Soldier pile wall

A cantilever soldier pile and lagging wall (no anchors or braces), per pile: the embedment by the simplified free-earth method of the Caltrans Trenching and Shoring Manual (AASHTO LRFD 3.11.5.6), the pile moment, shear and top deflection, the steel pile designed to AISC 360-22 and the lagging (timber to NDS 2024, or a concrete panel to ACI 318-19).

Inputs of the soldier pile wall #

• Wall and piles: excavation height H, pile spacing, the W or HP shape and its steel, the installation (a drilled hole filled with concrete below the excavation, whose diameter is the effective width, or a driven pile, whose flange width is), and the provided embedment D below the excavation.
• Soil and surcharge: one granular soil above and below the excavation (φ, γ), the backfill slope (Rankine Ka of the sloping backfill, horizontal component), a uniform surcharge q (adds Ka q over the full depth) and a lateral construction surcharge above the excavation (Caltrans minimum 72 psf).
• Embedment method: Kp (Rankine by default; Caltrans recommends a log-spiral value, which can be entered), a factor of safety on passive, the arching factor f (0.08φ ≤ 3 for granular soil by default, Caltrans Eq. 7-2-1), the embedment factor D/D0 (1.2), the point of fixity for the deflection (0.25D below the excavation) and the engineer's deflection limit.
• Pile design: the unbraced length (0 where the lagging against the front flange braces the compression flange), Cb, and the load factor on H for LRFD (ASD uses the service values).
• Lagging: timber boards (actual thickness, width, spacing, bearing length on the flange, reference values Fb, Fv and Fc⊥ and the factors CD, CM, CF and Cfu of the NDS Supplement Table 4A; DF-L No. 2 values prefilled) or a concrete panel (thickness, bars, f'c); the lagging pressure factor (0.6 where soil arching can develop, Caltrans 6-5).

Auto-design (editor toolbar) varies the embedment (1/2-ft steps), the W or HP pile (lightest first) and the lagging thickness; the excavation, spacing, soil and surcharges are kept. Objective: least steel and lagging. Every other input is kept; see Auto-design.

Checks performed #

The drawings (screen, report, DXF and PDF sheet) show the pile elevation with the retained grade, the excavation, the pile and its drilled hole, the provided and required embedment, the driving pressure above the excavation and the passive resistance below it (per pile); the shear and moment along the pile; and a plan of three piles with the lagging between the flanges. Pile tips, caps, anchors, drainage and the lagging installation are not part of the calculation.

Limitations #

• Cantilever walls only: anchored or braced walls are not covered.
• One granular soil; layered and cohesive soils, groundwater and sloping ground in front of the wall are not covered. Global stability, basal heave and seismic loads are not included.
• The required embedment uses the simplified method (no rigorous method); the strength of the concrete in the drilled hole is not checked.
• The deflection is a beam approximation from a point of fixity (Caltrans 7-3); a soil-structure analysis (p-y) is needed where movement matters.

Verification examples #

Verification status: 14 values compared in 3 examples (2 published, 1 hand calculations from the cited equations): 14 within tolerance, 0 recorded deviations. Thin: only 2 published examples. Code basis: the provisions it uses were read in the target edition.

Published worked examples (backend/tests/test_verify_soldier_pile_wall.py), Caltrans Trenching and Shoring Manual (July 2025, free at dot.ca.gov):

Example 7-1B, cantilevered soldier pile wall by the simplified method: W14x120 at 8 ft in 2 ft concrete-filled holes, H = 15 ft, φ = 35°, γ = 125 pcf, 72 psf construction surcharge.

The example's deflection (1.64 in.) comes from the Caltrans program with its own pile stiffness assumptions and is not compared.

Section 6-5.01, timber lagging: 4x12 DF-L No. 2 at 12 in., piles at 8.5 ft with 12 in. flanges, 580 psf × 0.6.

Hand calculation: a driven pile with an entered arching factor: D0 from the closed-form moment balance about O and the depth of zero shear from the quadratic force balance, within 0.1 %.