A Long-Term Record of Water Content and Pore Water Pressure in a Vegetated Clay Highway Cut Slope J. A. Smethurst, A. Sellaiya, A. P. Blake, and W. Powrie Abstract The major highway network in the UK was developed from the 1960s, and the earthworks are generally well engineered. However, as many of the earthworks get older, slope failures are becoming more common, with some posing a threat to the safety of transport operations. Field measurements of soil water content and pore water pressure changes within the surface zone of a highway cut slope in London Clay at Newbury, Berkshire, UK, have been carried out continuously since 2003. This paper describes and gives examples of the long-term field measurements from the site at Newbury and details a number of significant findings from the observations from the site. The paper explains how these have been used to calibrate appropriate models of seasonal cycles of pore water pressure and slope deterioration. Keywords Slope stability · Pore water pressure · Vegetation 1 Introduction Transport infrastructure is often significantly affected by slope failures. Failures in embankments have the potential to undermine roads and railways, while slips in cuttings may cause material to obstruct transport routes, posing risks to drivers and possible derailment of trains. J. A. Smethurst (B ) · A. Sellaiya · A. P. Blake · W. Powrie University of Southampton, Southampton, UK e-mail: jas@soton.ac.uk A. Sellaiya e-mail: a.sellaiya@soton.ac.uk A. P. Blake e-mail: a.p.blake@soton.ac.uk W. Powrie e-mail: wp@soton.ac.uk A. Sellaiya Tony Gee and Partners, Esher, UK © The Author(s), under exclusive license to Springer Nature Switzerland AG 2022 E. Tutumluer et al. (eds.), Advances in Transportation Geotechnics IV, Lecture Notes in Civil Engineering 166, https://doi.org/10.1007/978-3-030-77238-3_58 767