粉煤灰地层大断面连拱隧道超前支护研究

Study on Advanced Support of Large Section Multi-Arch Tunnel in the Layer of Pulverized Coal Ash

在粉煤灰地层中修建隧道往往会因其承载力低、受压沉降大等特点产生施工安全隐患,为防止拱顶产生过大沉降,在实际施工之前往往进行可靠的超前支护。本文以穿越粉煤灰地带的盐坪坝大断面双连拱隧道为工程背景,通过数值模拟分析不同超前支护方式下围岩的变形特征,研究各种超前支护方式对围岩的变形控制效果,最终比选出粉煤灰地层条件下大断面双连拱隧道最合理的超前支护方式。研究结果表明,在超前锚杆或者超前小导管作用下,隧道洞周水平位移呈现拱腰>拱肩>拱脚的变形规律,隧道竖向位移呈现拱顶>拱肩>拱底的变形规律,同时隧道变形主要以竖向变形为主。同时在4.5 m长、120°范围下的超前小导管支护下,左洞隧道拱顶沉降仅为8.73 mm,拱腰收敛仅为1.01 mm,相对来说支护效果最好。

The construction of tunnel in the layer of pulverized coal ash often has construction risks due to its low bearing capacity and large settlement under compression.In order to prevent excessive settlement of vault,reliable advanced support is usually carried out before the actual construction.This paper based on the engineering background of Yanpingba large section double arch tunnel crossing the layer of pulverized coal ash.Making use of numerical simulation to analyze the deformation characteristics of surrounding rock under different advanced support.And then study on the deformation control effect of various advanced support methods on surrounding rock.Eventually,choose the most reasonable advanced support method for the large section double arch tunnel in the layer of pulverized coal ash.The results show that the horizontal displacement around the tunnel presents the deformation law of arch waist>arch shoulder>arch foot and the vertical displacement of the tunnel presents the deformation law of arch top>arch shoulder>arch bottom under the action of advanced bolts or advanced small conduits.Meanwhile,the tunnel deformation is mainly vertical deformation.At the same time,under the advance small conduit support with a length of 4.5 m and a range of 120°,the settlement of the vault of the left tunnel is only 8.73 mm,and the convergence of the waist of the arch is only 1.01 mm,relatively,the effect of this advanced support is the best.