Fracture Traces Research Articles

The goodness-of-fit of models for fracture trace length distribution: Does the power law provide a good fit?

Fracture trace length distributions are often assumed to follow a power law, which implies that the distribution is scale-independent. The present study tests this assumption by evaluating the goodness-of-fit of three statistical models—the power law, piecewise power law, and lognormal distribution—upon a dataset of 57 trace maps that cover a range of fracture modes, host rock types, network scales, and topologies. The goodness-of-fit was assessed through the unbiased Kolmogorov-Smirnov (KS) test, which accounts for the fitting procedure and the degrees of freedom of each model. The results show that the power law provides a poor fit to trace length distributions, being rejected in 24 trace maps at a significance level of 0.05. In contrast, the piecewise power law and lognormal distribution demonstrated better fits across the fracture networks, with the piecewise power law performing the best overall. The poor fit of the power law can be attributed to mechanical and chemical controls on fracture growth, mainly fracture abutment, as well as stress shadowing and cementation, which affect growth rate at different length scales and result in scale-dependent trace length distributions. The consistent poor fit of the power law across various fracture networks suggests that these controls are prevalent in natural systems. While the power law remains a simple and effective model for trace length distribution, it should be recognized that it overlooks such controls that can influence the mechanical and hydraulic properties of fracture networks. Meanwhile, the fit of the piecewise power-law suggests the existence of a characteristic length where a transition in fracture growth occurs.

Assessing fragmentation and potential sliding zones in rock tunnels via computer vision technology

During the excavation of rock tunnels, accurately understanding the structural characteristics of the tunnel face is crucial for ensuring construction safety. The study evaluates the structural characteristics of the tunnel face by precisely characterizing and analyzing parameters like fracture trace length and dip angle, aiming to calculate the degree of fragmentation and potential sliding zones of the rock mass. In evaluating rock fragmentation degree, the study identifies and quantifies fracture trace lengths as a single-factor indicator to assess the fragmentation of the rock mass on the working face. By comparing with the p21 index, the reliability and reasonableness of the rock fragmentation evaluation are discussed. For the evaluation of potential sliding zones, a method for approximating the extraction of fracture traces is proposed. The assessment is then conducted based on multi-factor indicators, including fracture dip angle and length. Additionally, the advantages and disadvantages of various indicators under different calculation methods are discussed. The study finds that rock fragmentation indicators offer a more detailed and accurate description of the actual fracture density of the rock mass compared to the P21 index, proving to be generally more reliable under extreme conditions. Furthermore, the evaluation of rock fragmentation and potential sliding zones on the rock face can provide important references for the refined extraction of rock mass structural characteristics, ensuring the safe construction of tunnels.

REVIEW OF A CLINICAL CASE OF TRANSTROCHANTERIC FRACTURE

Introduction: Intertrochanteric or transtrochanteric fractures are defined as extracapsular fractures of the proximal femur that occur between the greater and lesser trochanter. A clinical case is described below from the time of the initial incident to the final ambulatory control and updated notes on the management of intertrochanteric fractures are made. Objective: to describe this clinical case objectively and to make an analysis of the subject. Methodology: An objective description of the clinical case and a review with analysis of a total of 17 articles, including review and original articles, as well as cases and clinical trials, of which 9 bibliographies were used because the information collected was not sufficiently important to be included in this study. The sources of information were Cochrane, PubMed and Google Scholar; the terms used to search for information in Spanish, Portuguese and English were: transtrochanteric fracture, femur fracture, intertrochanteric fracture, femur osteosynthesis. Results: the use of cephalomedullary nails reduces fracture collapse in comparison with the screwed plate. Cephalomedullary nails have been more effective in intertrochanteric fractures with subtrochanteric extension and in fractures with a reverse obliquity pattern. The type of surgical treatment is based on the fracture pattern and its inherent stability, since the failure rate is highly correlated with the choice of implant and fracture pattern. Conclusions: it is of utmost importance to know the proper management of a fractured patient, especially when the fracture is severe and life-threatening. The management of proximal femoral fractures will depend on their classification and the condition of the affected individual. Therefore, a good imaging study is essential. When deciding on a surgical approach, the material to choose in the procedures has to be ordered with planning and caution, because this will vary according to the type of fracture, being usual to perform different types of surgeries in intertrochanteric fractures being more common the use of intramedullary nails compared to femoral neck fractures, where it is more common the use of cannulated screws, or prosthesis depending on the type of fracture trace. Our clinical case gives a brief view on the surgical management of the pathology, which has to be understood for the best performance of the patient. KEY WORDS: fracture, transtrochanteric, femur, intertrochanteric.

