Cover systems with synthetic water‐repellent soils

Abstract

A cover system is a crucial component of engineered landfills, to minimize water percolation into the underlying waste. Capillary barriers are an alternative cover system, which has been widely used in the arid and semiarid regions as no cohesive, low-permeability materials are used. However, the performance of capillary barriers in tropical climate has been unsatisfactory (breakthrough observed). In recent years, synthetic water-repellent granular materials have drawn increasing attention due to their distinctive hydraulic behavior (inhibited water infiltration and high water entry pressure), suggesting they may also be used to improve the performance of cover systems. In this study, flume tests were conducted with inclined model slopes under artificial rainfall. By monitoring the surface runoff, lateral diversion, and basal percolation and conducting water balance analysis, the performance of monolithic cover, conventional capillary barrier, and water-repellent cover systems were evaluated. The study revealed that (a) the barrier effect and diversion capacity were significantly strengthened by induced water repellency, providing a promising solution to extend the application of capillary barrier covers; and (b) cover systems can be formed using one raw material to decrease the construction cost, by using synthetic water-repellent soil as the underlying layer.

Numerical investigation of the performance of engineered barriers in controlling stormwater runoff

“…Refs. [20][21][22]. Those systems aim to control percolation of rainfall water into the underlying waste, 22 and thus, research focused heavily on the analysis of the flow through the barrier [23][24][25] using numerical methods that are not taking into account the coupled flow-deformation characteristics, since the settlements of the cover is not a critical design criterion.…”

Crushed Glass and Oil Extracted from Palm Oil Sludge as Primary Materials in the Production of Hydrophobic Sand for Capillary Barrier Applications

“…This superior capillary force boosts the water retention of the top layer [2] and impedes the vertical infiltration of water at the interface of the layers [3]. The top stores the water during rainfall events and then releases it as lateral drainage or evapotranspiration [5]. Depending on its construction and context, this technology could be used to drain water and harvest it, or as an evapotranspiration cover in landfills.…”

“…The breakthrough point is reached when K Bottom = K Top , causing the barrier to no longer be effective [3]. The unsaturated hydraulic conductivities equal each other under a specific matric potential, also known as the water entry pressure (WEP) [5]. For WEP to occur, the top layer must accumulate a lot of water, to the point of saturation [9].…”

“…Unfortunately, capillary barriers may need up to four different hydraulically suitable soils; this can increase costs and does not perform well in tropical climates [10]. Nonetheless, it is possible to enhance the capillary barrier by making the coarse layer hydrophobic [5,[10][11][12][13].…”

“…Capillary barriers can be built with synthetic water-repellent soil to restrict infiltration of water, promote lateral diversion, increase the value of WEP to positive pressures and create a larger difference in the water retention capacity of the layers [5,10]. Studies have shown that hydrophobic capillary barriers perform better than conventional capillary barriers and are able to resist higher precipitation rates, making them more suitable for tropical climates [5,10]. Due to these characteristics, they can also be used in water harvesting for human intake or agricultural purposes.…”