Stabilising riverbeds with high density concrete

In recent years, civil engineering challenges have become increasingly more complex. Whilst high density concrete containing the natural mineral Magnetite has a history of use in civil engineering projects, contemporary designs have involved more innovative solutions; one of the most recent is the use of MagnaDense concrete to stabilise underwater structures and groundworks.

The Boston Barrier
In our changing climate, there is an ever increasing threat of flooding which in turn is leading to an emphasis on the improvement of flood defences. This is especially important for the town of Boston, Lincolnshire, which in 2008 saw the highest tidal surge ever recorded in the region, leading to the development of the Boston Barrier project. The project began in 2017 and is due for completion in 2021 and when complete will protect over 14,000 properties from tidal flooding.

The project is a partnership between the Environment Agency, Lincolnshire County Council, Boston Borough Council and Black Sluice Internal Drainage Board and will see the installation of two flood defence barriers as well as scour protection of the river bed.

Stabilising riverbeds
The River Witham runs through the county of Lincolnshire, beginning in Grantham and finishing in the Haven, a tidal region of the Wash. It is a fairly unique river because of the high flow of water running through it; the rate at which is recorded at 5.3 metres per second, an exceptionally high flow for an inland water course. It is also a major distribution channel for Lincolnshire industry and of vital importance to the county.

Due to the high velocity of water, the riverbed requires stabilisation to reduce the amount of movement of silt and other residues which settle, causing verges and holes. The solution is protection with mattresses to reduce scour, produced using concrete. Because of the shallow depth of the river and the force of the water, standard concrete would have caused the mattresses to be too thick, threatening safe passage of the vessels passing through.

The answer was to construct the scour protection mattresses with MagnaDense High Density Concrete. Supplied by LKAB Minerals, MagnaDense is a natural, high density aggregate which can provide densities of up to 4.1t/m3.

Produced by Subsea Protection Systems Ltd in Great Yarmouth, the heavyweight mattresses are constructed with concrete of 3.6t/m3 density and between 150 and 300mm thick. In total, 380 heavy weight mattresses will be installed over the course of the project.

Due to the short lead times in the project, the high density concrete is being produced at Breedon Group’s dedicated plant in close proximity to Subsea Protection System’s production facility. The concrete has been designed to achieve strengths of 40N at 28 days, achieved in part due to the properties of MagnaDense. The short setting time of just 24 hours and high early strengths were a vital part of this project, to allow full utilisation of mould use in order to achieve the required production output and meet the site installation programme.

A sustainable solution
It is a requirement that all projects in water are constructed using materials which can be recycled. In this case, the scour protection mattresses are designed to withstand 100 years beneath the water before being fully recyclable at the end of life. Concrete reclaimed from the bottom of water courses can be crushed and re-used in other applications.

About MagnaDense
MagnaDense is a naturally occurring mineral extracted from LKAB’s mines in Northern Sweden. It is an inert and non-toxic material resistant to corrosion and leaching. When utilised in offshore and under water applications, MagnaDense concrete lowers the centre of gravity, increases negative buoyancy and gives mechanical protection against sea motions.

Subsea Protection Systems
Subsea Protection Systems (SPS) is a leading supplier of scour concrete mattresses and other protection and stabilisation products to the subsea industry. The company designs and manufactures a wide range of solutions for the protection and stabilisation of pipelines, cables and other subsea assets.

SPS is experienced in using high density concrete in various projects, as a supplier to the energy sector for over 20 years. It is involved in all aspects of subsea projects including Offshore Wind Farms, Oil and Gas, Inshore and Coastal Protection.

One of the more recent and diverse projects was the development of concrete Kentledge blocks to act as weights for a temporary building at Heathrow Airport. The blocks were required to keep the temporary structure weighted to the ground. Space around the building was restricted so a high density concrete was required, adding extra weight in a restricted space available. The blocks were constructed with a density of 3.8 t/m3 and were designed to be removed once the building was no longer required.

LKAB Minerals is an international industrial minerals group with a leading position in a number of product applications. It has sales representation, offices, production units and deposits in 11 countries in Europe, Asia and the US and employs around 400 people. LKAB Minerals’ turnover was 212M EURO in 2018 and it supplied over 30 minerals to a range of industries, including construction, water treatment, polymers & coatings, agriculture and pharmaceuticals.

For details of MagnaDense please visit: www.lkabminerals.com