Investigation on dynamic splitting mechanical properties of weakly cemented siltstone based on digital image correlation method and FracPaQ algorithm

Soft strata composed of weakly cemented rock are frequently subjected to dynamic loads in underground energy mining engineering, yet the dynamic mechanical properties of these materials remain insufficiently explored. In this study, dynamic splitting tests were conducted on Brazilian disc specimens of weakly cemented siltstone to assess their dynamic mechanical and failure characteristics. The findings revealed that both dynamic strength and dissipated energy increased under higher stress rates. A dynamic splitting strength model for weakly cemented siltstone was subsequently developed based on the incubation time criterion. Additionally, the digital image correlation technology was employed to analyze strain variations during the initiation of the main crack, and the quantitative analysis of the fragmentation process indicated that average opening rates increased with rising stress rates. The FracPaQ algorithm was also applied to further characterize fracture patterns under varying stress rates, demonstrating that the Gaussian function accurately represented the relationship between deflection angles and fracture trace lengths. These research outcomes can provide essential mechanical parameters and a theoretical foundation for the safety assessment of weakly cemented rock strata in coal mining.

New constraints from in-situ U-Pb ages and fluid inclusions of calcite cement and structural analysis on multiple stages of strike-slip fault activities in the northern Tarim Basin, NW China

Dating the activity of complex faults and fracture systems is crucial for creating reliable geological models for various tectonics and subsurface engineering applications. This study presents a comprehensive study integrating U–Pb fracture cement dating, trace elements, and fluid inclusion temperature analysis with seismic analysis of faults, fault diagenesis, and burial history studies to better constrain faulting and fracture activities in an intra-cratonic strike-slip fault system in the northern Tarim Basin. Seismic profiles indicate at least three distinct phases of fault activity corresponding to the Middle Ordovician, Permian, and Paleogene periods. Fracture cementation and crosscutting relationships corroborate the identification of three fracturing stages. U–Pb dating of fractured cement has widely detected Middle Ordovician and Early Permian age intervals. Fluid inclusion homogenization temperatures from the fractured cements, ranging across < 50 °C, 70–130 °C, and 150–180 °C, correspond to three episodes of rapid subsidence during the Ordovician, Permian, and Neogene, respectively. These results suggest three phases of fault/fracture reactivation in the Middle Ordovician (prior to 470 Ma), Early Permian (prior to 295 Ma), and Cenozoic. The fault/fracture reactivation in the Ordovician is closely related to the regional tectonic transition from extension to compression, while fault and fracture reactivation in the Early Permian may be related to hydrothermal activity associated with large-scale igneous province and oil emplacement. Fault/fracture activity in the Cenozoic may be related to a reduction in subsidence, gradual reduction of geothermal gradients, and massive oil emplacement. This research underscores the significance of integrating geochemical and subsurface datasets for accurately determining the timing of faulting and fracturing in sedimentary basins.

Automatic detection and characterization of discontinuity traces and rock fragment size distribution using a digital image processing method

Rock materials naturally contain cracks and fractures, which may produce rock fragments or grains under geological and engineering conditions. Identification and characterization of the spatial extent of discontinuity traces and size distribution of fragments/grains are prerequisites for accurate geomechanical assessments of the stability of rocks containing natural or artificial discontinuities. This study introduces an advanced image processing methodology that leverages color gradient analysis and multi-threshold criteria to effectively detect and delineate fracture traces or boundary outlines. Furthermore, this approach facilitates the acquisition of precise fragment or grain size distribution statistics. To comprehensively characterize these discontinuity traces, the methodology employs the calculation of fractal dimensions alongside the use of an equivalent diameter conversion technique. These tools enable the quantification of the complexity and size distribution of the fragments or grains. The efficacy of this approach has been demonstrated through a series of case studies, encompassing a wide range of applications including digital images from numerical simulations, experimental tests, field observations, and micrographic analyses of rock structures. In these studies, the method proved capable of satisfactorily calculating the fractal dimensions of fractures, cracks, and contacts. Simultaneously, it accurately and efficiently determined the size distribution, as evidenced by frequency histograms and cumulative distribution curves obtained from the images. In essence, the proposed approach provides an automatic quantitative methodology to identify and characterize macroscopic and microscopic rock structures containing discontinuity traces or comprised of fragments/grains. This advancement holds significant potential for enhancing the precision and efficiency of geological and geomechanical assessments.

