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.

植物种类对由建筑垃圾构筑而成的三层土覆盖层系统防渗特性的影响研究

[1]Albright WH, Benson CH, Gee GW, et al., 2004. Field water balance of landfill final covers. Journal of Environmental Quality, 33(6):2317-2332.

[2]ASTM (American Society for Testing and Materials), 2006. Standard Test Method for Permeability of Granular Soils (Constant Head), ASTM D2434-68. ASTM, West Conshohocken, USA.

[3]ASTM (American Society for Testing and Materials), 2007. Standard Test Method for Particle-size Analysis of Soils, ASTM D422-63. ASTM, West Conshohocken, USA.

[4]ASTM (American Society for Testing and Materials), 2010a. Standard Test Methods for Specific Gravity of Soil Solids by Water Pycnometer, ASTM D854-10. ASTM, West Conshohocken, USA.

[5]ASTM (American Society for Testing and Materials), 2010b. Standard Test Methods for Liquid Limit, Plastic Limit, and Plasticity Index of Soils, ASTM D4318-10. ASTM, West Conshohocken, USA.

[6]ASTM (American Society for Testing and Materials), 2010c. Standard Test Methods for Measurement of Hydraulic Conductivity of Saturated Porous Materials Using a Flexible Wall Permeameter, ASTM D5084-10. ASTM, West Conshohocken, USA.

[7]ASTM (American Society for Testing and Materials), 2011. Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System), ASTM D2487-11. ASTM, West Conshohocken, USA.

[8]ASTM (American Society for Testing and Materials), 2012. Standard Test Methods for Laboratory Compaction Characteristics of Soil Using Standard Effort (12 400 ft-lbf/ft³ (600 kN-m/m³)), ASTM D698-12e2. ASTM, West Conshohocken, USA.

[9]ASTM (American Society for Testing and Materials), 2016. Standard Test Methods for Determination of the Soil Water Characteristic Curve for Desorption Using Hanging Column, Pressure Extractor, Chilled Mirror Hygrometer, or Centrifuge, ASTM D6836-16. ASTM, West Conshohocken, USA.

[10]Barnswell KD, Dwyer DF, 2011. Assessing the performance of evapotranspiration covers for municipal solid waste landfills in Northwestern Ohio. Journal of Environmental Engineering, 137(4):301-305.

[11]Barnswell KD, Dwyer DF, 2012. Two-year performance by evapotranspiration covers for municipal solid waste landfills in Northwest Ohio. Waste Management, 32(12):2336-2341.

[12]EPD (Environmental Protection Department), 2003. Homepage of Environmental Protection Department. EPD. http://www.info.gov.hk/epd

[13]Garg A, Leung AK, Ng CWW, 2015. Comparisons of soil suction induced by evapotranspiration and transpiration of S. heptaphylla. Canadian Geotechnical Journal, 52(12):2149-2155.

[14]GCO (Geotechnical Control Office), 2000. Geotechnical Manual for Slopes. Engineering Development Department, Hong Kong, China.

[15]GEO (Geotechnical Engineering Office), 2011. Technical Guidelines on Landscape Treatment for Slopes. GEO, Hong Kong, China.

[16]Harnas FR, Rahardjo H, Leong EC, et al., 2016. Physical model for the investigation of capillary-barrier performance made using recycled asphalt. Geotechnical Testing Journal, 39(6):977-990.

[17]Hauser VL, Weand BL, Gill MD, 2001. Natural covers for landfills and buried waste. Journal of Environmental Engineering, 127(9):768-775.

[18]Leung AK, Garg A, Ng CWW, 2015a. Effects of plant roots on soil-water retention and induced suction in vegetated soil. Engineering Geology, 193:183-197.

[19]Leung AK, Garg A, Coo JL, et al., 2015b. Effects of the roots of Cynodon dactylon and Schefflera heptaphylla on water infiltration rate and soil hydraulic conductivity. Hydrological Processes, 29(15):3342-3354.

[20]Limbachiya MC, Koulouris A, Roberts JJ, et al., 2004. Performance of recycled aggregate concrete. Proceedings of RILEM International Symposium on Environment-Conscious Materials and Systems for Sustainable Development, p.127-136.

[21]McCartney JS, Zornberg JG, 2010. Effects of infiltration and evaporation on geosynthetic capillary barrier performance. Canadian Geotechnical Journal, 47(1):1201-1213.

[22]Moon S, Nam K, Kim JY, et al., 2008. Effectiveness of compacted soil liner as a gas barrier layer in the landfill final cover system. Waste Management, 28(10):1909-1914.

[23]Ng CWW, Pang YW, 2000. Influence of stress state on soil-water characteristics and slope stability. Journal of Geotechnical and Geoenvironmental Engineering, 126(2):157-166.

