Shangxin Feng

Measurement while drilling (MWD) technology provides a novel methodology for the in situ determination of geomechanical properties by monitoring bit–rock interaction parameters during drilling, offering real-time lithological distribution identification without compromising efficiency. This paper reviews the application of MWD in geotechnical engineering, encompassing theoretical frameworks, technological evolution, engineering applications, challenges and new trends. The analysis reveals that most theoretical models of bit–rock interaction exhibit significant limitations in accurately predicting rock properties under field conditions. Advances in near-bit sensing and adaptive data processing are identified as critical drivers of methodological innovation. Key engineering applications—including formation identification, drilling optimization, and 3D geological visualization—are outlined, alongside actionable recommendations for development. Finally, five strategic research priorities are proposed for next-generation MWD systems: advancing bit–rock interaction theory, developing high-resolution near-bit sensors, enabling multi-source data fusion, supporting dynamic 3D model calibration, and facilitating continuous in situ stress measurement.

Real-time coal–rock identification is essential for intelligent mining, enabling hazard prevention and geological modeling. However, existing methods often suffer from unclear bit–rock interaction mechanisms, signal distortion, sensor remoteness, or delayed data acquisition, limiting their effectiveness in continuous operations. This study proposes a novel approach for real-time coal–rock identification based on multi-source near-bit drilling data. A near-bit data acquisition system was developed and positioned directly behind the drill bit, integrating sensors to capture high-fidelity parameters—including weight on bit (WOB), torque, rotational speed, rate of penetration (ROP), natural gamma ray, and borehole trajectory—thereby eliminating frictional interference from the drill string. A data-driven theoretical model was established to derive a near-bit drillability index (NDI) for rock strength and to correlate gamma ray responses with lithology. Field trials were conducted in a coal mine in northern Shaanxi, involving over 30 boreholes and systematic core validation. The results demonstrate that the method enables continuous, high-resolution identification of coal–rock interfaces and strength variations along the borehole trajectory, with interpreted results aligning well with core logs and achieving approximately 85% accuracy in strength estimation. By ensuring compatibility with conventional drilling rigs and supporting real-time data transmission and 3D geological updating, this study offers a practical and robust technical pathway for achieving geological transparency and real-time steering in underground coal mining.

The rock fragmentation mechanism of polycrystalline diamond compact (PDC) constitutes a fundamental research focus in petroleum and mining engineering. This study presents an experimental investigation into crack propagation failure characteristics during cutter-rock interaction. Through an integrated experimental approach combining mechanical testing with digital image correlation (DIC) monitoring, the complete failure process from microcrack initiation to macroscopic fracture network development was quantitatively characterized. Experimental observations demonstrate significant dependence of crack propagation patterns on PDC cutter geometry, particularly the back rake angle. Initial fracture development (Stage I) exhibits predominant shear failure mechanisms, with tensile crack formation becoming progressively dominant during sustained loading (Stage II). The DIC-derived Displacement Field analysis revealed three distinct crack interaction modes: parallel propagation, bifurcation merging, and hierarchical networking. These findings provide a solid theoretical foundation for further research on PDC rock-breaking mechanisms, contributing to the optimization of drilling operations in engineering applications.

This paper is an attempt to investigate the rock indentation behaviors of a conical pick under different loading rates (1, 2, 3, and 4 mm/min), indenter types (sharp and blunt indenters), and types of rock (concrete, limestone, granite). Serial indentation tests by indenters were first performed by an automatic universal testing machine and monitored by an i-SPEED high-speed camera to record the peak pick force, indentation depth, rock fracture area, and rock failure process. Accordingly, the effect of loading rates, rock brittleness, and pick type on rock indentation behaviors was subsequently analyzed for a sound understanding of rock fragmentation mechanisms with indenters. It was found that higher loading rates necessitate a higher pick force and indentation depth to achieve rock fragmentation, resulting in a larger fractured area. Notably, a positive linear relationship exists between loading rates, rock-breaking forces, and fracture areas. A sharp indenter induces multiple cycles of repeated crushing and chipping phases, resulting in an arcuate-shaped fracture pattern with a smaller fractured area. Conversely, the rounded blunt indenter leads to a single stage of compression, with cracks propagating directly through the rock specimen, producing a larger fractured area. In addition, rock brittleness is another key factor to control rock failure efficiency, with tensile strength serving as a significant component.

Field penetration index (FPI) is a representative key indicator for tunnel boring machine (TBM) performance estimation, however its application in real tunneling projects is still limited because of the lack of some theoretical knowledge on the relationships between FPI, rock mass properties, and TBM specifications. This study aims to establish a theoretical FPI model by analyzing the tool–rock interaction of disc cutters from a theoretical perspective. This was first done by comparison of the tool–rock interaction of the disc cutter with that of the polycrystalline diamond compact (PDC) bit, which indicated that they share similar rock breakage mechanisms and force equilibrium. A series of cutting tests were then conducted on granite, marble, and limestone to determine the relationship between rotary torque and applied thrust during the rock cutting. Referring to the test results and tool–rock interaction features of the PDC bit and disc cutter, a theoretical FPI model of the disc cutter was derived and verified using the field TBM performance dataset. It was found that the rotary torque was linearly correlated with the thrust but independent of the rotation speed during the rock cutting. In addition to the machine specifications’ contribution, rock mass parameters and abrasiveness purely control this linear relationship. The theoretical FPI model proved that FPI shows a strong positive linear relationship with rock mass properties (uniaxial compressive strength and rock integrity), even under different drilling conditions, providing a theoretical basis for empirical FPI model establishment. Therefore, in practical engineering, it is recommended to use multi-parameter rock mass classification system values—such as rock structure rating (RSR), rock mass rating (RMR), and tunneling quality index(Q)—instead of individual rock mass properties —such as uniaxial compressive strength, to establish or update semiempirical FPI models.

Test results on the suffusion of sand-rock mixtures (SRMs) in one-dimensional laboratory seepage tests are reported with details regarding the experimental setup and procedures. The nuclear magnetic resonance (NMR) systems were successfully applied to track fine-particle migration through pores and detect the pore size distribution of SRMs during suffusion. This article discussed the changes of pore size distribution and fine-particle migration and its effect on the suffusion mechanism at 0, 15, 30, 60, 90, and 120 min under the critical hydraulic gradient. Then, the mesostructural changes of mixtures—such as pore distribution, curvature coefficient, and pore fractal dimension—were analyzed to reveal the suffusion mechanism, and an original suffusion evaluation model was proposed. The results showed that the pore connectivity and fine-particle migrations as two controlling factors for suffusion are an interactive process. Furthermore, the pore size range was narrowed and mostly concentrated in large pores with an increase of pore volume, resulting in fine-particle migration and structural deterioration. Moreover, the suffusion evaluation model was divided into four stages by the mesostructural parameters variation.