基于波速成像技术的岩石破裂演化及损伤局部化效应研究

Fracture evolution and localization effect of damage in rock based on wave velocity imaging technology

开展粉砂岩单轴分级加载实验,利用波速成像技术获取岩石破裂过程的波速成像图,结合声发射时序参数,分析岩石破裂过程波速场与声发射的联合响应特征,并基于波速成像图研究了岩石破裂过程的损伤局部化效应。研究结果表明:波速成像能够三维可视化显示岩石内部损伤的大小、空间位置等信息,出现损伤的区域波速低,低波速聚集的区域往往对应严重损伤区域。声发射参数与波速成像分别从时间和空间的角度刻画岩石破裂过程裂纹的活动性变化过程,岩石破裂过程裂纹活动性增强,声发射事件率增大,低波速区域逐渐聚集,且面积逐渐增大。基于波速成像图,将岩石内部损伤划分为初始损伤区、渐进损伤区和破裂区,岩石破裂过程中渐进损伤区与破裂区均围绕初始状态下损伤区发展,具有典型的损伤局部化效应。通过捕捉波速成像图渐进损伤区与破裂区的空间发展趋势,可以预测微破裂的发展趋向,对于确定主破裂的位置具有实际意义。

By utilizing wave velocity imaging technology,the uniaxial multi-stage loading test was conducted on siltstone to attain wave velocity imagings during rock fracture.Based on the time series parameters of acoustic emissions(AE),joint response characteristics of the velocity field and AE during rock fracture were analyzed.Moreover,the localization effect of damage during rock fracture was explored by applying wave velocity imagings.The experimental result showed that the wave velocity imagings enable three-dimensional(3-D)visualization of the extent and spatial position of damage to the rock.A damaged zone has a low wave velocity and a zone where the low wave velocity is concentrated tends to correspond to a severely damaged zone.AE parameters and wave velocity imagings depict the changes in activity of cracks during rock fracture from temporal and spatial perspectives,respectively:the activity of cracks is strengthened,and the rate of AE events increases during rock fracture;correspondingly,the low-velocity zones are gradually aggregated and their area gradually increases.From the wave velocity imagings,the damaged zones in rock were divided into an initially damaged zone,a progressively damaged zone,and a fractured zone.During rock fracture,the progressively damaged zone and the fractured zone both develop around the initially damaged zone,showing a typical localization effect of the damage.By capturing the spatial development trends of the progressively damaged zone and fractured zone in wave velocity imagings,the development of microfractures can be predicted,exerting practical significance for determining the position of the main fracture.