Climate impacts on deformation and instability of vegetated slopes

Abstract

Eco-geotechnical engineering plays a pivotal role in enhancing global sustainability and upholding the performance of earthen structures. The utilization of vegetation to stabilise geotechnical infrastructures is widely recognized and embraced for its environmentally friendly attributes. The spectre of climate change further intensifies the focus on the effects of temperature and humidity on vegetated soil. Consequently, there is a pressing need for research exploring the influence of changing climates on vegetated infrastructures. Such research demands a holistic and interdisciplinary approach, bridging fields such as soil mechanics, botany, and atmospheric science. This review underscores key facets crucial to vegetated geotechnical infrastructures, encompassing climate projections, centrifuge modelling, field monitoring, and numerical methodologies.

Keywords

Vegetated slope / Plant-soil interactions / Rainfall / Temperature / Climate change

CRediT authorship contribution statement

Qi Zhang: Writing - review & editing, Writing - original draft, Investigation, Conceptualization. Haiyi Zhong: Writing - review & editing, Methodology, Formal analysis. Haowen Guo: Writing - review & editing, Project administration, Conceptualization. Junjun Ni: Writing - review & editing, Investigation, Conceptualization.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

References

[1] Allen, R. G., Pereira, L. S., Raes, D., & Smith, M. (1998). Crop evapotranspiration-Guidelines for computing crop water requirements-FAO Irrigation and drainage paper 56. FAOD05109.

[2] Alonso, E. E., Gens, A., & Josa, A. (1990). A constitutive model for partially saturated soils. Géotechnique, 40(3), 405-430. https://doi.org/10.1680/geot.1990.40.3.405

[3] An, N., Hemmati, S., & Cui, Y. (2017). Numerical analysis of soil volumetric water content and temperature variations in an embankment due to soil-atmosphere interaction. Computers and Geotechnics, 83, 40-51. https://doi.org/10.1016/j.compgeo.2016.10.010

[4] An, N., Hemmati, S., Cui, Y. J., Maisonnave, C., Charles, I., & Tang, C. S. (2018). Numerical analysis of hydro-thermal behaviour of Rouen embankment under climate effect. Computers and Geotechnics, 99, 137-148. https://doi.org/10.1016/j.compgeo.2018.03.008

[5] Anselmucci, F., Andó E., Viggiani, G., Lenoir, N., Peyroux, R., Arson, C., & Sibille, L. (2021). Use of X-ray tomography to investigate soil deformation around growing roots. Géotechnique Letters, 11(1), 96-102. https://doi.org/10.1680/jgele.20.00114

[6] Askarinejad, A. (2013). Failure mechanisms in unsaturated silty sand slopes triggered by rainfall. PhD thesis, ETH Zurich.

[7] Askarinejad, A., & Springman, S. M. (2015). Centrifuge modelling of the effects of vegetation on the response of a silty sand slope subjected to rainfall. Computer Methods and Recent Advances in Geomechanics: Proceedings of the 14th International Conference of International Association for Computer Methods and Recent Advances in Geomechanics, 2014 (IACMAG 2014). Taylor & Francis Books Ltd1339-1344.

[8] Basu, D., Misra, A., & Puppala, A. J. (2015). Sustainability and geotechnical engineering: perspectives and review. Canadian Geotechnical Journal, 52(1), 96-113. https://doi.org/10.1139/cgj-2013-0120

[9] Becker, A., & Grünewald, U. (2003). Flood risk in central Europe. Science, 300(5622), 1099. https://doi.org/10.1126/science.1083624

[10] Been, K., & Jefferies, M. G. (1985). A state parameter for sands. Géotechnique, 35(2), 99-112. https://doi.org/10.1680/geot.1985.35.2.99

[11] Boldrin, D., Leung, A. K., & Bengough, A. G. (2021). Hydro-mechanical reinforcement of contrasting woody species: a full-scale investigation of a field slope. Géotechnique, 71(11), 970-984. https://doi.org/10.1680/jgeot.19.SiP.018

