Chen Lei, Liu Taiyu, Jia Baoxin, Tang Jupeng, Liu Jiashun
School of Civil Engineering, Liaoning Technical University, FuxinLiaoning Province, 123000, China.
Key Laboratory of Disaster Management and Ecological Restoration in Resource-Depleted Mining Areas of Liaoning Province, Fuxin, 123000, Liaoning Province, China.
Sci Rep. 2024 Feb 23;14(1):4424. doi: 10.1038/s41598-024-54814-2.
Groundwater has a significant influence on the mechanical properties of surrounding rock. Aiming at the large deformation of surrounding rock of red layer soft rock tunnel affected by groundwater, the uniaxial graded loading tests were carried out on red beds soft rock with different water content. The failure process of the specimen was monitored by acoustic emission (AE) and the crack evolution law was analyzed, and the scanning electron microscopy (SEM) was used to compare the microstructure of the specimens before and after immersion. Combined with fractal theory, the monofractal and multifractal characteristics of AE ringing count during the loading process of red beds soft rock were analyzed. The results show that, with the gradual increase of water content, the AE ringing count before the yield stage gradually decreased, and the corresponding cumulative ringing count at the same time gradually decreased, and the decrease was large in the early stage of immersion, and decreased in the later stage. The cumulative ringing curve gradually slowed down, the internal crack appeared earlier, the cumulative ringing curve stepped significantly, the AE signal amplitude gradually weakened, and the bandwidth of each frequency band gradually decreased. The failure of red beds soft rock with different water content is dominated by shear crack, and with the gradual increase of water content, the proportion of shear crack increases gradually, and the AE b value decreases gradually. With the gradual increase of the relative peak strength, the correlation dimension D of red beds soft rock with different water content increases first and then decreases. At 80% of the relative peak strength, the correlation dimension D reaches its maximum value and then drops sharply until it is maintained at a relatively low level, and the correlation dimension D gradually decreases with the water content. The fitting correlation coefficients of different water content (lnC(r), lnr) are all above 0.9, indicating that the AE ringing count of water-bearing red beds soft rock has fractal characteristics, and the higher the correlation coefficient, the higher the self-similarity of AE ringing count sequence. As the weight q gradually increases, the generalized fractal dimension D(q) gradually decreases. When q ≠ 0, under the condition of the same q, D(q) presents a trend of first increasing and then decreasing. The multifractal characteristics of AE ringing count of red beds soft rock with different water content is inverted 'U' shape. From the natural state to immerse 1 d, the ∆α gradually increases, and from 1 to 7 d, the ∆α gradually decreases, where Δα = α - α represents the spectral width of the multifractal spectrum. When saturation is not reached, ∆f < 0 indicates that the number of cracks in the specimen is small, when saturation is reached, ∆f > 0 indicates that a large number of cracks are generated inside the specimen and macro cracks are formed, where Δf = f (α) - f (α) represents the frequency relationship between different signals of different sizes. This research can provide a reliable theoretical basis for the construction and maintenance of large deformation of water-rich soft rock tunnel excavation, and have certain engineering significance.
地下水对围岩力学性质有显著影响。针对受地下水影响的红层软岩隧道围岩大变形问题，对不同含水率的红层软岩进行了单轴分级加载试验。通过声发射（AE）监测试件的破坏过程并分析裂纹扩展规律，利用扫描电子显微镜（SEM）对比浸水前后试件的微观结构。结合分形理论，分析了红层软岩加载过程中AE振铃计数的单分形和多重分形特征。结果表明，随着含水率的逐渐增加，屈服阶段前的AE振铃计数逐渐减少，同时相应的累积振铃计数也逐渐减少，浸水初期减少幅度大，后期减小。累积振铃曲线逐渐变缓，内部裂纹出现较早，累积振铃曲线有明显台阶，AE信号幅值逐渐减弱，各频段带宽逐渐减小。不同含水率红层软岩的破坏以剪切裂纹为主，随着含水率的逐渐增加，剪切裂纹比例逐渐增大，AE b值逐渐减小。随着相对峰值强度的逐渐增加，不同含水率红层软岩的关联维数D先增大后减小。在相对峰值强度的80%时，关联维数D达到最大值，然后急剧下降，直至维持在较低水平，且关联维数D随含水率逐渐减小。不同含水率（lnC(r)，lnr）的拟合相关系数均在0.9以上，表明含水红层软岩的AE振铃计数具有分形特征，相关系数越高，AE振铃计数序列的自相似性越高。随着权重q逐渐增大，广义分形维数D(q)逐渐减小。当q≠0时，在相同q条件下，D(q)呈现先增大后减小的趋势。不同含水率红层软岩AE振铃计数的多重分形特征呈倒“U”形。从天然状态到浸水1 d，∆α逐渐增大，从1到7 d，∆α逐渐减小，其中∆α = α - α表示多重分形谱的谱宽。未达到饱和时，∆f < 0表明试件内裂纹数量少，达到饱和时，∆f > 0表明试件内部产生大量裂纹并形成宏观裂纹，其中∆f = f(α) - f(α)表示不同大小不同信号之间的频率关系。本研究可为富水软岩隧道大变形开挖施工及维护提供可靠的理论依据，具有一定的工程意义。
