Present support theories contain a number of shortcomings in the designation of fractured roof bolt parameters of rectangular or trapezoidal coal roadways.Roof fall accidents occur easily in this kind of roadway.Based...Present support theories contain a number of shortcomings in the designation of fractured roof bolt parameters of rectangular or trapezoidal coal roadways.Roof fall accidents occur easily in this kind of roadway.Based on the Bossinesq equations and the Mohr strength theory,we propose a theory of an anchored cluster structure for fractured roofs and have investigated the formation of such an anchored cluster structure,its self stability mechanism and mechanical properties.The results show that an anchor and the surrounding fractured rock can form a string-like supporting structure,referred to as the structure of an anchored cluster for rational bolt parameters.Not only can the structure maintain its own stability,but as well undertake the load of the overlying strata.The designated support parameters,based on anchored cluster theory can overcome the shortcomings of other support theories applied to a fractured roof of rectangular roadways or could not be calculated.Our anchored cluster theory can provide a theoretical basis for the design of support for rectangular fractured roofs.Furthermore,the theory will help to reduce the probability of roof fall accidents caused by local fractured rock blocks,which can destroy a supporting structure.展开更多
The‘twin cities’district of Rawalpindi–Islamabad is among the most endangered seismic regions in Pakistan,with the seismic hazard assessed(0.32 g)to intensity IX MMI for a 475-year return period.A seismic hazard ma...The‘twin cities’district of Rawalpindi–Islamabad is among the most endangered seismic regions in Pakistan,with the seismic hazard assessed(0.32 g)to intensity IX MMI for a 475-year return period.A seismic hazard map for Rawalpindi–Islamabad is presented herein,based on 85 shear-wave velocity(VS)profiles obtained through geophysical H/V measurements and from the geological map of the region.Relationships between the average top thirty-meter shear-wave velocities(VS30)and surficial geological units have been determined.The peak ground acceleration(PGA)maps for 150,475 and 2475-year return periods were converted into a seismic intensity map.Intensity increments for different soils were used to compute PGA values for 150,475 and 2475-year return periods.Sites located on softer ground experienced a higher degree of damage from moderate earthquakes.Due to the presence of soft clay or liquefiable soil and lateral spreading,a few locations may be classified as hybrid sites class C and D.This map is a critical step in facilitating code-based site classification and seismic design throughout Rawalpindi–Islamabad.Although the seismic hazard map based on seismic intensities is no longer used in engineering geology,it is still important in seismological analysis and for civil protection purposes.展开更多
基金provided by the National Natural Science Foundation of China (No.50774077)the Ministry of Education for New Century Excellent Talent Support Program of China (No.NCET-06-0475)the Science Foundation for Youth Scholar of China University of Mining and Technology (Beijing) (No.2009QZ01)
文摘Present support theories contain a number of shortcomings in the designation of fractured roof bolt parameters of rectangular or trapezoidal coal roadways.Roof fall accidents occur easily in this kind of roadway.Based on the Bossinesq equations and the Mohr strength theory,we propose a theory of an anchored cluster structure for fractured roofs and have investigated the formation of such an anchored cluster structure,its self stability mechanism and mechanical properties.The results show that an anchor and the surrounding fractured rock can form a string-like supporting structure,referred to as the structure of an anchored cluster for rational bolt parameters.Not only can the structure maintain its own stability,but as well undertake the load of the overlying strata.The designated support parameters,based on anchored cluster theory can overcome the shortcomings of other support theories applied to a fractured roof of rectangular roadways or could not be calculated.Our anchored cluster theory can provide a theoretical basis for the design of support for rectangular fractured roofs.Furthermore,the theory will help to reduce the probability of roof fall accidents caused by local fractured rock blocks,which can destroy a supporting structure.
文摘The‘twin cities’district of Rawalpindi–Islamabad is among the most endangered seismic regions in Pakistan,with the seismic hazard assessed(0.32 g)to intensity IX MMI for a 475-year return period.A seismic hazard map for Rawalpindi–Islamabad is presented herein,based on 85 shear-wave velocity(VS)profiles obtained through geophysical H/V measurements and from the geological map of the region.Relationships between the average top thirty-meter shear-wave velocities(VS30)and surficial geological units have been determined.The peak ground acceleration(PGA)maps for 150,475 and 2475-year return periods were converted into a seismic intensity map.Intensity increments for different soils were used to compute PGA values for 150,475 and 2475-year return periods.Sites located on softer ground experienced a higher degree of damage from moderate earthquakes.Due to the presence of soft clay or liquefiable soil and lateral spreading,a few locations may be classified as hybrid sites class C and D.This map is a critical step in facilitating code-based site classification and seismic design throughout Rawalpindi–Islamabad.Although the seismic hazard map based on seismic intensities is no longer used in engineering geology,it is still important in seismological analysis and for civil protection purposes.
