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Rainfall with heavy intensity and long duration is a main inducing factor that triggers landslides on anti-inclined rock slopes. Numerous interbedded anti-inclined rock (IAR) slopes in Southwest China frequently experience mountain collapses and landslides under heavy rainfall. Therefore, it is necessary to study the failure mode of IAR slopes during rainfall. In this study, the Linda landslide and Mari landslide, typical IAR landslides in the study area, were used as examples to build a physical model of IAR slopes under continuous rainfall conditions, and a self-made rainfall simulation system was used to mimic natural rainfall conditions. The multi-physics data of displacement, velocity, stress, strain, pore water pressure, and acoustic signals in model deformation and failure under rainfall conditions were obtained using multi-field monitoring technology. In addition, the materials' water content and mechanical parameters at different locations of the model were obtained after the experiment. The analysis results indicate that: in the first and middle periods of rainfall, the slope model experienced a shallow local deformation and a holistic toppling deformation; until the late rain, the failure of the IAR slope caused by rainfall finally presented a typical failure mode of multiple failures and collapses of regressive landslides. According to its multi-field evolution characteristics, the velocity and acoustic signals were highly consistent with the failure characteristics of the model, which could be used as landslide early warning indicators. In addition, it was observed that the shape of the multi-slip surfaces generated by the model was a concave double straight line extending from the slope toe to the slope surface and sharing the failure section at the slope toe. Finally, the deformation and failure process of the model could be speculated to be divided into five stages based on the deformation behavior and multi-field physical data feature: the initial interlayer dislocation stage, the deformation stage, the crack propagation stage, the retrogressive failure stage, and the holistic failure stage. The failure mode and deformation mechanism of IAR slopes under rainfall were revealed in the model test, which could provide appropriate guidance for the analysis and evaluation of similar landslides. Highlights: The failure of the interbedded anti-inclined rock slope model caused by rainfall presented a typical failure mode of multiple failures and collapses of regressive landslides. The velocity and acoustic signals are highly consistent with the failure characteristics of the model, and the shape of the multi-slip surfaces was a concave double straight line extending from the slope toe to the slope surface. According to its multi-field evolution characteristics, the deformation and failure process of the model under rainfall conditions can be divided into five stages. [ABSTRACT FROM AUTHOR]

Block-flexure toppling failures in interbedded anti-inclined rock (IAR) slopes present significant risks to infrastructure and safety. Based on the Linda landslide field investigations, this study conducted a series of physical modelling tests encompassing 15 slope angle and bedding angle combinations. The aim of 15 sets of tests was to explore the deformation and failure mechanisms in IAR slopes. The observations during the deformation and failure stages elucidated how changes in slope and bedding angles influence rock mass deformation and failure characteristics. The findings highlight that slope angle critically impacts IAR slope stability, while bedding angle notably affects deformation depth, failure area, and failure surface configuration. IAR slopes with bedding angles less than 60° tend to exhibit shallow, single-surface failures with the linear failure surface, whereas bedding angles exceeding 70° lead to deep-seated, large-area, multi-surface failures characterised by double-folded failure surfaces. The magnitude of the failure inclination angle increases with slope and bedding angles, ranging from 0 to 35°. Furthermore, deformation and failure in IAR slopes involve the progressive extension of cracks from the slope crest to the interior, eventually reaching the slope toe. Finally, the block-flexure toppling process in IAR slopes can be divided into an incubation deformation stage and an accelerated deformation stage, and based on curve characteristics, different deformation modes of the IAR slopes can be further classified as stepwise cumulative accelerated deformation mode and leap deformation mode. Highlights: Fifteen cases of physical modelling tests covering various slope angles and bedding angles were conducted to replicate the deformation and failure mechanism in interbedded anti-inclined rock (IAR) slopes; Slope angle plays a pivotal role in determining the stability of IAR slopes, whereas bedding angle controls slope deformation depth, failure area, and failure surface characteristics; The IAR landslide is a progressive failure process that extends from the slope crest to the slope toe; The deformation process of IAR slopes can be categorised into the incubation deformation stage and the accelerated deformation stage. Additionally, the deformation mode can be further classified as either stepwise cumulative accelerated or leap deformation modes. [ABSTRACT FROM AUTHOR]

