Assessment of an amended soil as a climate adaptive barrier: Element testing and physical modelling

This paper demonstrates the effectiveness of using waste from a drinking water treatment plant (water treatment residue WTR) to amend a natural soil and develop a climate-adaptive barrier layer (CABL) that can limit water migration into underlying layers, thereby mitigating climate risks for geotechnical infrastructure. Experimental results showed adding WTR to silty sand recovered from an active landslide site improved the soil’s engineering properties. In particular, a 5 % WTR amendment significantly enhanced water retention capacity and reduced saturated permeability, thereby improving its overall performance as a protective cover. Following this, a medium-scale physical model was developed to monitor water migration and suction evolution in a soil column with and without a CABL made from the WTR amended soil under atmospheric drying and artificial rainfall conditions. The amendment allowed the soil to store more water compared to unamended silty sand, delaying water infiltration into the underlying layers. Over 250 days of monitoring, the physical model indicated the effectiveness of the CABL in slowing the wetting and drying processes of the underlying soil. The enhanced water retention capacity of the CABL, combined with the contrasting unsaturated permeability values between the CABL and the natural soil, formed a barrier that slowed water infiltration and postponed the breakthrough point. Although the CABL did not entirely prevent breakthrough under simulated rainfall, the observed delay and increased water retention present clear advantage for developing more comprehensive mitigation systems. Vegetating the CABL or using multi-layered systems can enhance water loss through evapotranspiration or drainage, further reducing the risk of breakthrough. The outcome of this study not only contribute to the development of an effective soil cover system but also offers a sustainable pathway for the reuse of water treatment waste.