Fractured Rock Research Articles

The use of radar-optical remote sensing data and geographic information system–analytical hierarchy process–multicriteria decision analysis techniques for revealing groundwater recharge prospective zones in arid-semi arid lands

Abstract Arid/semi-arid regions face water challenges much like the Arabian Peninsula, which is primarily caused by continuing shortages and growing activities of reclaimed land, as well as industrial and domestic activities. Consequently, identifying groundwater prospective zones (GWPZs) has become essential for securing water resources. The study aims to delineate and predict the best areas of groundwater prospection and abstraction by implementing the analytical hierarchy process-geographic information system (GIS) techniques in a rough terrain that occupies ∼70% of fractured hard rocks including ∼34% of the basaltic flow sheet of Wadi Marawani, Saudi Arabia. To investigate the combined impact of the model, 13 input thematic maps, including elevation, slope, curvature, depression, drainage density, Topographic Wetness Index, distance to river, Stream Power Index, Terrain Roughness Index, geology, lineaments, Normalized Difference Vegetation Index, and rainfall factors, were created, and employed in the model, which was subsequently merged through GIS techniques to reveal prospective zones. These maps are mainly derived from Shuttle Radar Topography Mission, Sentinel-1, Landsat, and Tropical Rainfall Measuring Mission. The output map is categorized as very low, low, moderate, high, or very high, and excellent occupying ∼7%. This promising zone is the result of the intersection of several criteria that control groundwater occurrences. The results were enhanced by implementing optical and radar remote sensing data, and thus, suitable recharge places for the future governance and abstraction of groundwater have been identified using GIS–AHP–multicriteria decision analysis methods. For validation, large numbers of well/spring locations that reached 415 are used in total. The efficiency of the model is estimated at 79.90% (area under curve) based on the receiver operating characteristic curve. Moreover, the Interferometry Synthetic Aperture Radar coherence change detection image validated the predicted model and revealed areas of no-coherence areas marked in brown matched to vegetated areas and excellent zones of GWPZs. The applied methodologies and findings of this study present significant insights for water resources planning and management to develop groundwater resources in similar regions worldwide.

Modeling the mechanical properties of rock at different pore and confining pressures using the grain-based stress corrosion model

Summary A grain-based stress corrosion model is built from 3DEC-GBM (i.e., a three-dimensional discrete element grain-based model). The model employs the effective stress law and stress corrosion theory to study the time-dependent and time-independent deformation at the mesoscale of the sandstone with varying confining and pore pressures. The simulations adequately explain complex macroscopic time-independent behavior in terms of the mesoscale interaction of grains, and tension cracks were the dominant crack propagation pattern in the simulation for different confining and pore pressures. The traditional creep behavior observed in laboratory brittle creep experiments could also be accurately reproduced by the proposed model. The simulations show that the percentage of tension cracks in rock fractures decreases with increasing confining pressure and pore pressures. Increasing the applied differential stress and reducing the effective pressure can shorten time-to-failure and increase the creep strain rate, respectively. We conclude that the proposed model is an appropriate tool to analyze the deformation behavior of sandstone under coupled hydro-mechanical loading in both the short and long term.

Estimating Hydraulic Conductivity in Fractured Rocks Using Factorial Design and Borehole Imaging

Estimating Hydraulic Conductivity in Fractured Rocks Using Factorial Design and Borehole Imaging

Experimental and theoretical analysis of hard rock warming and fracture in microwave field

Experimental and theoretical analysis of hard rock warming and fracture in microwave field

Evaluating the Depth–Age Hypothesis for the Evolution of the Lunar Regolith

Abstract Lunar regolith is the fractured rock layer covering most of the lunar surface. This rock is fractured into regolith primarily by repeated meteorite impacts over eons. The depth of the regolith is determined by the maximum depth reworked by impactors. Older surfaces are expected to have thicker regoliths because they have been exposed to longer periods of bombardment than younger surfaces—a concept I refer to as the Depth–Age Hypothesis. To test the hypothesis, I compare published, measured regolith depths on mare basalts with published, measured surface ages of those mare. If the Depth–Age Hypothesis is correct, older mare surfaces should have thicker regoliths than younger surfaces. Contrary to the hypothesis, published data show that both younger and older lunar surfaces have median regolith depths ranging from about 3 to 9 m. Possible reasons for this finding include variations among measurement methods, reporting regolith depths with too great precision, and the inherent variability of the lunar regolith.

