---
title: "Well foundation, 4.5 m internal diameter"
subject: "Estimating and Costing"
chapter: 6
key: "semester_7/estimating_and_costing:well-foundation-4-5m-p"
source: https://www.bctengineer.com/q/semester_7/estimating_and_costing/well-foundation-4-5m-p
site: BCT Engineering
---

# Well foundation, 4.5 m internal diameter

Estimating and Costing · Chapter 6: Detailed Estimate

- Asked in: 2071 Chaitra, 9 marks
- Video: [Estimation of Open Well | Open Well Estimate | Quantity Surveying | #openwell #civilengineeringedu](https://www.youtube.com/watch?v=q9hGtb2leh8) — Civil Engineering Edu
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/estimating_and_costing/well-foundation-4-5m-p
- Whole chapter: https://www.bctengineer.com/md/semester_7/estimating_and_costing/chapter-6

## Question

Workout the quantity of well foundation of a bridge. The well is to be circular of 4.5 meter internal diameter with 800 mm wall in 1:6 cement and sand mortar. The well to be founded on strata 15 meter below bed of river which is dry during the hot weather. Bottom of the well to be plugged with 1.0 meter thick cement concrete 1:4:8 and the top to be sealed with 0.75 meter thick cement concrete 1:4:8 and central portion is to be sand filled.

## Short answer

Outer area 29.225 m², inner 15.904 m². Sinking: 29.225×15=438.37 m³. Brickwork: ring area ×15=199.81 m³. Bottom plug (1:4:8): 15.904×1.0=15.90 m³, top seal (1:4:8): 15.904×0.75=11.93 m³, total 27.83 m³. Sand filling: 15.904×(15-1-0.75)=210.73 m³.

## Answer

**Data.** Internal dia 4.5 m, wall 0.80 m, so outer dia = 4.5 + 2 × 0.8 = 6.10 m. Founding depth 15.0 m below river bed (dry). Assumptions: top of the well at bed level and the steining includes the curb.

- $A_o=\frac{\pi}{4}(6.10)^2=29.225$ m²; $A_i=\frac{\pi}{4}(4.5)^2=15.904$ m²; ring area $=13.320$ m².

| Item | Working | Quantity |
|---|---|---|
| Excavation / sinking | 29.225 × 15.0 | 438.37 m³ |
| Brick masonry 1:6 in steining | 13.320 × 15.0 | 199.81 m³ |
| Bottom plug, CC 1:4:8 (1.0 m) | 15.904 × 1.0 | 15.90 m³ |
| Top seal, CC 1:4:8 (0.75 m) | 15.904 × 0.75 | 11.93 m³ |
| Sand filling (15.0 − 1.0 − 0.75 = 13.25 m) | 15.904 × 13.25 | 210.73 m³ |

Total 1:4:8 concrete = 27.83 m³.

**Answer:** Excavation 438.37 m³; brickwork 199.81 m³; CC 1:4:8 = 27.83 m³ (bottom 15.90 + top 11.93); sand filling 210.73 m³.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What outer diameter is used for sinking in a well of 4.5 m internal dia and 800 mm wall?
   A. 5.3 m
   B. 6.1 m
   C. 4.9 m
   D. 5.7 m
   Answer: B. 4.5 + 2 x 0.8 = 6.1 m, area 29.225 m2. (Key point: Outer diameter)

2. What depth of sand filling is used?
   A. 15.0 - 1.0 - 0.75 = 13.25 m
   B. 15.0 m
   C. 15.0 - 1.0 = 14.0 m
   D. 15.0 - 0.75 = 14.25 m
   Answer: A. Sand fills what remains between the bottom plug (1.0 m) and top seal (0.75 m). (Key point: Sand fill depth)

3. Why is total 1:4:8 concrete 27.83 m3?
   A. Bottom plug and top seal are both 1:4:8: 15.90 + 11.93
   B. Only the bottom plug counts
   C. Plug uses outer area
   D. Plug and sand are added
   Answer: A. Both use the same mix and inner area 15.904 m2 x (1.0 + 0.75). (Key point: Total 1:4:8 concrete)

4. Brickwork in steining uses which area?
   A. Outer area 29.225 m2
   B. Inner area 15.904 m2
   C. Ring area 13.320 m2
   D. Sum of inner and outer
   Answer: C. Ring area x 15 m = 199.81 m3. (Key point: Steining area)

## Close variants set in other exams

- [Well foundation, 5 m internal diameter](https://www.bctengineer.com/question.md?key=semester_7%2Festimating_and_costing%3Awell-foundation-5m-k) — Estimating and Costing, chapter 6, asked 2×

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