Rural Roads in Afghanistan
I need to get loaded trucks through a rural part of Afghanistan. The roads between camps are made of silty sandy soil which will become wet (I am told) during winter. I have looked at having a local contractor use aggregate to lay on the surface but his price is too much. Is there a cheap short term solution such as an off-the-shelf temp road surface I could lay or a concrete system? Sorry to be a bit vague but the soils are strangely weak in that it is very powdery and yet very strong when compact. Any help would be appreciated.
Concrete is unlikely to work and expensive. It would likely crack and break making even more problems.
Aggregate rolled into the surface is good and stabilises the surface but may require a significant amount. Afghan roads typically do not have proper drainage - have you thought of forming and compacting a crown on the road and possibly manually compacting top drained surface using local labour with elephant foot compactor (or similar) Two road profile types we used in Afghanistan are attached.
Also if you leave much later in the year you will actually find ground surfaces will freeze and any thawing may just be on the surface. We worked frozen roads several times.
Alternatively some agencies have found convoys of horses and donkeys have been available and manageable to transport essential materials - it depends on what type and quantity of materials you are trying to move. Even very large convoys have been moved this way.
I was in Af'stan for almost a year with MSF and over wintered there. I was based at Tarin Kowt, Oruzgan, which is right in the centre of the country so the details I am about to pass on relate to my experience in that location.
As I remember it there was very little rain and what little there was fell over a 6-8 week period in Feb and March. The roads were affected but they remained passable and the main problem was trying to ford swollen rivers as the rains coincided with the start of the melting of the snow in the mountains upstream. We used double cab Toyota Hilux pickups and travelled between Kandahar, Tarin Kowt and another clinic at Derawod. In all the time I was there, and after hundreds of journeys, our vehicles only failed to complete a handful of journeys. If my memory serves correctly then the actual number was 3: Twice because of swollen rivers and once because of deep snow over a pass. Never due to the state of the road. We did have one muppet try and cross a river in spate and had to pull the prat out of the raging torrent with him and his driver sat on the roof as neither could swim but that was due to stupidity and nothing to do with the roads
On the route we took, once out of Kandahar, there was no sealed road and the dirt road was never maintained. It was in poor condition with severe corrugations being the least of the problems. There was one section where there ground conditions were terrible. The sand was so fine it was like talcum powder when dry and a deep slippery slime when wet. A road had been built on a high embankment but as this had been bombed to hell during the Soviet occupation it was impassable on anything but a trials bike. Even conditions as bad as this did not stop the 4x4 Hilux and they always got through. Our vehicles were fitted with winches and we made what looked like huge tent pegs that could be hammered into the ground with 'sledge' hammers and linked together with ropes to form an anchor point to winch from if necessary. We never had to use them. We never had to use the snow chains we made from materials we bought in Tarin Kowt bazaar either. The only time the snow stopped us it was because it had drifted so deep it was half way up the doors of the Hilux and snow chains wouldn't have made any difference.
So. To sum it up:
In my experience of Oruzgan
- Rain is not a massive problem for the roads but it is where they ford rivers.
- 4x4 Hilux pickups with local drivers always managed to get through even when heavily loaded.
The locals will want the best road possible and wont care how much it costs an NGO. Local contractors will try ... (more)
I worked in Nahine in Northeast Afghanistan for 14 months and took delivery of some truck loads of pipes from Pakistan, during some pretty difficult months of the year, so I sympathise with this request. I also know that some of the very fine clayey surfaces in that area were absolutely treacherous once it had rained. ACTED did some work on the road from Baghlan to Nahrine which helped greatly. So, you could contact ACTED, who have done a lot of road improvements work - they used to have some pretty good Afghan Engineers (in 2003).
Concern Worldwide used donkeys to bring aid to some areas of Northeast Afghanistan in 2002...the last resort, I guess, but maybe worth considering nevertheless.
This sounds like the 'black cotton soil' problem known to anyone building pavements in central Africa.
