Study On The Surrounding Rock Control Theory And Technology Of Ultra-Close Multiple-Seams Mining

The coal seams defer significantly in their occurrence: the thickness of coal seams varies from less than one meter to hundreds of meters; the number of useful coal seams ranges from one to tens; the is uneven; and sometimes such changes occur as merging and splitting because of the close spacing between lower and upper seams. Difference in interlamellar spacing between seams, especially extremely small distances affects the mining of adjacent coal seams heavily, and causes side effect on safety and highly efficient production.When the intelamellar spacing between seams is relatively big, the influence of the upper seam after being mined on the lower seam to be mined is actually little; its rule of coal mine pressure and mining method are free from the effect from the upper seam mined. But mining practice shows that with the narrowing of the spacing between two coal seams, especially when the distance between them is ultra close, the interaction between them will increase, and the continuity of the roof of the lower seam will be interrupted and its integral degree will be affected by the upper coal seam mining; on the lower seam is the gangue caved from the upper coal seam extraction, with the remaining pillar in the mining face forming a strong pressure on the underplate. The two factors will lead to changes in roof structure and stress on the part to be extracted in the lower seam. They will further give rise to many new phenomena in mine pressure when the lower seam is mined as is measured against single coal seam mining. The new phenomena are mainly manifested by the following. "When extraction is in process in the lower seam, roof falling and leakage, which at sever level may cause supports to be buried, is very likely to occur; air leakage in the working face, a firetrap, is hard to avoid when connected to the upper seam goaf; the scientific layout of roadway and supporting pattern is out of reach, thus rock pressure appearance becomes obvious and roadway supporting tends to be difficult to proceed. However, the existing theories and experiences on the control of roof strata in single coal seam mining cannot well explain this kind of rock pressure appearance and mechanism. Therefore in extra close seam mining exist many technological puzzles.In China, close seam occurrence and mining takes up great percentage and in almost every mine camp exists problems in mining of close coal seam group. So far, theory and practice research on the acting law and control of surrounding rocks in single coal seam mining has achieved great progress, while research on close seam mining, especially systematic research on ultra-close seam mining technology, is relatively few and far between. Most of the research on ultra-close seam mining is a practical and empirical qualitative summary.This thesis, taking coal seam group occurrence and mining condition in the lower groups of seams in Datong mining area as its object and adopting such methods as field investigation, theoretical analysis, numerical stimulation and industrial test, does some explorative research and comes up with the definition of ultra-close multiple coal seams, engineering classification of ultra-close multiple-seam roofs, law of strata pressure behaviors in lower seam mining, the control of roofs in working face, the rational roadway arrangement and the guarantee system for mining technology. The research achievements are as follows.(1) According to long wall face mining, with the elastic-plastic theory and slip-line field theory, combining roof falling characteristics in mining in the upper seam and stress distribution law, the roof destruction depth in the lower seam is worked out and the definition and estimated criterion of ultra-close multiple seams is obtained. At the same time, the ultra-close multiple seam spacing in the lower groups of seams in Datong mining area is determined with the coal seam group occurrence and mining conditions in the lower groups of seams in Datong mining area.(2) The roofs of ultra-close multiple-seam are divided into 3 types (false roofs, completetely broken roofs and fractured roofs) according to yield depth ratio, the leading parameter to classify the roofs of ultra-close multiple-seam.(3) In the example of Datong mining area, through on-site observation and numerical simulation analysis, the basic features and law of strata pressure behaviors in the working face of the lower seam mining in the ultra-close multiple seams is further disclosed. All these will lay a reliable practical as well as theoretical foundation for further research on the structure of overlying strata and strata control around longwall face in the lower seam mining in the ultra-close multiple seams.(4) In accordance with the roof structure characteristic in the ultra-close multiple seams mining, the "blocky-loosen" roof structure model is constructed with the lower seam mining as the loosen boundary condition; the roof strata structure stability is analyzed in the lower seam mining in the ultra-close multiple seams with the blocky and loosen theory; the roof falling mechanism is expounded in the lower seam mining in the ultra-close multiple seams; determination of the support in working face loading in the lower seam in the ultra-close multiple seams is researched theoretically. All the above provides a theoretical basis for the strata control around longwall face in the lower seam mining.(5) With theoretical analysis and numerical simulation computation, the coal pillar stability and the uneven stress distribution of coal pillar load in the floor seam in the ultra-close multiple seams mining is studied. Theoretical analysis is carried out about the tendency of the support structure to be locally overloaded in the gateway in nonuniform stress field. Local overloading causes local damage, and further leads to support structure destabilization. The method is proposed to determine the rational position of the mining gateway in the ultra-close lower seam. This method is confirmed through on-site observation.(6) Faced with the damaging influence of the upper seam mining on the roof of the ultra-close lower seam with the roof crushing and given to leakage and falling which at severe level may cause supports to be buried, and sever air leakage and become a flretrap, reinforcing technology of fractured roof, sealing and filling technology, parameters for shape and support of the rational section in the gateway, spatial control and techniques in beginning and ending mining, such safety assurance systems as end of mining face, fore support pattern, decompression ventilation and mistretarder fire prevention are determined through on-site observation. A set of perfect aid technology for ultra-close lower seam mining is achieved and provides reliable technical support for safe extraction in the ultra-close lower seam.In short, the thesis researches deeply and systematically into the theory and technology of surrounding rock control in ultra-close seams mining, solves the practical problems existing in ultra-close seams mining, and has scientific reference value to the future ultra-close seams mining, designing, planning.