Sinking railways

He was first told that it was impossible, so much so, that Parliament initially rejected the plan to build the railway across it in 1824. Draining the bog proved to be only a partial solution, and vast amounts of money was expended until Robert Stannard, one of the men working on the site, came up with the answer. He suggested laying timber in a herring bone fashion, combining it with moss, heather and brushwood hurdles and putting earth on top. Although Chat Moss has long since been drained to allow agriculture and railway tracks, it continues to subside from time to time. But so do other sites across the UK causing great inconvenience to users when repairs have to be made. Digging them up and improving the foundations, floating them if necessary, still solves the problems but is a massively expensive and time consuming business. Surely, in this day and age, with the aid of advanced engineering technology and materials, somebody has come up with something better? The Challenge Our challenge this month is to come up with a way of stabilising railway lines, not to mention roads and buildings, built on soft ground, without digging anything up. Civil engineers would normally think in terms of excavation and foundations, or driving in piles with a large hammer. But mechanical engineers think in terms of mechanisms. Whatever the solution, a mechanical solution is going to have to get underneath something and expand. Jacking up is possible, but something still has to sit underneath the jack to support it. Whatever the remedy is, it has to be simple, low cost, reasonably foolproof, and reliable over a long period of time. The solution offered below solves the problem most elegantly and at remarkably low cost. George Stephenson would have loved it, except that the enabling technologies had not been invented then. Once you see it, you may consider it obvious, except that it is innovative enough to be protected by patent. For those without access to the web, the solution will be described fully in our June edition. See if you can come up with anything better. Solution The base technology on which the solution to our May edition challenge is based, started in Finland, where they have a marshy landscape, which freezes hard in winter, and then melts in Summer. Finnish roads, where there are any, subside, and so do buildings, so they came up with the idea of injecting polyurethane foam under floors to lift them up again and provide a stable base. This led on to injecting the stuff under road slabs, and doing the same for them. Now comes the idea of drilling a small hole, inserting a geotextile tube, and then inflating it with foam. It is this idea, which is called by its inventors, Uretek UK, the "PowerPile", that offers a solution to stabilising railway lines running over soft ground. Uretek marketeer David Hughes told, us, when we asked how it compared with the original Stephenson solution, "It is same principle we work on. We inject polymer resins and a catalyst. It then expands and compresses the ground. Network Rail is very interested". For a rail solution, the tubes are pushed down through 40mm diameter holes, and can be expanded up to 350mm diameter between the lines and provide significant friction support in soft soils and peat. For non rail use, where the holes can be bigger, treatment depths can be 5m or more, and expanded diameter up to 1.5m. Compressive strength of the filled tube is said to typically be 4 to 6 MPa, although incorporating safety factors, this reduces to 1 to 2 MPa. Hughes said that, "We have done a couple of smallish railway jobs, lifting and stabilising platforms, and stabilising a railway embankment in a horizontal direction in the last couple of months." While not yet used beneath rail lines in the UK, PowerPiles have recently been used to successfully stabilise and underpin a historic building in the centre of York, three sides of which were party walls with other buildings, where alternative strategies would have been noisier, dirtier, longer, more expensive and liable to threaten the stability of the adjoining structures.