跨越通航河渠的桥梁,桥下净空问题不论在公路、铁路及其他跨河构筑物的建设上都是一个不可忽视的重要问题,且涉及面甚广。具体地说,一是通航桥孔的跨度问题,二是通航桥孔在设计最高通航水位时的最小桥下净高问题,三是航道等级和设计最高通航水位的采用频率问题。 由于过去普遍存在标准宁高勿低的思想,以为河道等级定高些,设计最高通航水位定高些,总比用低了好,过分强调要求桥下畅通无阻,所以有些省(区)对六级以下河渠多以六级航道标准作为最低标准。因而提出的净空要求不免有所偏高,给桥梁建设增加困难,投资及使用效果不尽合理。 本文提出了一些问题,这些问题如何解决?希望从事公路、水运基本建设的同志共同探讨,使交通事业在四化建设中稳步前进。 Crossing the navigation channel of the bridge, under the bridge headroom problems in the construction of roads, railways and other structures across the river are an important issue that can not be ignored, and involves a wide range. Specifically, the first is the span of navigable bridge holes. The second is the minimum height under the bridge for navigable bridge holes when designing the highest navigable water level. The third is the frequency of adoption of waterway classes and the design of the highest navigable water level. Due to the widespread prevailing standards of high and low standards in the past, it is thought that the grade of river courses will be higher and the highest designed navigable water level will be higher and lower than that of lower ones. Too much emphasis is placed on the unobstructed under the bridge, so some provinces (districts) Below the level of canal more than six waterway standards as a minimum standard. Therefore, the proposed clearance requirement can not help but be somewhat high, which makes it difficult for the construction of the bridge to increase its investment and use efficiency. This article raises some questions on how to solve these problems. We hope that comrades engaged in the basic construction of highways and waterways will jointly explore ways to make transportation progress steadily in the four modernizations.