Dynamic behavior of a running crack crossing mortar-granite interface with different interface inclinations

High-strength mortar is widely applied in fractured rock reinforcement due to its strong bonding strength, where crack propagation crossing the interface is commonly seen. To investigate the dynamic crack propagation behavior across the interface, A side material cleavage triangle (SMCT) sample was adopted in this study with different interface inclinations and mortar strength considered. Impact testing of a split Hopkinson pressure bar (SHPB) system was conducted and cohesive models were established to explore the penetration process of the extending crack. With the numerical result and the measurement of the crack propagation gauges (CPGs), the dynamic stress intensity factor (DSIF) was determined using an experiment-based numerical method. The investigation results show that the excited crack always propagates across the mortar-granite interface regardless of the stiffness difference, and this phenomenon remains unchanged with increasing interface inclination. For SMCT specimens, as the strength grade of mortar increases, the time taken for cracks to propagate through the interface increases. As the interfacial inclination increases, the time taken during crack penetration through the interface is longer. Using Python coding, cohesive elements can be embedded in batches in the numerical model to simulate crack propagation behavior at the interface. As the interface inclination increases, the DSIF in both the mortar and granite regions exhibits an upward trend.

Mixed-mode crack growth simulation in rock-like materials with the smoothing gradient-enhanced damage model associated with a novel equivalent strain

Accurately modeling mixed-mode crack propagation in rock-like materials remains challenging due to the complexity of the deformation states and mechanism of fracture throughout the loading history. The objective of this paper is to analyze the damage process in rock-like materials using an enhanced smeared damage model. The mixed-mode failure in rocks is captured using our recently developed smoothing gradient damage model in conjunction with a novel equivalent strain formulation, which is developed by combining both the bi-energy norm equivalent strain and the four-parameter equivalent strain. To validate the accuracy of the developed method, several commonly reported rock fracture examples are considered in which complex crack paths and responses are reproduced and compared with the available experimental data.

Nonlinear Dilatancy Seepage Model of Single Rock Fracture with Shear Broken

Nonlinear Dilatancy Seepage Model of Single Rock Fracture with Shear Broken

Experimental and numerical characterization of hydro-mechanical properties of rock fractures: The effect of the sample size on roughness and hydraulic aperture

Experimental and numerical characterization of hydro-mechanical properties of rock fractures: The effect of the sample size on roughness and hydraulic aperture

The study of mechanical properties and fracture evolution of coal-rock masses under hard roof-soft floor conditions

As the depth of coal mining in China continues to increase, the fracturing of coal rock masses has an increasingly complex impact on the surrounding rock roadways. The majority of the mine’s roadways run through coal rock masses with hard roofs and soft bottoms, which typically exhibit complex dynamic behaviour. To further research the mechanical behaviour and fracture evolution of coal rock masses under hard-roof and soft-floor conditions, the study is based on the majority of working faces in a mine, which have hard roofs and soft floors. Uniaxial compression tests were utilized to study the mechanical properties of coal rock masses under hard-roof and soft-floor circumstances, using acoustic emission monitoring, whole-process imaging technologies, and fractal dimension analysis. The experimental results are as follows: The uniaxial compressive strength of the coal rock mass is significantly higher than that of its weakest component. The results of the experiment are as follows: The uniaxial compressive strength of coal rock mass is significantly higher than that of its weakest component. Samples with different soft rock strengths exhibited dissipated energy greater than the accumulated energy before the stress maximum, accompanied by volume expansion and the formation of shear surfaces. Samples with higher soft rock strengths tend to exhibit brittle failure, while weaker samples show stress-softening behaviour. Internal fracture complexity varies amongst samples with varying soft rock strengths. A fractal study of the acoustic emission parameters was carried out utilizing MATLAB programming. The fractal analysis results show that acoustic emission ringing counts and energy time series of coal rock masses under hard-roof and soft-floor settings have good fractal properties. The fractal analysis results show that acoustic emission ringing counts and energy time series of coal rock masses under hard-roof and soft-floor settings have good fractal characteristics. Acoustic emission ringing counts tend to have a larger correlation dimension than acoustic emission energy. However, while the sample is fracturing on a vast scale, the ringing count correlation dimension fluctuates very little. The correlation dimension distribution of samples with lower strength is more concentrated after the stress maximum, implying that the deformation and fracturing of the floor rock in highways under hard-roof and soft-floor circumstances are more complex. Both the correlation dimension D of acoustic emission ringing counts and energy indicate a continuous fall before peak stress, which can be used to anticipate coal rock mass fracture. This study, based on the mechanical behaviour and fracture evolution of coal rock masses under hard-roof and soft-floor conditions, provides a foundation for disaster avoidance by controlling the stability and structural deformation of floor rock in hard-roof and soft-floor highways.

