Zhu Ting, Liu Yuanming
Faculty of Civil Engineering, Guizhou University, Guiyang, 550025, China.
Sci Rep. 2023 Sep 22;13(1):15812. doi: 10.1038/s41598-023-42458-7.
The double sidewall guide pit and centre cross diagram (CRD) methods are often used for the construction of large-section tunnels through water-rich fault fracture zones due to their long construction time and high construction cost. To shorten the construction period and save costs, the top heading and benching method (HB) and centre diaphragm (CD) can be chosen for construction. The construction parameters of the step and CD methods are optimized to ensure the surrounding rock stability and tunnel safety. By relying on the Tongzi Tunnel, we simulate the excavation of different step heights in the construction of the top heading and benching method (HB) and CD methods through numerical simulation, the laws of tunnel vault settlement, and changes in the surrounding rock stress, initial support axial force, bending moment and safety factor. The study shows that as the height of the upper step increases, the settlement of the vault and the convergence of the periphery increase, the initial support safety factor decreases, and the plastic zone of the surrounding rock increases at 30 m from the target face. The step height for the top heading and benching method (HB) of construction is optimized as follows. The ratios of the upper, middle and lower step heights are 0.45H, 0.35H and 0.2H, respectively. The CD method construction step height is optimized to the left (right) upper and left (right) lower step height ratios of 0.5H and 0.5H, respectively.
双侧墙导坑法和中隔壁法（CRD法）由于施工工期长、施工成本高，常用于穿越富水断层破碎带的大断面隧道施工。为缩短工期、节约成本，可选用正台阶法（HB法）和中隔墙法（CD法）进行施工。对台阶法和CD法的施工参数进行优化，以确保围岩稳定性和隧道安全性。依托桐梓隧道，通过数值模拟对正台阶法（HB法）和CD法施工中不同台阶高度的开挖、隧道拱顶沉降规律以及围岩应力、初期支护轴力、弯矩和安全系数的变化进行模拟。研究表明，随着上台阶高度的增加，距掌子面30m处拱顶沉降和周边收敛增大，初期支护安全系数降低，围岩塑性区增大。正台阶法（HB法）施工的台阶高度优化如下：上、中、下台阶高度比分别为0.45H、0.35H和0.2H。CD法施工台阶高度优化为左（右）上、左（右）下台阶高度比分别为0.5H和0.5H。
