| This paper takes a gently inclined thin uranium orebody with a buried depth of 50m as the engineering background,which has the characteristics of weak cementation and low strength.According to the physical and mechanical parameters of surrounding rock roof,the development of similar materials and the experimental study on similar physical model of longwall stope are carried out.By monitoring the roof settlement of the stope,the initial fracture process,breaking mode and settlement law of the roof are obtained.The main results of this paper are as follows:(1)According to the physical and mechanical parameters of the surrounding rock in the ore layer and based on the similarity theory,the geometry,gravity and stress similarity constants are determined to be C_L=20,C_γ=1,C_σ=20,respectively.Selecting river sand,cement,barite powder and bentonite as similar materials,the orthogonal test method was used to design and carry out experiments,and the relationship between the parameters of similar materials and physical and mechanical parameters was obtained.(2)The composition and proportion of similar materials are as follows:the particle size of river sand is 2.00mm,the ratio of cement to sand is 1:94(ash is cement,sand=river sand+barite powder),the content of barite powder is 13.60%,the amount of bentonite is 0,and the uniaxial compressive strength of the material is0.091MPa,which is 9.0%different from the target value 0.100MPa.(3)The monitoring results of roof settlement show that the roof settlement mainly occurs in mining,and in the process of mining 8m～16m,the roof settlement is about 2 times of that after mining,and the roof settlement after roof fracture is more obvious in mining,and the roof settlement curve shows that the roof settlement has the characteristics of obvious interval and abrupt change.In the24m～32m section of mining,the roof settlement increases sharply,and the roof settlement in this mining is significantly higher than that in the above-mentioned cycle mining,and there is an order of magnitude difference,and the roof is still in a state of continuous settlement for a long time after mining.(4)The first fracture step of the roof is 16m.The fracture crack of the roof first extends along the vertical direction,and with the mining progress,the crack in the roof gradually turns to the mining direction.after two horizontal turns,the crack extension height is 11.2m,and then the crack extends from horizontal to downward.Finally,the whole roof collapses,and the shape of the collapse is similar to trapezoid.The influence height of the first overall collapse of stope roof is 11.2m and the length is 32m.(5)The fracture results of the roof show that due to the fracture crack in the roof of the stope,the roof is still unstable and in a state of fracture subsidence after the end of mining,and the roof collapses as a whole after settling for a long time.When the roof breaks for the first time,it is necessary to pay continuous attention to the roof settlement and support the roof when necessary to control the roof pressure.Stope stoping needs to be carried out continuously,and can not stay too long after a certain mining cycle process or end,otherwise the roof may be pressed in a large area,resulting in pressure frame accident. |
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