Abstract: A system and a method for monitoring overlying roof rock and coal pillar in gob-side entry are provided. The system includes top monitoring stations, coal pillar comprehensive monitoring stations, roof stress monitoring stations, and a master computer. Top monitoring stations are arranged in the crossheading to monitor the working face, coal pillar comprehensive monitoring stations are arranged in the upper roadway of the lower coal seam working face to monitor the coal pillars, and roof stress monitoring stations are arranged in the mining area main roadway to monitor the coal pillars. Monitoring the stress and deformation distribution of coal pillars in the goaf and the movement and failure process of overburden strata structure through the master computer control each monitoring station. The monitoring stations ensure that the overburden strata movement monitoring stations are still in working condition after the goaf is formed by mining in the working face.

Abstract: Various configurations of play yards and play yard mattresses are presented herein. Each of the play yards and play yard mattresses is light weight and breathable, yet has sufficient structural integrity to support an enclosed child or infant. In some embodiments, the play yards and mattresses may be collapsible. In other embodiments, play yards feature a mattress placed above a base assembly, such that an interior space is formed between the mattress and base assembly, said interior space being substantially void of any articles or other materials. In another embodiment, play yards feature a base assembly having a centrally located hub assembly comprising a release button and sliding pins.