Effects of vegetation type on water infiltration in a three-layer cover system using recycled concrete

Abstract

To promote environmental sustainability, recycled construction concrete is suggested for civil infrastructure works. The aim of this study was to investigate the effects of vegetation type on water infiltration under extreme rainfall conditions in a proposed three-layer landfill cover system containing recycled concrete. Three soil columns, namely bare, covered with shrub (Schefflera arboricola), and covered with grass (Cynodon dactylon), were subjected to ponding tests. Each column was compacted with a bottom layer of silty soil, an intermediate layer of coarse recycled concrete aggregate, and an upper layer of fine recycled concrete aggregate. Water breakthrough occurred only in the bare cover system after 48 h of ponding, equivalent to a rainfall return period of greater than 1000 years in Hong Kong. Under the vegetated covers, suction maintained in the bottom silty soil layer was higher than under the bare cover by 49–52 kPa and hence no percolation was observed after 48 h of ponding. Comparing the two vegetated cover systems, suction maintained under the shrub cover was 2–12 kPa higher (2%–8% lower volumetric water content) than that under the grassed cover in the layers of recycled concrete. This implies that shrub cover can be more effective than grass cover in reducing water infiltration in humid climates.