Geobear was contracted by Kier to provide void filling and stabilisation services to a road bridge over a mainline UK railway.

Visual structural surveys indicated a sinking surface on the abutments at both sides of the bridge. This was very problematic as the bridge runs over a busy line on the UK rail network, therefore any work could cause significant disruption to both road and rail.

Following visual inspections further detailed surveys were conducted including dynamic probe testing, boreholes and log tests. Results showed a mixture of made ground with sand. Boulder clay was present every metre followed by layer of sand.

A solution was needed to deliver onsite repairs with minimal construction works in as shorter timescale as possible. Geobear were consulted to investigate and propose an injection solution to stabilise and strengthen the fill to ensure no further movement occurred.

The problem was being caused by voiding within the fill beneath the abutment, where sand was being washed out by water and physically being dug away by burrowing badgers. This weakened the integrity of the abutment and resulted in surface cracking.

Alternative solutions

The alternative for the client would include compaction grouting or end of casing to fill the voids, however the lack of control and potential for damage to rail drainage made this a slightly more challenging solution. With those methods the site set-up would have been much greater and the impacted road closure would have lasted many more weeks. There would also have been an impact on the operating railway with a potential reduction in line speed.

Why Geobear

Geobear were selected to provide the works due to the speed and non-disruptive nature of the solution. The railway line could remain fully operational whilst the work was being completed and road closure time scale would be minimised.

Geobear solution

The Geobear solution would see our geo-polymer material injected at multiple points and depths throughout each abutment.

Drawing a. illustrates the drilling points for the Geobear injections. Laterally there are ten rows of injection points across the full length of the abutment. The first four injection points to the left hand side are to a depth of 8 metres and then receding accordingly to the depth of firm ground.

Drawing b. shows the injection points across the span of the abutment. 76 holes were drilled to the required depths across the area, from 8m to 400mm

The main image shows the prepared surface pre-injection where you can see that each of the drilled holes has several tubes inserted. Due to the large cubic volume of soils that needed to be stabilised a pattern of works using multiple tubes was designed. This ensured that the material was delivered equally to all areas. The tubes varied in length as the work receded back along the abutment. The tubes nearest are 8 metres long with six other adjoining tubes cut at 1m interval lengths. The process for the injections meant that the 8m tubes were injected first across the area and then 7m and so on. This pattern was followed back to the far edge of the abutment until all injections were satisfactorily completed and the abutment fully stabilised.