested as per Modified Proctor Density Test and Sand Replacement Method respectively. Records of field density test shall be maintained in the approved format.
 
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