In a recent discussion by Rashida and Singh (Rock Mech Rock Eng, 2023) regarding our paper (Tan et al. Rock Mech Rock Eng 56:7599–7617, 2023) investigating the thermal effects on non-Darcian flow within heated rock fractures, several points were raised. They argued that the temperatures and durations in our experiments may not induce thermal expansion in fractured rock due to low thermal expansion coefficients. Additionally, they highlighted potential water phase changes during heating and recommended precautions, such as pre-heated water and confining pressure, which were not implemented in our experimental setup. In response, we provide further clarification. Firstly, concerning heating time, our focus is on temperature-induced alterations in fracture geometry during the heating process rather than after temperature stabilization. Secondly, our detailed analysis of the coefficient of thermal expansion for granite specimens confirms that thermal expansion does lead to fracture closure within the imposed temperature range, affecting flow characteristics. Lastly, considering the aims of the study, precautions against water phase changes were not implemented, but the potential water phase changes had a negligible effect on our results due to the low temperatures employed and the short water residence time in the fracture. In summary, we maintain the methodological soundness of our experimental setup and the appropriateness of the obtained results in alignment with the objectives of our study. The discussion and this response are helpful to further clarify our experimental results and eliminate potential ambiguities. Highlights: Temperature-induced alterations in fracture geometry during the heating process are noteworthy. Even minor fracture closure resulting from thermal expansion markedly influences flow behaviors. Low test temperatures render potential water phase changes inconsequential to our findings. [ABSTRACT FROM AUTHOR]

Water flow through fractured rocks in high-temperature settings is relevant to many subsurface geo-energy engineering projects including geothermal energy extraction, hydrocarbon production, and nuclear waste disposal. However, existing studies have either focused only on flow process within fractures at room temperature or on the thermal effect on fracture permeability. As a result, how and to what extent rock temperature affects the flow behavior in rock fractures remains poorly understood. Herein, we report an experimental study of the heated flow behavior in rock fractures at steady-state elevated temperatures under sequentially increasing flow rates. We find that rock temperature greatly affects the flow behavior within the fracture via two mechanisms: water properties variations and fracture closure. The former reduces the flow resistance, while the latter both reduces the effective hydraulic aperture and enhances the inertial effect. The more heterogeneous the initial aperture distribution is, the more significant the effect of the temperature-induced fracture closure on the flow nonlinearity will be. By combining the Forchheimer equation with water temperature measured at the fracture inlet and outlet, we quantitatively evaluated the effect of these two mechanisms on rock fracture permeability and flow nonlinearity. Finally, we develop an empirical expression for the critical hydraulic gradient of the fracture at different temperatures based on the nonlinear flow model for room-temperature fractures to quantify the emergence of non-Darcian flow. The findings from the present study are expected to shed insight into the prediction and evaluation of fluid flow within deep subsurface fractured reservoirs. Highlights: Physical mechanism of thermal effect on water flow in heated rock fractures is revealed experimentally. Thermal effect promotes non-Darcian flow by changing water properties and inducing fracture closure. A parametric model to predict onset of non-Darcian flow in heated fractures is proposed. [ABSTRACT FROM AUTHOR]

