双江口水电站主厂房开挖初期围岩变形破裂与稳定性分析研究

Investigation on deformation and cracking behaviors and stability analysis of surrounding rock mass of underground main powerhouse of Shuangjiangkou hydropower station during preliminary excavation

双江口水电站主厂房初步开挖过程中脆性破坏现象明显,煌斑岩脉影响洞段围岩变形问题突出。为此,在主厂房初期开挖结束之后,综合围岩变形多点位移计监测、围岩裂隙钻孔成像观测、地下厂房开挖过程数值仿真和煌斑岩脉对局部洞段变形影响的3DEC模拟等手段,提出基于围岩松动圈与厂房截面面积的洞室稳定性评价方法,对围岩变形破裂特征及其稳定性开展深入研究。结果表明:第一层开挖后主厂房围岩变形整体较小,但顶拱下沉相对较大。高应力下硬性花岗岩围岩时效性变形特征不明显,围岩变形主要受开挖掌子面影响,掌子面对煌斑岩脉影响洞段变形的控制作用范围约为1.5倍洞室跨度;此外,当前层开挖围岩浅部和深部均有裂隙分布,岩脉与均质岩石交界处开裂现象严重;开挖卸荷导致煌斑岩脉与其上盘岩层错动,产生剪切变形,致使该区域顶拱变形过大;增设完全穿过煌斑岩脉的锚索这一局部加固支护措施十分有效,显著改善了相关洞段的稳定性。研究成果将为该水电站后续开挖支护方案的优化及局部失稳部位加固措施的选择提供重要依据。

During the preliminary excavation of the main power house of Shuangjiangkou hydropower station,the brittle failure phenomenon is obvious,and the surrounding rock deformation of the area affected by porphyry veins is prominent.To this end,after the preliminary excavation of the main powerhouse,a comprehensive analysis is conducted on deformation and cracking behaviors of surrounding rock and stability of the cavern,which consists of monitoring of surrounding rock deformation by multi-point displacement meters,imaging observation of surrounding rock fractures by borehole camera,numerical simulation of excavation process and effects on local site deformation of the porphyry vein based on 3 DEC software.A novel method for evaluating the stability of caverns based on the surrounding rock loosening zone and the cross-sectional area of the cavern is proposed.The results show that,after the first floor excavation,the deformation of the surrounding rock of the main power house is small as a whole,but the top arch sinks relatively largely.The time-dependent deformation characteristics of the hard granite surrounding rock are not obvious.The surrounding rock deformation is mainly affected by the excavation driving face,and the control range of the excavation face to the deformation of the cave segment affected by the porphyry veins is about 1.5 times the cave span.In addition,there are cracks in the shallow and deep parts of the surrounding rock after excavation,and the cracking phenomenon at the junction of the veins and homogeneous rock is serious.Excavation unloading causes the slip of the upper plate of the porphyry veins,which results in shear deformation of the top arch of the cavern.It is very effective to add anchor cables that completely penetrates the porphyry veins,which significantly improves the stability of the relevant tunnel sections.The research results will provide an important basis for both the optimization of the subsequent excavation and support scheme of the hydropower station and the selection of reinforcement measures for local instability.