During shield tunneling in highly abrasive formations such as sand–pebble strata,nonuniform wear of shield cutters is inevitable due to the different cutting distances.Frequent downtimes and cutter replacements have ...During shield tunneling in highly abrasive formations such as sand–pebble strata,nonuniform wear of shield cutters is inevitable due to the different cutting distances.Frequent downtimes and cutter replacements have become major obstacles to long-distance shield driving in sand–pebble strata.Based on the cutter wear characteristics in sand–pebble strata in Beijing,a design methodology for the cutterhead and cutters was established in this study to achieve uniform wear of all cutters by the principle of frictional wear.The applicability of the design method was verified through three-dimensional simulations using the engineering discrete element method.The results show that uniform wear of all cutters on the cutterhead could be achieved by installing different numbers of cutters on each trajectory radius and designing a curved spoke with a certain arch height according to the shield diameter.Under the uniform wear scheme,the cutter wear coefficient is greatly reduced,and the largest shield driving distance is increased by approximately 47%over the engineering scheme.The research results indicate that the problem of nonuniform cutter wear in shield excavation could be overcome,thereby providing guiding significance for theoretical innovation and construction of long-distance shield excavation in highly abrasive strata.展开更多
Chinese People's Liberation Army,launched its new round of uniforms change. Besides snazzy clothes and lavish exhibitions,the military wear is always related to war either in the past,now or in the future. Could P...Chinese People's Liberation Army,launched its new round of uniforms change. Besides snazzy clothes and lavish exhibitions,the military wear is always related to war either in the past,now or in the future. Could PLA new dress mean a lot more…?展开更多
It wasn’t too long ago that the vast majority of Chinese wore nondescript Mao-style coats and caps in muted grays and blues-bringing uniformity to a population where individual dress styles were frowned upon. Tim...It wasn’t too long ago that the vast majority of Chinese wore nondescript Mao-style coats and caps in muted grays and blues-bringing uniformity to a population where individual dress styles were frowned upon. Times and tastes have changed. Today展开更多
基金Beijing Postdoctoral Research Activity Funding Project,Grant/Award Number:2022-ZZ-097Beijing Municipal Natural Science Foundation,Grant/Award Number:8182048。
文摘During shield tunneling in highly abrasive formations such as sand–pebble strata,nonuniform wear of shield cutters is inevitable due to the different cutting distances.Frequent downtimes and cutter replacements have become major obstacles to long-distance shield driving in sand–pebble strata.Based on the cutter wear characteristics in sand–pebble strata in Beijing,a design methodology for the cutterhead and cutters was established in this study to achieve uniform wear of all cutters by the principle of frictional wear.The applicability of the design method was verified through three-dimensional simulations using the engineering discrete element method.The results show that uniform wear of all cutters on the cutterhead could be achieved by installing different numbers of cutters on each trajectory radius and designing a curved spoke with a certain arch height according to the shield diameter.Under the uniform wear scheme,the cutter wear coefficient is greatly reduced,and the largest shield driving distance is increased by approximately 47%over the engineering scheme.The research results indicate that the problem of nonuniform cutter wear in shield excavation could be overcome,thereby providing guiding significance for theoretical innovation and construction of long-distance shield excavation in highly abrasive strata.
文摘Chinese People's Liberation Army,launched its new round of uniforms change. Besides snazzy clothes and lavish exhibitions,the military wear is always related to war either in the past,now or in the future. Could PLA new dress mean a lot more…?
文摘It wasn’t too long ago that the vast majority of Chinese wore nondescript Mao-style coats and caps in muted grays and blues-bringing uniformity to a population where individual dress styles were frowned upon. Times and tastes have changed. Today
