Equipment for field defences
As with digging holes, there is equipment that can be used by non specialists, and that which would ordinarily be used by the Royal Engineers. This can range from the most basic of sandbag filling devices to complex concrete support capabilities.
Hydraulic, compressed air or petrol driven post drivers can be used to ‘hammer in’ either wooden posts, steel pickets or T Profile stakes to secure and reinforce corrugated steel or timber revetting. They are mostly used in the fencing industry but they are perfectly suited to defence applications, especially in difficult and frozen ground.
Although petrol is not convenient to handle, a diesel powered compressor or hydraulic powerpack is an additional item of equipment to maintain. Manufacturers include Atlas Copco, Hycon, Petrol Post and Power Post.
Sand Bag Filling
Sand bags are simple, cheap and require no mechanical or electrical equipment to use, just a shovel.
Filling them is time-consuming, though.
Although we have seen the use of traffic cones as improvised filling funnels, BCB make a much more robust and effective device called the Sand Bagger. The British Army actually has some of these in service although making them more widely available is a quick and cheap means of improving capability. A team of 8 can get through approximately a tonne of fill material in an hour.
Concrete Canvas and Roadplates
Corrugated galvanised steel sheeting is simple to use, cheap and readily available, used for revetting and as support for top cover. It is difficult to envisage an alternative that is as cheap or simple to use but a couple of products spring to mind, although not directly analogous
Concrete Canvas is an innovative British product that is a flexible cloth impregnated with concrete that requires only water and air to cure. Although they do make a shelter, the main use us for ground reinforcement, culvert construction and other ground engineering tasks.
Normally emplaced with mechanical assistance, smaller rolls and pre-cut sheets could be used for smaller field defences. It could also be used to reinforce existing or hastily constructed defences, providing additional protection within hours.
A possible alternative to corrugated galvanised steel is injection moulded plastic. Road plates, ground decking, trench covers and plastic sheet piling are typical civilian applications.
Although Hesco is widely known, JS Franklin Defencell is much less known, yet it has a number of advantages over Hesco and several similarities. It is an all fabric system, available in a variety of sizes and configurations including a number that are specifically designed to be man portable and filled with hand tools.
Shown above is the M1, it weighs less than 10kg and provides a barrier that is approximately 1m x 1m x 5m. This is equivalent to nearly 300 sand bags.
The smallest in the range, the Ranger, weighs less than 1.5kg and can be filled with hand tools in less than 10 minutes, yet it provides equivalent protection to 40 sand bags.
Lightweight and re-usable filling frames are available that are designed to keep the top open whilst being filled.
Other geocell type products are also available from a number of manufacturers, commonly used in roadway and slope stabilisation, they would be invaluable in reinforcing overhead cover fill and a quick and easy replacement for traditional sandbags.
The UK has a number of specialist composite armour manufacturers, simple composite sheets and frames could easily be held in unit stores.
FY Composites in Finland manufacture a range of shelter components and a full system called the Rapid Armour Shelter System (RASS)
The panels can be clipped together with the void back filled.
When the digging is done, revetting the sides, reinforcing firing positions and providing top cover is the next task.
On a conventional battlefield I think our traditional model of casualty evacuation from battlefield to Role 3 Hospital direct and logistics using helicopters, will break down rapidly. The relative immunity of battlegroup, regimental and even brigade HQ’s from indirect fire will be challenged, especially if they are tented.
In such an environment, time will also be a resource in short supply. Units will have to move frequently and extended durations in a single location, the exception.
Using a HESCO Accommodation Bunker (HAB) is a great solution for above ground protection, it requires a great deal of fill material for the walls and is time-consuming to construct.
This is why digging beneath ground level is so attractive, it is quick, and the earth provides the side protection and necessary load bearing structure for top cover.
Low profile also means reduced detectability from observation across the EM spectrum.
Sides and bottoms will likely need reinforcement to support static and dynamic loads as support structures for overhead protection or entrance cover.
If timber is widely available, posts can simply be driven vertically into the ground by weight and force of a hydraulic arm on the excavator used for digging the hole. Backfill and compaction would create a strong load bearing vertical wall onto which the top cover could be placed.
Long steel pickets with corrugated galvanised steel could be used, tied back and windlassed as needed.
Again, none of this is complicated or at the cutting edge!
It does need stores to be established and maintained though and of course, there are a couple of alternatives to make things possibly quicker.
The first of these is a means of increasing the speed of driving either timber posts or still pickets to create the side walls of a shelter. Dedicated pile driving rigs are available but a vibratory excavator attachment is yet another quick and cheap improvement using widely available equipment from the civilian construction sector.
Different capacity devices can be matched to large excavators or smaller plant like the JCB 3CX, or even the lightweight skid steer excavator described above.