[24]Ng CWW, Menzies B, 2007. Advanced Unsaturated Soil Mechanics and Engineering. Taylor & Francis, London, UK.

[25]Ng CWW, Leung AK, 2012. Measurements of drying and wetting permeability functions using a new stress-controllable soil column. Journal of Geotechnical and Geoenvironmental Engineering, 138(1):58-68.

[26]Ng CWW, Woon KX, Leung AK, et al., 2013. Experimental investigation of induced suction distribution in a grass-covered soil. Ecological Engineering, 52:219-223.

[27]Ng CWW, Leung AK, Woon KX, 2014. Effects of soil density on grass-induced suction distributions in compacted soil subjected to rainfall. Canadian Geotechnical Journal, 51(3):311-321.

[28]Ng CWW, Liu J, Chen R, et al., 2015. Numerical parametric study of an alternative three-layer capillary barrier cover system. Environmental Earth Sciences, 74(5):4419-4429.

[29]Ng CWW, Ni JJ, Leung AK, et al., 2016a. Effects of planting density on tree growth and induced soil suction. Géotechnique, 66(9):711-724.

[30]Ng CWW, Ni JJ, Leung AK, et al., 2016b. A new and simple water retention model for root-permeated soils. Géotechnique Letters, 6(1):106-111.

[31]Ng CWW, Garg A, Leung AK, et al., 2016c. Relationships between leaf and root area indices and soil suction induced during drying–wetting cycles. Ecological Engineering, 91:113-118.

[32]Ng CWW, Coo JL, Chen ZK, et al., 2016d. Water infiltration into a new three-layer landfill cover system. Journal of Environmental Engineering, 142(5):4419-4429.

[33]Ni JJ, Leung AK, Ng CWW, et al., 2017. Investigation of plant growth and transpiration-induced matric suction under mixed grass–tree conditions. Canadian Geotechnical Journal, 54(4):561-573.

[34]Ni JJ, Leung AK, Ng CWW, 2018. Modelling effects of root growth and decay on soil water retention and permeability. Canadian Geotechnical Journal, in press.

[35]Pollen-Bankhead N, Simon A, 2010. Hydrologic and hydraulic effects of riparian root networks on streambank stability: is mechanical root-reinforcement the whole story? Geomorphology, 116(3-4):353-362.

[36]Poon CS, Qiao XC, Chan D, 2006. The cause and influence of self-cementing properties of fine recycled concrete aggregates on the properties of unbound sub-base. Waste Management, 26(10):1166-1172.

[37]Rahardjo H, Tami D, Leong EC, 2006. Effectiveness of sloping capillary barriers under high precipitation rates. Proceedings of the 2nd International Conference on Problematic Soils, p.39-54.

[38]Rahardjo H, Krisdani H, Leong EC, 2007. Application of unsaturated soil mechanics in capillary barrier system. Proceedings of the 3rd Asian Conference on Unsaturated Soils, p.127-137.

[39]Rahardjo H, Vilayvong K, Leong EC, 2011. Water characteristic curves of recycled materials. Geotechnical Testing Journal, 34(1):89-96.

[40]Rahardjo H, Santoso VA, Leong EC, et al., 2012. Performance of an instrumented slope covered by a capillary barrier system. Journal of Geotechnical and Geoenvironmental Engineering, 138(4):481-490.

[41]Rahardjo H, Satyanaga A, Harnas FR, et al., 2013a. Capillary barrier system for landfill capping. In: Manassero M, Dominijanni A, Foti S, et al. (Eds.), Coupled Phenomena in Environmental Geotechnics. CRC Press, London, UK, p.425.

[42]Rahardjo H, Santoso VA, Leong EC, et al., 2013b. Use of recycled crushed concrete and Secudrain in capillary barriers for slope stabilization. Canadian Geotechnical Journal, 50(6):662-673.

[43]Ramaswamy SD, Murthy CK, Nagaraj TS, 1983. Use of waste materials and industrial by-products in concrete construction. In: Concrete Technology and Design, New Concrete Materials. Surrey University Press, Guildford, UK, p.137-169.

[44]Ross B, 1990. The diversion capacity of capillary barriers. Water Resources Research, 26(10):2625-2629.

[45]Soilmoisture Equipment Corporation, 2009. Model 2100F Soilmoisture Probe Operation Instructions. Soilmoisture Equipment Corporation, Santa Barbara, USA.

[46]van Dijk B, 2018. Design of suction foundations. Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 19(8):579-599.

[47]Wan Y, Xue Q, Liu L, et al., 2016. The role of roots in the stability of landfill clay covers under the effect of dry–wet cycles. Environmental Earth Sciences, 75:71.

[48]Zhang WJ, Sun C, Qiu QW, 2016. Characterizing of a capillary barrier evapotranspirative cover under high precipitation conditions. Environmental Earth Sciences, 75:513.