地下水对围岩力学性质有显著影响。针对红层软岩隧道围岩受地下水影响较大的变形,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)监测试样的破坏过程,分析了裂纹演化规律,用扫描电子显微镜(SEM)比较了浸泡前后试样的微观结构。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,随着含水量的逐渐增加,产量阶段前的AE振铃计数逐渐下降,同时相应的累积振铃计数逐渐减少,在浸泡的早期下降幅度很大,并在后期下降。累积振铃曲线逐渐减慢,内部裂缝出现较早,累积振铃曲线阶跃明显,AE信号幅度逐渐减弱,各频段的带宽逐渐减小。不同含水率红层软岩的破坏以剪切裂纹为主,随着含水量的逐渐增加,剪切裂纹的比例逐渐增加,AEb值逐渐减小。随着相对峰值强度的逐渐增大,不同含水率红层软岩的相关维数D先增大后减小。在80%的相对峰值强度下,相关维数D达到最大值,然后急剧下降,直到保持在相对较低的水平,相关维数D随含水率逐渐减小。不同含水量的拟合相关系数(lnC(r),lnr)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逐渐增加,广义分形维数D(q)逐渐减小。当q^0时,在相同q的条件下,D(q)呈现先增大后减小的趋势。不同含水量红层软岩声发射振铃计数的多重分形特征呈倒U形。从自然状态到浸泡1d,Δα逐渐增加,从1到7d,Δα逐渐减小,其中Δα=αmax-αmin表示多重分形谱的谱宽。当没有达到饱和时,Δf<0表示试样中的裂纹数量少,当达到饱和时,Δf>0表示试样内部产生大量裂纹,形成宏观裂纹,其中Δf=f(αmax)-f(αmin)表示不同大小的不同信号之间的频率关系。该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。
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 = αmax - αmin 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 (αmax) - f (αmin) 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.