Rreach On Strata-pressure Behavior And Support Resistance Of Large Mining Height In Fully Mechanized Mining Face Of Shallow Seam

Shendong Mining Area is the largest modern energy base in China. According to the coalseam characteristics the general mining method is fully-mechanized once mining all heightwithout local small coalpits, and the mining height is 5.0m. With the continuous improvementof mechanization part of the mining face height reaches 6.0m, which has reached 7.0m in22303 work face of Bu lian-ta coal. The support rated resistance increases continuously, from3500kN, 7592kN, 10800kN, 12000kN to the present largest 16800kN, which makes the costof complete fully-mechanized large mining height equipments increase. In order to master theregularity, the dissertation integrates the methods of field measurement, theoretical analysiscalculation and numerical simulation, and relying on some projects, such as "Technologyresearch on the pressure behavior principle and surface movement observation inexperimental mining face of Zhang Jia-mao coal.", it researches the structure formed byoverlying rock collapsing because of mining influence, the pressure behavior and reasonablesupport resistance.The results show that the prominent features of pressure behavior in fully-mechanizedlarge mining height work face of shallow seam are the bedrock cutting off along the shelf fullthickness, which directly affects to the surface, and the overlying should be divided "twozones": caving zone and fracture zone. During the roof weighting time the dynamic loadperforms significantly, whose first weighting interval is about 54m, and the average periodicweighting interval is about 15m. The operation character of shield hydraulic support is anincreased resistance. During the periodic weighting the average resistance reaches43MPa(10799kN), and the pressure performs strongly with short time. 60% supports haveopened safety valves in the middle survey area. Both resistance and dynamic load coefficient of support in middle are bigger than ones in two sides, which shows that the pressure performsintensively in middle of work face.Numerical simulation and theoretical analysis verify that the roof structure of shallowseam has a single key layer which can not form a stable "masonry beam" structure after roofbreaking, and the key block is prone to slide instability behind support. The dissertationanalyzes the stability of the block in "step voussoir beam" model from anther point. Itestablishes the step subsidence angle, finds out its relationship to the rotation angle, andintroduces it into the "step voussoir beam" resistance calculation equation. The analysis of thekey block indicates that the mining height, the immediate roof thickness, and the thickness andfalling length of the key block are influence factors of step subsidence angle and convergence.Meanwhile the analysis shows that the step subsidence angle increases as the mining heightincreasing under the same occurrence conditions. This dissertation calculates the large miningheight support resistance by using the established resistance calculation equation with stepsubsidence angle, which is basically consentaneous with practical results. Meanwhile, itshows that the support bearing weight is far less than the all overburden weight, and the loadtransfer-effect exists. Finally it determines 12000kN rated resistance support basically meetsthe requires of roof control in fully-mechanized large mining height work face of shallowseam, which is verified by field practice.Through research the dissertation basically graspes the principle of pressure behavior infully-mechanized large mining height work face of shallow seam in Shendong Mining Area,and determines reasonable support resistance. Moreover, it complements the previousdefinition of shallow beam, and provides scientific evidence for mining in other similar fullymechanizedwork face.