# Soil Nail Wall Calculator

Nail count and length, grout volume, facing concrete and mesh.

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

## Quick result

With the default inputs (Wall length 30 m, Wall height 6 m, Horizontal spacing 1.5 m, Vertical spacing 1.5 m, Nail length 6 m, Drill hole diameter 110 mm, Grout fill factor 1.25, Nail bar diameter 25 mm, Facing thickness 100 mm, Mesh spacing 200 mm, Mesh bar diameter 6.5 mm): **Number of soil nails 80 bars**

## Inputs

| Parameter | Type | Default | Unit | Note |
|---|---|---|---|---|
| Wall length | number | 30 | m |  |
| Wall height | number | 6 | m | Vertical height; adjust for battered faces |
| Horizontal spacing | number | 1.5 | m |  |
| Vertical spacing | number | 1.5 | m |  |
| Nail length | number | 6 | m | Usually 0.6-1.0 times the excavation depth |
| Drill hole diameter | number | 110 | mm |  |
| Grout fill factor | number | 1.25 | — | 1.2-1.3 in sand, higher in soft or collapsing ground |
| Nail bar diameter | number | 25 | mm | HRB400 φ22-32 typically |
| Facing thickness | number | 100 | mm |  |
| Mesh spacing | number | 200 | mm | Same both ways, usually 150-250 mm |
| Mesh bar diameter | number | 6.5 | mm |  |

## Formula

- **Wall area**: A = length × height
- **Nail count**: n = ⌈length ÷ h-spacing⌉ × ⌈height ÷ v-spacing⌉
- **Grout volume**: V = π ÷ 4 × hole² × total length × fill factor
- **Nail bar weight**: W = total length × dia² × 0.00617
- **Facing concrete**: V = A × thickness × 1.05
- **Mesh weight**: W = A × metres per m² × dia² × 0.00617

## Worked example

30 m by 6 m at 1.5×1.5 m spacing, 6 m nails in 110 mm holes: 20×4 = 80 nails, 480 m total, 5.70 m³ grout, 1851 kg of bar, 18.9 m³ facing, 469.2 kg of mesh.

## Questions

### Soil nails versus ground anchors?

Prestress is the essential difference. Anchors are tensioned to actively compress the ground, with bonded and free lengths plus a head; soil nails are passive, fully grouted, and only engage as the soil moves. Soil nail walls therefore tolerate movement — typically 0.1-0.5% of excavation depth — and suit poorly where nearby structures are movement-sensitive. Anchors control movement better but occupy ground beyond the site boundary.

### Why is the grout fill factor above 1?

Because the real hole is bigger than the theoretical cylinder: drilling over-breaks, grout penetrates the surrounding sand, and soft ground sloughs and necks before collapsing into voids. Grout always exceeds π/4 × d² × L. Use 1.2-1.3 in sand, 1.25-1.4 in silt, over 1.5 in soft or collapsing strata. A factor above 2 signals voids or grout escape and needs investigation.

### What ground suits a soil nail wall?

Silt, sand, gravelly soil and weathered rock above the water table or after dewatering — ground that can be drilled and provides pull-out resistance. It is unsuitable in mud and muddy soil (very low capacity, high creep), loose sand (holes collapse), and un-dewatered ground (grout diluted, holes unstable). Soil nail walls are generally limited to about 12 m depth; deeper needs a special review.

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