[12] Cascini, L., Cuomo, S., Pastor, M., & Sorbino, G. (2010). Modeling of rainfall-induced shallow landslides of the flow-type. Journal of Geotechnical and Geoenvironmental Engineering, 136(1), 85-98. https://doi.org/10.1061/(ASCE)GT.1943-5606.000018

[13] Chen, H., Lee, C. F., & Law, K. T. (2004). Causative mechanisms of rainfall-induced fill slope failures. Journal of Geotechnical and Geoenvironmental Engineering, 130(6), 593-602. https://doi.org/10.1061/(ASCE)1090-0241(2004)130:6(593)

[14] Coelho, M. B., Mateos, L., & Villalobos, F. J. (2000). Influence of a compacted loam subsoil layer on growth and yield of irrigated cotton in Southern Spain. Soil and Tillage Research, 57(3), 129-142. https://doi.org/10.1016/S0167-1987(00)00153-7

[15] Coumou, D., & Rahmstorf, S. (2012). A decade of weather extremes. Nature Climate Change, 2(7), 491-496. https://doi.org/10.1038/nclimate1452

[16] Dai, F. C., Lee, C. F., & Wang, S. J. (2003). Characterization of rainfall-induced landslides. International Journal of Remote Sensing, 24(23), 4817-4834. https://doi.org/10.1080/014311601131000082424

[17] Delage, P., Sultan, N., & Cui, Y. J. (2000). On the thermal consolidation of Boom clay. Canadian Geotechnical Journal, 37(2), 343-354. https://doi.org/10.1139/t99-105

[18] DiBiagio, A., Capobianco, V., Oen, A., & Tallaksen, L. M. (2024). State-of-the-art: parametrization of hydrological and mechanical reinforcement effects of vegetation in slope stability models for shallow landslides. Landslides, 1-30. https://doi.org/10.1007/s10346-024-02300-1

[19] Doussan, C., Pierret, A., Garrigues, E., & Pagès, L. (2006). Water uptake by plant roots: II-modelling of water transfer in the soil root-system with explicit account of flow within the root system-comparison with experiments. Plant and Soil, 283(1), 99-117. https://doi.org/10.1007/s11104-004-7904-z

[20] Eab, K. H., Takahashi, A., & Likitlersuang, S. (2014). Centrifuge modelling of root-reinforced soil slope subjected to rainfall infiltration. Géotechnique Letters, 4(3), 211-216. https://doi.org/10.1680/geolett.14.00029

[21] Environment Bureau (2015). Hong Kong climate change report. Hong Kong, China.

[22] Feddes, R. A., Kowalik, P., Kolinska-Malinka, K., & Zaradny, H. (1976). Simulation of field water uptake by plants using a soil water dependent root extraction function. Journal of Hydrology, 31(1-2), 13-26. https://doi.org/10.1016/0022-1694(76)90017-2

[23] Fischer, E. M., & Knutti, R. (2015). Anthropogenic contribution to global occurrence of heavy-precipitation and high-temperature extremes. Nature Climate Change, 5(6), 560-564. https://doi.org/10.1038/nclimate2617

[24] Fisher, R. A. (1926). On the capillary forces in an ideal soil; correction of formulae given by WB Haines. The Journal of Agricultural Science, 16(3), 492-505. https://doi.org/10.1017/S0021859600007838

[25] Fourie, A. B. (1996). Predicting rainfall-induced slope instability. Proceedings of the Institution of Civil Engineers-Geotechnical Engineering, 119(4), 211-218. https://doi.org/10.1680/igeng.1996.28757

[26] Fredlund, D. G., & Rahardjo, H. (1993). Soil mechanics for unsaturated soils.

[27] John Wiley & Sons.Gallipoli, D., Gens, A., Sharma, R., & Vaunat, J. (2003a). An elasto-plastic model for unsaturated soil incorporating the effects of suction and degree of saturation on mechanical behaviour. Géotechnique, 53(1), 123-135.

[28] Gallipoli, D., Wheeler, S. J., & Karstunen, M. (2003b). Modelling the variation of degree of saturation in a deformable unsaturated soil. Géotechnique, 53(1), 105-112.

