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Well foundation: excavation, sinking, brick, PCC curb

Short answer

Dry earthwork to water table is 20.18 m3; sinking below water table is 54.15 m3; brick masonry 1:6 steining is 30.78 m3; M25 RCC curb is 0.867 m3.

Work out quantity of well foundation of bridge foundation. 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 sealed with 0.45 m thick (1:4:8) cement concrete as well cover. Estimate quantities for the following works. a) Earthwork in excavation b) Sinking of well c) Brick masonry work in (1:6) cement sand mortar d) PCC for RCC in curb

Data. Internal dia = 2.0 m; masonry wall 0.30 m, so outer dia = 2.0 + 2 × 0.30 = 2.60 m. Founding depth below GL = 14.0 m (including the 0.4 m curb); water table at 3.8 m; well rises 0.6 m above GL.

  • Outer cross-section Ao=π4(2.60)2=5.309A_o=\frac{\pi}{4}(2.60)^2=5.309 m²
  • Annular area of steining =π4(2.602−22)=2.168=\frac{\pi}{4}(2.60^2-2^2)=2.168 m²

a) Earthwork in excavation (above water table)

Dry excavation from GL to 3.8 m: 5.309 × 3.8 = 20.18 m³.

b) Sinking of well (below water table)

The remaining depth 14.0 − 3.8 = 10.2 m is sunk by dredging under water: 5.309 × 10.2 = 54.15 m³. (If a single item is wanted, total = 74.33 m³.)

c) Brick masonry (1:6) in steining

Height of steining = 14.0 − 0.4 (curb) + 0.6 (above GL) = 14.20 m.

Volume = 2.168 × 14.20 = 30.78 m³.

d) PCC (M25) for RCC curb

Curb ring area is the same, depth 0.4 m: 2.168 × 0.4 = 0.867 m³ (reinforcement is measured separately in kg).

The 0.45 m well cover (1:4:8) is not asked here; it is π/4 × 2.0² × 0.45 = 1.41 m³.

Answer: Excavation 20.18 m³; sinking 54.15 m³; brickwork 30.78 m³; curb concrete 0.867 m³.

✓ Answer checked by Claude Opus 5.5 (high effort)

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