小断面铁路隧道凿岩台车钻孔施工光面爆破技术研究

Smooth Blasting Technique of a Small-section Railway Tunnel Constructed with Drilling Jumbos

Ⅳ级围岩小断面隧道全断面施工如何增加进尺长度、控制围岩超欠挖、减少围岩扰动,一直是施工过程中重要的技术难题,尤其是采用凿岩台车施工,因受设备结构(推进梁过长)和开挖工艺(初期支护紧跟掌子面)的影响,容易造成开挖进尺较短和超挖量过大的问题,导致工期延误和施工成本增加。同时超挖控制不到位,初期支护背后容易形成空洞,对隧道结构稳定产生一定影响。基于此,以某铁路隧道爆破开挖为工程背景,通过改进原有爆破方案,多次开展现场光面爆破试验,不断优化光爆参数,并在周边孔施工中采用内层长孔加外层短孔同时起爆的方式,提出了一套适合于Ⅳ级围岩小断面铁路隧道带钢架施工的光面爆破方案。应用效果表明:隧道进尺由原来每循环的2.4~2.6 m增加到3.0~3.3 m,线性平均超挖量由原来的0.35~0.4 m减少到0.2~0.25 m,确保了隧道开挖轮廓线平整,有利于二次衬砌的施工质量。

As for the full-face construction of small-section tunnels in surrounding rocks of grade IV,increasing the advance length,controlling the over-and under break of surrounding rocks and reducing the disturbance to surrounding rock are always the important technical problems during construction process.Particularly in the case of using rock drilling jumbos,it is easy to cause the problems of short advance length and excess over-break due to the influence of equipment structure(the feed beam is too long)and excavation technology(the initial support is close to the tunnel face),which would result in the delay of construction period and the increase of construction cost.Furthermore,when the over-break can not be controlled,it is easy to form a cavity behind the initial support,which has a certain impact on the stability of the tunnel structure.In view of this,taking the blasting excavation of a railway tunnel as the engineering background,this paper improves the original blasting scheme,carries out on-site smooth blasting tests,and constantly optimizes the smooth blasting parameters.By using the method of simultaneous initiation of inner long holes and outer short holes in construction of peripheral holes,a set of smooth blasting scheme is proposed,which is suitable for construction of a small section railway tunnel with steel frame in grade IV surrounding rock.The application results show that the tunnel advance length is increased from the original 2.4~2.6 m to 3~3.3 m per cycle,and the linear average over-break is reduced from the original 0.35~0.4 m to 0.2~0.25 m,ensuring the flatness of the tunnel excavation contour and the construction quality of the secondary lining.