[29] Gens, A. (2010). Soil-environment interactions in geotechnical engineering. Géotechnique, 60(1), 3-74. https://doi.org/10.1680/geot.9.P.109

[30] Gerscovich, D. M. S., Vargas, E. A., Jr., & De Campos, T. M. P. (2006). On the evaluation of unsaturated flow in a natural slope in Rio de Janeiro, Brazil. Engineering Geology, 88(1-2), 23-40. https://doi.org/10.1016/j.enggeo.2006.07.008

[31] Gray, D. H., & Leiser, A. T. (1982). Biotechnical slope protection and erosion control. Van Nostrand Reinhold Company Inc.

[32] Griffiths, D. V., & Lane, P. A. (1999). Slope stability analysis by finite elements. Geotechnique, 49, 387-403. https://doi.org/10.1680/geot.1999.49.3.387

[33] Griffiths, D. V., & Marquez, R. M. (2007). Three-dimensional slope stability analysis by elasto-plastic finite elements. Geotechnique, 57(6), 537-546. https://doi.org/10.1680/geot.2007.57.6.537

[34] Guglielmi, S., Pirone, M., Dias, A. S., Cotecchia, F., & Urciuoli, G. (2023). Thermohydraulic numerical modeling of slope-vegetation-atmosphere interaction: Case study of the pyroclastic slope cover at Monte Faito, Italy. Journal of Geotechnical and Geoenvironmental Engineering, 149(11), Article 05023005. https://doi.org/10.1061/JGGEFK.GTENG-1124

[35] Guo, H., Ng, C. W. W., & Zhang, Q. (2024). Three-dimensional numerical analysis of plant-soil hydraulic interactions on pore water pressure of vegetated slope under different rainfall patterns. Journal of Rock Mechanics and Geotechnical Engineering, 16(9), 3696-3706. https://doi.org/10.1016/j.jrmge.2023.09.032

[36] Guo, H., Ng, C. W. W., Ni, J., Zhang, Q., & Wang, Y. (2023). Three-year field study on grass growth and soil hydrological properties in biochar-amended soil. Journal of Rock Mechanics and Geotechnical Engineering, 16(7), 2764-2774. https://doi.org/10.1016/j.jrmge.2023.08.025

[37] Huber, D.G., & Gulledge, J. (2011). Extreme weather and climate change: Understanding the link, managing the risk. Arlington: Pew Center on Global Climate Change.

[38] Hulme, M., Barrow, E. M., Arnell, N. W., Harrison, P. A., Johns, T. C., & Downing, T. E. (1999). Relative impacts of human-induced climate change and natural climate variability. Nature, 397(6721), 688-691. https://doi.org/10.1038/17789

[39] Idso, S. B., Aase, J. K., & Jackson, R. D. (1975). Net radiation—soil heat flux relations as influenced by soil water content variations. Boundary-layer Meteorology, 9(1), 113-122.

[40] Indraratna, B., Fatahi, B., & Khabbaz, H. (2006). Numerical analysis of matric suction effects of tree roots. Proceedings of the Institution of Civil Engineers-Geotechnical Engineering, 159(2), 77-90. https://doi.org/10.1680/geng.2006.159.2.77

[41] IPCC (2013). Eds.Stocker, T. F., D. Qin, G. K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex & P.M. Midgley. Cambridge University Press, Cambridge, United Kingdom and New York.

[42] IPCC (2021). Eds.Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu & B. Zhou. Cambridge University Press, Cambridge, United Kingdom and New York.

[43] Javankhoshdel, S., Cami, B., Chenari, R. J., & Dastpak, P. (2021). Probabilistic analysis of slopes with linearly increasing undrained shear strength using RLEM approach. Transportation Infrastructure Geotechnology, 8, 114-141. https://doi.org/10.1007/s40515-020-00118-7

[44] Kamchoom, V., Leung, A. K., & Ng, C. W. W. (2014). Effects of root geometry and transpiration on pull-out resistance. Géotechnique Letters, 4(4), 330-336. https://doi.org/10.1680/geolett.14.00086

[45] Karoly, D. J. (2009). The recent bushfires and extreme heat wave in southeast Australia. Bulletin of the Australian Meteorological and Oceanographic Society, 22(1), 10-13.

