Equations to predict vertical deflection and maximum stress of buried pipes under overburden

The structural integrity and safety of buried pipes are mainly governed by the deflection and the maximum stress, which are controlled by the earth pressure exerted around the pipe. The earth pressures surrounding a buried pipe are idealized in the existing design equations. New deflection and stress equations are developed in this study taking into account the following factors: (i) the relative pipe-soil stiffness ratio; (ii) the bedding condition at the pipe haunches; and (iii) the soil friction angle governing the at-rest earth pressure in addition to the one mobilized by pipe displacement. The lateral earth pressure is assumed to be uniformly distributed and a function of pipe deflection. The vertical reaction at the pipe bottom is affected by the pipe-soil bedding condition. Design charts are provided to facilitate the engineering application process. The vertical deflection and the maximum stress of buried pipes are most sensitive to variations in the pipe-soil stiffness ratio between 0.005 and 0.5. The proposed equation predicts the maximum pipe stresses close to those measured, and the predicted vertical pipe deflections are usually conservative, i.e., overestimated. For flexible and semi-rigid pipes with a low pipe-soil stiffness ratio (≤0.1), the proposed method performs better compared to the existing design equations, such that the mean absolute error is the lowest and the coefficient of determination is the highest.