# Ground Anchor Calculator

Anchor count, length and grout volume - the prestressed upgrade to soil nails.

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

## Quick result

With the default inputs (Wall length 40 m, Number of rows 3 rows, Horizontal spacing 2 m, Free length 6 m, Bond length 8 m, Drill hole diameter 130 mm): **Number of anchors 60 bars**

## Inputs

| Parameter | Type | Default | Unit | Note |
|---|---|---|---|---|
| Wall length | number | 40 | m |  |
| Number of rows | number | 3 | rows |  |
| Horizontal spacing | number | 2 | m |  |
| Free length | number | 6 | m | Anchor head to bond start, crossing the slip surface |
| Bond length | number | 8 | m | Bond must reach stable ground, normally ≥ 3 m |
| Drill hole diameter | number | 130 | mm |  |

## Formula

- **Per row**: n = ⌈length ÷ spacing⌉
- **Total**: N = per row × rows
- **Length**: L = free + bond
- **Grout**: V = N × π×(d/2)² × bond length

## Worked example

A 40 m wall, 3 rows at 2 m spacing, 6 m free + 8 m bond, 130 mm holes: 20 per row, 60 total, 14 m each, 840 m total; bond grout 60×π×0.065²×8 ≈ 6.4 m³.

## Questions

### What is the difference between an anchor and a soil nail?

The core is active versus passive. A nail bonds full length and only mobilises once the soil moves, so it is passive, deflects more and carries no prestress. An anchor bonds only over its bond, its free length can stretch, and after tensioning it actively holds the wall against the ground - less movement, better control, for displacement-sensitive deep pits and tight neighbours. Anchors have a free length and head anchorage, nails do not, so anchors cost more.

### How long should the bond be?

It is back-calculated from the pull-out capacity, not guessed. A longer bond holds more, but the gain tapers because stress is not uniform along it - effective bond runs about 10-20 m in soft ground and only 3-6 m in rock. It must also reach stable ground and pass well beyond the slip surface. Final length comes from pull-out tests and the design capacity; this tool just quantities the length you enter.

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