大跨拱桥基坑开挖的深孔光面爆破技术

Deep Hole Smooth Blasting Technology for Foundation Pit Excavation of Long-span Arch Bridge

为控制开挖轮廓的成型效果与减弱爆破作用对保留岩体的扰动,以跨金沙江特大拱桥云南岸约51 m深且一次开挖约20 m深的基坑爆破为工程背景,主爆孔采用逐孔起爆加强松动爆破设计与施工,周边孔采用光面爆破设计与施工,总结了一套适用于深陡拱桥基坑开挖的深孔光面爆破技术,并对光爆孔内气体作用过程、孔壁膨胀压力和爆破损伤范围进行理论计算与分析。爆破结果表明:采用深孔光面爆破技术可以形成平整的开挖轮廓面,相对完整岩体的半孔率可达90%以上,相对破碎岩体的孔痕保留较少但超欠挖依然可控,极大地降低了岩壁表面的应力集中;光面爆破装药段附近不会形成粉碎区,且保留岩体的最大损伤范围约49 cm,充分保证了岩壁稳定与施工安全;光面爆破施工过程中采取台阶底部开挖面缓倾向于临空面、棉质细绳绑扎药卷牵引装药以及每间隔5~7个光爆孔设置孔内起爆雷管与孔外传爆雷管等工程措施以确保爆破的可靠性、安全性及经济性,取得了良好的社会和经济效益,同时也对类似工程具有一定的指导和借鉴作用。

In order to control the forming effect of excavation profile and reduce the disturbance of preserving rock mass caused by blasting,the foundation pit blasting at the Yunnan bank of the large arch bridge across Jinsha river,whose total depth is about 51 m and one-time excavation depth is about 20 m,is taken as the engineering background.Reinforced loose blasting with hole-by-hole initiation was applied to the main blasting holes and smooth blasting was used for the contour holes.A kind of deep hole smooth blasting technology which can be applied to foundation pit excavation of the deep and steep arch bridge is presented.In addition,the action process of gas,the expansion pressure at the hole wall and the damage range of the smooth blasting hole were theoretically calculated and analyzed.The blasting results show that a flat excavation profile,with more than 90%half-hole ratio of relatively intact rock mass and less reserved hole marks of relatively cracked rock mass whose overbreak and underbreak can still be controlled,can be formed by using the deep hole smooth blasting technology,which greatly reduces the stress concentration on the rock wall surface.The crushing zone will not be formed near the charge section in the smooth blasting and the maximum damage range of the reserved rock mass was about 49cm,which fully ensured the rock wall stability and construction safety.In the process of smooth blasting construction,engineering measures were also taken to ensure the reliability,safety and economy,including slowly tilting the excavation surface at the bottom of the bench to the free surface,tying the explosive charge with cotton rope for traction,and setting detonators inside and outside the hole every 5~7 smooth blast holes.