Plastic zone analysis and support optimization of shallow roadway with weakly cemented soft strata

Based on a shallow roadway with weakly cemented soft strata in western China, this paper studies the range and degree of plastic zones in soft strata roadways with weak cementation. Geological radars were used to monitor the loose range and level of surrounding rocks. A mechanical model of weakly cemented roadway was established, including granular material based on the measured results. The model was then used to determine the plastic zone radium. The predicted results agree well with measured results which provide valuable theoretical references for the analysis of surrounding rock stability and support reinforcing design of weakly cemented roadways. Finally, a combined supporting scheme of whole section bolting and grouting was proposed based on the original supporting scheme. It is proved that this support plan can effectively control the deformation and plastic zone expansion of the roadway surrounding rock and thus ensure the long-term stable and safe mining.

Experimental study on failure mechanism of soft rock-coal bodies in abandoned mines under cyclic dynamic loading

During the construction and operation of a pumped storage power station in an abandoned mine,the soft rockcoal body structure,comprising the roof and the residual coal pillars,encounters a complex stress environment characterized by cyclic loads.The study of its failure mechanism under cyclic dynamic loading holds significant theoretical and practical importance to stay the safety and stability of the abandoned mine pumped storage power station.In this paper,we take“roof-residual coal pillar”soft rock-coal combinations with different percentages of rock as the research object,and study their mechanical properties,failure mechanism,energy evolution characteristics and acoustic emission distribution characteristics through cyclic dynamic loading experiments.The results of the experiment indicate that:(1)Both weak cyclic dynamic loading and high rock percentage enhance the deformation resistance of soft rock-coal combinations.Under low-disturbance horizontal cyclic loading,its peak strength and modulus of elasticity increase with increasing rock percentage.(2)Under low-disturbance horizontal cyclic loading,an increasing trend is observed in the average total strain energy density,dissipation energy density,and elastic energy density of the combinations as the percentage of rock increases.(3)Under lowdisturbance horizontal cyclic loading,as the percentage of rock increases in the soft rock-coal combinations,the degree of failure in the rock body part progressively intensifies,while the destruction of the coal portion progressively decreases.(4)The large number of acoustic emission signals are generated at the instant of destabilization and destruction of the coal-rock combinations,mainly dominated by the signals generated by the destruction of the coal body.Acoustic emission counts and absolute energy at key point N2 decrease as the percentage of rock increases.The b value is primarily distributed in the cyclic dynamic loading stage and the failure stage,both displaying zones of sudden increase and sudden decrease in b value.

A NOVEL AERONAUTICAL STATIC INVERTER WITH HIGH FREQUENCY PULSE DC LINK

A new combined soft switching technique and a novel topology of aeronautical static inverter with high frequency pulse dc link are proposed in this paper, namely an electrical isolated converter can realize soft switching of two stage cascade converters. It lays technical foundation for high power density, high efficiency and low cost aeronautical static inverter. The operation and design approach of this topology are carefully analyzed and studied. The validity of this topology is verified by simulation and test.