Pressurised water flow in fractured permafrost rocks revealed by borehole temperature, electrical resistivity tomography, and piezometric pressure

Abstract. Rock slope instabilities and failures from permafrost rocks are among the most significant alpine hazards in a changing climate and represent considerable threats to high-alpine infrastructure. While permafrost degradation is commonly attributed to rising air temperature and slow thermal heat propagation in rocks, the profound impact of water flow in bedrock permafrost on warming processes is increasingly recognised. However, quantifying the role of water flow remains challenging, primarily due to the complexities associated with direct observation and the transient nature of water dynamics in rock slope systems. To overcome the lack of a quantitative assessment, we combine datasets of rock temperature measured in two deep boreholes (2016–2023), with electrical resistivity tomography measurements repeated monthly in 2013 and 2023; the site-specific temperature–resistivity relation determined in the laboratory with samples from the study area; and borehole piezometer data. Field measurements were carried out at the permafrost-affected north flank of the Kitzsteinhorn (Hohe Tauern range, Austria), which is characterised by significant water outflow from open fractures during the melt season. Borehole temperature data demonstrate a seasonal maximum of the permafrost active layer of 4–5 m. They further show abrupt temperature changes (∼ 0.2–0.7 °C) at 2, 3, and 5 m depth during periods with enhanced water flow and temperature regime changes between 2016–2019 and 2020–2022 at 10 and 15 m depth, which cannot be explained solely by conductive heat transfer. Electrical resistivity measurements repeated monthly reveal a massive decrease in resistivity from June to July and the initiation of a low-resistivity (< 4 kΩ m) zone in the lower part of the rock slope in June, gradually expanding to higher rock slope sections until September. We hypothesise that the reduction in electrical resistivity of more than an order of magnitude, which coincides with abrupt changes in borehole temperature and periods of high water heads up to 11.8 m, provides certain evidence of snowmelt water infiltration into the rockwall becoming pressurised within a widespread fracture network during the thawing season. This study shows that, in addition to slow thermal heat conduction, permafrost rocks are subjected to sudden push-like warming events and long-lasting rock temperature regime changes, favouring accelerated bottom-up permafrost degradation and contributing to the build-up of hydrostatic pressure, potentially leading to slope instability.

Pressure effect on wave propagation in saturated porous rocks with aligned fractures

