Physical and numerical modeling of an inclined three-layer (silt/gravelly sand/clay) capillary barrier cover system under extreme rainfall

Ng, Charles Wang Wai; Liu, Jian; Chen, Rui; Xu, Jie

doi:10.1016/j.wasman.2014.12.013

Cited by 86 publications

(39 citation statements)

References 21 publications

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“…This study is characterized by infiltration of water into an initially dry sample comprising three sample materials of contrasting pore sizes. Under such conditions, the capillary barrier effect can effectively influence the flow (Jansik et al, 2011; Ng et al, 2015; Prédélus et al, 2015). The results of the experiment presented here show that the intensity of capillary barrier formation strongly depends on the inflow rate.…”

Section: Discussionmentioning

confidence: 99%

Impact of Infiltration Rate on Residual Air Distribution and Hydraulic Conductivity

Šácha

Sněhota

Trtik

et al. 2019

Vadose Zone Journal

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Core Ideas Infiltration experiments were conducted on a sample under two boundary conditions. Time‐lapse neutron imaging was used to determine water distribution in the sample. Significant air entrapment was detected in the case of slow drip irrigation infiltration. Gravity‐driven ponding infiltration led to much less air entrapment. Air entrapment led to one order of magnitude lower conductivity in the case of drip irrigation. The dynamics of water infiltration into soil have a strong influence on the subsequent distribution of air trapped inside pores. We present results of two infiltration experiments conducted on an artificially prepared sample under ponding and drip irrigation boundary conditions, with concurrent neutron imaging of the sample. A cylindrical sample was packed with two grades of sand and disks of fine porous ceramic in an axially symmetrical geometry. The configuration of the sample provided a number of interfaces between regions of higher and lower hydraulic conductivity. Infiltration was started in dry media. The bottom boundary condition was seepage face. Water was applied on the sample surface during the experiment with drip irrigation at a water application rate about one order of magnitude lower than the minimum flux reached during the ponding experiment. Despite this low application rate, ponding eventually occurred on the top of the sample due to an unexpectedly low infiltration rate. Neutron tomographic imaging revealed massive air entrapment in the coarse sand regions of the sample during slow infiltration under drip irrigation conditions. In contrast, during the ponded infiltration experiment, the air was mostly flushed out from the coarse sand regions by gravity‐driven water flow due to greater hydraulic head. Neutron imaging showed that the capillary barrier effect, air entrapment, and entrapped air redistribution were responsible for the observed low infiltration capacity of the sample during the slow‐infiltration‐dominated drip irrigation experiment. It is reasonable to assume that similar phenomena can occur in natural soils having highly heterogeneous structures.

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Section: Discussionmentioning

confidence: 99%

Impact of Infiltration Rate on Residual Air Distribution and Hydraulic Conductivity

Šácha

Sněhota

Trtik

et al. 2019

Vadose Zone Journal

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“…Some other studies also demonstrated that the runoff coefficient can be greater than 1.0 for sand-covered slopes during runoff and sediment generation (Martínez-Murillo et al, 2013;Zhao et al, 2013;Zhang et al, 2017a). With increasing amount of sand cover, the time period before runoff and sediment generation increased, demonstrating that sand-covered areas at low elevations can intercept runoff and sediments generated from slopes and that sand layers can provide storage and release of runoff and eroded sediments (Ng et al, 2015). The storage and release processes could be the main reasons why SS generated a large amount of eroded sediments.…”

Section: Influences Of Sand Cover Pattern On Erosion Processes Of Loementioning

confidence: 92%

Influences of sand cover on erosion processes of loess slopes based on rainfall simulation experiments

Zhang

et al. 2018

J. Arid Land

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Aeolian-fluvial interplay erosion regions are subject to intense soil erosion and are of particular concern in loess areas of northwestern China. Understanding the composition, distribution, and transport processes of eroded sediments in these regions is of considerable scientific significance for controlling soil erosion. In this study, based on laboratory rainfall simulation experiments, we analyzed rainfall-induced erosion processes on sand-covered loess slopes (SS) with different sand cover patterns (including length and thickness) and uncovered loess slopes (LS) to investigate the influences of sand cover on erosion processes of loess slopes in case regions of aeolian-fluvial erosion. The grain-size curves of eroded sediments were fitted using the Weibull function. Compositions of eroded sediments under different sand cover patterns and rainfall intensities were analyzed to explore sediment transport modes of SS. The influences of sand cover amount and pattern on erosion processes of loess slopes were also discussed. The results show that sand cover on loess slopes influences the proportion of loess erosion and that the compositions of eroded sediments vary between SS and LS. Sand cover on loess slopes transforms silt erosion into sand erosion by reducing splash erosion and changing the rainfall-induced erosion processes. The percentage of eroded sand from SS in the early stage of runoff and sediment generation is always higher than that in the late stage. Sand cover on loess slopes aggravates loess erosion, not only by adding sand as additional eroded sediments but also by increasing the amount of eroded loess, compared with the loess slopes without sand cover. The influence of sand cover pattern on runoff yield and the amount of eroded sediments is larger than that of sand cover amount. Furthermore, given the same sand cover pattern, a thicker sand cover could increase sand erosion while a thinner sand cover could aggravate loess erosion. This difference explains the existence of intense erosion on slopes that are thinly covered with sand in regions where aeolian erosion and fluvial erosion interact.

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“…As one of the important components of solid waste disposal, final cover systems minimize the percolation into the underlying waste and limit the emission of landfill gas. In recent years, there has been increasing interest in applying alternative forms of earthen final cover in final cover systems (Stormont et al 1996(Stormont et al , 1998(Stormont et al , 1999Nyhan et al 1997;Khire et al 2000;Albright et al 2004Albright et al , 2010Parent et al 2006;Aubertin et al 2009;Benson et al 2004Benson et al , 2012Apiwantragoon et al 2014;Zhan 2015;Ng et al 2015;Rahardjo et al 2015). Currently, there are generally two types of earthen final cover: monolithic cover and capillary barrier cover (CBC).…”

Section: R a F T Introductionmentioning

confidence: 99%

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

Zhan

Jiao

et al. 2017

Can. Geotech. J.

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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.

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Physical and numerical modeling of an inclined three-layer (silt/gravelly sand/clay) capillary barrier cover system under extreme rainfall

Cited by 86 publications

References 21 publications

Impact of Infiltration Rate on Residual Air Distribution and Hydraulic Conductivity

Impact of Infiltration Rate on Residual Air Distribution and Hydraulic Conductivity

Influences of sand cover on erosion processes of loess slopes based on rainfall simulation experiments

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

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