大型地下厂房洞室群围岩开挖松弛效应与渗透性演化特征

Excavation-Induced Relaxation Effects and Evolution of Hydraulic Conductivity in Surrounding Rocks of Large-Scale Underground Caverns

锦屏一级水电站地下厂房洞室群开挖规模巨大,赋存于极高至高地应力和低强度岩体环境下,且受f13、f14、f18断层切割,其围岩稳定性将成为影响工程安全和正常运行的重要因素之一.结合现场声波监测资料,采用裂隙岩体等效弹塑性本构模型以及基于Hoek-Brown参数的偏应力破坏准则对开挖松弛区进行模拟与评价.此外,重点关注洞室群围岩在地下厂房开挖过程中渗透特性的演化,并采用SVA方法对其防渗排水措施的渗控效应进行分析与评价.研究结果表明:采用塑性屈服区以及偏应力破坏准则表征围岩开挖松弛效应是合理的,高地应力、低强度应力比是造成锦屏一级地下厂房围岩开挖松弛区较大的主要原因;洞室群围岩在地下厂房开挖过程中渗透特性可增大3个数量级,影响范围达35m;围岩渗透特性演化对渗流场具有显著影响,影响程度取决于与洞室群的距离以及防渗排水措施的渗控效应.

With large-scale excavation, Jinping-Ⅰ underground powerhouse is subjected to extremely high to high in-situ geostress. The surrounding rocks are of low uniaxial compressive strength and cut through by f13, f14 and f18 faults.Therefore, the stability of surrounding rocks would be an important factor which could affect the safety and normal operationof the project. Combined with sonic wave monitoring data, the excavation-induced relaxation zones were assessed with an equivalent elasto-plastic model and a constant deviatoric stress criterion based on the Hoek-Brown parameters of the surrounding rocks, respectively. Besides,special attention was paid to the hydraulic conductivity evolution of surrounding rocks during the excavation process, and the seepage control effects were analyzed and assessed by the SVA method. The results show that：It was reasonable to characterize the excavation-induced relaxation effects with plastic yield zones and constant deviatoric stress criterion,and high geostress and low strength-stress ratio were the main factors leading to large relaxation zones of Jinping-Ⅰ underground powerhouse;the hydraulic conductivity of surrounding rocks could increase by 3 orders of magnitude during the excavation process with the influence scope reaching 35,m; the hydraulic conductivity evolution could significantly influence the seepage field,which was mainly decidedby the distance to the caverns and the seepage control effects.