Utilizing semantic-level computer vision for fracture trace characterization of hard rock pillars in underground space

This study utilizes a semantic-level computer vision-based detection to characterize fracture traces of hard rock pillars in underground space. The trace images captured by photogrammetry are used to establish the database for training two convolutional neural network (CNN)-based models, i.e., U-Net (University of Freiburg, Germany) and DeepLabV3+ (Google, USA) models. Chain code technology, polyline approximation algorithm, and the circular window scanning approach are combined to quantify the main characteristics of fracture traces on flat and uneven surfaces, including trace length, dip angle, density, and intensity. The extraction results indicate that the CNN-based models have better performances than the edge detection methods-based Canny and Sobel operators for extracting the trace and reducing noise, especially the DeepLabV3+ model. Furthermore, the quantization results further prove the reliability of extracting the fracture trace. As a result, a case study with two types of traces (i.e., on flat and uneven surfaces) demonstrates that the applied semantic-level computer vision detection is an accurate and efficient approach for characterizing the fracture trace of hard rock pillars.

Mechanical properties of medium-temperature thermoelectric materials based on tin and lead tellurides

The strength and thermoelectric properties of PbTe and Sn0.9Pb0.1Te medium-temperature polycrystalline specimens with p and n conductivity types, respectively, have been studied. The specimens have been produced using extrusion and spark plasma sintering. The strength parameters of the materials were studied using uniaxial compression at 20 to 500 °C. The structure of the materials was studied using X-ray diffraction and electron microscopy. The electrical conductivity and the Seebeck coefficient were measured simultaneously using the four-probe and differential methods. The temperature conductivity and the specific heat capacity were measured using the laser flash and differential scanning calorimetry methods. The PbTe and Sn0.9Pb0.1Te materials produced using extrusion and spark plasma sintering prove to be single-phase and have homogeneous compositions. For comparable synthesis methods, the dislocation density in the Sn0.9Pb0.1Te specimens is by an order of magnitude lower than in the PbTe ones. Study of the mechanical properties of n and p conductivity type specimens over a wide temperature range from 20 to 500 °C has shown that their deformation is plastic and has no traces of brittle fracture. For these plastic materials, the strength criterion has been accepted to be the arbitrary yield stress corresponding to the stress at a 0.2% deformation. The 20 °C yield stress of PbTe and Sn0.9Pb0.1Te is far higher for the specimens produced by extrusion. For all the test temperatures and synthesis methods the Sn0.9Pb0.1Te specimens have a higher strength than the PbTe ones. The PbTe and Sn0.9Pb0.1Te specimens produced by extrusion have better thermoelectric properties than the spark plasma sintered ones. The heat conductivity of the PbTe and Sn0.9Pb0.1Te specimens is almost the same regardless of compaction method.

A Workflow for Interpretation of Fracture Characteristics Based on Digital Outcrop Models: A Case Study on Ebian XianFeng Profile in Sichuan Basin

Abstract Collecting information about fracture attributes through outcrops measurement is crucial for analyzing the scale, distribution, orientation, and spatial arrangement of fractures. The emergence of digital outcrop models (DOMs) provides a new technology for quantitative interpretation of fractures. However, large-scale DOMs pose additional challenges to the practical application, particularly in the interpretation of geological elements (e.g. fractures). This research proposes a workflow for fracture characteristics interpretation based on DOMs. First, DOMs are generated using light detection and ranging scanning technology. Then, a 3D visualization platform is developed based on OpenSceneGraph. We use level-of-detail technology to reconstruct DOMs for multiscale fast visualization of large-scale models. Finally, in order to realize the quantitative interpretation of fractures, we propose the best-plane fitting and the feature information (orientation, length, spacing, etc.) extraction methods for two types of fractures (exposed fracture walls and fracture traces). The proposed methods are applied to extract attributes of fractures in Dengying Formation (second member), Ebian, Xianfeng, southwest Sichuan Basin, China. The results provide the basis for reservoir evaluation in this area.

