Research On Support Technology And Supporting Materials Of Double Side Entry Rataining Under Deep Thin Coal Seam Mining

Because the shallow resource gradually decreases and exhausts, underground mining from shallow to deep has become an inevitable trend. However, with the increasing of mining depth, a series of technical problems have to be solved, such as complicated geological environment, high gas pressure, underground stress and temperature, soft rock control and so on. In such intricate environment, the traditional “U” type ventilation system which easy to causes gas accumulation and transfinite on the top corner of working face seriously affects the efficient production and limits the scale and speed of deep underground coal mining. By using the gob-side entry retaining technology, it can achieve the “Y” type ventilation system of work face which will tackle the problem above. The regular way of gob-side entry retaining is to layout support on one side of roadway. If there are supports on both sides, namely, “double side goaf” gob-side entry retaining, the roadway can be used for gas extraction which will create great economic value. Whereas such technology is rarely used in deep extremely thin coal seam mining. The study about the complexity of stress state, failure characteristics and control of surrounding rock need to be carried out.By using the self-developed rotating plane stress similar material simulation test system, the characteristic of movement and damage and the distribution of abutment pressure during “double side goaf” gob-side entry retaining are studied. Through mechanic analyze, the mechanical model of “double side goaf “gob-side entry retaining of the deep thin coal seam is proposed. Then according to the analyses of the key block B of basic roof, the movement of overlaying state and the stability factors of support, the designing of gob-side entry retaining both inside and beside are optimized. For the entry support is relatively mature, this thesis is forced on the selection of supporting materials, the laws of deformation and breakage of them. Such research provides bases for in suit gob-side entry retaining. Some main conclusions are drawn as follows:① Through similar material simulation experiment, the movement law of overlying strata of deep extremely thin coal seam under repetitive mining was clearly observed. Unlike the deformation and breakage of roofs of medium thickness and thick coal seam, the immediate roof can almost fill the gob. For this reason, there is not sufficient space for upper state to deform. Accordingly, the rock breaking angle, the maximum depth of abscission layer and other parameters which were acquired through the experiment are important for the control of surrounding rock and the roadway support of gob-side entry retaining in thin coal seam.② The stability of key block institutional state of basic roof have extremely important influence on the lower support of gob-side entry retaining. It is also the key factor to analyze whether success of gob-side entry retaining is being achieved. By theoretical analysis, different stages of mining have different effects on the stability of key blocks.③ Through summarizing and studying the defects and deficiencies of typical gob-side entry retaining, the entry and roadside supporting technology which has the advantages of coupling stiffness, harmonious deformation and can jointly bear the upper load is proposed.④ According to the analysis of the deformation and mechanical response of supporting material, the “waste bag, bolt and metal mesh” supporting system can be compressed at early stage that results in stress relieve. While it provides rapidly increasing bearing force with the further compaction which can satisfy the requirements of deformation and strength of gob-side entry retaining in deep thin coal seam mining.