[46] Krahn, J. (2003). The 2001 RM Hardy Lecture: The limits of limit equilibrium analyses. Canadian Geotechnical Journal, 40(3), 643-660. https://doi.org/10.1139/t03-024

[47] Lann, T., Bao, H., Lan, H., Zheng, H., Yan, C., & Peng, J. (2024). Hydro-mechanical effects of vegetation on slope stability: A review. The Science of the Total Environment, 926, 171691. https://doi.org/10.1016/j.scitotenv.2024.171691

[48] Leung, A. K., Kamchoom, V., & Ng, C. W. W. (2017). Influences of root-induced soil suction and root geometry on slope stability: A centrifuge study. Canadian Geotechnical Journal, 54(3), 291-303. https://doi.org/10.1139/cgj-2015-0263

[49] Leung, F. T., Yan, W. M., Hau, B. C., & Tham, L. G. (2015). Root systems of native shrubs and trees in Hong Kong and their effects on enhancing slope stability. Catena, 125, 102-110. https://doi.org/10.1016/j.catena.2014.10.018

[50] Li, X. S., & Dafalias, Y. F. (2000). Dilatancy for cohesionless soils. Géotechnique, 50(4), 449-460. https://doi.org/10.1680/geot.2000.50.4.449

[51] Liu, S. Y., Shao, L. T., & Li, H. J. (2015). Slope stability analysis using the limit equilibrium method and two finite element methods. Computers and Geotechnics, 63, 291-298. https://doi.org/10.1016/j.compgeo.2014.10.008

[52] López, B., Sabaté S., & Gracia, C. A. (2001). Vertical distribution of fine root density, length density, area index and mean diameter in a Quercus ilex forest. Tree Physiology, 21(8), 555-560. https://doi.org/10.1093/treephys/21.8.555

[53] Lozano-Parra, J., Pulido, M., Lozano-Fondón, C., & Schnabel, S. (2018). How do soil moisture and vegetation covers influence soil temperature in drylands of Mediterranean regions? Water, 10(12), 1747. https://doi.org/10.3390/w10121747

[54] Luterbacher, J., Dietrich, D., Xoplaki, E., Grosjean, M., & Wanner, H. (2004). European seasonal and annual temperature variability, trends, and extremes since 1500. Science, 303(5663), 1499-1503. https://doi.org/10.1126/science.1093877

[55] Meijer, G. J., Muir Wood, D., Knappett, J. A., Bengough, A. G., & Liang, T. (2023). Root reinforcement: continuum framework for constitutive modelling. Géotechnique, 73(7), 600-613. https://doi.org/10.1680/jgeot.21.00132

[56] Monteith, J. L. (1965). Evaporation and environment. Symposia of the Society for Experimental Biology, Vol. 19, Cambridge University Press (CUP) Cambridge,205-234.

[57] Muthert, L. W. F., Izzo, L. G., Van Zanten, M., & Aronne, G. (2020). Root tropisms: Investigations on earth and in space to unravel plant growth direction. Frontiers in Plant Science, 10, 486545. https://doi.org/10.3389/fpls.2019.01807

[58] Ng, C. W. W., Guo, H., Ni, J., Zhang, Q., & Chen, Z. (2022a). Effects of soil-plant-biochar interactions on water retention and slope stability under various rainfall patterns. Landslides, 19(6), 1379-1390.

[59] Ng, C. W. W., Guo, H., Ni, J., Zhang, Q., Chen, R., & Zhang, Y. (2023). Effects of plant- biochar interaction on the performance of a landfill cover system: field monitoring and numerical modelling. Canadian Geotechnical Journal, 60(11), 1663-1680. https://doi.org/10.1139/cgj-2022-0310

[60] Ng, C. W. W., Guo, H., Ni, J., Chen, R., Xue, Q., Zhang, Y., & Zhang, Q. (2024a). Long- term field performance of non-vegetated and vegetated three-layer landfill cover systems using construction waste without geomembrane. Geotechnique, 74(2), 155-173.

