Study On The Mechanical Model Of Rotational Speed Of Key Stratum And Its Application

The influence mechanisms of rotational speed of hinged blocks of voussoir beam structure on weighting events in stopes and the critical height of overlying key strata affecting weighting events are one of the most important but unsolved problems in the research field of the ground pressure in stopes.On the one hand,how the rotational speed of hinged blocks of the lowest voussoir beam structure affects the weighting events in stopes,and the influence factors of the rotational speed of hinged blocks of the lowest voussoir beam structure are not clear yet.On the other hand,it is not clear whether the relative relationship of size between the rotational speeds of hinged blocks of the adjacent-two voussoir beam structure affects the rotational speed of hinged blocks of the lowest voussoir beam structure and the load acting on supports.The study on abovementioned issues is of great significance to determine the reasonable working capacity of the support.For this purpose,the mechanical model of rotational speed of hinged blocks of voussoir beam structure is established.And the influence mechanisms of rotational speed of hinged blocks of voussoir beam structure on weighting events and the critical height of key strata affecting weighting events based on this mechanical model are studied by means of theoretical analysis,simulation experiment and field measurement.The mechanical model of rotational speed of hinged blocks of voussoir beam structure is established and the rotational speed equation of hinged blocks of the voussoir beam structure is derived based on the fixed axis rotation theorem,elastoplastic theory and kinematics principle.The larger the overlying load on the hinged blocks of voussoir beam structure,the shorter the length of the block and the faster the rotational speed.For hinged blocks of the lowest voussoir beam structure,the faster the rotational speed,the faster the increase of support resistance,and the greater the shrinkage of the hydraulic column as well as the stronger the ground pressure appears.At the same time,when the rotational speed of hinged blocks of the upper voussoir beam structure is greater than that of hinged blocks of the lower voussoir beam structure,there will be an extra compressive cladding effect generated on the hinged blocks of the lower voussoir beam structure,and the rotational speed of hinged blocks of the lower voussoir beam structure will increase,and further increase the intensity of weighting events.The results have been verified by similar physical simulation experiments in the laboratory.Based on the rotational speed equation of hinged blocks of voussoir beam structure and the stability analysis of voussoir beam structure,the load transfer criterion of the adjacent-two voussoir beam structure is revealed,and the calculation method of transferring load is provided.According to the rotational speed equation of hinged blocks of voussoir beam structure,conservation of kinetic energy and conservation of momentum,the change of rotational speed before and after the interaction between the adjacent-two voussoir beam structure and the increment of load layer thickness corresponding to the increment of rotational speed are obtained.The compressive cladding effect from hinged blocks of upper voussoir beam structure on the hinged blocks of the lower voussoir beam structure generated in the rotational process is illustrated in the form of "load layer thickness increment",and the influence mechanism and degree of the rotational speed of hinged blocks of the upper voussoir beam structure on weighting events in stopes and the support load are quantified.The determination method and discriminant process of the critical height of key strata affecting weighting events are proposed.Based on the load transfer criterion of adjacent voussoir beam structure in overburden taking two-layer voussoir beam structure existed in overburden as an example,the combination types of rotational motion of two-layer voussoir beam structure are classified and the number of voussoir beam structure for diverse combination types affecting the load on supports,i.e.the range of key strata whose fracture and movement affecting the load on supports,is explained.Taking 52304 working face of Daliuta coal mine in Shendong coalfield and 8203 working face of Tongxin coal mine in Datong coalfield as examples,the corresponding critical heights of key strata affecting weighting event are theoretically analyzed,which are also verified by the measured results.