基于深度学习的复杂地层钻孔图像岩体结构面识别方法

Deep learning-based method for rock discontinuity recognition in complex stratum borehole images

基于钻孔电视图像的结构面调查是一种应用广泛的勘测方法,可为岩体质量评价和工程设计提供基础数据支撑。然而,复杂地层中结构面形态各异,宽度差异大且对比度低,传统算法难以准确完整地识别。为此,该文提出一种基于改进的U-Net网络模型的钻孔电视图像结构面识别方法。首先,采用更深层次的编码解码网络结构,处理对比度低导致的结构面局部断裂问题,并结合通道注意力机制和残差模块提高编码阶段各层级对结构面特征的提取能力。其次,在较低层级跳跃连接中引入多尺度空间注意力模块,提高对复杂形态结构面处理能力,丰富编码层结构面语义特征;同时,通道注意力也被用于充分融合来自编码层和解码层的多通道结构面信息。然后,通过利用与地质作用下地层变形类似的透视变形等方式扩增钻孔图像数据,并结合焦点损失和Dice损失进行联合训练,以减轻图像数据不平衡问题,增强网络泛化能力。最后,将同一钻孔图像作为训练集,邻近钻孔图像作为测试集进行消融和对比实验。结果表明,相比于已有相关网络模型,该文所提方法能更有效地针对复杂地层钻孔图像,较准确、完整地识别各类岩体结构面,精确率和召回率均超过77.00%,比改进前的U-Net网络分割效果分别提高了7.96%和14.99%。该文方法可为现场结构面钻孔调查以及岩体质量评价提供技术支撑。

[Objective]Discontinuities are vital components of rock mass,significantly affecting its strength,deformation,and seepage characteristics.They provide essential parameters for rock mass classification and engineering design.Borehole television technology is a widely used method for capturing these discontinuities within the rock mass,offering high-resolution in situ images.However,in complex strata,the discontinuities appear in various morphologies with significant width differences.Coupled with the rapid texture changes on rock wall faces,these discontinuities create a highly uneven contrast,making it challenging for traditional algorithms to recognize them accurately.To address this challenge,this study introduces an improved deep learning network model specifically designed for borehole images of complex strata.[Methods]The proposed model,based on the U-Net architecture,incorporates a deeper encoding-decoding network structure.This structure effectively handles semantic information related to discontinuity breaks caused by uneven contrast.The model integrates channel attention mechanisms and residual modules,enhancing feature extraction capabilities at different levels in the encoding stage.In addition,the channel attention mechanism fuses multichannel discontinuity information from both encoding and decoding layers.A multiscale spatial attention module introduced in the lower-level skip connection improves the ability to process complex morphological discontinuities and enriches the semantic features of discontinuities in the coding layer.In this study,the borehole image data are augmented in various ways,such as using perspective deformation similar to the stratum deformation under geological action.This study also employs joint training with focal loss and Dice loss to handle imbalanced image data.The generalization ability of the network model is thoroughly validated through ablation studies and comparative experiments using the same borehole image as the training set and neighboring borehole images as the test set.For comprehensive quantitative evaluation,this study uses several metrics,including precision,recall,F1-Score,and F2-Score.[Results]Our experimental evaluation,conducted on a self-made borehole image dataset,indicated that compared to several common image segmentation network models,our proposed model significantly improved the recognition capability of rock discontinuities in borehole images from complex strata while ensuring faster computational efficiency.The precision and recall on the test set for the proposed model reached 78.23%and 77.85%,respectively.This marked an improvement in segmentation performance by 7.96%and 14.99%,respectively,compared with the basic U-Net model.Both the F1-Score and F2-Score were close to 78%.Although the model size was 18.13 MB and had approximately twice the parameters of the base U-Net,the deeper network hierarchy reduced the number of channels of shallow high-resolution feature maps,resulting in a reduction in computational load.The model achieved an FPS of 85,which was slightly higher than that of the basic U-Net model.[Conclusions]This study meticulously improves upon the basic U-Net model by strategically incorporating the attention mechanism,residual connections,and multiscale convolutions.The improved model exhibits high accuracy and robustness.It effectively confronts the challenges associated with balancing detailed features and high-level semantics owing to significant width differences in discontinuities within complex strata.Furthermore,it addresses issues related to incomplete extraction of discontinuities caused by uneven contrast between discontinuities and rock wall surfaces.As such,this improved model provides strong technical support for the automatic identification of rock discontinuities in on-site borehole investigations.