为了适应国民经济发展的需要,营业铁路的更新改造要求扩建、增建桥梁涵洞的数量越来越多,规模也愈来愈大。往常增建小孔径的涵渠,多采用既有线吊(扣)轨梁维持行车、支撑开挖。较大孔径的涵洞和桥梁则多采用便 In order to meet the needs of the development of the national economy, the renovation and transformation of commercial railways requires the expansion of the number of additional culverts and the increasing scale of bridges and culverts. Often increase the construction of small-aperture culverts, more use of existing line hanging (buckle) rail beam to maintain driving support excavation. Larger aperture culverts and bridges are more used