In order to access remote reserve areas, some U.S.coal mines have to maintain aged underground entries for a great distance.However, high humidity, warm temperature, and time dependent deterioration can cause progress...In order to access remote reserve areas, some U.S.coal mines have to maintain aged underground entries for a great distance.However, high humidity, warm temperature, and time dependent deterioration can cause progressive roof deterioration and unexpected roof falls, and pose a great challenge to ground control engineers.With an active belt structure in place and limited space, re-bolting becomes very costly, less effective,and, sometimes, impractical and unfeasible.To gain long-term entry stability and serviceability, operators typically rehabilitate the aged belt entries by installing standing steel set supports.In the last several years,Keystone Mining Services, LLC,(KMS) has assisted many coal mines with their belt entry rehabilitation projects, evaluated the ground condition of various aged belt entries, and designed different standing steel set support systems.This paper presents a case study of a large-scale roof fall that occurred at an aged belt entry in a mine located in an eastern coalfield, analyzes root causes of excessive deformation of square sets that were installed in an adjacent entry, evaluates the adequacy of an existing rehabilitation square set, and develops remedial recommendations for future rehabilitation practice.Based on the case study, the paper outlines design guidelines for rehabilitation steel sets that include field evaluation, engineering considerations, design assumptions, steel structural analysis, and field installation quality control.展开更多
In the context of China’s proactive implementation of the Belt and Road Initiative(BRI),unraveling the BRI’s effect on corporate behavior is of vital importance to China’s policymaking on overseas investment.With t...In the context of China’s proactive implementation of the Belt and Road Initiative(BRI),unraveling the BRI’s effect on corporate behavior is of vital importance to China’s policymaking on overseas investment.With the BRI’s enactment as a quasi-natural experiment,this paper employs the difference in differences(DID)method to investigate the BRI’s effect on the financing constraint for Chinese enterprises.Our study finds that the BRI’s implementation has significantly reduced financing constraints for BRI enterprises,and the effect is more significant for emerging advantageous industries and export-oriented node cities.展开更多
文摘In order to access remote reserve areas, some U.S.coal mines have to maintain aged underground entries for a great distance.However, high humidity, warm temperature, and time dependent deterioration can cause progressive roof deterioration and unexpected roof falls, and pose a great challenge to ground control engineers.With an active belt structure in place and limited space, re-bolting becomes very costly, less effective,and, sometimes, impractical and unfeasible.To gain long-term entry stability and serviceability, operators typically rehabilitate the aged belt entries by installing standing steel set supports.In the last several years,Keystone Mining Services, LLC,(KMS) has assisted many coal mines with their belt entry rehabilitation projects, evaluated the ground condition of various aged belt entries, and designed different standing steel set support systems.This paper presents a case study of a large-scale roof fall that occurred at an aged belt entry in a mine located in an eastern coalfield, analyzes root causes of excessive deformation of square sets that were installed in an adjacent entry, evaluates the adequacy of an existing rehabilitation square set, and develops remedial recommendations for future rehabilitation practice.Based on the case study, the paper outlines design guidelines for rehabilitation steel sets that include field evaluation, engineering considerations, design assumptions, steel structural analysis, and field installation quality control.
基金Youth Program of the National Natural Sciences Foundation of China (NSFC) “Study on Underwriters’ Behaviors in the Full Life-Cycle of Corporate Bonds” (Grant No. 71802085)Youth Program of the National Humanities and Social Sciences Foundation “Study on the Promotion Incentives of SOE Executives and the Concealment of Corporate Bad News: Theoretical and Empirical Analysis” (Grant No. 18YJC630211)Youth Program of the Humanities and Social Sciences Research Foundation of the Ministry of Education “Study on the Economic Consequences of Corporate Investment and Financing Maturity Mismatch: Analysis Based on a Corporate Risk Perspective” (Grant No. 19YJC630232)
文摘In the context of China’s proactive implementation of the Belt and Road Initiative(BRI),unraveling the BRI’s effect on corporate behavior is of vital importance to China’s policymaking on overseas investment.With the BRI’s enactment as a quasi-natural experiment,this paper employs the difference in differences(DID)method to investigate the BRI’s effect on the financing constraint for Chinese enterprises.Our study finds that the BRI’s implementation has significantly reduced financing constraints for BRI enterprises,and the effect is more significant for emerging advantageous industries and export-oriented node cities.