Automated mapping of bedrock-fracture traces from UAV-acquired images using U-Net convolutional neural networks

This contribution presents a novel U-Net convolutional neural network (CNN)-based workflow for automated mapping of bedrock fracture traces from 0.55 cm spatial resolution aerial photographs, acquired by unmanned aerial vehicles (UAV), over the Wiborg Rapakivi granite outcrops in the islands off the coast of the Loviisa Region in Southern Finland. The workflow comprised training a U-Net CNN using a small subset of photographs with manually traced fractures for optimizing the network parameters using the root mean squared propagation optimizer and sigmoidal focal loss function for semantic segmentation of input images and pixel-wise identification of fracture traces. The ridge detection algorithm was then applied to the U-Net prediction results, followed by vectorization of the fracture-traces pixels as vector polylines representing the traces of fractures. Both intensity values of the pixels and topological connectivity were used in the process of vectorization. Quantitatively the results were assessed using various accuracy assessment metrics. Qualitative evaluations of the results were implemented by comparisons of orientations and length-frequency distributions of automatically- and manually-mapped traces.The results show that the model has the class-balanced accuracy score 0.945, predicting 88.79% of the fracture-trace pixels. Bedrock outcrops with well-exposed surfaces present high true positive rates (>99%). The demonstration (test) site has the class-balanced accuracy score of 0.873 and 75% true positive rate. Additionally, the fracture trace networks replicate the orientation distributions of the manually digitized traces. The length distributions of automatic traces, however, differ with varying intensity from the manual trace length distributions. However, this study demonstrates that the workflow can be successfully applied to UAV-acquired images for fast and efficient automated mapping of bedrock-fracture traces during the initial phases of structural characterization of a region.

Uniaxial compressive strength (UCS) and SEM study of liquid nitrogen for waterless hydraulic fracturing in coalbed methane reservoirs of Karaganda Basin in Kazakhstan

Four different cryo-fracturing liquid nitrogen (LN2) treatment processes are compared for stimulation of coal. Namely, peak compression strength, acoustic emission, and energy absorption tests, plus scanning electron microscope (SEM) observations for fracture evolution were conducted for freezing time (FT), freezing-thawing cycle (FTC), negative freezing-thawing cycle (NFTC) and positive freezing-thawing cycle (PFTC) LN2 exposure processes for both dried and water-saturated specimens. The positive and negative freezing-thawing cycle experimental processes are novel variations on multi-contact cryogenic stimulation reported for the first time. In all freezing-thawing processes, water-saturated experiments exhibited lower Uniaxial Compression Strength (UCS) peaks compared to dry coal samples, presumably due to the additional frost forces degrading the overall sample integrity. For all LN2 exposure processes using dry coal specimens, the compaction line decreased and the elastic line decreased in acoustic emission (AE) tests, concurrent with a reduction in compressive strength, as LN2 treatment time increased. This trend reversed in water-saturated samples, highlighting the importance of sample water content on fracturing potential. Energy absorption analyses clearly showed that the strength of coal samples decreased with increasing the freezing time and freezing-thawing cycles, as the LN2 treatment produced more cracks and damage to coal. Furthermore, SEM analysis and image processing confirmed that all LN2 treatment processes resulted in the generation of fractures evident in fracture trace statistic changes on the surface of coal samples. FTC and PFTC processes showed the greatest promise as stimulation methods due to the extent of the network of fractures created. Engineering results were augmented with the inclusion of the geological setting, important for the transportability of these outcomes to coals of similar origin.