The issue is one of groundwater control. If this soil is silty then it will become very weak, maybe even fluid, when it is (a) wet and (b) subjected to cyclic loading, i.e. traffic. Loss of strength can be very dramatic with true silts. The options are either to stop it becoming wet by draining and capping it or to put a big thickness of free-draining gravelly fill to cushion the loading and assist drainage of the soil. 500mm or more of granular road base may be needed for the second option.
If the area is low-lying and subject to seasonal water logging then the option of keeping the subsoil dry is not practical and a concrete pavement is not likely to last very long as it will not have enough support. It may be possible to design concrete pavements to bridge short distances but that's hard to say from here.
Temporary road surfaces may do the job but they tend to be expensive - usually more so than gravel - so probably only useful for short lengths. You'd need a fairly heavy duty one, I expect. For example, a quick trawl of the web found http://www.groundprotection.co.uk/duradeck/duradeck.php which offers Duradeck polythene panels that claim to take loads up to 80T over soft ground. A 1200x2400 panel weighs 39kg and the basic cost is £299 ($540) per panel in UK (obviously, this is negotiable for quantity). There are other similar products, some available nearer to you - this gives an idea. The success of such a system will depend on how soft the ground actually gets.
An alternative could be to use a combination of a mesh to reinforce the granular base so that it does not need to be so thick. Whether that is cost effective depends on the availability/cost of mesh locally and the weakness of the ground with which you are dealing.
Another issue with these types of fine-grained soil could be frost susceptibility in which ground freezing expands and breaks up the soil structure, weakening it. I guess that will be the case during an Afghan winter. Again, not a problem if the ground stays dry.
I think that's probably as much I as can suggest without more information on the soil properties and groundwater conditions. I hope it helps give a bit of context. I might be able to get some practical info on temporary roads if it would help.
I suggest starting by investigating whether the road can be drained by digging ditches and installing culverts to avoid water logging, if there is time.
Geo textile membrane under 400mm of hardcore to stop earth pumping to the surface. Grade roads with camber to shed water to ditches. Stabilise soil with lime or cement Sorry, but with trucks going over it, you need to spend money as options 2&3 will possibly not work!!
Concrete and temporary surfaces would most likely cost far more than gravel which presumably is relatively local.
It may be that you can significantly improve the road performance by improving its construction. You mention that the soil is hard when dry so if you can get the water off before it soaks in it will help. Mind you, heavy trucks are a tough test for any road material.
The critical point is to get water off the road as quickly as possible by using a camber cross section with large flat drains (1/2 the road width on each side) which provide the material to make the camber. The side drains are diverted away from the road at regular intervals to keep water flow down and prevent erosion and water logging.
The new surface needs thorough compaction with hand rammers or rollers. A bit of moisture helps, but if it's already muddy it's too wet.
Earth Roads: Their construction and maintenance from the Development Bookshop is what I used many years ago in Zambia and it covers all the basics.
Another possibility is this material that I heard of from South Africa. It's a stabiliser that you mix into the soil. I have no personal experience of it but I believe DFID were trialling it in Mozambique a few years ago. Could be worth contacting them. www.ecobond.co.za
One option might be to reinforce and isolate the sub-grade with a geo-textile or something similar. If a conventional geo-textile is not available, you could see what similar local resources exist. Some grain sacks are made of woven slit-film, which is essentially a geo-textile. In Sri Lanka, we had a road project where Palmyra leaves were laid in a mat, with a lot of overlapping, and then topped by a few inches of crushed stone for a running surface. The fibres in the leaves, randomly cross-laid, accomplished the same effect. The geo-textile of fibrous material could be placed directly on the fine soil and then topped off with 15-25 cm of better material such as crushed stone, bank-run gravel, or whatever you can find. This approach won't eliminate the need for surfacing, but should reduce the required thickness.
The Russian Military used PSP - Perforated Steel Planking (also called Marston Mat) to build airstrips in Afghanistan - this is probably the best solution - Faizabab airstrip used to be (maybe still is) all PSP, and Bagram's aprons were all the same. It's the same material that is sold sometimes as 'sand ladders' for 4x4 vehicles, but was designed to interlock. Not sure where it could be sourced, but it is possible that some of the Russian material has now been replaced at airstrips and might be available.
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