Stabilising Riverbeds with High Density Concrete - LKAB Minerals
Boston barrier construction

The riverbed of the River Witham requires stabilisation to reduce the amount of silt movement and other residues which settle, causing verges and holes. The answer is to construct the scour protection mattresses with MagnaDense High Density Concrete.

In recent years, civil engineering challenges have become increasingly more complex. While 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. In turn, this leads 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. This unwanted record lead to the development of the Boston Barrier project. Beginning in 2017, the project is due for completion in 2021. Once complete, it 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 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 watercourse. It is also a significant 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. MagnaDense is a natural, high density aggregate which can provide densities of up to 4.1t/m3.

Flood defence scour protection mattresses constructed with high density concrete for stabilising riverbeds
The scour protection mattresses are produced using MagnaDense high density concrete

Short lead times and high early concrete strength

Subsea Protection Systems Ltd in Great Yarmouth produces the heavyweight mattresses . Each mattress has a concrete density of 3.6t/m3 and is between 150 and 300mm thick. In total, they will install 380 heavyweight mattresses over the course of the project.

Due to the short lead times in the project, Breedon Group’s dedicated plant close to Subsea Protection System’s production facility produces the high density concrete. 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. It allows full utilisation of mould to achieve the required production output and meet the site installation programme.

A sustainable concrete solution

It is a requirement that all construction projects in water use 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.

Contact us to find out more about this and other MagnaDense Civil Engineering projects.