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Soil-Structure Interaction and Imperfect Trench Installations for Deeply Buried Corrugated Polyvinyl Chloride Pipes

The imperfect trench installation method has been used to reduce earth pressure on buried rigid pipes by inducing positive soil arching over the pipe. Because they are relatively flexible, corrugated thermoplastic pipes induce a small amount of positive soil arching. Therefore, there has been little research on the effects of imperfect trench installation on flexible pipes, such as those fabricated with corrugated thermoplastic. A study was done of the soil-structure interaction for corrugated poly-vinyl chloride (PVC) pipes and the efficiency of the imperfect trench method for their installation. The soil-structure model was simulated with the Duncan soil model and Selig soil parameters by using the finite element method. The geometry of a soft zone was optimized to maximize the earth load reduction effects for imperfect trench installations. The optimization process was based on parametric studies of the geometry and location of the soft zone, combined with bedding and sidefill treatments to reduce earth pressures. Predictor equations for earth load, maximum stress, and deflection of corrugated PVC pipes were formulated that incorporate the proposed optimum soft zone geometry and installation techniques. Parametric studies revealed that the optimum geometry of the soft zone in the proposed imperfect trench installations could reduce the maximum wall stress in corrugated PVC pipes by 85%.