Experimental Researches On Fly-ash Used As Railway Roadbed Filler

Railway roadbed is civil engineering construction built to meet the requirement of railway pavement and transportation, which has to guarantee the elevation and stability of railway coping, the connection to bridges and tunnels and a complete transfixion of the whole railroad. Apart from the requirements in intensity, rigidity and stability, durability must be another quality of the roadbed. The design of filler and post-construction subsidence are the new problems to be solved in modern railway designing.With the development of the railway technologies in China, dramatic changes have occurred in roadbed designing. As the principal part of the railway construction, the material as roadbed filler has received wide recognition, hence studies on the nature of different filling materials have been canied out and valuable experience has been learnt. Despite of that, there are few studies on industrial waste used as roadbed. Except some briefly concerned construction inspection and engineering samples, no systematical researches have gone deep into the mechanism of some industrial waste,The utilization of light filler has now become one of the efficient ways dealing with post-construction subsidence, which has been brought into a major focus of attention. Instances have been provided of using foam boards and projects have been launched abroad of applying rubber soil to pave the roadbed, but those filler materials have not yet been widely studied due to their narrow utilizing scope and high cost.As castoff of coal-fired power plants, fly-ash has been piled in great scrap heaps and more land has been occupied, which has seriously polluted the environment and increasingly threatening the natural ecosystem and the quality of people's life. Being a kind of primarily important crude energy, coal still plays a major role today in a society undergoing severe shortage of energy. In terms of the present energy consuming speed,coal will maintain several centuries and hold considerable proportions in quite a long period. Moreover, enormous amounts of ash dregs are to be produced when coal being utilized. Usually 250-300 kg fly-ash are to be produced from the burning of every ton of coal. The emission of fly-ash was increased to over 120 million tons in China in 2000 and is increasing at the rate of over 7 million tons per year.Besides being a common material, fly-ash is a most useful civil construction material, which has been applied to different fields. Despite the numerous studies and utilization of fly-ash used to make concrete, a systematical investigation into fly-ash applying to filling out and build the roadbed is to be carried out. At present, the comprehensive utilization ratio of fly-ash in China is about 30%, that is, most amount of it has not been utilized yet, which is becoming a severe ecological problem barricading the development of economics and society.Fly-ash has always been promoted by engineers and technicians as an ideal material because of its relatively low weight (usually 10KN/ m~3) when used as a stable light filler. However, studies on fly-ash have not been widely carried out these years owing to the insufficient concern over roadbed engineering. Furthermore, strict requirements for railway security have greatly restricted the utilization of new materials. Nevertheless, the rapid development of railway engineering has made post-construction subsidence another control target of roadbedding, together with the intensity, stability and durability. The new target requires the corresponding ground processing for the constantly-changing target value of the speed. According to incomplete statistics, the cost to ground processing for average-speed trains in general areas surpassed that of the roadbed investment by 10%, the cost in soft areas by 50%, and the cost to areas for special passenger transportation lines goes much higher. Therefore, it is of great significance to make proper use of fly-ash and decrease the investment in roadbed processing.The present dissertation, based on current information from home and abroad and starting with indoor experiments, has studied and analyzed the mechanical characteristics of fly-ash, made basic researches on its physical properties, its static and dynamic intensifying properties from the angle of mechanism and transformation laws of fly-ash. It has also conducted relevant experiments and made numerical analysis about the compaction, condensation, bearing capacity and stability of fly-ash railroad embankment and shown the interrelationship among some of the guidelines. In addition, it has probed into the mechanic properties of fly-ash mixture and the optimum proportion between foundation bedding and slope protection block body. Finally, with the engineering benefit of fly-ash being analyzed, the dissertation has made a summary of the engineering characteristics of fly-ash, and explored the controllability of fly-ash through illustrating some specific engineering cases, the conclusion of which are drawn as follows,1. Fly-ash can be used as road embankment filler according to some static and dynamic experiments, and the improved fly-ash can be used as roadbed filler; 2. Fly-ash has favorable engineering properties and is much better than ordinary soil in its water content, compaction, self-subsidence etc.3.Fly-ash packed with soil won't cause pollution to water or the surrounding environment.4. Fly-ash is low in weight and therefore superior to ordinary soil in ground processing and gross roadbed (beneath the fly-ash layer) subsidence. Meanwhile, fly-ash used as roadbed filler has favorable engineering and economical significance in waste recycling, optimal land utilization and the reduction of ash emission.