Block-flexure toppling is the most common toppling mode occurring in interbedded anti-inclined slopes. With the development of hydropower projects in Southwest China, numerous deep-seated large-area toppling failures have become revealed along the Yalong River, seriously threatening the construction and operation of hydropower infrastructure. With the Mari landslide as the research focus, a geological field investigation, base friction physical model test, and numerical simulation test were carried out to study the evolutionary process of slope failure. The results demonstrate that the deep-seated toppling in the study area initiated and developed with the river downcutting process, and the landslide was the final result of the toppling deformation. The interbedded structure of layered rock masses, the steep slate foliations in the slope, and the cross joints in the metamorphic quartz sandstone perpendicular to the rock layer are the controlling factors of the toppling deformation. The landslide induced by toppling mainly developed in the highly deformed zone, where multiple failure surfaces developed, and the location and shape of the failure surfaces were controlled by the cross joints in the metamorphic quartz sandstone. The evolutionary process of the deep-seated large-area toppling in the study area mainly underwent four stages: the initial slope formation stage, the rock column bending and cracking stage, the failure surface penetration stage, and the failure stage. [ABSTRACT FROM AUTHOR]

Exploring mechanical properties of red bed rock of Badong Formation Section two (b2) from the Three Gorges Reservoir is crucial to determine the instability mode of reservoir slopes. In order to reveal the energy evolution laws for b2 rocks under different stress paths, loading tests, unloading tests, and cyclic loading-unloading tests were conducted, respectively. The results show that stress paths have significant influences on the mechanical properties and energy evolution characteristics of b2 rocks and the failure mechanism under three stress paths is revealed. Relative to the loading tests, the mechanical parameters of b2 rocks are deteriorated under the unloading conditions. In addition, the increasing trend of cumulative dissipation energy (CDE) is similar with that of total absorption energy (TAE) and the ESE-strain curves are characterized by multistep rise. For cyclic loading-unloading tests, the areas of hysteretic loop gradually increase as the cycle times increase, and the TAEs and the coefficient of the cumulative dissipation energy (CCDE) also increase gradually with approximately linear characteristics, while the CDEs gradually increase in an abrupt rate. This work can contribute to provide the failure mechanism of b2 rocks for evaluating the stability of reservoir slopes from the energy perspective. [ABSTRACT FROM AUTHOR]

The accurate determination of crack initiation stress (CI) is significant for understanding rock deformation and failure. In this paper, a new concept is introduced, namely the relative compression strain response (RCSR), which represents the compressive deformation of the rock before dilatancy of the rock is introduced. An RCSR-based method for determining CI is proposed and compared with existing methods, i.e., (1) the volumetric strain (VS) method, (2) the lateral strain (LS) method, (3) the crack volumetric strain (CVS) method, (4) the cumulative acoustic emission hit tangent (CAEHT) method, and (5) the lateral strain response (LSR) method. Data for the comparison are collected from 227 uniaxial compression test and 222 compression test for diverse rock types. The comparison results show that, the CI determined using the proposed method is in good agreement with that determined using the existing methods. The CI values determined using different methods are similar, at approximately 0.5 of uniaxial compressive strength (UCS). The ratio of CI to peak strength (PS) is approximately 0.55 under triaxial compression, which is greater than the CI/UCS ratio. According to the analysis of variance (ANOVA), there is no statistical difference among the existing methods. Compared with the exisiting methods, the proposed method has advantages of avoiding users judgment subjectivity Thus, the RCSR method can be employed to determine the CI under uniaxial and triaxial compression. [ABSTRACT FROM AUTHOR]

This paper outlines the spatial-temporal evolution of a landslide. A multiple monitoring system that consists of a three-dimensional (3D) laser scanner, a particle image velocimeter (PIV), earth pressure cells (PCs), and a thermal infrared (TIR) imager were designed and employed for a 1 g landslide model case study. The displacement, velocity, lateral earth pressure and surface temperature were recorded during the evolution of a landslide. Four stages of evolution were identified using the measured displacements: the initial stage, the uniform stage, the accelerated stage and the failure stage. The deformation, lateral earth pressure and surface temperature of a landslide were monitored during each stage. The distribution of the lateral force with depth varied significantly during movement, and the depth of the maximum soil pressure increased with movement. The surface temperature of the moving mass was significantly higher than the surface temperature of the nonmoving mass. The average change in surface temperature showed a significant increase in surface temperature followed by a decrease in surface temperature prior to failure. This study provides procedures and solutions for landslide monitoring, interpreting landslide initiation and detecting landslides. [ABSTRACT FROM AUTHOR]

