Geological and topographical challenges in fault zones pose significant risks to the structural integrity of buried pipelines. Previous studies have shown that continuously buried pipelines using loose sand as backfill material experience severe damage under active fault displacement. This study proposes the use of super-absorbent- polymer concrete (SAPC) as an alternative trench backfill to mitigate structural damage in buried pipelines subjected to reverse fault movement, as opposed to conventional backfill with loose sand. This study begins with the preparation of lightweight porous concrete containing large super-absorbent-polymer aggregates, followed by mechanical property testing to establish a constitutive model of SAPC. The SAPC is then employed to backfill the trench of a fault-crossing pipeline. A finite element model is developed to analyze the pipeline-SAPC trench- soil interaction and evaluate the performance of the pipeline when the trench is backfilled with SAPC. Critical parameters such as SAPC backfill length, overlying thickness, and elastic modulus are also examined for their effects on the performance of a buried pipeline. The numerical results indicate that compared with conventional backfill with loose sand, the critical reverse fault displacement of the pipeline can generally be increased by over 100 % after using SAPC as the backfill material. Optimal pipeline performance is observed when the SAPC backfill length is approximately 60 times the pipeline diameter. Besides, a thinner overlying SAPC thickness will generally enhance the performance of buried steel pipelines under reverse fault movement. Additionally, by adjusting the sand-cement ratio and SAP volume fraction, a SAPC with a higher elastic modulus can slightly improve the performance of the fault-crossing pipeline.

Utilizing natural expansive clays that are available on-site as sewer trench backfill can cause destructive deformations due to volume changes, which are caused by seasonal climatic changes. Such deformations result in manhole structures protruding from the surface, which cause damage to the surrounding infrastructure and generate potential trip hazards. In this study, mixtures of recycled materials with minor sensitivity to moisture variations and superior compactibility were investigated using geomechanics theories associated with granular materials as an alternative backfill material. Blends of recycled glass (RG), plastic (RP), and tire-derived aggregates (TDA) were mixed on-site, wetted to the required moisture content (MC), and used to backfill excavated trenches around two manhole structures and extended to approximately 11 m along the trench. A benchmark trial was constructed by backfilling with natural soils available on-site according to the normal procedure. The full-scale trial sites were instrumented using settlement plates and MC sensors at various locations and depths for performance monitoring. The results of approximately 17 months of field monitoring showed that settlements over both areas that were backfilled with recycled blends were <20% of those over areas backfilled with site-won soils. Approximately 82% of the settlements in the recycled blends occurred during construction. In contrast, trenches that were backfilled with site-won soils continued to exhibit deformation due to consolidation and swell-shrink cycles. The outcome of this study could contribute to the United Nations' Sustainable Development Goals, in particular, Goal 12, by improving the industry's confidence in the reuse of wastes in geotechnical applications.