The Research And Evaluation On Foundation Deformation In Goaf Of Colliery Area And Influence In The Railway Construction

With the development of railway industry, as an adverse geologic problem in the railway construction, goaf is becoming a more and more prominent problem, especially, in some new being built mining areas in east China and north China where there will be quite a lot of railways to be built in the following years. In the survey of railway, the definition of the boundary and influence range of goaf, the evaluation of top plate deformation and foundation stability and the adoption of treating measures will have a big influence on the railway alignment, optimization and cost estimation. By-pass is the predominant principle adopted for goaf; in the unmined areas, some safe coal columns will be reserved to make sure the operating, safety of railway. However, in some areas where many mines have been exploited, the proposed railway alignment has to cross the goaf inevitably, therefore, it is very important on the railway industry to evaluate the affection of mined-out areas to the stability of railway and adopt the correct measures according to their property.The main types and property of goaf are introduced in detail; ground deformation and damage caused by mining and the main factors which affect the foundation stability are discussed in this paper. A prediction and evaluation of foundation stability for goaf is made on some large coal mine. The aspects for the study are as following:1. Based on the data collected and investigated in the great deal of railway projects in China over years, the types and property of goaf are summarized systematically. For the private small size mines, there are goafs caused by different excavating methods such as branch method, hanging-plate method, wall method, lane column method, room column method and incomplete column method and so on. For the public mines, there are two main types: wall method and column method. According to the thickness of coal layer, wall method can be divided into integer-mined method and layer-by-layer-mined method; according to the advancing direction of working surface, it can be divided into trend long wall method and inclining long wall method. In column method, there are room method, room column method, lane column method and strip method etc.2. The subsidence and deformation in goaf are studied systematically. Main factors, which affect the ground deformation and foundation stability, are determined, those are: mechanic property of overlaying rocks, strata formation and its location, inclining angle of coal layer, mining methods, top plate managing method, natural condition of coal layer, size of goaf, repeatedly mining, hydrogeologic condition, geological structure and topography. The damaging property of new and old goafs, forms and property of ground deformation and analysis of the railway to the foundation stability are dissertated. The probability integral method for the calculation of ground deformation in goaf is introduced and number simulating analysis is carried out.3. The methods and content for the evaluation of foundation stability are discussed and some evaluating methods are introduced such as stress transferring method of small relaxing body, collapsing arch method and arch top collapsing and jamming method for small size goaf and some others for the large size goaf. The influence of railway to the foundation stability is analyzed in the aspects of load and vibration.4. According as the above-mentioned theory, the prediction and evaluation on foundation deformation and stability in goaf are made in some large coal mine. The geological condition, coal layers, main mining layers, top and bottom plate management, mining method and distribution of goaf are dissertated systematically; by the method of comparison and analysis, the rock shifting parameter is fixed in accordance with the property of the mine. Then the estimation of deformation is made by calculation and a conclusion is drawn. The result has been used in practice and got a good effect.5. The calculating method and procedure for the protecting coal column in railway projects are introduced; the reliability of protecting coal column is analyzed, and a column is designed and calculated based on an actual example. The countermeasure is discussed when railway passes the goaf. The general treatment principles and measures such as grouting are dissertated. And the test of treating effect forgoaf is discussed.