Since the mining of longwall faces, the existence of large structures in the overburden and the form of this structure have been an important topic in mining science research. What form has always been an important topic in mining science research. Pressure arch hypothesis It was proposed by the Germans Huck and Gillizel in 1928. The hypothesis says: Longwall coal starting from the opening cut in the face to form a pressure arch, after arch with the face forward and expand, until the dome reaches the surface. In front of the work, the front arch a formed in the coal body and the rear rock fall form the rear arch b, a and b are stress-increasing zones, and the working face is in the stress-reduced zone. The weight of the rock inside the pressure arch. Advantages: can explain the reasons for the surrounding rock unloading; Disadvantages: Failure to explain the development process of rock deformation, movement and destruction, and the relationship between the support and the surrounding rock. 2. Cantilever beam hypothesis It was proposed by Stoke in Germany in 1916. The hypothesis says: The top surface above the working face and the goaf can be regarded as a beam. One end is fixed in the rock body, and the other end is in an overhanging state. When the overhanging degree is large, a regular periodic breaking occurs, causing a cycle. Pressure, near the coal wall, the roof sinking amount is the smallest, and the performance of the roof pressure is also small. Pre-cracking hypothesis Proposed by Belgian scholar A. La Paz in 1850. think: (1) Due to the influence of mining, the continuity of the overburden strata on the working face is destroyed, and thus becomes a discontinuous body. (2) There are stress reduction zones, stress increase zones and mining influence zones around the mining face. (3) Pseudoplastic body, the bracket should have sufficient supporting force and working resistance. 4. Articulated rock block hypothesis It was proposed by the Soviet scholar Kuznetsov from 1950 to 1954. think: (1) The damage of the overburden on the working surface can be divided into a falling belt and a regular moving belt thereon. (2) The fallen belt is divided into upper and lower parts. When the lower part is fallen, the rock blocks are disorderly. When the upper part is fallen, the arrangement is regular, but the difference from the regular moving belt is not related to the horizontal horizontal pressing force. . The regular moving belts can be hinged to each other to form a multi-link hinge, and regularly sink in the gondola. (3) The working face bracket is in two different states, “given load†and “given deformationâ€. Electrical Insulation Pet Film Electrical Insulation Pet Film,1Mil Fire Proof Bopet Film,Anti Burning Polyester Film,Mdf Board Pet Film Flame Retardant Mianyang Prochema Commercial Co.,Ltd. , https://www.gustek.com