算BuildCalc

Soil Nail Wall Calculator

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

Quick answer

With the default inputs: Wall length 30 m · Wall height 6 m · Horizontal spacing 1.5 m etc.Number of soil nails 80 bars

Edit the inputs below to recalculate.

Inputs

m
m
Vertical height; adjust for battered faces
m
m
m
Usually 0.6-1.0 times the excavation depth
mm
1.2-1.3 in sand, higher in soft or collapsing ground
mm
HRB400 φ22-32 typically
mm
mm
Same both ways, usually 150-250 mm
mm

Result

Number of soil nails
80bars
Wall area180.0m²
Nail grid20 × 4rows
Total nail length480m
Total drilling480m
Grout volume5.70m³
Nail bar weight1851.0kg
Facing concrete18.90m³
Mesh weight469.2kg
Steel per m²12.9kg/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.

Formula

Wall areaA = length × height
Nail countn = ⌈length ÷ h-spacing⌉ × ⌈height ÷ v-spacing⌉
Grout volumeV = π ÷ 4 × hole² × total length × fill factor
Nail bar weightW = total length × dia² × 0.00617
Facing concreteV = A × thickness × 1.05
Mesh weightW = 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.

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.

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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.