Replacement of complete filter media of rapid sand gravity filter at Garacharma water treatment plant SW supply of graded gravel and silica sand from mainland river

Supplying and stacking of filter media of graded gravel (pebbles) from mainland river of sizes of density of above 1600 Kg/cum to be used as filter media shall be hard, durable, predferably rounded stone, free from clay, sand, ioam and organic impurities of any kind, having average specific gravity of not less than 2.5, water absorption not more than 0.50% and conforming to IS: 8419 (Part-I) - 1977 and reaffirmed 2010 as per the direction of Engineer-in-Charge at site.

Graded Gravel of size 40 mm to 60 mm

Graded Gravel of size 20 mm to 40 mm

Graded Gravel of size 10 mm and down graded

Supplying and stacking of silica sand, dry, clean from mainland river, washed of all impurities like vegetation, lime pieces etc. as per IS: 8419 (Part-I) 1977 and reaffirmed 2010 as per the direction of Engineer-in-Charge.

The shape, size and quality shll satisfy the following norms. a) Filter sand shall consists of hard, durable grains of silica, shall be of resistant quartz of quartzite and free from clay, fine particles, soft grains and dirt of every description. b) Effective size shall be 0.40 to 0.70 mm. c) Uniformity coefficient D60/D10 shall not be more than 1.40 not less than 1.50. d) Ignition loss shall no be more than 0.70% by weight. e) Soluble fraction in HCL shall not exceed 5% by weight. f) The minimum silica content in sand shall be 90% g) Shall have an average specific gravity of not less than 2.50 h) Wearing less shall not exceed 3%