[61] Ng, C. W. W., Kamchoom, V., & Leung, A. K. (2016a). Centrifuge modelling of the effects of root geometry on transpiration-induced suction and stability of vegetated slopes. Landslides, 13, 925-938.

[62] Ng, C. W. W., Leung, A. K., & Ni, J. (2019). Plant-soil slope interaction. CRC Press.

[63] Ng, C. W. W., Leung, A. K., Kamchoom, V., & Garg, A. (2014). A novel root system for simulating transpiration-induced soil suction in centrifuge. Geotechnical Testing Journal, 37(5), 733-747. https://doi.org/10.1520/GTJ20130116

[64] Ng, C. W. W., Ni, J. J., Leung, A. K., & Wang, Z. J. (2016b). A new and simple water retention model for root-permeated soils. Géotechnique Letters, 6(1), 106-111.

[65] Ng, C. W. W., Ni, J. J., Leung, A. K., Zhou, C., & Wang, Z. J. (2016c). Effects of planting density on tree growth and induced soil suction. Géotechnique, 66(9), 711-724.

[66] Ng, C. W. W., & Zhan, L. T. (2007). Comparative study of rainfall infiltration into a bare and a grassed unsaturated expansive soil slope. Soils and Foundations, 47(2), 207-217.

[67] Ng, C. W. W., Zhang, Q., Ni, J., & Li, Z. (2021). A new three-dimensional theoretical model for analysing the stability of vegetated slopes with different root architectures and planting patterns. Computers and Geotechnics, 130, 103912. https://doi.org/10.1016/j.compgeo.2020.103912

[68] Ng, C. W. W., Zhang, Q., Zhang, S., Lau, S. Y., Guo, H., & Li, Z. (2024b). A new state- dependent constitutive model for cyclic thermo-mechanical behaviour of unsaturated vegetated soil. Canadian Geotechnical Journal, Accepted.

[69] Ng, C. W. W., Zhang, Q., Zhou, C., & Ni, J. (2022b). Eco-geotechnics for human sustainability. Science China Technological Sciences, 65(12), 2809-2845.

[70] Ni, J., Cheng, Y., Wang, Q., Ng, C. W. W., & Garg, A. (2019b). Effects of vegetation on soil temperature and water content: Field monitoring and numerical modelling. Journal of Hydrology, 571, 494-502.

[71] Ni, J., Leung, A. K., & Ng, C. W. W. (2019a). Modelling effects of root growth and decay on soil water retention and permeability. Canadian Geotechnical Journal, 56(7), 1049-1055.

[72] Ni, J., Leung, A. K., Ng, C. W. W., & Shao, W. (2018). Modelling hydro-mechanical reinforcements of plants to slope stability. Computers and Geotechnics, 95, 99-109. https://doi.org/10.1016/j.compgeo.2017.09.001

[73] Nyambayo, V.P., Potts, D.M., & Addenbrooke, T.I. (2004). The Influence of Permeability on The Stability of Embankments Experiencing Seasonal Cyclic Pore Water Pressure Changes. In Proceedings, Skempton Conference, Advances in Geotechnical Engineering, London, UK, 2, 899-910.

[74] Pedone, G., Tsiampousi, A., Cotecchia, F., & Zdravkovic, L. (2022). Coupled hydro-mechanical modelling of soil-vegetation-atmosphere interaction in natural clay slopes. Canadian Geotechnical Journal, 59(2), 272-290. https://doi.org/10.1139/cgj-2020-0479

[75] Penman, H. L. (1948). Natural evaporation from open water, bare soil and grass. Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences, 193( 1032), 120-145. https://doi.org/10.1098/rspa.1948.0037

[76] Pollen, N., & Simon, A. (2005). Estimating the mechanical effects of riparian vegetation on stream bank stability using a fiber bundle model. Water Resources Research, 41, 7. https://doi.org/10.1029/2004WR003801

[77] Potts, D.M., & Zdravkovic, L. (1999). Finite Element Analysis in Geotechnical Engineering: Theory. Thomas Telford, London.

