Jackson recently won a design and build contract to construct new flood defences in Newhaven, East Sussex, for the Environment Agency.
This project covers both banks of Newhaven, including the commercial areas near the port, and has a total scheme value of £17m.
The design includes earth embankments, concrete walls and flood gates to protect 431 homes and 387 businesses in the area. The project also includes a temporary flood gate over an existing railway line, and a demountable flood barrier which can be quickly deployed across the highway during a significant flood event.
Construction will begin in November 2016 and is scheduled to finish in 2019.
67% carbon reduction in concrete is a UK first
Jackson Civil Engineering has achieved a 67% reduction in CO2 by using a new type of ‘cem-free’ concrete on a flood defence project in Woodbridge, Suffolk, for the Environment Agency.
This is the first time this concrete has been used in the UK commercially, and the potential for reducing carbon emissions on future construction projects is extensive.
Concrete is a significant contributor to the carbon footprint of the construction industry. The concrete ordinarily used on this type of flood defence project consists of 50% GGBS and 50% Portland cement, which has a typical CO2 value of 158 Kg per m3. In comparison, cem-free concrete is made up of 95% ground-granulated blast-furnace slag (GGBS) and a 5% alkali activator, and has a CO2 value of 52kg per m3.
Although not suitable for all applications, the cem-free concrete was successfully used as an infill in a 265m section of flood wall. This amounted to 51 cubic metres, about 35% of the total concrete used, which achieved a CO2 saving of 5 ½ tonnes. To put this in perspective, it would take five acres of forest one whole year to redress the balance of this carbon output, using the traditional material.
Pro’s and cons
As well as the potential for significant carbon savings, cem-free concrete has better long-term durability, produces less heat in the reaction, making it more suitable for large pours, and requires fewer expansion joints.
There are, however, some minor drawbacks, which make it unsuitable for some applications. For example, during the trials the material did not respond well to floating, which made it unsuitable for use in the floor slab, although with work on the mix design this should be overcome.
The curing time is also slower, which means that shuttering would have to be left for a day or two longer than usual. However, on the right project, with sufficient programming this issue could be overcome.
Jackson’s Project Manager Ashley Tate said: “Over the course of this project, we’ve learned a great deal about the suitability of cem-free concrete going forward. On the right project, and with the correct planning, this material has the potential to generate significant carbon savings for construction.”
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Jackson is currently upgrading nine weirs along the Thames under a design and build contract for the Environment Agency.
The project involves replacing up to 40 weir gates, and installing new head gear, control kiosks and handrailing to five of the weirs. The team has also designed and installed new fish and eel passes on three weirs.
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The Jackson site team recently got more than they bargained for whilst working on a £1.1m scheme to improve the conveyance capacity of the River Soar, just outside Leicester, to reduce the risk of flooding in the area.
The works involve reprofiling and reinstating the river bank, and also constructing new flood embankments at three locations along the river. At one of these sites, on 10th November 2015, the team unearthed some unexploded White Phosphorous Mortars, left over from the Second World War. Jackson General Foreman Dean Hanley explains what happened:
“It was about 3:30pm, and I received a phone call from the guys excavating on the river bank who reported white smoke coming out of the ground where they’d been working. I was at one of the other sites at the time, so I instructed them to evacuate the area and call the police immediately.
When I got to the site, from quite a distance away I could see the smoke coming out of the ground. My background is in the military and I’ve been trained to identify all different sorts of bombs, so I knew what it was straight away.
The police arrived shortly after, and due to my experience, they asked me to speak to Captain Jonnie Barlow from the Nottingham EOD (Explosive Ordnance Disposal) Regiment, who asked me to describe what was happening. He confirmed my suspicions, that it was likely to be a White Phosphorous Mortar, left over from WW2.
Unfortunately, by this time the light was failing, so it was just too risky for the EOD team to do anything that evening. Instead, with the help of the police, we securely cordoned off the whole area, including a number of footpaths, and secured the site for the evening.
