Factors controlling the seasonal variation in soil water content and pore water pressures within a lightly vegetated clay slope

Abstract

Seasonal cycles of soil water content cause shrinking and swelling in clay soils, which can in turn contribute to strain-softening and progressive slope failure. This paper presents and analyses six years of field measurements of soil water content and pore water pressures in the upper layers of a lightly vegetated London Clay slope near Newbury, UK, and shows how they can be related quantitatively to the climate using a water balance model. The field observations are set in the context of a 40-year run of rainfall data for the site. Moderately extreme rainfall and drought events were experienced over the period [2003][2004][2005][2006][2007][2008], allowing almost the full variation in likely pore water pressures to be characterised. Pore water pressures were found to return to near hydrostatic during most winters. Variations in summer rainfall, particularly during June-August, are shown to have a large influence on the magnitude of the cycles of pore water pressure and effective stress. The 40-year rainfall dataset is used to calculate approximate return periods for the observed soil conditions, and provides a benchmark for calculating the impacts of expected climate change on similar sites.

Forecasting infrastructure resilience to climate change

“…j Improvements in modelling capability, including modelling platforms capable of managing large volumes of data generated by sophisticated, high-resolution physical-based models (e.g. Booth et al, 2013;Clarke et al, 2006;Davies et al, 2008;Rouainia et al, 2009;Smethurst et al, 2006Smethurst et al, , 2012. j The development of detailed deterministic, physical-based models capable of dealing with dynamic equilibria and threshold exceedance.…”

Current and future role of instrumentation and monitoring in the performance of transport infrastructure slopes

“…Smethurst et al 2012;Springman et al 2012). This information obtained from instrumentation may be vital in understanding deterioration and modes of failure (of which there may be many); this information can feed back into improved conceptual and numerical models that seek to identify assets that may be at risk.…”

“…Several commercially available devices; fairly widely used to measure soil moisture content in the near-surface zone of infrastructure slopes (e.g. Smethurst et al 2012;Glendinning et al 2014). Most likely to be used for applications (1), (3), (4) and (5) in Table 2 (continued) (Glendinning et al 2014;Gunn et al 2015).…”

Correlating hydrologic reinforcement of vegetated soil with plant traits during establishment of woody perennials

“…Vegetation is known to provide slope stabilisation via mechanical reinforcement through root anchorage (Mickovski et al 2009;Ghestem et al 2014b;Kamchoom et al 2014;Meijer et al 2016). Change in soil shear strength due to transpiration-induced matric suction (known as hydrologic reinforcement) is also increasingly recognised to be important for slope hydrology and stability (Lim et al 1996;Simon and Collison 2002;PollenBankhead and Simon 2010;Smethurst et al 2012;Leung and Ng 2013;Garg et al 2015;Ng et al 2015;Smethurst et al 2015). Extensive field and laboratory studies have shown that transpiration-induced suction could be maintained in the soil during and after rainfall Ng et al 2014;Rahardjo et al 2014;Leung et al 2015a;Ng et al in press).…”