A section of railway track, built on a 5m high embankment, known as Alveley Wood in Shropshire on the Severn Valley heritage railway (SVR) is showing signs of distress.
Figure 1. Track deformation due to embankment instability in Alveley Wood
The distress, seen typically as a deformation of the track with 350mm deviation from the design track geometry and 9-15mm per year of track tilt, is believed to be a result of a slope of instability, see Figure 1. Track deformation appears along an approximately 80m section of the railway line on the western side of the River Severn. The railway embankment consists of a loose ash fill resting on weather firm clay. Within the firm clay, there is a very soft clay layer with plastic slip surfaces. This is thought to be an ancient slip surface which is the underlying reason for the identified movement.
Geobear has been developing a novel solution to stabilise slopes in earthworks using geopolymer injections. Due to the non-disruptive nature of this technology, geopolymer injections can provide a cost-effective solution to this type of problem on the Severn Valley heritage railway. Therefore, a trial was carried out in July to carry out the injection treatment on a 10m section on the embankment shoulder to compact the loose ash and strengthen the slip surface (soft clay).
As part of the design works for the trial, Geobear carried out extensive numerical modelling to optimise the amount and location of the injections and provide adequate performance of the railway as shown in Figure 2.
The installation of the treatment was carried out over a period of two days using Geobear’s railway mobile injections unit. The works consist of the
installation 135 injection tubes under the track bed and on the embankment shoulder to inject approximately two tonnes of geopolymer material, see Figure 3
Figure 3. Embankment injection treatment
To understand the level of improvement achieved by the injection treatment, lightweight dynamic probing was carried out before and after the injections. The testing was carried out on the embankment shoulder on the top of the ash fill layer; one test was performed before the treatment and two tests were performed after the treatment, see Figure 4. The testing showed that the injections has improved the shear strength for the shear zone approximately a factor 3.
Figure 4. The effect of the geopolymer injections on the shear zone layer shear strength
In conclusion, the trial has demonstrated geopolymer injection can effectively be used to treat slope instability problems on the infrastructure with minimum disruption compared to other traditional solutions. To discuss any aspect of this trial please contact [email protected].