Rock fracturing is widespread in the upper crust of the earth. Nearly all in-situ rocks are subject to subsurface pressures. Understanding the influence of effective pressure (difference between confining stress and pore pressure) on the elastic properties of fractured rocks is crucial for estimating in-situ seismic properties. Wave-Induced Fluid Flow (WIFF) and fracture Elastic Scattering (ES) attenuation mechanisms have been widely studied. However, the effects of effective pressure on WIFF and ES mechanisms in fractured rocks are relatively unexplored. To investigate the pressure influence on WIFF and ES in P and SV wave propagation, we developed a pressure-dependent dynamic model to incorporate Multi-shaped Microcracks' Squirt Flow (MMSF), Fracture-Background WIFF (FB-WIFF), Biot Flow, and ES mechanisms with non-linear elastic and hyper-elastic deformation stages. The results show that both the WIFF and ES mechanisms are affected by effective pressure, except for the ES mechanism of normal incident SV waves. The WIFF is more susceptible to effective pressure than the ES mechanism. In addition, the closure of microcracks (soft pores) during effective pressure loading continuously decouples the MMSF mechanism from the FB-WIFF, Biot Flow, and ES mechanisms, causing the increase in the velocity of the P- and SV- waves and the variations in the attenuation processes. These wave propagation characteristics help to understand the hydraulic properties of in-situ fractured rocks. By comparing model predictions with ultrasonic laboratory velocity data under varying effective pressure loading, we validated our model.

Real-time rock strength and fractures determination based on Measurement while drilling method via rock drillability index: an in-situ study

Real-time rock strength and fractures determination based on Measurement while drilling method via rock drillability index: an in-situ study

Multi-Fracture Propagation Law and Numerical Simulation of Hydraulic Fracturing in Carbonate Rock with Natural Fractures

Multi-Fracture Propagation Law and Numerical Simulation of Hydraulic Fracturing in Carbonate Rock with Natural Fractures

Analyzing Drill Core Logging Using Rock Quality Designation–60 Years’ Experience from Modifications to Applications

The accurate analysis of rock cores is of primary importance for designing in and on the rock mass environment. There are several methods for analyzing boreholes, but the most accepted and widely used method is the rock quality designation (RQD) value, which has been a core rating metric for six decades. The RQD value serves as: (1) an important input parameter for rock mass classifications such as RMR and Q; (2) a basis for calculating the Geological Strength Index (GSI) of boreholes; and (3) a key indicator in assessing rock mass quality, particularly in highly fractured or weak rock masses. The original RQD method has several drawbacks and shortcomings, which have led to numerous proposed amendments. This review paper aims to: (1) summarize alternative methods of calculating the RQD value; (2) analyze the sensitivity of different rock mass classifications to the accuracy of this value; and (3) present a systematic analysis of the practical implications of modified RQD methods, emphasizing advancements such as DFN modeling, seismic RQD techniques, and machine learning-based approaches. The findings provide a comprehensive framework for more robust and versatile assessments of rock mass quality.

Slit tube responses and rock fracture characteristics in slit charge blasting under high in situ stress

AbstractDeep mining of natural resources, like coal, is increasingly utilizing directional blasting technology with slit charge for rock blasting at greater depths. This study, based on numerical simulation methods, analyzes the dynamic behavior of slit charge blasting in three aspects: slit tube dynamic response, hoop stress evolution, and crack propagation. According to research findings, the failure mode of the slit tube mainly manifests as a tensile fracture of the inner wall and a shear fracture at the end connection, where the end connection of the slit tube is the weak point of the overall structure. The dynamic response of the slit tube mainly exhibits radial response in the vertical direction of the slit and hoop response in the slit direction. The hoop tensile stress plays a crucial role in determining the spread of cracks caused by explosions. As the in situ stress increases, the peak hoop tensile stress reduces, and the peak hoop compressive stress increases. This hinders the propagation of cracks. In addition, the directional impact is most pronounced in the middle of the borehole, with the longest primary directional crack observed. Conversely, the directional impact is least favorable near the bottom of the borehole. When the in situ stress reaches 60 MPa, the purpose of directional fracture has not been achieved, suggesting combining presplit blasting for in situ stress relief to improve rock breaking efficiency.