Earthquake waves influence rock toppling stability, and the effects of local earthquake propagation and topographic also affect slope deformation. Detailed engineering geology conditions of slopes are obtained and a geomechanical characterization of rock topplings is performed. To study the input earthquake waves and slope interactions, a dynamic analysis is performed using the UDEC 4.0 discrete element method (DEM) numerical code under viscoplastic conditions. The earthquake signals are representative of different peak ground acceleration, Arias intensities, and frequencies, and are used in the study of different rock topplings with different height, slope angle, and strata dip angle. The derived outputs are processed for the earthquake propagation study and to assess the induced deformation mechanisms in terms of resulting displacements, plastic zone features, and deformation mode. The results prove that an interaction exists between stratigraphic and topographic effects on earthquake wave propagation, and that these effects cannot be assessed independently. The obtained results describe the effect of topography and geological settings in rock topplings, amplifying or de-amplifying earthquake ground motion, and demonstrate that the tensile state dominates at the slope surface but evolves with depth. A shear state dominates at the toe or in the deep part of rock topplings. The rock toppling deformation mode may develop into a composite of tension fractures at the crest and sliding at depth. Compared with the static scenario, under earthquake load, tensile deformation evolves over a larger area at the crest and develops a shear zone at the toe and in the substrata. The necessary earthquake-induced toppling conditions are discussed, and the UDEC 4.0 DEM method and conventional pseudostatic approach are compared. This study shows there are a broader range of deformations inside the slope. [ABSTRACT FROM AUTHOR]

Huangtupo landslide, volumetrically the largest, most complex landslide in the Three Gorges Reservoir region of China, is a dangerous mass on which the district of Badong has been inadvertently situated. Risk remediation efforts include the construction of a large observational tunnel and monitoring system that are unique in the world. This tunnel and its side branches permit detailed mapping of its 3D structure while providing samples for laboratory analysis. The new investigations validate that the Huangtupo landslide is a composite of several independent landslides and that movement occurs along the major rupture zones as well as on interlayer sliding zones in the underlying Badong Formation. Uranium-thorium disequilibrium dating establishes that the northern part of the landslide, called the Riverside Slump, underwent at least two periods of movement at about 100 and 40 ka (ka stands for a thousand years). These events were induced by the steep slope created by the downcutting of the Yangzte River. The results from in situ displacement monitoring over a 7-year period confirm that the central part of the landslide is creeping at a slow, relatively stable rate of about 15 mm/year rather than being in a stage of acceleration under the protection of anchored concrete beams and other defense structures at its toe. Available data suggest that engineering measures can control the independent landslides that together constitute the huge Huangtupo mass, which will avoid the need for costly relocation of thousands of people. [ABSTRACT FROM AUTHOR]

The distribution of soil pressure in landslides above anti-slide piles is a key factor in their design. The paper describes the evolution of stresses near soil-piles by testing a physical scale model during progressive loading. Displacement monitoring data on the surface of the landslide during loading discloses four main evolutionary stages: the initial stage of deformation, the uniform deformation stage, the accelerating deformation stage, and the damage stage. During initial deformation, the vertical distribution of soil pressure above anti-slide piles is sigmoidal, with the highest pressures occurring in the middle and upper parts of the slide mass. Next, during the uniform deformation stage, the soil pressure begins to assume a parabolic shape in a vertical profile, and this shape is fully realized during subsequent accelerating deformation. Finally, during the damage stage, the soil pressure relaxes to low values near the center of the slide mass, effectively inverting the parabola. Thus, the distribution of soil pressure above anti-slide piles changes in a complex manner during deformation, and these effects must be accommodated in the analysis and design of anti-slide piles. [ABSTRACT FROM AUTHOR]

