白鹤滩特高拱坝坝肩柱状节理玄武岩开挖爆破试验研究

Experimental Study on Blasting of Columnar Jointed Basalt of Baihetan High Arch Dam

柱状节理玄武岩具有表面易破碎、易松弛等性状特点,作为300 m级高拱坝坝肩基岩世界罕见。柱状节理玄武岩基岩面岩体施工处理,经常出现边坡预裂面破坏,预裂面超欠挖严重、预裂面半孔率低、岩体扰动等问题。为解决破碎岩体边坡开挖的稳定,减少预裂爆破对建基面稳定的危害,根据白鹤滩水电站左岸坝肩柱状节理玄武岩物理及力学特性,通过预裂爆破与光面爆破对比试验,以确定爆破类型;并优化预裂爆破装药线密度、孔排距等参数。结果表明:预裂爆破综合效果优于光面爆破。通过在爆前、爆后布置物探监测仪器对周围岩体损伤进行监测,得出预裂爆破孔0.6 m的间距及线密度240 g/m装药参数,对柱状节理玄武岩实现基岩面扰动最小,达到最佳爆破效果。为强卸荷岩体高拱坝基础开挖提供了理论和实践借鉴。

As the characteristics of fragile surface and easy relaxation,it is rare that the columnar jointed basalt is the base rock of the 300 m high arch dam abutment.During the construction of bedrock surface on the columnar jointed basalt rock,some problems often occur,such as destruction of the pre-crack surface of slope,serious pre-excavation of the pre-crack surface,low half-hole ratio of pre-crack surface and rock mass disturbance.In order to solve the stability problem of the broken rock mass excavation and reduce the pre-splitting blast damage to the foundation surface stability,a blasting type was determined by comparison test of the pre-splitting blasting and smooth blasting according to the physical and mechanical characteristics of the columnar jointed basalt on the left bank of Baihetan Hydropower Station.Meanwhile,The parameters of charge line density and hole row spacing of pre-split blasting were optimized.The results show that the comprehensive effect of pre-splitting blasting is better than smooth blasting.The damage of surrounding rock mass was monitored by arranging geophysical monitoring instruments before and after explosion.The blasting parameters of 0.6 m spacing of pre-splitting blasting hole and 240 g/m linear density are obtained,which can minimize the disturbance to the bedrock surface of columnar jointed basalt and achieve the best blasting effect.It provides theoretical and practical reference for foundation excavation of high arch dam with strongly unloaded rock mass.