Dock Piling Embedment and Lateral Load

A piling is a cantilever fixed in soil, and its lateral capacity depends on the soil's lateral bearing over the embedded length rather than on how hard it was to drive. That distinction is the whole point: driving to refusal establishes AXIAL capacity against a hard layer and says nothing about the lateral resistance in the soft material above, which is what resists a boat pushing sideways -- so a piling that refused on a shallow hard stratum can be axially sound and laterally inadequate at the same time. The relation is the nonconstrained case the building code gives for posts and poles, applied to a marine pile: the required depth grows with the load and with the height of that load above the mudline, and shrinks with the pile's width and the soil's lateral bearing. SCOUR is what makes this a marine problem rather than a fence problem, and it attacks from both directions at once. Scour lowers the effective mudline, so the cantilever above it LENGTHENS and the moment rises, while the embedment below it SHORTENS -- and the pile has to be driven deeper by the scour depth on top of the deeper embedment the longer cantilever demands. Both effects are computed here rather than described, because the combined answer is materially deeper than either alone suggests. Two conditions sit outside the arithmetic. Marine borers consume untreated or damaged timber below the waterline, so a pile's section is not a constant over its life and a design that assumed full section can lose it. And the loads themselves are larger than they look: berthing energy goes as the SQUARE of the approach speed, so a vessel arriving twice as fast delivers four times the energy, and wind on a moored vessel, current, and ice all add. The lateral load is ENTERED and it is the input this is most sensitive to. This does not compute berthing energy, wind or current loading, or ice; it does not check the pile's own bending capacity or its section loss, address group effects where piles are close together, evaluate uplift or axial capacity, or account for a sloping mudline. The geotechnical report, the applicable code, and a marine structural engineer govern.

the nonconstrained embedment d = 0.5 A (1 + sqrt(1 + 4.36 h / A)) with A = 2.34 P / (S1 b); scour lengthens the cantilever by the scour depth and the pile must be driven that much deeper below the ORIGINAL mudline on top of the deeper embedment the longer cantilever demands.

The nonconstrained lateral embedment relation the building code gives for posts and poles, applied to a marine pile, with the soil's lateral bearing ENTERED from the geotechnical information for the site rather than inferred from the driving record. It does not compute berthing energy, wind or current loading, or ice; it does not check the pile's own bending capacity or its section loss to marine borers, address pile group effects, evaluate uplift or axial capacity, or account for a sloping mudline.

One code relation evaluated twice; no code text is reproduced.

Estimate. AHJ and licensed professional govern.

Field names used by the API: lateral_load_lb, height_above_mudline_ft, pile_diameter_in, soil_lateral_bearing_psf_per_ft, scour_ft, existing_embedment_ft, moment_ftlb, embedment_ft, scoured_moment_ftlb, scoured_embedment_ft, total_depth_needed_ft

• The lateral load is entered berthing energy, wind, current and ice are not computed herea marine structural engineer
• Soil bearing from the geotechnical report the driving record says nothing about lateral resistancethe geotechnical report
• Full section assumed marine borers consume untreated or damaged timber below the waterlinethe inspection record