中文摘要：

300 m级高拱坝建基面开挖造成的岩体卸荷松弛对高拱坝的整体稳定性影响巨大。白鹤滩拱坝左岸建基面开挖至628 m高程时也出现了卸荷松弛、结构面错动等现象。基于变形加固理论,提出了使用不平衡力作为坝基岩体松弛卸荷的定量判据,阐释了不平衡力分析岩体开裂与坝基卸荷时效松弛的理论基础,通过试验和数值模拟的对比说明了不平衡力应用于卸荷松弛判据的准确性。使用三维非线性有限元程序TFINE,对白鹤滩拱坝原始地形和开挖过程进行精细模拟,分析了开挖过程中建基面基础（尤其是结构面）的卸荷松弛演变过程。分别对无基础处理、预留保护层和施加锚索情况下的开挖卸荷松弛进行了研究分析。模拟结果表明,在开挖到630 m高程时,在结构面交汇处和坡面出露段附近结构面的不平衡力与屈服区出现集中情况,这与观测到的建基面卸荷松弛以及结构面出现错动裂缝等现象符合;继续开挖过程中,LS331、LS3318不平衡力较大,相对比较危险。另外,坝体底部的陡坎开挖成型时,陡坎底部的不平衡力增加较明显,需减缓陡坎坡度。预留保护层和建基面锚固对控制松弛卸荷作用较小。

英文摘要：

The excavation-induced relaxation of dam base surface can enormously affect the global stability of 300 m level-high arch dams. Unfortunately, for Baihetan arch dam, serious excavation-induced relaxation and structural plane dislocation are discovered in the left slope when the dam base surface is excavated to the elevation of 628 m. Based on the deformation reinforcement theory, the unbalanced force is used as a quantitative index to evaluate the degree of excavation-induced relaxation of dam base surface. Then, the theoretical basis of rock cracking and relaxation based on the unbalanced force can he analyzed. Simultaneously, the accuracy of using the unbalanced force to evaluate excavation-induced relaxation is illustrated by experiments and numerical simulations. Employing the 3D nonlinear FEM programme TFINE, the excavation-induced relaxation evolution process of the arch dam＇s left base surface of Baihetan, particularly the shear moving of the structural plane, is elaborated. Three excavation situations are investigated respectively： excavation without foundation treatments, excavation with reserved protective layer and excavation with anchoring. The simulated results show that the unbalanced forces and yield zones of structural planes are concentrated near the intersection zones and outcrops of structural planes, which fit the observations of relaxation of dam base surface and dislocation of structural planes well. LS331 and LS3318 are more dangerous than the other structural planes owing to larger unbalanced force during excavation. The unbalanced force near the scarp bottom obviously increases during excavation of the scarp, so the gradient of the scarp should he slackened. Relatively speaking, reserving the protective layer and setting anchoring have little influence on controlling the excavation-induced relaxation.