Groundwater Prospecting Using a Multi-Technique Framework in the Lower Casas Grandes Basin, Chihuahua, México

Groundwater is a strategic resource for economic development, social justice, environmental sustainability, and water governance. The lower Casas Grandes River Basin, located in the state of Chihuahua, México, is in a semi-arid region with increasing groundwater demand and regional challenges such as drought and depletion of aquifers. Even though there is official information about the availability of groundwater, a comprehensive aquifer characterization requiring an interdisciplinary investigation using a diverse suite of tools and multiple data sources has yet to be carried out. This study presents a multi-technique framework to evaluate potential sites to drill for groundwater resources and reduce the risk of unsuccessful drilling. The main components of the methodology include wellhead leveling correction with a differential global positioning survey to define piezometric levels, principal component analysis using LANDSAT-8 images, application of geospatial tools, geophysics analysis using time domain electromagnetic surveys (TDES) and vertical electric soundings (VES), and structural geohydrology to define aquifer characteristics. The results showed that using the proposed framework steps improved the possibility of identifying subsurface layers with lower resistivity values that could be related to groundwater. Low resistivity values (35 Ohm-m) were found at depths from 50 to 85 m at sites where the regional static water level reached a depth of 245 m, indicating the potential location of a shallow groundwater resource at a site where the intersection of a fracture trace was identified. This procedure can be used in other regions in the world where limited information is available for groundwater exploration, thus reducing the risk of drilling dry wells in complex hydrogeological environments.

The correlation of slip transmission/blockage with the fracture in Al-Mg alloy

An in-situ tensile test of Al-6wt.%Mg alloy has been conducted to explore the relations between slip transmission with fracture behavior. Detailed in-situ electron backscatter diffraction characterization and analysis of 1400 grain boundaries (GBs) were carried out at five different strain states. Three slip transmission parameters, Schmid factor m, Luster-Morris parameter m′, and residual Burgers vector Δb, were analyzed to characterize the dislocation-GBs interactions. Both intergranular and intragranular fracture was observed in the tensile test. The intergranular fractures tend to occur at slip-blocked GBs due to local strain concentration. The intragranular fracture traces coincide with grains having GBs where slip transmission traces were observed. The revealed correlations of slip transmission/blockage with fracture can be applied to failure analysis and simulation of polycrystalline materials.

Hydrogeologic and geomorphic processes in a karst landscape and seasonably-cold climate: Linking spatial distribution and morphometric dynamics of closed depressions to bedrock fractures in a wastewater spray irrigated agricultural and forest system located at the site of the Living Filter in Central Pennsylvania, United States

The Living Filter at Pennsylvania State University in Central Pennsylvania receives on average 1.5 million gallons per day (MGD) of secondary treated wastewater effluent year-round since 1962. The objective of this study was to identify and relate any bedrock fracture traces and surface depressions to any surficial or geomorphologic processes currently underway as a result of irrigation. The Living Filter is underlain by a massive dolomite with fractures trending near N-S that were previously documented using photogrammetry. A manual process was developed in order to determine the trend and location of several fracture traces within the Astronomy site section of the Living Filter. A semi-automated isolation scheme was next used to identify and correlate closed depressions to the location of fracture traces in the Living Filter. A predominant but slight NE-SW trend was observed among fractures at N5E in the area north of the Pennsylvania Furnace Anticline. A high occurrence of depressions was noted in the area of fractures compared to non-fractured bedrock. The depressions in this area were found to have a net gain of 8000 ft2, the result of which was from the net loss of 5000 ft2 within the agricultural portion of the site and a net gain of 13,000 ft2 within the forested portion of the site. Cross sections of several depressions within cropped areas indicated a lower angle slope corresponding to a V-shape while depressions within forested areas were characterized by a traditional U-shape and previously established steeper slope. These findings will enhance the current understanding of the different morphologic characteristics of both forested and agricultural depressions in karst topography. The workflows implemented here can be implemented in similar sites that display topographical variances from the bedrock fractures.

The characteristics of natural open fractures in acoustic borehole image logs from the pre-salt Barra Velha formation, Santos Basin, Brazil

