为了解决盾构在城市环境中长距离掘进时刀盘修复难题，结合北京铁路地下直径线工程的成功经验，阐述带压动火的整体思路，介绍带压动火作业的现场实施情况，分析在焊接过程中保障作业空间安全、气体环境的防爆安全、人员健康和作业可控的技术要求，研究高压焊接技术涉及的焊接方法、焊接设备、焊接材料和焊接工艺等系列问题，形成了完整的技术体系，并取得了良好的应用效果。

During the construction of Beijing underground rail transit line, the cutterhead of the shield machine has to be repaired in the urban area. In the paper, the concept of dynamic fire under pressure is presented, the site conditions of operation under dynamic fire are described, the technical requirements for the safety, health and environment of the welders are analyzed, the welding method, welding equipment, welding materials and welding techniques under pressure are studied, thus a complete technological system is established. In the end, satisfactory effect has been achieved in the project.