to obtain the stress distribution law in the cut roof rock layer under roadway mining 9. The mechanical structure model of the continuous beam under a uniformly distributed load was established by Jiang et al. To analyze the stability of the open-off cut roof, scholars simplified the roof as a beam through the method of theoretical analysis to investigate the stability 7, 8. With the increase in mine production and the enlargement of fully mechanized mining equipment in recent years, the section of the open-off cut has continuously enlarged, and it is more difficult to control the stability of the surrounding rock 4, 5, 6. Influence of nearby small kiln cross-border mining and geological structure and other factors, the open-off cut has to be laid below the mining gob when the lower slice coal resources mining. Due to the limitation of the technical level, layered mining technology is adopted for mining in the early stage of resource development 1, 2, 3. The maximum minable thickness of the coal seam is up to 12.5 m in the Yushenfu mining area in Northern Shaanxi, China.

It is comprehensively determined that the thickness of the top coal of open-off cut is set as 3.5 m, the stability is moderate, and the field application shows that the integrity of the top coal is good after support, and the maximum off-layer value is 6 mm, which can satisfy the production requirements. The sinking amount in the two zones is smaller as the thickness of the top coal becomes larger. The deformation changes from exponential to linear to logarithmic in the roof fall risk zone, and it changes from linear to logarithmic in the roof fall warning zone as the number of excavations increases. In the direction of the span of the top coal can be divided into the roof fall risk zone and the warning zone.

In the vertical direction, the top coal of the large open-off cut is divided into mining and excavation disturbance zones under the influence of the upper slice coal mining and the excavation disturbance. The results show that the top coal thickness is greater than 3.4 m without tension cracks. The destabilization extremum conditions of the open-off cut top coal were derived from by elastic–plastic theory, and the optical fibre sensing technology was utilized to monitor the top coal deformation law with different thicknesses (3, 3.5, and 4 m) in the physical similar simulation experiment in the paper. Collins also sees a connection between the rollback of abortion rights to the attacks on gender-affirming care for transgender people.The reserved thickness of top coal has an important influence on the stability of a large section open-off cut under gob in the thick seams slicing mining. I believe they should be able to have an abortion.”Īs Collins sees it, Lynn was explaining - in her own way - the idea of bodily autonomy. 'But I’m thinking of all the poor girls who get pregnant when they don’t want to be, and how they should have a choice instead of leaving it up to some politician or doctor who don’t have to raise the baby. “Personally, I think you should prevent unwanted pregnancy rather than get an abortion. “That’s also why I won’t ever say anything against the abortion laws they made easier a few years ago,” she wrote in the 1976 memoir. She said birth control was as a way for women to protect themselves: “The feelin’ good comes easy now/Since I’ve got the pill/It’s gettin’ dark it’s roostin’ time/Tonight’s too good to be real/Oh, but daddy don’t you worry none/’Cause mama’s got the pill,” she sang.Īnd she did not mince words about her feelings about abortion.

The sinking city achievements