Determining and computing the number of rows in staggered (quincunx) soil-nail layouts: count rows by vertical spacing (row spacing) only; the offset does not count (the 1.4 m/0.7 m criterion), including first/last row distances, the row minimum, and the excavation-layer linkage

Topic Positioning

How to count rows for staggered (quincunx) elevation layouts of soil-nail walls (including composite walls): distinguishing row spacing (vertical spacing) from the inter-row offset; a three-step row-count method; first/last-row construction checks; the row minimum; and linkage with excavation layers and nail-count takeoff.

Core Conclusions

1. Master rule: rows are counted by vertical spacing (row spacing) only; the offset does not count. The geometry of staggered layout is that adjacent rows offset by half a spacing: where drawings note "spacing 1.4 m, staggered", 0.7 = 1.4/2 is the offset; rows are counted at 1.4 m. Only an explicit "vertical spacing = 0.7 m" counts rows at 0.7 m — below the usual range and rare, so clarify with the designer first. Counting rows by the offset doubles rows (and nails).

• Term (JGJ/T 219-2010 Clause 2.0.9): staggered arrangement — "the placement of spacers at the midpoints of adjacent rows and columns".

2. Reasonable spacing ranges (to judge whether a notation is normal):

• JGJ 120-2012 Clause 5.3.3: "Soil nails' horizontal and vertical spacings should be 1-2 m; for deep excavations or low shear strength, take smaller values. Nail inclination 5-20 degrees. Nail lengths are set so all rows are evenly stressed and the ratios of nail forces to ultimate capacities are similar."
• DB11/489-2016 Clause 6.2.15: spacing preferably 1.2-2.0 m, locally < 1.2 m in weak soils; length 0.5-1.2 times wall height (lower for dense sand and stiff clay, >= 1.0 for soft plastic clay; top nails preferably longer).
• GB 50739-2011 Clause 5.2.1: lengths and spacings may be preselected from Table 5.2.1 and finalized by stability analysis; the table lists horizontal and vertical spacing in separate columns — row counting uses the vertical column only (verify table values).

3. Three-step row count:

• (1) First row: "the vertical distance from the first row to grade is preferably 0.5-2.0 m" (DB62/T 25-3111-2016 Clause 7.3.4);
• (2) step down by row spacing;
• (3) end check: "the lowest row is not more than 2/3 row spacing from the toe and not less than 0.5 m"; "rows should not be fewer than two" (DB62/T 25-3111-2016 Clause 7.3.4); minimum also per GB 50739-2011 Clause 5.4.1: "rows preferably >= 2".

4. Elevation layout forms: "On elevation, nails may be staggered (quincunx) or grid-aligned"; "vertical layout should be long-top short-bottom or long-middle short-top/bottom (top nails not too short)" (DB62/T 25-3111-2016 Clause 7.3.4); "long-middle, short-top/bottom is preferred" (GB 50739-2011 Clause 5.4.1 and commentary: best value-for-money; equal lengths only for shallow pits, steep slopes, good soil, short nails).

5. Linkage with excavation layers: "Nails, anchors, or struts are constructed layer by layer — one layer of excavation per row; the dig surface should not be more than 500 mm above the nail/anchor, each layer's depth = the nail/anchor vertical spacing" (DB62/T 25-3111-2016 Clause 17.1.4). I.e., rows = excavation layers; layer thickness follows row spacing.

6. Linkage with nail counts: Staggering is only a positioning mode and does not change the tributary area per nail (still horizontal x vertical spacing, e.g., 1.4 x 1.4 = 1.96 m2/nail); total count approximately = net slope area / (horizontal x vertical spacing); per-row count = row length / horizontal spacing, rounded up.

7. Example: slope 5.6 m, first row 0.7 m below grade, row spacing 1.4 m: rows at 0.7/2.1/3.5/4.9 m = 4 rows; last row 5.6 - 4.9 = 0.7 m from toe, satisfying 0.5 <= 0.7 <= (2/3) x 1.4 = 0.93 m.

Applicable Boundaries

• Applies to row determination and checking of staggered layouts for building-excavation soil-nail/composite walls; rows are finally per the design and stability verification (GB 50739-2011 Clause 5.2.1 requires stability analysis and parameter adjustment).
• Local standards govern locally (this card includes Beijing DB11/489-2016 and Gansu DB62/T 25-3111-2016 calibers); values may differ.
• Ambiguous notations (e.g., "1.4 x 0.7" without saying which is row spacing) must not be assumed — clarify with the designer.
• Only row determination and layout construction are covered — not stability verification, facing, or grouting details; values are excerpts from the cited standards — verify current editions.

Further Reading

• JGJ 120-2012 Technical Specification for Retaining and Protection of Building Excavations, Clause 5.3.3 and Chapter 5 (nail parameters per Clauses 5.2.2-5.2.5).
• GB 50739-2011 Technical Code for Composite Soil Nail Wall Retaining of Excavations, Clause 5.2.1 (Table 5.2.1), Clause 5.4.1 and commentary.
• DB11/489-2016 Technical Specification for Retaining and Protection of Building Excavations, Clause 6.2.15.
• DB62/T 25-3111-2016 Technical Specification for Building Excavation Engineering, Clauses 7.3.4 and 17.1.4.
• JGJ/T 219-2010 Technical Specification for Application of Bar Spacers in Concrete Structures, Clause 2.0.9.