## 3 Geostructures Vulnerabilities  
The performance of geostructures on the transport network is related to the interactions between the atmosphere and subgrade (Figure 3). For the UK rail network, it also directly links back to the construction history of a chosen geostructure. For instance, [PERSON], et al. [2] reported the presence of variable permeability for clay fill due to embankment age and therefore construction techniques. This variation is important to consider as the degree of permeability impacts the pore pressure/atmospheric response of a structure. In addition, variability in the quality of the fill material (again linked to its construction history) is also an important factor for the resilience of compacted soil. This was demonstrated by [PERSON] [43] using numerical modelling, where the inclusion of soft alluvial clay lenses within London Clay embankment fill material and small changes in maximum winter pore water pressures significantly decreased the number of shrink-swell cycles required until slope failure. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Construction/ Maintenance** & **Railway Only** & **Railway and Highway** \\ \cline{2-3}  & **Pre-Regulation—19 th and Early 20 th Century** & **Post-Regulation—Mid 20 th and 21 st Century** \\ \hline Fill Material & Embankment fill sourced from adjacent cuttings with no quality control [1] & Due to the new specifications, material was still sourced from cuttings, but now exceptions were made for material deemed ‘unsuitable’, e.g., import of fill material during the construction of the Preston By-Pass [35] \\ \hline Compaction & End-tipping was conducted with no compaction except at bridge abutments due to occurrence of differential settlement [14] & Earthqu were constructed to an ‘end-product’ criterion by setting a required percentage density or method compaction [13] \\ \hline Slope Angle & Embankments were formed at the angle of repose, due to end-tipping, and trimmed to 1:2 (vertical: horizontal), in some cases up to 1:1.5 and 16 m in height [5] & Based off stability analysis and empirical observation of different geologies, e.g., infinite slope analysis, method of slices, and finite element calculated using Factor of Safety (FoS) for various construction stages \\ \hline Foundations & No consideration was made and topsoil was often left in place [5] & Topsoil stripped and various ground improvement techniques used to provide adequate foundation conditions such as geotextiles, deep soil mixing, shallow stabilisation, vibro stone columns and drainage \\ \hline Vegetation Management & Line-side gangs managed growth of vegetation to minimise the occurrence of line-side fires due to steam locomotion [21] & Mid-late 20 th century, no management of vegetation was made on railway geostructures, however several vegetation standards now exist to manage risk and capitalise on its use for bioengineering [9] \\ \hline Interventions & Ash packed under tracks to combat settlement and in situ burning of clay fills and the addition of ash took place to remediate landslides [9] & Asset management procedures including various monitoring techniques such as piezometers, inclinometers, remote sensing, tiltmeters, and measurement of track geometry \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Comparison between both the pre-regulation and post-regulation construction techniques for embankments used during the founding of the UK railway and highway (motorway) network. Figure 3: Profile of typical transport systems ([PERSON], et al. [44], reproduced under the Creative Commons Attribution license, CC BY-NC-ND 4.0). Despite this, [PERSON], et al. [2] suggests that due to the likelihood of increased future evapotranspiration in certain future scenarios (i.e., where Very High Water Demand (VHWD) trees are situated), infiltration may be reduced and an increase in surface run-off may be predominant.