CONCRETE CANVAS AS A HARD ARMOUR FACING TO REINFORCED SOIL STRUCTURES
In this blog post, we will showcase a compilation of case studies demonstrating the use of Concrete Canvas as hard armour facing for reinforced soil structures.
In September 2013, Concrete Canvas (CC) was used as an erosion control solution on a section of bridge abutment in Taupiri, New Zealand. The CC was being installed as a capping layer to an existing geogrid system. Shotcrete was initially considered for the project, but would require specialist equipment and labour, as well as extending the installation time.
Bulk rolls of CC5 were delivered to site and cut to lengths of between 1m and 7m to match the varying height of the slope. This ensured that there was no wastage as each length was tailored to match the slope face exactly. Using a rough terrain cherry picker and spreader beam, each length was then lifted to the top of the slope and fixed in place using 300mm steel ground pegs at the crest and toe. This became more difficult on the sections of abutment directly under the bridge, an issue that was solved by reversing the process and fixing the CC to the toe of the slope first. Subsequent layers of CC were then positioned with an overlap of 100mm to the adjacent layer and screwed together with 30mm screws at 200mm intervals using an auto-fed screwdriver. Once the CC had been secured, it was then hydrated using on-site equipment and a water truck. .
Fletcher Construction were very impressed with the ease with which CC was installed. Project time was also considerably reduced; the 200sqm installation was completed by a team of 3 in just over 5 hours, whereas shotcreting the slope was estimated to take 1-2 days
CC5 was cut to length on site to match the varying height of the abutment
“200sqm installation was completed by a team of 3 in just over 5 hours”
In 2015, Concrete Canvas® GCCM* (CCTM) was used in Australia to protect a temporary soil bund and transform it into a permanent structure, by providing UV protection and preventing animals from nesting. The temporary geosynthetic reinforced soil bund wall was constructed using reinforcing geogrids to create a wrap around structure, with the geotextile liner installed to provide the facing and contain the soil temporarily for the short life of the structure. However, the clients requirements changed, with the structure needing to be in place permanently. The clients had hoped that vegetation growth would establish over time, but after 8-years in service this could not be maintained all season and the facing geotextiles were exposed to UV degredation. Birds were also damaging the facing geotextiles by burrowing in the structure. Shotcrete was used as a temporary filler but was never considered viable as a permanent facing due to cracking from settlements and temperature and moisture changes
To provide a long term solution and protection against damage from animals and UV damage to the facing geotextile, Concrete Canvas was installed to encapsulate the entire bund. Bulk Rolls of CC8™ were brought to site and lifted into place using an excavator with spreader beam attachment. The vertical layers of CC8™ were overlapped by 100mm, with the overlapping layers jointed using a screws and suitable sealant. At the toe, the CC was secured within anchor trenches and backfilled with excavated substrate, or where a segmental block wall facing was present, the CC was mechanically fixed into the segmental blocks instead. Polymer earth percussion anchors were installed into the bund to ensure the CC conformed to the bund profile eliminating voids
The client was impressed with the speed and ease in which CC™ could be installed, with 3,200m² installed by a team of 4 in 3 days without specialist training or equipment
In July 2018, Concrete Canvas® GCCM* (CC) was used to provide slope protection at a newly constructed fish hatchery in the West of Scotland. The project involved the design of reinforced concrete slab bases for the header tanks, shed and external tanks. The header tank mounding and slopes were made up with dug material and layered and tracked in with a geogrid in 450mm layers. The consulting engineer specified CC5™ to reinforce the side slopes with anchor trenches dug at the crest and toe of the slopes to prevent undermining and provide a neat edge termination. Various alternatives were originally considered but CC was ultimately chosen due to its speed and ease of installation and its flexibility in terms of site access, as the project was located in a remote location only accessible by ferry. CC5™ was supplied in bulk rolls which, following delivery, were mounted on a spreader beam and lifted by an excavator. The material was cut to the required length on site using a Stihl cut-off saw in order to reduce material wastage. Ladders were then placed along the side slopes to allow safe access for the installation crew during the installation.
The rolls were installed in vertical layers and secured at the crest and toe of the slope into 150mm anchor trenches using 250mm x 12mm steel ground pegs. Subsequent layers of material were overlapped by 100mm and sealed together with Everbuild Clearfix sealant and jointed using screws at 200mm intervals, creating a neat, flush joint between layers. The anchor trenches were subsequently backfilled and compacted with as-dug material. Once installation was completed, the CC was hydrated using a simple hand pump water system. Following the CC installation, the contractor poured a concrete slab around the mound perimeter and the header tanks and pipes were installed on top.
Following the CC installation, the contractor poured a concrete slab around the mound perimeter and the header tanks and pipes were installed on top. The installation team were impressed by the speed and ease of installation of CC on a site with heavily restricted access.
In total 280m² of CC5™ were installed in 3 days with a crew of 4 people without specialist training or plant equipment and will provide long-term slope reinforcement around the header tanks. “We are delighted with the finished article.
By using CC we were able to create a clean and tidy, but critically, small, base for the header tanks to sit on. If we had used conventional concrete, it would have had to be a much larger base which would have required significant tree felling.”