Search

Gypsum mines are generally exploited using room and column mining methods. Gypsum tends to become soft when encountering water, which often causes multiple geological disasters of ground subsidence. In Pizhou, Jiangsu Province, as of April 2023, a total of 35 ground collapses in 28 locations occurred, most of which were point shaped collapses with a diameter of less than 50m, and pumping type collapses are relatively rare. Taking the gently inclined gypsum mine in Pizhou as an example, the MatDEM method was introduced to conduct numerical simulation and mechanism analysis research. The results show that the pumping collapse of the gypsum mine caused groundwater to enter the mine pit, weakening the strength of the gypsum, causing secondary roof fall, blocking and ultimately stopping the channel collapse. After water filling, the overall stability of the goaf became worse, which is prone to induce secondary collapse. In response to the current situation, relocation and avoidance measures are proposed as well as monitoring, early warning, and engineering governance measures for prevention and control. [ABSTRACT FROM AUTHOR]

The portable air purifier can't uniformly remove the PM2.5 at each personnel position in a room, which causes the unevenness of PM2.5 distribution. In order to achieve priority purification of PM2.5 at the personnel position, experiments and simulations were conducted here to determine the time required for the purifier to reduce the PM2.5 concentration in a room to 15 μg/m3 (hereafter referred to as the purification time) in each area of the room at different wind speeds. SPSS was used to conduct regression analysis of the simulated data and determine the contribution rate of each impact factor, and assess the prediction model for the purification time. This prediction model can be used to calculate the purification time of any location in rooms of different sizes. The results show that, there was a nonlinear relationship between the purification time and impact factors, however, when the purifier wind speed is determined, PM2.5 purification time shows a linear relationship with the remaining impact factors. The contribution rate of the initial PM2.5 concentration to the purification time was largest. Increasing the wind speed will further increase the contribution rate of the initial PM2.5 concentration, but reduce the contribution rate of the air supply angle, personnel distance, and personnel angle. [ABSTRACT FROM AUTHOR]