Todmorden is an area that’s sustained a long history of problems associated with flooding events. Lying at the bottom of a steep sided valley with the hills on either side being watersheds.
A combination of the recent flooding and long standing under scouring of the old remedial works caused the bank to slip. With the slip located opposite residential properties, something needed to be done to protect the stream and the properties.
The topography of site presented many problems, with only limited access along the opposite bank at the rear of the gardens, coupled with no access to the crest of the slope above and only personnel access across the stream to the slip meant that all of the plant and equipment had to be loaded out across the stream using large cranes. Ainscough supplied the crane and undertook 7 lifts to get all the equipment over the stream.
The saturated and porous nature of the ground meant that at the first attempt at drilling, grout flush was seen to be finding its way through the slope and emerging elsewhere. This obviously presented a huge risk of polluting the stream below. So with this in mind, a land drain was installed along the crest of the slope to act as initial diversion of the water coming down from the hillside above, with an outfall entering the stream away from the site area.
Following on from the above and now realising that the slope was water logged, the slope itself would need drains installing. Using traditional drains using open hole drilling and then inserting the drains was not going to be possible due to the holes collapsing. To get around this plati-drains were installed.
To protect the stream, a daily regime of over-pumping was put into place to clear the stream. At the start of the shift, a fish rescue took place and the pumps were switched on. At the end of the shift, so long as there was no evidence of any grout emerging in the stream, bed the pumps were switched off overnight. This allowed the stream to refill slowly to avoid stirring up the sediment.
Once the main works were complete the final task was to hydraseed the slope. With the difficult access it was decided that CAN would undertake this working on ropes, but with mixing and direction from Aquaseeders stationed on the opposite bank.
The complete works comprised the installation of:
- 81 soil nails using A-Frame drill Sled
- 354m2 macmat
- 115m2 reno mattress
- 4 plati-drains
- 40lin m crest drainage
- 260m2 hydraseeding
Duration: 14 weeks
Client: VBA JV (VolkerStevin, Boskalis Westminster, Atkins)
Location: Calderdale, West Yorkshire