Acoustic emission characteristics and damage constitutive model of fractured sandstone under uniaxial compression

To investigate the statistical laws of acoustic emission energy (AEE) avalanche dynamics of sandstone under varying fracture lengths and dip angles, as well as to determine the relationship between acoustic emission (AE) parameters and damage variables, we studied the mechanical properties and AE characteristics of sandstone with a single fracture subjected to uniaxial compression with the aid of the Shimadzu AG-IS test system and the PCI-2 AE system. The AEE characteristics of fractured sandstone under load were analyzed based on the statistical method of avalanche dynamics, with emphasis on AEE distribution, aftershock sequence, and waiting time distribution. The Weibull distribution function that incorporates a correction coefficient β was employed to optimize the Weibull parameters based on the strain equivalent hypothesis theory, which led to the establishment of a statistical damage constitutive model for fractured rock. The results indicated that the peak strength of rock samples initially decreases and then increases with increasing fracture dip angle, and decreases with increasing fracture length. The AEE of the rock sample followed a power-law distribution, with a power-law index ranging from 1.62 to 1.81, which was independent of fracture length and dip angle. The aftershock sequence also adhered to a power-law distribution, whereas the waiting time exhibited a multi-power-law distribution. The proposed statistical damage constitutive model aligned more closely with the experimental curves compared to previous models that normalizes AEE.

Dynamic Failure Mechanism and Fractal Features of Fractured Rocks Under Quasi-Triaxial Static Pressures and Repeated Impact Loading

Mastering the dynamic mechanical behaviors of pre-stressed fractured rocks under repeated impact loads is crucial for safety management in rock engineering. To achieve this, repeated impact loading experiments were performed on produced fractured samples exposed to varying pre-applied axial and confining pressures using a split Hopkinson pressure bar test system in combination with a nuclear magnetic resonance imaging system, and the dynamic failure mechanism and fractal features were investigated. The results indicate that the dynamic stress–strain curves exemplify typical class II curves, and the strain rebound progressively diminishes with growing impact times. The impact times, axial pressure, and confining pressure all significantly affect the dynamic peak strength, average dynamic strength, dynamic deformation modulus, average dynamic deformation modulus, maximum strain, and impact resistance performance. Moreover, under low confining pressures, numerous shear cracks and tensile cracks develop, which are interconnected and converge to form large-scale macroscopic fracture surfaces. In contrast, specimens under a high confining pressure primarily experience tensile failure, accompanied by localized small-scale shear failure. Under low axial pressure, some shear cracks and tensile cracks emerge, while at high axial pressure, anti-wing cracks and secondary coplanar cracks occur, characterized predominantly by shear failure. In addition, as the confining pressure grows from 8 to 20 MPa, the fractal dimensions are 2.44, 2.32, 2.23, and 2.12, respectively. When the axial pressures are 8, 14, and 20 MPa, the fractal dimensions are 2.44, 2.46, and 2.52, respectively. Overall, the degree of fragmentation of the sample decreases with growing confining pressure and grows with rising axial pressure.

Experimental Study on the Behavior of Gas–Water Two-Phase Fluid Flow Through Rock Fractures Under Different Confining Pressures and Shear Displacements

Understanding the flow behaviors of two-phase fluids in rock mass fractures holds significant importance for the exploitation of oil and gas resources. This paper takes rock fractures with different surface roughness characteristics as its research object and conducts experiments on the gas–water seepage laws of fractures under various confining pressures and shear displacements. The results indicate that the higher the fracture surface roughness, the larger the equivalent fracture width and the higher the single-phase permeability of gas/water in the fractures. During gas–water two-phase flow, when the water phase split flow rate is high, the influence of the confining pressure and fracture surface morphology on the water phase is significantly higher than that on the gas phase. The relative permeability at the isosmotic point of the fractures increases with the increase in confining pressure and decreases with the increase in roughness. After the dislocation of shale fractures, the interphase resistance within the fractures reduces. The relative permeability of the water phase increases more significantly compared to that of the gas phase. The water phase split flow rate at the isosmotic point does not change significantly, and the relative permeability at the isosmotic point increases. This research is helpful for guiding the protection based on the conductivity capacity of the rock mass fracture network.

Groundwater recharge estimation from multiple independent methods in the fractured hard rock aquifers in the Densu River Basin, Ghana

Groundwater recharge estimation from multiple independent methods in the fractured hard rock aquifers in the Densu River Basin, Ghana