Soil Nail Wall Calculator
Nail count and length, grout volume, facing concrete and mesh.
Quick answer
With the default inputs: Wall length 30 · Wall height 6 · Horizontal spacing 1.5 etc.Number of soil nails 80 bars
Edit the inputs below to recalculate.Inputs
Result
Number of soil nails
80bars
| Wall area | 180.0m² |
| Nail grid | 20 × 4rows |
| Total nail length | 480m |
| Total drilling | 480m |
| Grout volume | 5.70m³ |
| Nail bar weight | 1851.0kg |
| Facing concrete | 18.90m³ |
| Mesh weight | 469.2kg |
| Steel per m² | 12.9kg/m² |
This is a quantity take-off only, not a stability check. Whether a soil nail wall stands depends on pull-out capacity, internal and external stability, and must be designed from the ground investigation by a qualified engineer; nail length is usually 0.6-1.0 times the excavation depth, longer in soft ground. Soil nails are unsuitable in mud, muddy soil, loose sand or water-bearing ground, where holes will not stand and grout bodies cannot grip. Facing concrete includes 5% rebound.
Reverse: known result, work out one input
Enter a target result; the other inputs stay fixed and this one is worked out.
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 |
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.
How to work it out
- Count the nails: horizontal rows = wall length ÷ horizontal spacing, vertical rows = height ÷ vertical spacing, multiplied and rounded up, usually on a staggered or rectangular grid.
- Total length = count × length per nail. Lengths normally shorten with depth (the upper rows carry more), so a uniform length undercounts the top and overcounts the bottom.
- Grout volume = count × π/4 × hole diameter² × nail length × a filling factor of 1.2-1.3. Grout is what develops the anchorage.
- Face concrete = wall area × thickness (80-150 mm), C20 sprayed.
- Mesh = wall area × weight per m² (φ6.5 at 200 both ways is about 2.6 kg/m²), plus the bearing bars at each nail head, typically 2φ12 continuous.
Where it goes wrong
- Uniform nail length — upper nails must pass through the active slip surface into stable ground, usually 6-9 m, while lower ones need only 3-5 m; one length wastes the bottom and starves the top.
- Ignoring the grout filling factor — holes overbreak, so 20-30% more grout is needed, and at 1.0 the nails pull out.
- Using 50 mm face thickness — the code requires at least 80 mm of sprayed concrete and 100-150 mm on important work; thinner cracks and spalls.
- No drainage — weepholes and a drainage channel behind the face are essential, or water pressure builds and bursts the facing.
Material and cost
Complete soil-nailed wall 180-350 CNY/m² including nails, grout, facing and mesh; nails 60-120 CNY/m. Sprayed concrete 80-150 CNY/m³.
On site
- Pull-out test at least 1% of nails and never fewer than three; shortfalls mean adding nails or length.
- Excavate in lifts no deeper than the vertical nail spacing — dig a lift, install a row, spray a layer. Over-excavation is what causes collapses.
- Soil nailing is unsuitable in mud, soft silty clay, loose sand or wet ground; those need a different system.
Basis
- JGJ 120-2012 Technical specification for excavations, Chapter 5 (soil nailing)
- GB 50330-2013 Technical code for building slopes
- GB 50202-2018 Code for acceptance of foundation construction, Chapter 7
FAQ
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.
Cite this page
Use this format in reports, method statements or coursework. The link is permanent.
Building Calculator. Soil Nail Wall Calculator. 2026-10-25. https://jianzhujisuan.com/en/soil-nail-wall
Results are estimating aids only and are not a design basis. Construction and final accounts must follow the drawings, the applicable standards and an approved method statement. Anything affecting structural safety, shoring or falsework must be checked by a suitably qualified engineer.