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在铁路或公路的桥樑施工中,经常遇到大、中桥墩台位置处在河流中的情况,过去多采取筑岛沉井的施工方法来解决,如能采用明挖基底方法施工则是比较经济的,如成渝铁路线黄鳝溪中桥改沉井施工为明挖后仅工料费即节省了41.6%。因为明挖基底时工作场地宽阔,有利于集中劳动力进行突击,在时间上比较快速;又不象沉井施工时,技术性较复杂,需要用水泥钢筋等贵重材料。但采用明挖基底方法施工,需要具备一定的条件,否则反将费工费时,甚至因影响安全而不得不中途改变施工方法。这些条件是:
In the construction of railways or roads and bridges, it is often encountered that the large and medium bridge piers are located in rivers. In the past, more construction methods were used to solve the problems such as the construction of open caisson of islands. Economically, such as the construction of the Huangshuixi Zhongqiao Cavity Improvement Pipeline on the Chengdu-Chongqing-Shantou Railway Line, the savings of only the cost of the material after the excavation was 41.6%. Because the work site is open when the base is open-cut, it is conducive to the concentration of the labor force for surprise strikes, and it is relatively fast in time; unlike the construction of the open caisson, it is technically complex and requires the use of expensive materials such as cement reinforcement. However, the use of open-bottom basement construction requires certain conditions; otherwise, it will be time-consuming and even inconvenient to change the construction method due to the impact on safety. These conditions are: