大跨软弱围岩隧道三岔口施工技术

结合扩建金华至温州高速铁路某双线隧道的修建情况，介绍了在大跨铁路隧道软弱围岩段横洞进主洞三岔口施工关键技术。即采用单侧小导坑（3m×3m）进入主洞洞身进行开挖，于主洞中线处达到拱顶高程，逐步扩挖至标准断面，并进行初期支护，再依次落底施工下台阶，直至全断面成型；交岔口段横洞设置10榀异形拱架及门架横梁，以保证施工安全，同时门架横梁作为主洞钢架落脚支撑。通过采取上述措施保证了洞室结构的整体稳定，有效避免了安全事故的发生。

Construction Techniques for the Intersection of a Large-Span Tunnel in Soft Surrounding Rock

With the construction of a certain double-track tunnel of the extension project of the Jinhua-Wenzhou High-speed Railway as a practical example,introduced in the paper are the key construction techniques for an intersection of a large-span railway tunnel in soft rock section with the adit going into the main cave. The excavation is performed with the unilateral small heading （3 m × 3 m） going into the main cave,and when the midline of the main cave reaches the crown elevation,it will be gradually expanded to the standard section with the initial support provided,following which the lower construction benches will be realized step by step, until the whole cross-section is formed;at the lateral hole of the intersection, 10 different-shaped arches and the door-frame beams are erected so as to ensure the safety of construction. At the same time the door-frame beams are used as the support upon which the main steel supports of the main cave are laid. With those measu＇res taken, the overall stability of the tunnel structure is ensured, with accidents in safety effectively avoided.