Transversely isotropic rock composed of two interbedded layers has been rarely studied, although landslides frequently occur in bedded rock masses. With reference to the interbedded rock mass in the Miaowei Reservoir area of Yunnan Province, China, this study prepares transversely isotropic specimens made of two interbedded materials to investigate the fracture and mechanical behaviors of interbedded rock. The effect of the bedding plane dip angle and the application of the findings to an anti-dip interbedded rock slope are also studied. Specifically, two groups of isotropic specimens and five groups of transversely isotropic specimens are tested in a series of triaxial compressive tests; based on these tests, the crack types, failure modes and mechanical parameters are analyzed, and one damage model and its application to the failure probability analysis of an anti-dip interbedded rock slope are investigated. The experimental results show that twelve crack types, eight failure modes and five axial stress-strain curve types can be summarized and are significantly affected by the dip angle. The recognition of these crack types and failure modes can improve the qualitative instability analysis of bedded rock masses in the reservoir area, and five mechanical parameters, including peak stress, strain related to peak strength, residual strength, elastic modulus and Poisson's ratio, exhibit fluctuating variation trends versus the dip angle and confining stress due to the influence of the dip angle. Two groups of theoretical curves from the proposed damage model correspond with the pre-peak features of the test stress-strain curves. The proposed failure probability model considering rock damage shows good practicality when applied to an anti-dip interbedded rock slope; the slope displays discrete failure probabilities in various parts, e.g., the slope toe, slope shoulder and weaker layer show higher failure probabilities, and the relaxation behavior increases the failure probabilities and gradually eliminates the discreteness. Relevancy analysis shows that the strength of transversely isotropic rock is more sensitive to the elastic modulus, dip angle of bedding plane, confining stress and composition of the rock. • Transversely isotropic rock made of two interbedded materials is prepared; • Fracture behaviors and damage model of simulated transversely isotropic rock are investigated; • Instability analysis of an anti-dip interbedded rock slope is conducted. [ABSTRACT FROM AUTHOR]

Brittleness is an important mechanical property of rock masses and a key index used in various engineering practices particularly to evaluate hydraulic fracturing, rock fragmentation and rock burst. However, rock brittleness is a concept remaining to be determined since there are no unique standards available. In this study, two methods to determine the brittleness index are proposed by considering the pre-peak failure energy and post-peak fracture energy, which are regarded as key factors in determining whether brittle failure of rock occurs. By taking the Longmaxi Formation shale as an example, the energy evolution laws of shales under different confinements are first analyzed, and the evaluation methods are then examined and applied to these rocks. The results show that these brittleness indexes for shales are capable of describing the transition from absolute plasticity to absolute brittleness. The applicability and performance of the proposed indexes are further validated against large uniaxial and triaxial compression test datasets for different rock types. Application of these brittleness indexes to the tested rock types clearly demonstrate that the two indexes have opposite variation trends with rising confining pressure. Compared with the previous evaluation methods, the rationality of the methods proposed in this study is also verified. These results indicate the proposed brittleness indexes can reflect the brittle characteristics of the rock and the whole process of deformation and failure of the rock. Accordingly, these methods seem to offer reliable evaluations of the brittleness of rock in various engineering practices, although further validation is necessary. • The energy evolution laws of shales under different confinements are revealed. • The brittleness indexes that consider the failure energy before the PS and the fracture energy after the PS are established based on the energy evolution. • The rationality of the proposed brittleness indexes is verified based on sufficient datasets for different rock types collected from various literatures. • Influence of the confining pressure on the brittleness indexes determined by different criteria is revealed. [ABSTRACT FROM AUTHOR]