The EOD team then arrived at first light, and were able to detonate the remaining mortar safely. They did this by attaching plastic explosives to the device, and then detonating it when all their operatives were safely out of the 50 metre exclusion zone. They also managed to build a bund around the device in order to contain the explosion.”
This is the third UXO that Dean has come across in his construction career, and it’s thanks to his experience and quick thinking that the situation was controlled safely and calmly.
Once the EOD team had disposed of the final mortar, Captain Barlow gave the team the all clear so they could recommence work. He said: “Going forward, Dean should be present whilst the team are working in the area where the UXO was discovered, as I have full confidence he knows the types of ordnance that may be present, and will act accordingly should a similar situation arise.”
History of the White Phosphorous Mortars
In 1940, when the invasion of Britain seemed imminent, the British Government adopted the use of Grenade, No. 76, or Special Incendiary Phosphorus grenade, which consisted of a glass bottle filled with a phosphorous mixture similar to Fenian fire, plus some latex. These were improvised anti-tank weapons, hastily fielded in 1940 when the British were awaiting a German invasion after losing the bulk of their modern armaments in the Dunkirk evacuation. It came in two versions, one with a red cap intended to be thrown by hand, and a slightly stronger bottle with a green cap, intended to be launched from the Northover projector, a crude 2.5-inch black-powder grenade launcher.
During this time, these mortars, along with other munitions, were stashed in strategic locations across the country in preparation for invasion, but were thankfully never required. To this day, unexploded ordnances left over from WW2 continue to be unearthed and dealt with by EOD teams across the country.
What are White Phosphorous Mortars?
On contact with air (when the mortar casing is broken) the phosphorous reacts and creates an explosion. Theoretically, a brand new mortar bomb could be carried around in your pocket quite safely, however, the mortars discovered on the banks of the River Soar had been in the ground for a long time, and their casings had eroded. It only took a small knock from the excavator to crack their cases, which is why one of them went off underground, and the EOD team had to be extremely careful with the remaining device.
Client: Environment Agency
Jackson Civil Engineering recently completed work on a £4.5m flood alleviation scheme in Steeple Bumpstead, Essex.
The village was at a high risk of flooding because two brooks, from Bumpstead and Helions Bumpstead, meet in the village. Following periods of heavy rainfall in 2007 and 2009, the brooks burst their banks, and numerous houses in the village were flooded.
Following these events, work began in February 2013 to re-profile sections of each channel, and included the replacement of six river crossings, including footbridges, road bridges and a ford.
The project was chosen to champion the ICE’s ‘This is Civil Engineering’. This is a national initiative which aims to illustrate the importance of civil engineering to the public, and the Steeple Bumpstead project was thought to be a shining example as it combined such a variety of construction methods with challenging conditions, restricted access and a very strong public interface.
Client: Environment Agency
Jackson was appointed by the Environment Agency to construct the UK's largest inalnd flood defence scheme. Spanning 27Km, the flood defence scheme aimed to protect 16,000 homes in Nottingham.
The scheme was constructed in sections to aid project management. The team had to cope with a variety of contrasting working environments, all of which posed their own unique challenges.
Much of the route ran through built-up areas so first class public liaison with residents and businesses was a must. We also had to plan our work around major events such as The Robin Hood Marathon and Race for Life, both of which took place along the riverbank. We also worked adjacent to a live railway line, over a high pressure gas main, under 132Kv overhead cables, and in Attenborough Nature Reserve, a SSSI.
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Client: Environment Agency
Jackson Civil Engineering's Godmanchester project has picked up a British Construction Industry 'Outstanding Contribution Award'.
Jackson recently completed the Godmanchester Flood Risk management Scheme, a £9.2 million project to protect over 500 residential and commercial properties in the town from flooding.
The 1.5km defences were constructed along the river bank, which flows through the centre of the town. The project was particularly challenging as the majority of the construction work was carried out in frequently used public areas and private residential gardens.
The project received a number of awards, including a highly coveted ‘Environment Agency Exemplar Award’ for exemplary health, safety and environmental management, and also an ‘British Construction Industry Outstanding Contribution Award’.