# Deep Well Dewatering Calculator

When drawdown exceeds 5-6 m, wellpoints run out of suction - size deep wells instead.

- Page: https://jianzhujisuan.com/en/deep-well-dewatering
- Category: Construction (https://jianzhujisuan.com/en/c/construction)
- Chinese version: https://jianzhujisuan.com/zh/deep-well-dewatering.md
- Data checked: 2026-10-25

## Quick result

With the default inputs (Pit length 30 m, Pit width 20 m, Drawdown 6 m, Permeability Medium sand 8 m/d, Aquifer thickness 10 m, Well diameter 400 mm, Screen length 3 m): **Deep wells (with 1 spare) 4 wells**

## Inputs

| Parameter | Type | Default | Unit | Note |
|---|---|---|---|---|
| Pit length | number | 30 | m |  |
| Pit width | number | 20 | m |  |
| Drawdown | number | 6 | m | Water table down to 0.5 m below formation |
| Permeability | select | Medium sand 8 m/d | — |  |
| Aquifer thickness | number | 10 | m |  |
| Well diameter | number | 400 | mm |  |
| Screen length | number | 3 | m |  |

## Formula

- **Equivalent radius**: r₀ = √(area/π)
- **Radius of influence**: R = 2S√(kH) (Kusakin, k in m/d)
- **Total inflow**: Q = 1.366·k·(2H−S)·S / lg(R/r₀)
- **Per-well yield**: q = 65π·d·L·∛k (d, L in m)
- **Well count**: n = ⌈Q/q⌉ + 1 (spare)

## Worked example

A 30×20 m pit, 6 m drawdown, medium sand k=8 m/d, 10 m aquifer, 400 mm wells, 3 m screen: r₀ = 13.82 m, R = 2×6×√(8×10) = 107.3 m, inflow Q ≈ 1031 m³/d; per-well yield q = 65π×0.4×3×∛8 ≈ 490 m³/d, so 3 wells plus one spare = 4.

## Questions

### When do I use deep wells instead of wellpoints?

Look at drawdown and soil. Wellpoints rely on vacuum suction and only manage 5-6 m of practical drawdown; beyond that use deep wells. Wells also deliver far more per unit (tens to hundreds of m³/d) and suit permeable sands and gravels. In silt and clay the permeability is so low the water will not move, and wells do worse than wellpoints or open pumping. Decide on permeability first - deep is not automatically a well.

### Why add a spare well?

A dewatering system runs continuously, and any one failure - a clogged screen, a dead pump, a power cut - lets the level recover locally, and that is where flooding and slope failures start. The spare runs cold and cuts in the moment something trips. More wells mean any one failure matters less, so on a large pit the spare ratio can reach 15-20%; this tool starts at +1 and larger jobs should add proportionally.

## Related tools

- [Plaster and Render Calculator](https://jianzhujisuan.com/en/plaster-coat): Mortar, cement and sand by layer for internal plastering.
- [Mortar Mix Design Calculator](https://jianzhujisuan.com/en/mortar-strength): Trial strength, cement, water and sand, and the mix by mass.
- [Labour Days and Crew Calculator](https://jianzhujisuan.com/en/labor-productivity): Man-days, crew size and labour cost from output rates.
- [Line-of-Balance Duration Calculator](https://jianzhujisuan.com/en/schedule-flow): Rhythmic flow duration with overlap and break adjustments.
- [Material Storage Area Calculator](https://jianzhujisuan.com/en/material-storage): Net footprint, total area and a suggested bay size.
- [Dewatering Calculator](https://jianzhujisuan.com/en/dewatering): Pit inflow by the equivalent-well method, then well count.

---

Generated by BuildCalc. All calculations run in your browser; no data is uploaded. Formulas follow national standards and common trade practice; local codes govern.