Field measurements of water storage capacity in a loess–gravel capillary barrier cover using rainfall simulation tests

Abstract

A 30 m long × 20 m wide capillary barrier cover (CBC) test site was constructed at the Jiangcungou landfill in Xi’an, China. The cover consisted of a compacted loess layer with a thickness of 0.9 m underlain by a gravel layer. After the cover surface was kept bare and exposed to natural climate conditions for nearly 5 months, one artificial rainfall event was implemented at the site. Vegetation was established at the test site after the first rainfall event. Four months later, a second artificial rainfall event was applied to the surface of the vegetated site. The pore-water pressures (PWPs) and volumetric water contents (VWCs) of the cover were monitored using jet-filled tensiometers and time-domain reflectometry moisture probes, respectively. Surface runoff and percolation were measured using field collection devices. The field measurements demonstrated a more rapid response of PWPs to the rainfall compared to the response of the VWCs. Percolation was observed when the PWPs near the interface reached the water-entry value of the gravel at local points. At that moment, the measured VWC near the interface was less than the VWC according to the water-entry value. The observation indicated that preferential flows took place in the compacted loess during the rainfall. As a result, the maximum water storage capacity was not reached at the onset of percolation. When percolation ceased, the average PWP near the interface decreased below the water-entry value, while the VWC near the interface was higher than that at the onset of percolation. Water storage at the completion of percolation was approximately 5% greater than that at the onset of percolation. Compared with the monolithic loess cover, the loess–gravel CBC increased the available water storage capacity by 41% at the completion of percolation. Vegetation had an insignificant influence on water storage capacity.

Effects of In-Situ Drying–Wetting Cycles on the Stress-Dependent Water Retention Behavior of Intact Loess

“…Soil samples were obtained from three different depths (i.e., 1.0, 3.0, and 5.0 m), and each of them was tested at two vertical net stresses (i.e., 0-50 kPa). It should be pointed out that the vertical net stress of 50 kPa is close to the in-situ stress state and related to many geotechnical problems, such as subgrade settlement and shallow slope failure [4,8]. Comparisons of the obtained six WRCs would reveal the influence of drying-wetting and stress on the water retention behavior.…”

“…Understanding the stress-dependent water retention curve (WRC) of intact loess is essential for addressing many geotechnical problems in loess regions, such as rainfall-induced excessive embankment settlement [1][2][3], failure of landfill cover system [4][5][6] and slope instability [7,8]. Thus, some experimental studies have been carried out in this area.…”

A simple and rapid in situ method for measuring landfill gas emissions and methane oxidation rates in landfill covers

“…The measurements were conducted on 3 July, 17 July and 31 July 2016. More details of the testing site could be found in Zhan et al (2016). Figure 3 shows the contour map for LFG (CH 4 and CO 2 ) emission rates on the surface of the CBC at different dates.…”

Development and numerical validation of a simplified method of analysis for the final steady state of sloping capillary barriers under constant intensity rain

“…Horizontal or nearhorizontal CBs have been used for landfill cover systems, to reduce rainfall infiltration into the landfill and hence reduce the generation of leachate (e.g. [3], [4], [5]). Sloping CBs have been used to enhance stability of natural or constructed slopes under rainfall (e.g.…”