The mechanics of arching in induced trench construction – a new theoretical formulation

Abstract

Full-scale experimental case studies have shown that the induced trench construction method effectively reduces the vertical earth load that is exerted on culverts installed beneath high embankments. Induced trench culverts are traditionally designed on the basis of Marston’s theory; however, various theoretical shortcomings of this formulation have recently come to light. In this paper, a new induced trench theoretical formulation is presented. The proposed analytical model employs inclined shear planes within the embankment fill; such geometry is consistent with experimental findings reported in the literature, and leads to positive arching resulting from a reduction in vertical stress and an increase in horizontal stress (thus increasing the lateral earth pressure coefficient within the induced trench zone). A series of parametric studies are performed using finite element software. The proposed theoretical formulation is shown to be in good agreement with the numerical results, and correlations are developed to provide guidance in selecting the appropriate values of: 1) the induced trench lateral earth pressure coefficient, and 2) the height to the plane of equal settlement. Two instrumented full-scale induced trench case studies are discussed, and the proposed theoretical formulation is shown to produce results that are in good agreement with the experimental data.