When landslides occur remedial work usually needs to be undertaken as quickly as possible to restore access to affected areas. However, there is often the added complication that access to the site can be severely restricted. In such cases, specialist knowledge and equipment can be vital and it is the ability of CAN to be able to deliver this that has seen the business undertake many slope stabilisation projects where access has been difficult and complicated.

Wembley Depot

Chiltern Railway has a depot at Wembley that when it was first constructed was cut into a face made up of London Clay. It was originally retained by short, augered soil nails and a weldmesh and ballast-filled facing system. However, that system had started failing evidence of this was seen by the bulging of the face.

Once Carillion, the contractor employed by Chiltern Railway to remedy the faults, had removed the old facing exposing the weldmesh behind, it became evident that the nails were failing and the weldmesh had ruptured with voids appearing.

At this point, CAN was subcontracted in to install more, longer soil nails across the face, with additional nails in the areas that were failing. The situation was somewhat complicated by the fact that one end of the site was only accessible during the night due to trains running close by throughout the day. To expedite the works as quickly as possible separate day and night shifts were mobilised.

Following the installation of the soil nails, the face was then sprayed with concrete to provide a new hard facing.

On this project, access was the main problem - with all materials and equipment having to be brought to site via road rail vehicles from the road rail access point (RRAP) which was approximately 800m down the line. Loading at the RRAP was also an issue as it was the entrance to a busy storage facility. This meant that loading and unloading had to take place at night. As the works progressed the designers assessed the face on a regular basis and determined that additional nails were required. Yet despite this and the complications with access, the job was completed on time.

Cockermouth Castle

Cockermouth Castle is a Grade 1 listed building. It was built in the 10th century as Norman stronghold and is located on the River Derwent in Cumbria. It was in danger of ruin and required immediate attention following heavy rain and flooding which occurred in December 2015 triggering erosion of the slope on which it was built. There was a serious risk of the castle collapsing into the river below.

CAN undertook the work needed to protect the Castle from collapse as a design and build contract, where it acted as the principal contractor. This approached allowed CAN to select the best techniques for the project and offer the best value result. At the same time, CAN's design needed to ensure that techniques used provided a sympathetic and safe solution to strengthen and protect the bank.

The work undertaken included the installation of inclined drains, 200 soil nails and over 840m² of Geobrugg's new small diameter TECCO G45/2 mesh. All of this was done while dealing with all types of weather, rising river levels and a precariously balanced castle buttress.

This fine blanket of high-tensile steel wire facing mesh is barely visible, but the reduced mesh width will efficiently stabilise the fine-grained soil while allowing the slope to naturally colonise with vegetation and most importantly, will maintain the structural integrity of the castle's foundations.

Todmorden

Todmorden in Calderdale, West Yorkshire, is an area that has a long and sustained history of problems associated with flooding events, lying as it does at the bottom of a steep-sided valley with the hills on either side being watersheds.

A combination of recent flooding and long-standing under scouring of the old remedial works caused a bank to slip. With the slip located opposite residential properties, something needed to be done to protect not only the stream but also the properties.

The topography of site presented many problems for CAN's engineers, with only limited access along the opposite bank at the rear of the residential 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 Crane Hire supplied the crane and undertook seven 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. 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.

As a result of that change, it was realised that the slope was waterlogged, this meant 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, from Platipus 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 work, in addition to the four Plati-Drains, included the installation of 81 soil nails using A-frame drill sled; 354m² MacMat from Maccaferri; 115m² Reno Mattress; 40 linear metres crest drainage; and 260m² of hydraseeding.