Load Coefficient for Ditch Conduits Covered with Geosynthetic-Reinforced Granular Backfill

Conduits buried in narrow trenches and covered with granular soil backfills are commonly used for several services. Because of soil arching action, a significant fraction of self-weight of the backfill is transferred to the wall. The load on top of the conduit is expressed as $C_d\gamma B^2$ where$\mathit{\gamma }$ is the unit weight of granular backfill, $\mathit{B}$ is the trench width, and ${\mathit{C}}_{\mathit{d}}$ is the load coefficient, which increases with depth. Values of ${\mathit{C}}_{\mathit{d}}$ for ditch conduits covered with granular backfills have been presented in the literature. Recent research has shown that providing a layer of geosynthetic above the conduit, anchored at both the walls, can reduce the overburden load transferred to the conduit. This paper is aimed at formulating a theoretical framework for computing the load coefficient ${\mathit{C}}_{\mathit{dR}}$ for ditch conduits covered with geosynthetic-reinforced granular backfills. The new ${\mathit{C}}_{\mathit{dR}}$-value takes into account the load reduction attributable to soil arching as well as geosynthetic arching but ignores the soil-geosynthetic frictional/adhesion interaction in the analysis for simplicity’s sake. It is shown that the ${\mathit{C}}_{\mathit{dR}}$-values depend on the stiffness of the geosynthetic layer and the rut depth, among other factors that govern the unreinforced case. The developed expression should be useful for field applications of geosynthetics in buried structures and for developing standards for such applications.