[78] Potts, D.M., & Zdravkovic, L. (2001). Finite Element Analysis in Geotechnical Engineering: Application. Thomas Telford, London.

[79] Rahardjo, H., Satyanaga, A., Leong, E. C., Santoso, V. A., & Ng, Y. S. (2014). Performance of an instrumented slope covered with shrubs and deep-rooted grass. Soils and Foundations, 54(3), 417-425. https://doi.org/10.1016/j.sandf.2014.04.010

[80] Roose, T., & Fowler, A. C. (2004). A model for water uptake by plant roots. Journal of Theoretical Biology, 228(2), 155-171. https://doi.org/10.1016/j.jtbi.2003.12.012

[81] Rouainia, M., Davies, O., O’Brien, T., & Glendinning, S. (2009). Numerical modelling of climate effects on slope stability. Proceedings of the Institution of Civil Engineers-Engineering Sustainability, 162(2), 81-89. https://doi.org/10.1680/ensu.2009.162.2.81

[82] Sauer, T. J., & Horton, R. (2005). Soil heat flux. Micrometeorology in Agricultural Systems, 47, 131-154. https://doi.org/10.2134/agronmonogr47.c7

[83] Schär, C., Vidale, P. L., Lüthi, D., Frei, C., Häberli, C., Liniger, M. A., & Appenzeller, C. (2004). The role of increasing temperature variability in European summer heatwaves. Nature, 427(6972), 332-336. https://doi.org/10.1038/nature02300

[84] Smethurst, J. A., Briggs, K. M., Powrie, W., Ridley, A., & Butcher, D. J. E. (2015). Mechanical and hydrological impacts of tree removal on a clay fill railway embankment. Géotechnique, 65(11), 869-882. https://doi.org/10.1680/jgeot.14.P.010

[85] Smethurst, J. A., Clarke, D., & Powrie, W. (2006). Seasonal changes in pore water pressure in a grass-covered cut slope in London Clay. Géotechnique, 56(8), 523-537. https://doi.org/10.1680/ssc.41080.0029

[86] Smethurst, J. A., Clarke, D., & Powrie, W. (2012). Factors controlling the seasonal variation in soil water content and pore water pressures within a lightly vegetated clay slope. Géotechnique, 62(5), 429-446. https://doi.org/10.1680/geot.10.P.097

[87] Smith, P.G.C. (2003). Numerical analysis of infiltration into partially saturated soil slopes. PhD thesis, Imperial College London.

[88] Sonnenberg, R., Bransby, M. F., Bengough, A. G., Hallett, P. D., & Davies, M. C. R. (2012). Centrifuge modelling of soil slopes containing model plant roots. Canadian Geotechnical Journal, 49(1), 1-17. https://doi.org/10.1139/t11-081

[89] Steudle, E. (2000). Water uptake by plant roots: an integration of views. Plant and Soil, 226(1), 45-56. https://doi.org/10.1023/A:1026439226716

[90] Stott, P. (2016). How climate change affects extreme weather events. Science, 352(6293), 1517-1518. https://doi.org/10.1126/science.aaf727

[91] Świtała, B. M., Askarinejad, A., Wu, W., & Springman, S. M. (2018). Experimental validation of a coupled hydro-mechanical model for vegetated soil. Géotechnique, 68(5), 375-385. https://doi.org/10.1680/jgeot.16.P.233

[92] Świtała, B. M., & Wu, W. (2018). Numerical modelling of rainfall-induced instability of vegetated slopes. Géotechnique, 68(6), 481-491. https://doi.org/10.1680/jgeot.16.P.176

[93] Tang, A. M., Hughes, P. N., Dijkstra, T. A., Askarinejad, A., Brenčič M., Cui, Y. J., & Van Beek, V. (2018). Atmosphere-vegetation-soil interactions in a climate change context; impact of changing conditions on engineered transport infrastructure slopes in Europe. Quarterly Journal of Engineering Geology and Hydrogeology, 51(2), 156-168. https://doi.org/10.1144/qjegh2017-103