Natural open fractures have been reported in the Barra Velha Formation (BVE) in the pre-salt lacustrine carbonate reservoirs in the Santos Basin offshore Brazil. These fractures contribute to excess permeability i.e., well test permeability is significantly larger than core permeability or log derived permeability, and they are therefore important for the fluid flow in the reservoirs during production and injection. In this paper we summarize the characteristics of natural open fractures in acoustic borehole image logs (BHI) in 19 wells from the BVE reservoirs and discuss their distribution, occurrences and formation. The data quality is overall good and consistent so that results can be compared between wells. The P21 fracture intensity, which is fracture trace length per area (bore hole wall) was used, instead of Terzaghi corrected P10 fracture intensity which do not distinguish between minor and major fractures. Mean P21 fracture density shows a variation of 2 orders of magnitude between interpreted wells. Data binning was used in the analysis of P21 fracture intensity vs petrophysical parameters to reduce the effect of sampling volume being much smaller than the representative elementary volume (REV) of the fracture pattern. P21 fracture intensity shows a positive correlation with silica content, which varies in the carbonates, whereas the porosity is less important for fracture intensity. The occurrence of fractures is also associated with vug-fraction estimated from the acoustic BHIs. Fractures are also frequent in fault damage zones, above and below cavities. The main orientation of the fractures is NNW-SSE, that is in the same direction as the dominating fault trend, and this indicates a structural control on fracture formation. Natural open fractures are rare in high porosity rocks with a shrubby or grainy texture, and also in intervals with a conglomeratic appearance in the BHI image logs.

Rough discrete fracture network multi-parameter joint modeling based on improved neural spline flow

Discrete fracture network (DFN) modeling is a popular method for studying reservoir characteristics. However, on one hand of the existing DFN studies, the correlations that may exist among the multi-dimensional parameters of the fracture (dip, dip direction, trace length, aperture, and roughness) were ignored and each property was estimated independently. On the other hand, the 3D DFN models were simplified as flats without roughness. Therefore, this study proposes a simulation method for the rough discrete fracture network while considering multi-parameter joint distribution to make up for the stated deficiencies: (1) An improved deep learning model for the joint distribution estimation and joint sampling of the multi-dimensional parameters of the fracture is proposed, which is the Neural Spline Flow improved by the Multimodal Distribution (NSF-MD). The initial distribution of the Neural Spline Flow (NSF) is improved from a unimodal Gaussian to a multimodal mixed Gaussian, which enhances the fitting ability of the NSF model for the multimodal joint distribution. (2) A modeling assumption of the 3D rough fracture surface is presented to improve the conventional flat ones. In this way, a 3D rough fracture surface is generated by the NURBS tensor product of the fractal traces, and the fractal trace is simulated parametrically based on the fractal dimension. Finally, an outcrop DFN modeling application from southwest China indicates that the NSF-MD can simulate the correlations among the fracture multi-dimensional parameters and that the 3D rough discrete fracture network model (RDFN) increases the representation of the fracture roughness. The Wasserstein distance, which is an indicator quantifying the accuracy of the joint multi-parameter estimation, of the NSF-MD model was 72.4% and 81.9% better than that of the NSF model and that of the conventional method with parameters estimated independently, respectively. The relative distance error (RDE) and the global angle error (GAE) of the fractal traces were 87.9% and 88.3% more accurate than those of the conventional linear traces, respectively.

Morphometric Analysis of the Rawandoz River Basin, Erbil, Kurdistan Region, Iraq

In this research detailed morphometric investigation of the Rawanduz river basin in the northeastern part of Erbil, Iraq has been made. The study area covers an approximately 977.68 km2. Digital Elevation Model data (DEM 12.5 m), Remote sensing and GIS methods were used for studying basin morphometric parameter such as linear, aerial, and relief aspects, as well as to delineate lineaments in the study area.The results reveal that there is an opposite correlation between stream order, stream number, and length of streams in the research region basin by R2 values (R2 = 0.77 and 0.73) which is good value depending on statistical analysis. Streams were also ordered, with a total of 6376 streams totaling 2376.4 km in length. The basin's elongation ratio (0.54), circulation ratio (0.45), and form factor (0.23) data suggested that it was semi-elongated to elongated in nature, with poor permeability material, high relief, steep slopes, and main drainage pattern types affected by lineaments and fracture traces. In the research region, the stream frequency value is 5.6 km2 which is a high value suggesting impermeable lithology and enhanced surface runoff in the basin area. The drainage density in the investigated area is 2.43 km-1. The Rawanduz river basin's high drainage density value (2.43 km-1) reveals a fine drainage texture value (38.77 km-3). This study will help decision-makers and local residents to benefit from the resources for the sustainable development of the basin area.

