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当岩块从原有的地质环境中取出时,它在原位岩体中受到的应力将被解除,其物理力学性质亦会发生变化,从而产生卸荷效应。通过自行设计的岩块波速–应力试验,研究了岩块的波速–应力关系。研究发现:波速–应力关系曲线可以较清楚地反映出岩石受荷过程中体积变形的3个阶段;波速–应力关系曲线基本上以σ=σc=(1/4～1/3)Rc为界,当σ<σc时,岩样波速随应力增大迅速增加,波速–应力关系符合幂函数曲线,当σ>σc时,岩样波速逐渐达到峰值,随后迅速下降,波速–应力关系符合二次函数曲线;波速–应力试验过程中,当应力增加到岩样在原位状态下同试验加荷方向下所受的应力时,波速增加速度急剧变缓。根据岩块的波速–应力关系提出了岩样的卸荷指标,并将其定义为岩块在原位所受应力对应的波速与未受荷时的波速之比,通过试验和计算得到黄岛地下水封石油洞库场区片麻岩和闪长岩的卸荷指标分别为1.13和1.08。
When a rock mass is removed from the original geologic environment, its stress in the in-situ rock mass will be relieved and its physical and mechanical properties will also change, resulting in the unloading effect. Through the self-designed rock mass velocity-stress test, the relationship between rock mass velocity and stress is studied. The results show that the wave velocity-stress relationship curve can clearly reflect the three stages of volume deformation during rock loading. The wave velocity-stress relationship curve is basically bounded by σ = σc = (1/4 - 1/3) Rc When σ <σc, the wave velocity increases rapidly with increasing stress, and the wave velocity-stress relationship accords with the power function curve. When σ> σc, the rock mass velocity reaches the peak gradually and then decreases rapidly. The wave velocity-stress relationship conforms to the second When the stress increases to the stress of the rock specimen in the same state under the same loading direction as the test specimen, the rate of increase in wave velocity slows down rapidly during the wave velocity-stress test. According to the wave velocity-stress relationship of rock mass, the unloading index of rock sample is proposed and defined as the ratio of the wave velocity corresponding to the stress of the rock mass in situ to the wave velocity of the rock mass unloaded. By the experiment and calculation, The unloading indicators of gneiss and diorite in the groundwater seal oil hole depot area are 1.13 and 1.08 respectively.