Geological Model for Jackfield Location of Jackfield

The Jackfield site is bounded by the River Severn to the north, the Jackfield Tile Museum to the west and the footbridge across the Severn near The Boat Inn to the east; the southern boundary runs approximately NW-SE through Woodhouse Farm. The slopes on this side of the river are used for pasture and have little or no trees except for either side of Salthouse Road and the lower valley sides which are situated towards the westerly and easterly boundaries.

Jackfield lies on the southern bank of river Severn within the Ironbridge gorge. The village is located in an unstable part of the Ironbridge Gorge, where several landslips have been recorded (Scatena & Lugo, 1995). In line with this, in April 1952, a mega landslip occurred in the Ironbridge Gorge at Jackfield leading to the destruction of more than 20 households with other houses descripted on the paper. Outlined below are the locations of selected landslides in the UK.

Figure 1 -- Locations of selected landslides in the UK.

The Geology of the Gorge

The geology of the gorge is very complex with alternating beds of permeable rocks such as limestone and sandstones, and more impermeable layers of grey shale, clays, and thin beds of coal seams as well as ironstones. The frequent layers of clay, often 5 metres thick produce slip zones where one layer can slide upon another with through flow water acting as a lubricant.

The slope in Jackfield has been subjected to rapid degradation by melt waters during the last glacial period and the high groundwater levels associated with post glacial conditions (Bentleya & Siddle, 1990). This makes the riverbanks to be weak and can easily slide.

Figure 3 -- Main features of a landslip.

In addition, river erosion undercut the valley sides and removes support at the slopes along the Salthouse Road. Besides, valley development has initiated a cycle of land sliding activity as slope processes strive to reach equilibrium (deBoer, 1992). As opposed to river and rain, the accelerated degradation of the slopes...

Furthermore, the geological structure in the form of faulting may be providing conduits for groundwater and back scraps for slope movement, for example The Doughty and Tuckies Faults.
The ground movement observed from the geomorphological mapping identified land units of multiple rotational back tilted blocks of various stages of degradation and translational failures with secondary rotational failures.

The presently active translational failure in the Salthouse Road sub-unit is a reactivation of the 1952 slip. Ground movement of this area is currently occurring, evidenced during a recent walkover. The failure in 1952 was triggered by heavy rainfall and subsequent high groundwater levels; this is likely to have been the trigger for the most recent ground movement, although no data is available for actual rainfall in this period.

The failed area of the lower slope contains substantial made ground deposits where the slip plane lies at the interface with the underlying clay and further upslope the slip plane can be observed at ~5m depth within the weathered clay.

The areas of instability coincide with areas that have been mined at shallower depths than Area B. For Red Tile Clay and Sulfur Coal (Meyer, Schuster, & Sabol, 2002). The combined effect of more than one seam being mined may have involved greater bed separation of the overlying strata and subsidence, which has reduced the integrity and strength of the material resulting in the localized instability along the Salthouse Road subunit.

The area of the 1952 slip is located on the outside bend of the river where more turbulent water erodes the toe and removes support of the ground upslope. Borehole instrumentation has availed that the Salthouse Road sub-unit is currently active and areas outside this sub-unit are relatively stable.

In this region,…