Several years ago I did some geotechnical consulting work for various bauxite mining projects along the north coast of Suriname. The mines were located in swampy areas and overlain by very soft clays. The picture below shows the general terrain when crossing a swamp. Such haulroads were needed to access the small satellite bauxite pits, which were spread several kilometres apart.
Suriname swamp road for mine
Where haulroad construction was concerned, there were no hard rock or road aggregate supplies nearby but there were significant amounts of fine sand on the large “islands” within the swamp. Road building mainly relied on end dumping truck loads of sand, allowing it to settle and sink into the swamp, and then continue adding more sand until the settling process stopped. This resulted in high cost roads and very slow progress in construction. Periodic rainfalls would also cause havoc with the trafficability on the fine sands.
Where there was significant swamp vegetation (like in the photo), it would be buried and help form a mat to support the road and minimize the sand losses into the sub-grade. However in other parts of the swamp the vegetation was minimal and therefore sand settling losses could be high.
Geotextiles were applied in some areas using a geogrid and these were successful although large amounts of sand were still required. Once a road was built, the next issue became the vehicle trafficability on the fine sand surface, especially when rains occurred. The sand would rut and require constant grading and repair. Final road surfacing would consist of laterite when available, which is a high iron off-grade bauxite and could be compacted to form a hard surface but would degrade and get slippery in the rain. Had coarse aggregate been available locally, road performance would have been much better but one has to work with what is there.
Recently I saw a video about a geo-cell solution for building roads with sand only. The website is The PRS-Neoweb™ Cellular Confinement System (www.prs-med.com). I think there are other similar geotextile solutions available but this is one that is well described on their website. Sand is placed into the geoweb and eventually forms a stiffer layer. I presume that one could place the sand using mobile equipment or hydraulically by pumping coarse sand as a slurry.
Geocell geotextile for road construction
In hindsight, I would have liked the opportunity to test this geoweb system in the swamps of Suriname. Potentially it would have been a good solution to prevent both sand losses and create a more trafficable surface using sand only. I’m not sure if the best placement of the geoweb would have been along the base of the road to support the sand load from sinking into the swamp or near the surface of the road to help create a more trafficable surface. Building a road over a swamp is similar to building a road out onto a tailings pond, so there could be application there too.
Geotextiles have many applications in the mining industry and may have many cost savings related to initial construction and subsequent operation. There can be significant up-front costs to purchasing geotextiles but don’t let that scare you away. They are definitely worth a look.