Sparse tunnel advance borehole data constrain the precise spatial prediction of rock mass strength, posing challenges to engineering safety. To address this, this paper proposes a machine learning model integrating random forests with adaptive regularization to enhance predictive performance under small sample conditions. This method characterizes spatial variability in rock mass by introducing local correction coefficients and employs random forests for spatial interpolation. It employs adaptive regularization to dynamically balance the model's goodness-of-fit against the spatio-temporal smoothness of its predictions. Comparisons with support vector machines, gradient-boosted trees, and Kriging demonstrate that the random forest model achieves higher prediction accuracy and better generalization across training, validation, and test datasets. Its mean absolute error and root mean square error are significantly lower than those of the comparison methods. Residual analysis further reveals that the random forest's error distribution most closely approximates a normal distribution, exhibiting minimal variance and robust statistical reliability. Using the derived calibration parameters, a three-dimensional rock mass strength field was generated and risk zoning was performed, achieving intuitive visualization of potential hazardous areas. This method provides an effective and reliable new approach for rock mass strength analysis and risk assessment based on limited geological forecast data.
Mine water geothermal energy is emerging as an important renewable heat resource in former mining regions, offering opportunities for low-carbon heating, cooling, and thermal energy storage while supporting socio-economic regeneration. This perspective article provides an overview of the twelve contributions included in the Mine Water Energy thematic collection, covering resource assessment and mapping, drilling and development risk reduction, operational monitoring, thermal interference, climate change impacts, thermal energy storage, and regulatory and governance challenges. Together, these papers demonstrate significant advances in the understanding and deployment of mine water energy systems, while highlighting the need for continued research, collaboration and data sharing, coordinated subsurface planning, and supportive policy frameworks to enable their sustainable large-scale adoption.
The term bell pit is frequently applied to small, circular excavation features encountered within Coal Measures strata; however, its appropriateness is debated where classic bell-shaped morphology and spoil mounds are absent. Mining historians increasingly favour the terms shallow shafts or circular extraction shafts in such contexts, particularly where the target mineral is uncertain. This paper presents a detailed case study from Blackfordby, North West Leicestershire, where over 300 unrecorded shallow shafts were identified during pre-development ground investigation and archaeological works. The site lies within the Pennine Lower Coal Measures, where coal seams are thin and variable and historically associated with exploitation of industrial minerals including fireclay, pot clay and ironstone. A full site strip revealed a dense, grid-like arrangement of circular shafts up to 5 m deep, backfilled with loose mudstone gravel which were frequently water-bearing. The shafts did not exhibit classic bell pit profiles and failed to terminate within coal seams. Archaeological artefacts recovered from site date the activity to the 19 th century and suggest a potential link to local ceramic and brickmaking industries. Comparison with a nearby site at Hartshorne demonstrates similar shallow shaft morphology, colour differentiation and lack of identifiable coal extraction, supporting interpretation as exploratory or evaluative excavations for industrial minerals rather than coal. The findings highlight the limitations of coal-centric models for interpreting shallow mining features within the Lower Coal Measures and emphasise the importance of integrating geological, archaeological and geotechnical evidence. From a development perspective, the case study illustrates the significant ground risk posed by such features and demonstrates how bulk excavation and re-engineering can provide a cost-effective, low-risk remediation strategy while avoiding long-term mining legacy constraints.
Tensile strength and fracture toughness are critical mechanical properties governing fracturing behaviors of shale. However, the mechanical properties of continental shales remain poorly understood. Mechanical property measurements on an organic-rich continental shale from the Yanchang Formation were conducted using Brazilian tests (BT) and semi-circular three-point bending tests (SCBT), combined with acoustic emission (AE) tests. Variations in tensile strength and fracture toughness versus inclination angles θ are analyzed. The results show that both tensile strength and fracture toughness exhibit pronounced anisotropy. Tensile strength varies from 1.09 MPa at θ = 60° to 7.50 MPa at θ = 0°, whereas fracture toughness ranges from 0.056 MPa·m 0.5 for cracks propagating parallel to bedding to 0.659 MPa·m 0.5 for cracks propagating perpendicular to bedding. The maximum anisotropy ratios for tensile strength and fracture toughness are 6.89 and 11.78, respectively. The Chang 7 shale exhibits stronger anisotropy than those reported for marine shales, including the Longmaxi, Marcellus, and Mancos shales. These differences are closely associated with its bedding structure and high organic content. The experimental data provide a basis for characterizing the mechanical properties of the shale, and the findings also offer useful insights for hydraulic fracturing design in continental shale reservoirs.
Rainfall-induced landslides are widely distributed on vegetated slopes in northern Guangdong, China. The instability mechanism of vegetated slopes under heavy rainfall remains insufficiently understood based on field studies. This paper utilized dye infiltration tests to explore the relationship between root characteristics and seepage characteristics; and slope rainfall tests were carried out to monitor rainfall infiltration processes, mechanical and hydraulic responses, and slope deformation and failure. The results showed that coarse roots (>2 mm diameter) greatly enhanced rainfall infiltration rates and promoted homogeneous flow in shallow slope soil. Owing to the mechanical reinforcement of roots, surface erosion and internal suffusion were not evident, allowing the slope to effectively resist deformation. With continuous rainfall, water infiltrated downwards along root-soil interfaces and formed preferential flow, which was mainly controlled by fine roots (<2 mm diameter). Once infiltration reached the maximum root depth, water accumulated locally in that area to form high porewater pressure. Deformation initially occurred at the top of the slope, and the slope was prone to overall failure along the maximum root depth. These findings improve our field-based understanding of failure mechanisms in vegetated slopes.
