Lateral Earth Pressure on Lagging in Soldier Pile Wall Systems-Article

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The article presents a theoretical method for estimating lateral earth pressure on lagging in soldier pile and lagging excavation-support walls. Unlike rigid retaining walls, these systems allow soil to arch between the stiffer steel piles, reducing pressure on the lagging. Traditional design approaches, including the Goldberg-Zoino chart and Terzaghi’s trap-door analogy, have limitations: they may rely on narrow assumptions, omit surcharge loads or alternative materials, or lack a published theoretical basis.<br /><br />The proposed model represents the soil behind the lagging as a three-dimensional, silo-shaped sliding wedge. It accounts for soil weight, uniform surface surcharge, friction along the sides of the soil “silo,” and active earth pressure. The model predicts that pressure increases with depth to a maximum, then remains approximately constant—a pattern consistent with field experience. For common granular soils, the maximum pressure occurs at a depth of about 1.4 times the lagging’s clear span. Without surcharge, the maximum pressure is proportional to soil unit weight, clear span, and the active earth-pressure coefficient.<br /><br />Calculated lagging thicknesses compare reasonably well with Goldberg-Zoino recommendations, especially for larger spans. The model also permits analysis of surcharge loads and different lagging materials, making it useful for conditions beyond standard design charts. Case histories, including an existing brick wall used as lagging, support the model’s practical relevance.<br /><br />The authors caution that the method assumes lagging is substantially more flexible than the soldier piles; rigid materials may need to resist full active earth pressure. Cohesion can greatly reduce predicted pressure, but its use in temporary shoring design requires caution because it may weaken over time or with moisture.

Keywords

soldier pile

lagging

lateral earth pressure

excavation support

soil arching

surcharge load

active earth pressure

silo-shaped wedge

Goldberg-Zoino

Terzaghi trap-door