大断面隧道下穿既有高压输电铁塔施工方案比选及其应用

 李家冲大断面公路隧道下穿既有高压输电铁塔，施工风险高。在风险分析的基础上，提出可能的应对措施，通过建立高压输电铁塔与大断面隧道施工相互作用的三维数值模型，对注浆加固山体后采用双侧壁导坑法开挖、H型框架梁加固塔基后三台阶留核心土法开挖、以及塔基托换后三台阶留核心土法开挖等方案进行比选，提出采用H型框架梁将高压输电铁塔塔基连成整体的加固方案。数值计算及现场实施效果表明：采用H型框架梁对铁塔基础进行加固，铁塔基础成为整体结构后再进行大断面隧道三台阶留核心土开挖，可有效控制铁塔的累计沉降及不均匀沉降，铁塔受力与变形均在容许的范围之内，在保证铁塔和隧道施工安全的同时，加快了施工进度，技术经济效果非常明显，可供类似工程参考。

CONSTRUCTION SCHEME CHOICE OF LARGE-SPAN TUNNELS UNDER-PASSING HIGH VOLTAGE TRANSMISSION TOWER AND ITS APPLICATION

Lijiachong large-span tunnel is excavated below the existing high-voltage transmission tower,and the risk of tunnel construction is very high.Several possible schemes for tunnel construction and foundation reinforcement of high-voltage transmission tower were presented based on risk analysis;and comparison among tunnel excavation using two-side wall drift heading method after mountain grunting consolidation,tunnel excavation using three bench method with the core of surrounding rock remained after tower foundation were reinforced with H-shaped framed girders,and tunnel excavation using three bench method with the core of surrounding rock remained after tower foundation were underpinned are introduced through a 3D numerical analysis of the interaction between tunnel construction and high-voltage transmission tower.The scheme of using H-shaped framed girders to connect the foundations as a whole is adopted.It is shown that after the pile foundations were connected with H-shaped framed girders,the foundations worked as a whole,tunneling using three bench method with the core of surrounding rock remained became safety.Cumulative settlement and uneven settlement were well controlled,and the forces and deformations of the tower were in the allowable ranges.By reinforcing the tower foundations using the H-shaped framed girders,Lijiachong tunnel safely passed beneath the transmission tower;and good economical and technical results are obtained.The results can provide a reference for similar projects.