The imperfect trench installation method is used to reduce earth pressure on buried concrete pipes. Few quantitative refinements to the imperfect trench installation method, however, have been added since the fundamental mechanics of the reverse arching action were proposed by Marston and Spangler. There have been limited research results published regarding, primarily, qualitative aspects of earth load reduction for imperfect trench conditions. This paper identifies variables that significantly affect earth loads, as well as the effects of bedding and sidefill treatments. An optimum geometry for imperfect trench installations with regard to a soft material zone is presented to maximize the earth load reduction effects. The optimization process was based on parametric studies of the geometry and location of the soft zone, bedding, and sidefill treatments to reduce earth pressures. Predictor equations for earth load reduction rates were formulated incorporating the optimum geometry for the soft zone and be...