Full-scale assessment of spacing and array configuration in multi-conduit underground distribution systems

Underground power distribution cables are typically installed using multi-conduit systems, in which the minimum spacing between adjacent conduits is prescribed primarily for electrical and thermal safety. However, such considerations are less critical for medium-voltage distribution systems and do not reflect the geotechnical behavior of closely buried conduits. This study presents a full-scale laboratory investigation to evaluate how conduit spacing affects soil-structure interaction and mechanical response under static and repetitive loading. Two configurations, a conventional spaced arrangement and a non-spaced arrangement, are constructed in a large instrumented soil chamber. Miniature cone penetration tests are conducted prior to loading to verify that the prepared backfill satisfied the target compaction level. Measurements of vertical soil pressure and conduit deformation reveal clear behavioral differences between the two configurations. The non-spaced configuration shows stress redistribution behavior consistent with the formation of a continuous arching mechanism, which is associated with reduced deformation under both static and cyclic loading. In contrast, the spaced configuration develops localized arching above individual conduits and exhibited greater deformation accumulation during repetitive loading. Supplemental uniaxial compression testing confirms that the stress levels mobilized in the full-scale experiments remain well within the elastic range of the polyethylene conduit, indicating minimal risk of structural yielding regardless of spacing. Overall, the results indicate that eliminating spacing does not compromise structural safety and produces favorable stress redistribution and deformation responses under the tested installation conditions. These findings suggest the need for further geotechnical evaluation of configuration requirements in medium-voltage distribution conduits.