Combined use of geocell reinforcement and rubber–soil mixtures to improve performance of buried pipes

Abstract

Service trench provision and maintenance of buried pipes represent major cost items in the utilities industry. Using recycled material in order to optimize the design of the buried pipe system can lead to significant cost reductions, but only if performance is not degraded. The main purpose of the paper is to investigate the mitigation of strain in buried flexible service pipes and of the settlement of backfill over such pipes by the use of geocell reinforcement (as 3D-inclusion reinforcement) with rubber–soil mixtures under repeated loading conditions. Two rubber sizes (namely chipped and shredded rubbers), three different percentages of rubber content in the mixture, two positions for soil–rubber mixture inside the trench, four levels of repeated loading and the addition of geocell reinforcement over the pipe are the variables considered. Soil surface settlement, vertical diametral strain of the pipe (as an indication of pipe wall deflection) and stress distribution in the trench, especially on pipe’s crown, are assessed and evaluated. Both cumulative and resilient strains are considered. Using a material with high resilience, like the rubber–soil mixture, could lead to some critical issues that should be considered. These include the larger settlement of the soil surface, transfer of a larger pressure onto the pipe and, consequentially, greater pipe wall strain. For the chipped rubber and soil mixture, the pipe has the highest strains under the cyclic loading irrespective of the amount of rubber in the soil. However, the shredded rubber and soil mixture, dependent on the amount of rubber content, is able to reduce the soil settlement and plastic pipe’s diametral strain, attenuating the pipe’s accumulating strains and, finally, protecting the buried pipe from fatigue under repeated loadings. This benefit is enhanced by the combined action of geocell reinforcement over rubber-modified soil. According to the results, the minimum soil surface settlement and vertical diametral strain are provided by 5% of shredded rubber–soil mixture placed over the pipe with a geocell, giving values of, respectively, 0.30 and 0.53 times those obtained in the unreinforced and untreated soil.