Sheet Piling and Reinforcement
Lightweight plastic sheet piling is also worth experimenting with, it is stronger than might be imagined. Short steel sheet piling could also be used in place of post and corrugated steel because with the speed improvements derived from using vibratory piling attachments means it might actually be quicker.
Any post, picket or pile needs to both penetrate the ground from the base of the excavation and support the side walls to ground level so they are likely to be quite long, depending on the depth of the trench and strength required. Those shorter driven pickets will be secured using additional pickets and steel wire windlassed to tension.
One of the advantages of vibratory drivers over more conventional top hammer devices is the piles can be driven in from the side, thus not placing limitations on the height of the excavator’s arm, and this the depth of the pile or post.
It might also be preferred, if using sheet piling, to drive the piles into the ground before excavating.
Short sheet piles are commonly used for trenching
The innovative Concrete Canvas could also be used for side wall reinforcement although it is likely that it would need securing to prevent tipping and intrusion into the excavation.
With the benefit of engineering plant, longer bulk rolls can be used. After hydration it is achieves 80% strength in less than 24 hours.
Using inclined side walls would mean more soil to be excavated and a greater span for top cover but it would reduce the need for side wall reinforcement. For the base of the excavation, concrete canvas would provide useful ground reinforcement, especially in wet conditions.
The second video above shows how the Concrete Canvas shelter can be earth bermed, instead of adding protection on the sides and top, simply burying such a shelter in an excavated hole provides the same effect in less time.
Concrete Blocks and Sandbags
Sandbags still remain a viable construction product although with the benefit of mechanical plant the ‘bags’ can be larger and filled much quicker. Defencell or even HESCO Bastion gabions can also be used for sidewall construction although the more narrow cells could be used.
With a readily available source of fill material, continuous bags can be used. The fill rate is pretty impressive, 300 ft per hour, the second video shows an even more impressive fill rate. Individual sand bags can also benefit from excavator attachments. With the assistance of hydraulics, sand bags are still a very useful means of providing reinforcement.
Finally, if we do have the luxury of time, interlocking concrete blocks can be used, like those from Kite Bricks or Legio (yes, that is correct!)
The second Arch-Lok video is particularly interesting, construction is not as long as one would imagine.
Another now widely civilian system is the ‘trench shield’ or ‘trench box’ used to prevent excavations from collapsing and burying workers. They are simple, two outer surfaces supported by spreaders or bracing, usually constructed of steel and emplaced by cranes or excavator although newer designs are increasingly taking advantage of lighter materials such as aluminium and glass reinforced plastics. They are available in a wide range of sizes and designs can usually be stacked and joined. Inflatable designs are used for shallow excavations.
With the hole excavated, top and sides established (with any combination of the various methods above), the final task is to put the roof on.
Roof construction usually comprises beams, a deck and fill. If steel beams are used, some deck is used to provide a surface onto which to place the fill material. In smaller trenches, steel pickets are used for the beam and corrugated steel, the deck. If logs are used as the roof beams, they can be close laid to negate the requirement for any deck, fill material is imply placed on top of the logs. Sandbags or fabric would normally be used to stop water and fill material falling through the gaps. Approximately 200m of logs or 500m of earth ( 4 courses of sand bags) are generally used for protection against shell splinters with the depth of fill increased to provide greater protection. The composition of this cover material, split between cushioning and buster layers, can be varied, and beams or posts laminated and crossed for greater protection.
HESCO make a ready-made system for bunker roofs called the Lightweight Bunker Roof. It is conventionally used with HESCO bastion as the sidewalls but it could equally be used for an excavation. It is supplied as a kit and can be used for spans between 2.3m and 3.3m. The single kit is 5m long although multiple units can be connected together to make longer structures. 4 personnel and a single excavator can build a single LBR in less than half a day, the fill requirement for the roof is 10m3
The HESCO Expeditionary Elevated and Ground Mounted Sangar products also feature a roof deck that can be used to support a considerable weight of roof fill material.
With the beam/deck in place, the fill material is simply placed on top, often the spoils from the excavation. Geotextiles and geocell type materials can be used to stabilise the fill material, Defencell or other containers for example.
Which brings me on to an essential component of pretty much every Think Defence post, the ISO container.
Burying an ISO container might be seen as a quick and easy method of creating a buried shelter but they are not designed to carry weight across their top surfaces. When stacked, weight is transferred through the corner posts. So, if buried containers are used, they would still need a roof beam and deck to support the top fill material or they would collapse, and collapse much quicker than expected.
There are many variations on the theme, designs for 2 or 4 man Battle Trenches, firing platforms for automatic weapons or missiles, mortars, field shelters and vehicle pits, but the principles of ‘cut, reinforce and cover’ remain.
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