随着中国水力发电工程的快速发展，大埋深的工程建设愈发普遍，高地应力、高渗压的问题频频出现，如何确保深埋岩体开挖卸荷过程中、亦或者是开挖卸荷完成后，其围岩的稳定性是目前亟待解决的关键科学问题。基于此，本文以黄河上游某水电站的引水隧洞工程建设为背景，以标段内的花岗岩为对象，围绕高地应力、高渗压以及卸荷扰动等外部条件，研究开挖隧洞围岩的流变力学特性。综合采用了试验、理论加数值模拟等手段，研究卸荷岩体的变形行为以及时效特征，综合本次研究主要结论包括以下几点：
（1）进行了高应力条件下的瞬时力学特性试验，探讨了围压与弹性模量以及特征应力点之间的变化规律，发现三轴条件下试件的弹性模量与围压值呈正相关。特征点应力值中的裂隙闭合应力σ_cc受围压变化影响较小，起裂应力σ_ci、屈服应力σ_cd、与峰值应力σ_f均随围压增大变化明显。对比分析了加、卸载条件下花岗岩试件的变形特征、强度特征以及破坏模式，发现卸荷条件下花岗岩试件更易产生应力跌落现象，其破坏形态更为复杂、裂纹较多，更易发生突然破坏，所获取的成果为后续卸荷流变试验提供了有益的基础。
（2）基于三轴瞬时力学特性试验成果，开展卸荷损伤试验并制备了卸荷损伤试件，以卸荷损伤试件为对象开展了高地应力条件下卸荷花岗岩的流变试验、高地应力恒定渗压条件下卸荷花岗岩的流变试验以及高地应力变幅渗压条件下卸荷花岗岩的流变试验。发现卸荷损伤花岗岩存在着典型流变三个特征阶段，流变试验过程中其侧向流变行为更为明显，初始围压20MPa下卸荷花岗岩的长期强度为三轴峰值强度的63.6%。渗压介入后，卸荷花岗岩的流变力学性质明显减弱，破坏强度降低、流变历时减少、长期强度下降。恒定渗压条件下，围压是控制渗压作用的重要因素，初始围压越低，渗压对卸荷花岗岩流变特性影响越明显。变幅渗压条件下，渗压对卸荷花岗岩试件流变性质的影响受轴向应力水平控制，高应力下渗压越大，流变量越大、流变速率越快，侧向扩容现象越明显。此外，对比不同渗压条件下的卸荷花岗岩长期强度可知，其长期强度随渗压值增长呈非线性下降趋势。
（3）根据卸荷花岗岩试件流变试验过程中所表现出的行为特征，确定了以Burgers模型描述卸荷花岗岩试件流变行为，并对不同条件下的卸荷花岗岩试件流变数据进行参数辨识获得了流变计算参数，并且试验结果和拟合结果的相关系数平均值为0.956，相关性较好，也证实了Burgers模型能够较好的描述卸荷花岗岩的流变行为，这也为后续的数值模拟计算提供了基础。
（4）基于卸荷岩体力学思想，考虑了卸荷作用的影响区域，分析了全断面开挖条件下隧洞围岩的瞬时变形特征，发现全断面开挖后，洞周围岩应力状态发生明显重分布，洞周两侧围岩3~5m范围内出现明显应力集中现象。从围岩的损伤区范围以及主应力的分布云图可以看出，洞周两侧围岩是应力集中、损伤程度较大的危险区域，应在施工过程中重点关注，并及时做好支护措施。利用有限差分软件建立了考虑卸荷扰动区域的三维数值模型，结合参数辨识获取的流变参数，对隧洞全断面开挖完成后渗压影响下的洞周围岩时效变形特征进行了数值模拟计算分析，发现洞周围岩应力分布同样随时间发展存在明显的重分布过程，表现为自临空面向内延伸逐渐扩散、影响程度逐渐降低的特征，并且洞周围岩的位移变形随时间发展不是一个匀速的过程，而是存在着减速变形阶段、稳定变形阶段、加速变形阶段，以及最终重新达到稳定阶段的过程。
 

