Civil Engineering April 2021 | Vol 29 No 3

Civil Engineering April 2021 25 in laboratory testing have facilitated proper characterisation of unsaturated soils, while data from field studies dem- onstrate that measurement of negative pore water pressure can now be added to routine monitoring systems. Considering the performance of the sensors discussed and their associated costs, it appears that the hinderances to the application of unsaturated soil mechanics in practice are rapidly falling away.  REFERENCES Fredlund, D. G. 2018. Role of the soil–water characteristic curve in unsaturated soil mechanics. The 7th International Conference on Unsaturated Soils, Hong Kong, (eds C. W. W. Ng, A. K. Leung, A. Chiu & C. Zhou), pp. 3–26. Gaspar, T.A.V., Jacobsz, S.W. 2019. Towards the application of unsaturated soil mechanics in practice. Civil Engineering, April 2019. SAICE, pp. 69–73. Jacobsz, S. W. 2018. Low cost tensiometers for geotechnical applications. The 9th International Conference on Physical Modelling in Geotechnics, CRC Press, pp. 305–310. Jacobsz, S. W. 2019. TUKS tensiometer measures to –1.7 Mega Pascal, Civil Engineering 27(1), 24-26. Metergroup (n.d.). Teros 21. User manual. Mendes, J., Gallipoli, D., Toll, D. G. & Augarde, C. E. 2008. A system for field measurement of suction using high capacity tensiometers. Unsaturated Soils: Advances in Geo-Engineering. Proceedings of the 1st European Conference on Unsaturated Soils, CRC Press/Balkema, Durham, UK, pp. 219–225. Mpye, G. D. (2020). The effect of increased axle loading on saturated and unsaturated railway foundation materials. PhD Thesis, University of Pretoria, Pretoria, South Africa. Toll, D. G., Lourenço, S. D. N., Mendes, J., Gallipoli, D., Evans, F. D., Augarde, C. E., Cui, Y. J., Tang, A. M., Rojas, J. C., Pagano, L., Mancuso, C., Zingariello, C. & Tarantino, A. 2011. Soil suction monitoring for landslides and slopes. Quarterly Journal of Engineering Geology and Hydrogeology 44(1), pp. 23–33. Toll, D. G., Mendes, J., Gallipoli, D., Glendinning, S. & Hughes, P. N. 2012. Investigating the impacts of climate change on slopes: field measurements. Geological Society, London, Engineering Geology Special Publications 26(1), pp. 151–161. Tripathy, S., Al-Khyat, S., Cleall, P. J., Baille, W. & Schanz, T. 2016. Soil Suction Measurement of Unsaturated Soils with a Sensor Using Fixed-Matrix Porous Ceramic Discs, Indian Geotechnical Journal 46(3), pp. 252–260. Vandoorne, R. (2021). Characterisation of railway formation materials for the application of unsaturated soil mechanics. PhD Thesis, University of Pretoria, Pretoria, South Africa. Figure 5 Suction measurements beneath a railway formation using both tensiometers and fixed-matrix porous sensors Pore water pressure (kPa) 0 30 Sep 2020 23 Sep 2020 16 Sep 2020 9 Sep 2020 2 Sep 2020 26 Aug 2020 19 Aug 2020 12 Aug 2020 5 Aug 2020 29 Jul 2020 22 Jul 2020 15 Jul 2020 8 Jul 2020 1 Jul 2020 –5 –10 –15 –20 –25 –30 –35 Daily rainfall (mm) 7 6 5 4 3 2 1 0 Fixed-matrix porous sensor Tensiometer Daily rainfall