Natural fracture characterization of the Los Catutos Member (Vaca Muerta Formation) in the southern sector of the Sierra de la Vaca Muerta, Neuquén Basin, Argentina

The Vaca Muerta Formation is the main source rock of the Neuquén Basin in Argentina. The interest in this unit has grown over the years as it is considered an excellent unconventional exploration target. It is characterized by a naturally fractured succession of dark organic-rich shales deposited due to a marine transgression during the Late Jurassic to Early Cretaceous. In the Sierra de la Vaca Muerta area, the southernmost sector of the Agrio fold and thrust belt, a carbonate-dominated interval in the Vaca Muerta Formation is outcropping characterized by tabular micritic limestones intercalated with marls known as the Los Catutos Member. This member usually exposed large pavements that allow good observations of the fracture pattern and lengths. We performed a natural fracture network analysis over the mid-upper Tithonian Los Catutos Member outcrops. 585 fractures were measured in the field, and 665 fracture traces were manually mapped using an aerial image acquired by an unmanned aerial vehicle (UAV). Four main sub-perpendicular to the bedding fracture sets were identified, trending WNW-ESE, N–S, NW-SE, and NE-SW. The fracture length distribution was analyzed using the maximum likelihood estimator technique, revealing a lognormal distribution as the best fit for the sets recognized in the UAV image (WNW-ESE, N–S, and NE-SW). Also, the fracture system was classified as stratabound given the spatial and length distribution. The relative chronology between the four fracture sets was established based on the observed abutting relationships; furthermore, based on a fold test, a pre-folding origin was deduced. Finally, a regional interpretation for fracture formation is proposed considering the structure and tectonic history of the basin. The WNW-ESE oriented set formed by the longest fractures together with the orthogonal N–S oriented cross-joints, give rise to a ladder pattern; this arrangement likely responds to an along-foredeep stretching scenario that characterized this area during the Paleocene. Then, the NW-SE and NE-SW oriented fracture sets were emplaced, probably associated with the layer parallel shortening phase installed before the onset of major thrusting and folding from the late Miocene onwards.

Blast damage zone influence on groundwater fluxes through backfilled open pits

The blast damage zone (BDZ) surrounding backfilled pits could significantly influence groundwater flow, increase flowrate through backfilled wastes, and potentially increase the dispersion of contaminants to the environment. A conceptual model of the fracture network of the BDZ was first proposed, which consisted of circular fracture oriented along the pit walls, and with a decreasing density with the distance to it. Realistic model parameters were also estimated based on the literature; BDZ equivalent permeability was analytically derived and used in 3D numerical models of conic open pits considering different backfilling scenarios. A total of 16 500 BDZ models were generated to assess the general influence of the BDZ on the flow and the influence of each parameter (fracture trace and attenuation length and fracture radius, aperture, and anisotropy). Results showed that the BDZ generally contributes to reduce (up to three orders of magnitude) the groundwater flow through backfilled tailings, but contributes to increase (by up to 250%) the flow in backfilled waste rocks, especially for wide and fractured BDZ in small pits. This study therefore suggests that the BDZ could be a self-sufficient containment structure to limit contaminant transports from backfilled tailings to the environment, but increases the risk considering waste rock.

Sensitivity Analysis of Fracture Geometry Parameters on the Mechanical Behavior of Rock Mass with an Embedded Three-Dimensional Fracture Network

The existence of fractures has a significant influence on the mechanical properties of a rock mass. The sensitivity of the rock mass’s mechanical properties to the fracture’s geometric parameters is conducive to improving the measurement accuracy of fractured rock mass engineering. Firstly, the fracture geometric parameters in the dam site area of Lianghekou Hydropower Station were counted using the ShapeMetriX3D system. Then, the effect of the fracture’s geometric parameters on the deformation characteristics, failure mode, and mechanical parameters of the rock mass were investigated based on the RFPA3D under the uniaxial compression test. The results showed that the stress–strain curves of the fractured rock mass mainly exhibited elastic-brittle characteristics. The failure pattern of the fractured rock mass was mainly defined by a compressive-shear composite. Additionally, the influence of the fracture’s geometric parameters on the uniaxial compressive strength (UCS) was greater than that of elastic modulus. The sensitivity of the UCS to fracture trace length was more significant.