Accurate assessment of brittleness of rock material is of great significance in the fields of underground mining engineering and unconventional oil and gas reservoirs. In this study, the existing methods for determining rock brittleness were reviewed in detail. Nevertheless, they encounter their own limitations in dealing with some special situations. Therefore, two brittleness indexes under compression are proposed based on energy evolution analysis in the complete process of deformation and failure of the rock. The proposed brittleness indexes consider the elastic strain energy and the dissipation energy before peak strength (PS) and the influence of post-peak stress drop. Then, the applicability of the proposed brittleness indexes is validated by the collected datasets of uniaxial and triaxial compression tests results under different confinements for ten rock types. The results indicate that the values of two proposed indexes have positive correlations with confining pressure while have negative correlations with the rock brittleness. Finally, seven brittleness indexes are selected to further compare the rationality of the proposed brittleness indexes. The comparisons show that the results determined by the two brittleness indexes are different from other brittleness indexes while they can also describe the brittle characteristics of each rock types. The comparisons also prove either insufficient physical basis or inappropriate expression strategy in the existing brittleness indexes. Accordingly, the proposed methods for determining the rock brittleness seem to offer reliable evaluations of the rock brittleness in various rock types. This study provides a novel approach for quantitative evaluation of the rock brittleness, the results of which improve the existing methods and also enrich our understanding of the rock brittleness. • The merits and disadvantages of existing evaluation methods are revealed. • The method to determine the brittleness index is proposed. • An amount of data for different rock types were collected from various literatures. • Influence of σ 3 on the brittleness index is revealed. [ABSTRACT FROM AUTHOR]

• A damage constitutive model based on Weibull distribution and unified strength theory is developed. • The evolution of damage in rocks is analysed which reflects the damaging extent of rocks. • The physical meanings of model parameters are proved to correspond to reality. The deformation-induced damage of rocks in underground space always results in the long-term instability of engineering projects. In this paper, a damage mechanics based on the constitutive model related to the Weibull distribution and unified strength theory is developed. This model considers the statistical damage, strain softening and damage weakening of rocks in the deformation process. To verify the feasibility of this model, the model parameters were mathematically confirmed, four experimental examples were cited to illustrate the features of the axial pressure versus axial strain under various confining pressures, and five experimental examples were cited to compare the distinction of the axial pressure obtained from the proposed model versus the confining pressure with Mohr-Coulomb criterion. Then, the evolution of damage in the deformation process was analyzed based on the proposed model. Finally, the physical meanings of the model parameters were discussed. The results mainly reveal that the proposed model has a good consistency with the experimental examples, the evolution of damage contains three stages with the deformation process, and the model parameters have distinct physical meanings. [ABSTRACT FROM AUTHOR]

Toppling is a widespread failure mode in natural and excavated anaclinal rock slopes and threatens the construction and operation of important infrastructure such as hydropower and transportation corridors in southwest China. Therefore, comprehending the mechanisms underlying toppling is essential for relevant landslide prediction and prevention. In this study, we developed a physical model of an anaclinal rock slope using the Linda landslide as a site case. Based on field monitoring using Gopro cameras, high-speed cameras, strain sensors, stress sensors, and acoustic emission systems, the evolution of the anaclinal rock slope model was analysed. The reliability of the physical model test was verified by comparing the deformation characteristics of the landslide site with those of the slope model. The monitoring results suggested that the slope deformation process could be divided into five stages: an initial interlayer dislocation stage, a deformation initiation stage, a crack generation and propagation stage, a crack penetration stage, and a failure stage. The rock mass could be categorised into four deformation zones: the fresh zone, weakly toppled zone, moderately toppled zone and highly toppled zone. Acoustic emission sensors deployed near the failure-prone region held the potential to serve as early warning indicators for landslides on anaclinal rock slopes. Valley incision played a significant role in the formation of sliding surfaces in anaclinal rock slopes. Furthermore, the model experiment observed multiple failure surfaces and the failure behaviour of the landslide rock mass, shedding light on their connection to the deformation process and the stress state in the model. The study revealed the deformation and failure mechanism of an anaclinal rock slope from many perspectives and deepened our understanding of toppling type of landslides. • Detailed study of Linda landslide's background and structure. • In-depth analysis of anaclinal rock slope using multi-field monitoring. • Summarized complex anaclinal rock slope failure mode and rock mass features. • Emphasized valley incision's role in forming sliding surfaces on anaclinal slopes. • Revealed the generation of multiple failure surfaces during toppling deformation. [ABSTRACT FROM AUTHOR]