With the rapid development of hydropower projects in China, the construction of large burial depths is becoming more and more common, and the problems of high ground stress and high seepage pressure appear frequently. How to ensure the stability of the surrounding rock and the reasonable selection of the support structure during and after the excavation and unloading of the deeply buried rock is a key scientific problem that needs to be solved. Based on this, this paper takes the construction of a diversion tunnel of a hydropower station in the upper reaches of the Yellow River as the background, and takes the granite in the subject section as the object to study the rheological and mechanical properties of the excavated tunnel surrounding rock around the external conditions such as high ground stress, high seepage pressure and unloading disturbance. Tests, theories plus numerical simulations were used to study the deformation behavior of the unloaded rock mass and the time-dependent characteristics, and the main conclusions of this study include the following.

(1) Tested for transient mechanical properties under high stress conditions. It was found that the elastic modulus of the specimens under triaxial condition was positively correlated with the surrounding pressure, while the fracture closure stress σ_cc was less affected by the change of surrounding pressure, and the cracking stress σ_ci, yield stress σ_cd, and peak stress σ_f all changed significantly with the increase of surrounding pressure. The deformation characteristics, strength characteristics and damage modes of granite specimens under loading and unloading conditions are compared and analyzed, and it is found that granite specimens under unloading conditions are more prone to stress drop phenomenon, their damage patterns are more complex, more cracks, more prone to sudden damage, and the reaction in engineering is mostly rock explosion and other phenomena. The obtained results provide a useful basis for the subsequent unloading creep test.

(2) Based on the results of the triaxial transient mechanical properties test, the unloading damage test was carried out and the unloading damage specimens were prepared, and the creep test of unloaded granite under high ground stress, creep test of unloaded granite under high ground stress constant seepage pressure and creep test of unloaded granite under high ground stress variable seepage pressure were carried out with the unloaded damage specimens as the objects. It was found that there existed three characteristic stages of typical creep in unloaded damaged granite, and its lateral creep behavior was more obvious during the creep test, and the long-term strength of unloaded granite under the initial peritectic pressure of 20 MPa was 63.6% of the triaxial peak strength. After the intervention of seepage pressure, the creep mechanical properties of unloaded granite were obviously weakened, and the damage strength was reduced, the creep epoch was decreased, and the long-term strength was decreased. Under the condition of constant seepage pressure, the surrounding pressure is an important factor to control the effect of seepage pressure, and the lower the initial surrounding pressure, the more obvious the effect of seepage pressure on the creep properties of unloaded granite. Under the condition of variable seepage pressure, the effect of seepage pressure on the creep properties of unloaded granite specimens is controlled by the axial stress level, the higher the seepage pressure under high stress, the larger the creep volume and the faster the creep rate, and the more obvious the lateral expansion phenomenon. In addition, comparing the long-term strength of unloaded granite under different seepage pressure conditions, it can be seen that its long-term strength shows a non-linear decreasing trend with the increase of seepage pressure value.

(3) According to the behavior characteristics exhibited during the creep test of unloaded granite specimens, the Burgers model was determined to describe the creep behavior of unloaded granite specimens, and the creep calculation parameters were obtained by parameter identification of the creep data of unloaded granite specimens under different conditions, and the average value of the correlation coefficient between the test results and the fitting results was 0.956, which was a good correlation, and also confirmed that the Burgers model can describe the creep behavior of unloaded granite specimens better. Burgers model can describe the creep behavior of unloaded granite better, which also provides the basis for the subsequent numerical simulation.

(4) Based on the idea of unloading rock mechanics, the influence area of excavation disturbance was divided, and the deformation characteristics of the surrounding rock caused by tunnel excavation were compared and analyzed under two conditions with or without considering unloading effect. Secondly, a three-dimensional numerical model considering the unloading disturbance area was established by using finite difference software, and the time-dependent deformation characteristics of the rock around the tunnel were simulated and analyzed after the completion of the tunnel excavation in full section. The development is not a uniform process, but a process of deceleration deformation stage, stable deformation stage, accelerated deformation stage, and finally reaching the stable stage again.