Prediction of vertical pressure in a trench as influenced by soil arching

A series of model tests was performed to investigate the effect of soil arching on the vertical pressure imposed on the bottom of a trench during backfilling. Soil arching can reduce some portion of the vertical pressure generated by the overburdening soil weight in a trench. To determine theoretically the vertical pressure based on the available formula, two unknown factors must be found: (1) the horizontal stress acting on the trench wall, which is related to the lateral earth pressure coefficient, and (2) the wall friction mobilized between the fill soil and the trench wall. However, appropriately determining those two factors is extremely difficult. Therefore, this paper proposes a novel method using the soil arching coefficient to capture the vertical pressure. The soil arching coefficient is here defined as a constant value that depends on neither the internal friction angle of the backfill soil nor the width of the trench. Qualitative and quantitative tests show good agreement between the vertical pressure predicted by the proposed method and experimental data measured in both laboratory and field tests.