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Well foundation: sinking, brick, sand filling, PCC

Short answer

Outer area 5.309 m², inner 3.142 m², ring 2.168 m². Sinking: outer area × 14 m = 74.33 m³. Brickwork: ring area × 14.20 m = 30.78 m³. Sand filling: inner area × 13.75 m = 43.20 m³. PCC cover: inner area × 0.45 m = 1.414 m³.

Work out quantity of well foundation for bridge. The well is to be circular of 2 m internal diameter with 300 mm thick masonry wall in 1:6 cement sand mortar. The well is founded in strata 14.00 m thick. Water table remains at 3.80 m depth. Well curb at bottom is RCC with M25 grade concrete mix and is 400 mm deep. The well rises 60 cm above ground level. Top of well is to be sealed with 0.45 m thick (1:4:8) cement concrete as well cover. Estimate quantities for the following works. a) Sinking of well. b) Brick masonry work in (1:6) cement sand mortar. c) Sand filling. d) PCC for RCC in well cover.

Data. Internal dia 2.0 m; wall 0.30 m, so outer dia = 2.60 m. Depth of well below GL = 14.0 m (curb included); well rises 0.6 m above GL; curb 0.4 m; cover 0.45 m thick placed inside the top of the bore.

  • Outer area Ao=5.309A_o=5.309 m²; inner area Ai=π4×22=3.142A_i=\frac{\pi}{4}\times 2^2=3.142 m²; ring area 2.1682.168 m².

a) Sinking of well

Ao×14.0=5.309×14=A_o\times 14.0 = 5.309\times 14 = 74.33 m³ (of this, 3.8 m is above the water table: 20.18 m³ and 54.15 m³ below it, which is priced separately if required).

b) Brick masonry (1:6)

Height = 14.0 − 0.4 + 0.6 = 14.20 m; volume = 2.168 × 14.20 = 30.78 m³.

c) Sand filling

Filling goes from the top of the curb to the underside of the cover: height = 14.0 + 0.6 − 0.4 − 0.45 = 13.75 m; volume = 3.142 × 13.75 = 43.20 m³.

d) PCC (1:4:8) in well cover

Volume = Ai×0.45=3.142×0.45=A_i\times 0.45=3.142\times 0.45= 1.414 m³.

Answer: Sinking 74.33 m³; brickwork 30.78 m³; sand filling 43.20 m³; well cover concrete 1.414 m³.

✓ Answer checked by Claude Opus 5.5 (high effort)

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