Andrew Barr

It seems Scotland's Chapter 8 chevrons permit a delicious local variation...

Excavator sitting beside hole at bomb location

Three defused bombs loaded into trucks

EOD team posing around one of the 900kg bombs

I was looking forward to seeing some german bunds, but it looks like they were pretty confident in their ability to remove the fuses. Not the first bombs these gents have seen!

In this position they'll have better access and more space to build protective structures around the bombs in case they do detonate - similar to the Great Yarmouth bomb in 2023. bsky.app/profile/andr...

Pictures indicate that the bombs have been found in a more open area by the river, which would would factor into the EOD team's decision to attempt to defuse the bombs in place.

Cologne evacuates thousands so WW2 bombs can be diffused The German city cordons off a huge area, calling it the largest evacuation since the end of World War Two.

Someone at the BBC is about to realise they've mistranslated 10cwt and 20cwt as 10 tonne and 20 tonne - these are ~450kg and ~900kg bombs! Still, that's about one and a half tonnes of actual explosive to deal with in a dense urban area.
www.bbc.co.uk/news/article... #cologne

This has obviously had tragic consequences for the crew of the Cuauhtémoc, but avoided additional casualties amongst the bridge users.

The bow of the Dali directly struck one of the main piers of the Key Bridge – the energy of that collision was huge. In comparison, masts are relatively weak and flexible, and so break easily in a collision with a stiff bridge deck.

Two dead as Mexican Navy ship crashes into Brooklyn Bridge At least 19 people are injured after the towering masts of training sailboat clip New York City's famous bridge.

Comparisons will inevitably be made with the collapse of the Key Bridge in Baltimore last year. If you're wondering why the Brooklyn Bridge seems to have gotten off lightly, structurally this is like being clipped by a car's wing mirror instead of directly hit by a bus.
www.bbc.com/news/article...

The fantastic cartographer @MtnMapper made this physical map of the North Pole region available for free. Source: shadedrelief.com/arctic

You know a machine is fun when it gets its own lab and a big interlocked cage. Testing this week at @sheffunieng.bsky.social's Thermomechanical Compression (TMC) facility: 500kN at up to 1200C!

This is a great study on the history and techniques of Hong Kong’s bamboo scaffolding. multimedia.scmp.com/infographics...

Via things magazine

Shout out to @sky-follower-bridge.dev, I've just filled my timeline with lots of the best people from the other place with a few clicks. 🤩

I've had an empty account sitting here for ages, but finally had enough of the other place. Glad to see there's some interesting folk in the room already. :)

Andrew wearing a hi vis jacket standing in front of a cargo bike and a large steel rig for panel blast testing.

Hi, I'm Andrew. I research blast loading and dynamic material behaviour, enabling the development of effective systems to protect lives and infrastructure. (I blow stuff up to stop stuff blowing up.) 💥

The tools used by government agencies like Dstl to plan these EOD operations rely on research on the behaviour of soils under very rapid loading, prediction of blast waves in urban environments, and the effects of ground shock. These are all things I'm involved in researching - follow for more info!

Even though the EOD team was unable to disarm the bomb without detonation on site, the mitigation measures seem to have worked perfectly, without any injuries or serious damage caused. All thanks to sand (and a lot of clever people). 👏

In the video you can see that the sheet piles themselves become projectiles, but mostly fall back within the area of the enclosure. The scaffolding struck by a pile will need repair, a few car windows are broken, and there's some damage to the river wall.

The crater following the explosion, showing several sheet piles from the enclosure roof perforated with small holes from bomb casing fragments. Also visible is the damage to the river wall. (Oliv3r Drone Photography)

The sheet piles that formed supported the sand on the enclosure roof are perforated with holes from the bomb casing fragments. These fragments were then captured by the sand in the walls and roof - no fragment damage has been reported.

Still of the bomb during detonation, showing dark clouds of detonations products and jets of sand. (Norfolk Police)

The blast is channelled upwards through the sand on top of the enclosure, resulting in the jets of sand visible in this image. Kinetic energy in the sand is kinetic energy that isn't available to the air shock, so full marks there. What about fragments?

An attempt was then made to destroy the explosive by controlled burning, which is riskier as there is a chance of a transition to detonation. This did indeed happen, but luckily we have drone footage to see the sand enclosure in action! 💥

Once the protective structure was in place the work to deactivate the bomb could begin. An initial plan to cut into the bomb and render it safe to transport had to be abandoned, after water used in the cutting process threatened the stability of the sand walls.

As an explosion would also result in a shock transmitted into the ground, nearby buried utilities were also taken into account, such as the presence of gas mains. The EOD team, Dstl, local authorities and utility providers will have all worked together to finalise a solution.

Aerial view of the completed protective structure. (Norfolk Police)

The design of the enclosure will vary depending on factors such as the type of explosive device and the proximity of other structures: in this case it looks like an extra L-shaped wall has been added to protect nearby houses.

Hesco MIL1 units filled with sand.

A younger Andrew filling some Hesco MIL1s.

Hesco MIL units are like a conventional gabion steel mesh, but lined with a geotextile material that allows them to be filled with finer soils like sand. Machinery can be used to do all the heavy lifting, then some compaction by foot and you're done.
So easy even I can do it...

Filling Hesco MIL units with sand using excavators. (ITV)

Filling Hesco MIL units with sand using excavators. (ITV)

Instead, the EOD team made use of Hesco MIL units and excavators to rapidly build a hefty sand enclosure around the bomb, with more sand on the roof supported by steel sheet piles.

Surrounding an explosive device with a sand-filled structure is an effective way to capture fragments and absorb some of the energy of the explosion, significantly reducing the risk to the public.
But building large structures with sandbags requires a lot of time and labour.

British Army participating in Nato's Black Eagle exercise in Poland in 2014. Sandbags are used to fortify a simple defensive position.

Sandbags used to form a communications trench on the Western Front, WW1. (National Library of Scotland https://digital.nls.uk/74549344)

That brings us to sand. Sand is fantastic at slowing down fast-moving projectiles and absorbing shocks, thanks to friction between the sand particles and the energy required to move it around (it's heavy).
Of course, sandbags are not a recent invention!

Ideally, all of these threats are eliminated by an Explosive Ordnance Disposal (EOD) team removing the device and destroying it far away from the public.
But when the device is too dangerous to move, the alternative is to deactivate or destroy the device in place.

A large unexploded shell sits beside the fragments recovered from an exploded shell, where the casing has broken into thousands of smaller pieces. (Wikimedia)

SC 250s have a total mass of 250kg of which 130kg is a high explosive such as TNT.
Detonating 130kg of TNT in an urban area is a bad idea [citation required] due to the risks of death/injury and damage from:
💥Fragmentation of the bomb casing
💥Shock waves in air
💥Ground shock

EOD specialists examine the bomb by the riverside. Photo by Oliv3r Drone Photography.

Example of an SC 250 bomb. Note that the tail fin was not present on the Great Yarmouth bomb. Image by CAT-UXO.

In February 2023 a WW2 bomb was discovered during dredging work in the River Yare. It's common to unearth old bombs during construction work in the UK, and they still pose a real danger 80 years later.
This appears to have been a German SC 250.