Numerical and theoretical study of load transfer behavior during cascading pillar failure

To further study the load transfer mechanism of roofemulti-pillarefloor system during cascading pillar failure(CPF),numerical simulation and theoretical analysis were carried out to study the three CPF modes according to the previous experimental study on treble-pillar specimens,e.g.successive failure mode(SFM),domino failure mode(DFM)and compound failure mode(CFM).Based on the finite element code rock failure process analysis(RFPA^(2D)),numerical models of treble-pillar specimen with different mechanical properties were established to reproduce and verify the experimental results of the three CPF modes.Numerical results show that the elastic rebound of roofefloor system induced by pillar instability causes dynamic disturbance to adjacent pillars,resulting in sudden load increases and sudden jump displacement of adjacent pillars.The phenomena of load transfer in the roofemulti-pillarefloor system,as well as the induced accelerated damage behavior in adjacent pillars,were discovered and studied.In addition,based on the catastrophe theory and the proposed mechanical model of treble-pillar specimen edisc spring group system,a potential function that characterizes the evolution characteristics of roof emulti-pillarefloor system was established.The analytical expressions of sudden jump and energy release of treble-pillar specimenedisc spring group system of the three CPF modes were derived according to the potential function.The numerical and theoretical results show good agreement with the experimental results.This study further reveals the physical essence of load transfer during CPF of roof emulti-pillarefloor system,which provides references for mine design,construction and disaster prevention.

Bearing characteristics and fatigue damage mechanism of multi-pillar system subjected to different cyclic loads

Aiming to investigate the fatigue damage mechanism and bearing characteristics of multi-pillar system under cyclic loading,a series of axial cyclic loading tests with different cyclic amplitudes were carried out on triple-pillar marble specimens.The acoustic emission(AE)and digital image correlation(DIC)were jointly applied to monitoring and recording damage evolution and failure behavior of each pillar,which reproduced the cataclysmic instability process of underground pillar groups.Experimental results indicated that the cyclic amplitude exceeding the threshold of damage initiation weakened the resistance to deformation,resulting in obvious release of dissipated energy and the reduction of bearing capacity.Conversely,after low-amplitude cyclic loading,both the pre-peak bearing capacity and the post-peak ductility of the pillar system increased due to the compaction of initial defects,indicating that the peak bearing capacity was closely related to the extent of pre-peak fatigue damage.The axial strain of each pillar was measured by DIC virtual extensometer to present the damage extent during cyclic loading phase.Meanwhile,fracture evolution of typical load drop points was also characterized by transverse strain fields(εxx),and observations showed that the damage extent of key pillar undergoing high-amplitude cyclic loads was more serious and violent,accompanied by the ejection of rock debris and loud noises.

Interconnectivity in the Region of Eurasia:Mongolia’s Presence in the SCO(Shanghai Cooperation Organization)

The Shanghai Cooperation Organization(SCO)was formed in 2001 after breakdown of the socialist system and the Soviet Union as a new form of cooperation between former socialist countries in Eurasian region.Mongolia joined the SCO in 2005 with an observer member status.Since 2007,Presidents of Mongolia began to participate every year to the Summit of the heads of SCO member states.By the initiative of Mongolian President,in 2014 the tripartite format of the meetings of the leaders of three countries:Russia,China,and Mongolia were established.In June 2016,during the third meeting of the leaders of Russia,China,and Mongolia in Tashkent(Uzbekistan),“The Russia-China-Mongolia Economic Corridor Program”document was signed.This program is aiming to develop the infrastructure of three countries,ensuring the competitiveness of products on the world market,and strengthening the Eurasian integration.The content of this program is combining the main ideas of Chinese“Belt-Road”megaproject,Russian initiative for developing of Eurasian economic integration and Mongolian“Steppe Road”project.The main goal of the“Steppe Road”initiative is to involve Mongolia to become the transit territory for transportation of natural gas,oil,and other products between Russia and China.In conclusion,the author gives some comments regarding the issue of full membership status of Mongolia to the international organization—SCO.