GEOMETRIC FEATURE–BASED IDENTIFICATION OF ROCK MASS DISCONTINUITIES USING ADAPTIVE HIERARCHICAL CLUSTERING

Discontinuities such as joints, fractures, and bedding planes play a decisive role in controlling the stability and safety of underground engineering structures. Accurate identification and grouping of these discontinuities are essential for tunnel excavation, slope stabilization, and foundation design. Conventional identification methods primarily depend on normal vector estimation combined with directional clustering algorithms. However, these approaches often suffer from reduced accuracy under uneven orientation density, omission of critical discontinuities, and the need for manual parameter tuning. To address these limitations, this study proposes a novel discontinuity identification framework based on geometric feature analysis and adaptive statistical clustering.

Limitations of Conventional Directional Clustering Methods

Traditional approaches rely heavily on estimating surface normals from point cloud data and grouping them via clustering techniques such as k-means or density-based methods. These strategies encounter three key challenges:

(1) performance degradation when discontinuity orientations are unevenly distributed,

(2) loss of small or sparse structural sets, and

(3) dependence on manually predefined cluster numbers or thresholds.

Such limitations reduce reliability in complex geological environments, where discontinuities vary significantly in scale, persistence, and spatial arrangement.

Geometric Feature–Driven Discontinuity Detection

The proposed method shifts focus from purely directional clustering to geometric feature analysis of rock mass point clouds. By examining spatial distribution variability and structural continuity, the framework captures both local and global geometric characteristics. An adaptive region-growing algorithm is integrated to detect independent discontinuities even under irregular rock mass geometries. This enables accurate segmentation across diverse rock shapes and sizes while minimizing sensitivity to noise.

Adaptive Hierarchical Clustering Based on Fisher Distribution

Recognizing that rock mass orientations typically follow a Fisher distribution, the study introduces a statistically grounded adaptive hierarchical clustering algorithm. Unlike conventional methods requiring preset cluster numbers, this approach automatically determines the optimal number of structural sets through statistical analysis of orientation dispersion. By eliminating manual intervention, the method enhances automation, objectivity, and reproducibility in discontinuity grouping.

Noise Resistance and Multi-Scale Feature Integration

A key strength of the framework lies in its integration of local geometric attributes (e.g., curvature, point density variations) with global structural trends. This multi-scale feature fusion reduces interference from measurement noise and incomplete data. The method demonstrates robustness in handling complex geological conditions, including intersecting discontinuities and variable persistence lengths, ensuring reliable detection across heterogeneous rock masses.

Experimental Validation and Engineering Significance

The proposed approach was validated using three real-world rock mass models and benchmarked against three mainstream directional clustering algorithms. Results indicate superior accuracy, improved detection of optimal discontinuity sets, and enhanced robustness under uneven orientation distributions. By offering a reliable and efficient tool for automated discontinuity detection and grouping, this method significantly strengthens geotechnical analysis, supporting safer underground excavation design and construction decision-making.

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BOREHOLE PRESSURE SHEAR TESTER (BPST) FOR IN-SITU EVALUATION OF WEATHERED GEOMATERIALS

Accurate characterization of weathered geomaterials—comprising residual soils and weathered rocks—is essential for ensuring the stability and safety of civil engineering structures. These materials exhibit transitional behavior between soil and rock, making their mechanical properties difficult to assess using conventional techniques. Laboratory testing is often impractical because obtaining undisturbed samples from weathered layers is extremely challenging. Consequently, reliable in-situ testing methods are crucial for capturing true field conditions and improving geotechnical design accuracy.

Limitations of Conventional Field Testing Methods

Traditional field tests are typically developed either for soils or for intact rock masses, leading to significant shortcomings when applied to intermediate geomaterials. Weathered layers possess heterogeneous structures, variable stiffness, and complex failure mechanisms that standard tests cannot fully capture. As a result, existing techniques may produce unreliable estimates of deformation and shear strength, potentially compromising engineering decisions for foundations, slopes, and underground structures.

Development of the Borehole Pressure Shear Tester (BPST)

To address these limitations, this study introduces the Borehole Pressure Shear Tester (BPST), an innovative device that combines the principles of pressuremeter testing and borehole shear testing. The BPST applies controlled horizontal pressure and shear forces directly within a borehole, enabling simultaneous assessment of deformation characteristics and shear strength parameters. This integrated approach provides a more comprehensive understanding of the mechanical behavior of weathered geomaterials compared to single-mode testing methods.

Testing Procedure and Measurement Capabilities

The BPST operates by expanding against the borehole wall while applying tangential shear displacement, replicating realistic stress conditions encountered in situ. This allows direct measurement of deformation modulus and shear resistance under controlled loading paths. By capturing both normal and shear responses in a single test, the device reduces uncertainty associated with extrapolating parameters from separate tests and improves efficiency in field investigations.

Experimental Validation on Residual Soils

Empirical tests conducted on residual soils at simulated high relative densities and varying overburden stresses demonstrated the effectiveness of the BPST. The measured deformation moduli and shear strength parameters showed strong agreement with results obtained from conventional triaxial compression and direct shear tests. This correlation confirms the accuracy and reliability of the device for characterizing intermediate geomaterials under realistic field conditions.

Implications for Geotechnical Design and Infrastructure Safety

The introduction of the BPST represents a significant advancement in geotechnical site investigation. By enabling accurate in-situ evaluation of weathered layers, the device enhances predictive modeling, supports safer foundation design, and reduces uncertainty in stability assessments. Its ability to characterize materials that fall between soil and rock categories makes it particularly valuable for projects involving slopes, tunnels, deep foundations, and infrastructure built on weathered terrain.

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