金沙江白鹤滩水电站地下厂房玄武岩洞室群施工技术创新

Technological innovations in construction of underground caverns in basaltic rocks at Baihetan Hydropower Station on Jinsha River

白鹤滩水电站地下厂房基本对称布置在金沙江下游高山峡谷河段左右岸的玄武岩山体内,各安装8台单机1000 MW的水轮发电机组,其单机容量、总装机容量、主厂房跨度(34 m)、穹顶型尾调室直径(最大48 m)及地下洞室群规模均居世界地下厂房之首.厂房洞室群布置复杂、相互关联、挖空率高,位于以水平构造应力为主的高地应力区,围岩隐裂隙发育、坚硬性脆、起裂强度低,局部发育柱状节理玄武岩,多处围岩被长大软弱缓倾角错动带切割,洞室群开挖施工的安全稳定面临严峻挑战.针对高地应力环境下白鹤滩地下厂房脆硬玄武岩内部破裂、错动带不连续变形、洞室群围岩时空变形联动效应的响应特征和演化规律,遵循地下厂房洞室群“认识围岩、利用围岩、保护围岩、监测围岩、反馈优化”的建设思路和“开挖一层、分析一层,预测一层,验收一层”的工作程序,提出了“超前预控制、垂直薄分层、平面细分区、进尺短步长、爆破精细严、快速强支护、全程勤量测、数据快反馈、动态反演优化”的玄武岩洞室群围岩时空变形调控全过程施工技术,确保了白鹤滩地下厂房的安全优质有序建设,促进了中国水电工程建设技术进步,对同类工程具有指导意义.

The two underground powerhouses on the left and right banks of Baihetan Hydropower Station(BHT-HS)are symmetrically arranged inside basaltic rocks in the alpine gorge reach of the lower Jinsha River.Each of them is equipped with 8 sets of 1,000 MW hydraulic turbine generators,with the largest unit capacity,total installed capacity,span of main powerhouse(i.e.34 m),diameter of domeshaped tail-regulating chamber(max diameter of 48 m)and scale of underground caverns around the world.Due to complex layout,interaction between caverns and high hollowing rate,the construction process of the underground cavern group is faced many challenges.For example,the cavern excavation is located in the high ground stress area dominated by horizontal tectonic stress;the underlying basalt fractures are well developed,and the rock is hard and brittle,with low crack initiation strength;columnar jointed basalts develop locally;a number of large and weak gently-sloped shear zones develop diagonally cutting the main powerhouse.Following the construction ideology of“understanding,utilization,protection,monitoring,and feedback analysis on the surrounding rock masses during the construction period”,and with the engineering construction procedure of“the excavation,analysis,prediction and inspection of each rock layer”,this paper proposes a set of innovation construction technologies including“advanced pre-control,thin vertical layer,small planar partition,short excavation progress,fine blasting,strong and quick support,short interval monitoring,quick feedback,precise dynamic optimization”to control the internal cracking of the hard and brittle basaltic rocks,discontinuous deformation of staggered zones and spatio-temporal deformation of underground caverns in high geostress.It has promoted the safe and orderly construction of BHT-HS,the technical progress of the construction of hydropower station projects in China,and may also be applicable to the design and construction of similar projects worldwide.