基于工程类比的高地应力地下洞室高边墙围岩支护强度评价

Assessing Support Strength of Surrounding Rock of High Sidewalls in Underground Caverns with High Geostress Using Analogy Method

高地应力地下厂房高边墙围岩支护强度的评价对于保证大型地下工程围岩稳定性具有重要意义。猴子岩水电站地下厂房地应力高、强度应力比低,施工开挖中出现喷混凝土开裂、岩锚梁错位、岩体开裂、锚墩内陷等典型的围岩变形破坏现象,对洞室安全造成严重威胁。通过多点位移计、锚杆和锚索的应力监测数据分析,将猴子岩和锦屏Ⅰ级水电站地下厂房进行比较,提出了预应力锚索和锚杆的单位面积预应力支护强度计算方法,并根据评价结果对局部洞段进行针对性的围岩补强支护设计。结果表明:猴子岩地下厂房围岩变形整体上比同期的锦屏Ⅰ级围岩变形大,而锚索应力水平比锦屏Ⅰ级小,锚杆应力水平整体相当;猴子岩地下厂房下游边墙的支护强度大于锦屏Ⅰ级下游边墙的支护强度,上游边墙的支护强度小于锦屏Ⅰ级下游边墙相应部位支护强度,猴子岩地下厂房上游边墙补强支护后的围岩变形得到有效控制,表明了补强措施的有效性。研究可为类似高地应力地下洞室围岩支护设计和支护强度评价提供参考和借鉴。

Assessing the support strength of surrounding rock of high sidewall is of crucial significance for the surrounding rock stability in underground projects of high geostress.Due to high geostress and low strength-to-stress ratio,the underground powerhouse of Houziyan Hydropower Station experienced typical deformations and failures of surrounding rock during construction and excavation,including cracking of shotcrete layer,dislocation between rock anchor beam and anchor pier,and cracking of rock mass,posing severe threat to the safety of the underground cavern.By analyzing the data from multi-point displacement meter and anchor stress monitoring,we proposed the formula and method for assessing the prestressed supporting strength per unit area of prestressed anchor cables and anchor rods,and further designed corresponding reinforcement measures for sidewalls according to the assessment results.Our findings revealed that the deformation of the surrounding rock of Houziyan underground powerhouse was larger than that of the Jinping I-stage project in the same period,while the stress level of anchor cable was smaller,and the overall stress level of anchor rod was equivalent to that of Jinping I-stage project.The supporting strength of Houziyan’s downstream sidewall was larger than that of Jinping’s downstream sidewall,whereas that of upstream side wall lower than that of Jinping’s downstream sidewall.In the later period,the deformation and displacement of surrounding rock after the reinforcement of the upstream and downstream sidewalls of Houziyan underground powerhouse was effectively controlled,and the deformation rate gradually reduced and finally stabilized,manifesting the effectiveness of the measures.