[94] Towhata, I., Kuntiwattanaku, P., Seko, I., & Ohishi, K. (1993). Volume change of clays induced by heating as observed in consolidation tests. Soils and Foundations, 33(4), 170-183. https://doi.org/10.3208/sandf1972.33.4_170

[95] Tsiampousi, A., Zdravković L., & Potts, D. M. (2013). A three-dimensional hysteretic soil- water retention curve. Géotechnique, 63(2), 155-164. https://doi.org/10.1680/geot.11.P.074

[96] Vardon, P. J. (2015). Climatic influence on geotechnical infrastructure: a review. Environmental Geotechnics, 2(3), 166-174. https://doi.org/10.1680/envgeo.13.00055

[97] Volkmar, K. M. (1993). A comparison of minirhizotron techniques for estimating root length density in soils of different bulk densities. Plant and Soil, 157, 239-245. https://doi.org/10.1007/BF00011052

[98] Waldron, L. J. (1977). The shear resistance of root‐permeated homogeneous and stratified soil. Soil Science Society of America Journal, 41(5), 843-849. https://doi.org/10.2136/sssaj1977.03615995004100050005x

[99] Webster, P. J., Toma, V. E., & Kim, H. M. (2011). Were the 2010 Pakistan floods predictable? Geophysical Research Letters, 38(4), L04806. https://doi.org/10.1029/2010GL046346

[100] Wheeler, S. J., Sharma, R. S., & Buisson, M. S. R. (2003). Coupling of hydraulic hysteresis and stress-strain behaviour in unsaturated soils. Géotechnique, 53(1), 41-54. https://doi.org/10.1680/geot.2003.53.1.41

[101] Woodman, N. D., Smethurst, J. A., Roose, T., Powrie, W., Meijer, G. J., Knappett, J. A., & Dias, T. (2020). Mathematical and computational modelling of vegetated soil incorporating hydraulically-driven finite strain deformation. Computers and Geotechnics, 127, 103754. https://doi.org/10.1016/j.compgeo.2020.103754

[102] Wu, T. H., Kokesh, C. M., Trenner, B. R., & Fox, P. J. (2014). Use of live poles for stabilization of a shallow slope failure. Journal of Geotechnical and Geoenvironmental Engineering, 140(10), Article 05014001. https://doi.org/10.1061/(ASCE)GT.1943-5606.000116

[103] Wu, T. H., McKinnell, & Swanston, D. N. (1979). Strength of tree roots and landslides on Prince of Wales Island, Alaska. Canadian Geotechnical Journal, 16(1), 19-33. https://doi.org/10.1139/t79-003

[104] Yin, J. H. (2009). Influence of relative compaction on the hydraulic conductivity of completely decomposed granite in Hong Kong. Canadian Geotechnical Journal, 46(10), 1229-1235. https://doi.org/10.1139/T09-053

[105] Zhang, J. Z., Huang, H. W., Zhang, D. M., Phoon, K. K., Liu, Z. Q., & Tang, C. (2021). Quantitative evaluation of geological uncertainty and its influence on tunnel structural performance using improved coupled Markov chain. Acta Geotechnica, 16, 3709-3724. https://doi.org/10.1007/s11440-021-01287-6

[106] Zhang, J. Z., Jiang, Q. H., Zhang, D. M., Huang, H. W., & Liu, Z. Q. (2024). Influence of geological uncertainty and soil spatial variability on tunnel deformation and their importance evaluation. Tunnelling Underground Space Technol, 152, 105930. https://doi.org/10.1016/j.tust.2024.105930

[107] Zhang, L. L., Zhang, J., Zhang, L. M., & Tang, W. H. (2011). Stability analysis of rainfall- induced slope failure: A review. Proceedings of the Institution of Civil Engineers- Geotechnical Engineering, 164(5), 299-316. https://doi.org/10.1680/geng.2011.164.5.299

[108] Zhong, H. Y., Wang, Y. K., Zhang, S., Zhang, Q., & Ng, C. W. W. (2023). Effects of extreme drought-rainfall on slope failure mechanisms: centrifuge modelling. Canadian Geotechnical Journal, 61(4), 820-826. https://doi.org/10.1139/cgj-2023-0133