The influence of wetting and drying cycles (WDC) on the strength weakening of typical rocks in soft and hard interbedded rock masses is vital to comprehend the mechanism of numerous bank slope failures in soft and hard interbedded strata induced by water level fluctuations. How WDC affect the strength of intact rocks in red stratum of the Badong Formation, a typical sliding-prone interbedded stratum in the Three Gorges area, is a topic worthy of comprehensive investigation. In this study, the effects of WDC on the physical and strength parameters of silty mudstone and silty sandstone were examined by performing a series of experiments on a total of 116 rock samples. Models of strength weakening were developed for the two rock types to express the relations between the strength deterioration coefficient (ratio of the weakened and initial value of strength parameters) and the number of WDC. The results indicate that treatment with WDC causes increases in the water absorption rate, and decreases in longitudinal wave velocity, tensile strength, cohesion and internal friction angle for both silty mudstone and silty sandstone samples with the rate of change decreasing with an increasing number of WDC; the variations in physical and strength parameters are larger for silty mudstone compared with silty sandstone; the effects of WDC on tensile strength and cohesion are higher than on internal friction angle for the studied rock types; Intergranular cracks and intragranular cracks were observed to increase with the number of WDC, evolution mode of rock microstructures was proposed, and the main weakening mechanisms induced by WDC was summarized as microcracks growth by mineral expansion and contraction, which weaken the strength of the studied rocks with the impact depending mainly on the mineral contents and microstructures in rocks. Finally, the established strength weakening models were applied in the numerical model to investigate the influence of WDC on the strength of rock mass with silty mudstone and silty sandstone interbedded layers in the Badong Formation. The obtained results provide useful guidance to reasonably evaluate the long-term stability of soft and hard interbedded bank slopes in reservoir area. • Typical rocks in a interbedded red stratum were sampled from the field. • Experiments were performed on 116 rock samples under wetting and drying cycles. • Effect on tensile strength and cohesion are higher than on internal friction angle. • Mineral expansion, contraction and dissolution induces weakening of rocks. • The test data were used to study strength weakening of interbedded rock mass. [ABSTRACT FROM AUTHOR]

• Impacts of water flow on hydrodynamic heat transfer in rock fractures were experimentally elucidated. • Parametric models linking heat transfer behaviors with flow rate and fracture geometry were developed. • Effect of nonlinear flow resistance on the feasibility of heat extraction was quantified. Hydrodynamic heat transfer in rock fractures is crucial for many geophysical processes and engineering activities, notably in harnessing geothermal energy. Despite extensive research, characterizing hydrodynamic heat transfer in rock fractures, complicated by their geometric heterogeneity, remains a formidable challenge. To address this challenge, we experimentally investigated the hydrodynamic heat transfer in rock fractures with diverse geometric features at steady-state elevated temperatures. We found that both heterogeneous fracture geometry and elevated temperatures promote the transition of fracture flow from a linear to nonlinear regime. This flow regime transition enhances the heterogeneity of heat transfer intensity within the fracture and exacerbates the increase in heat transfer efficiency with flow rate. At a fortyfold increase in flow rate, the heat transfer coefficient in the most heterogeneous fracture rises by approximately 72 times, compared to about 28 times in the least heterogeneous one. Leveraging experimental data, we developed parametric models linking heat transfer coefficients, outflow temperature, and heat recovery rate to flow rate and geometric features, yielding a theoretical formulation for the maximal heat recovery rate. By introducing the concept of an energy conversion rate, we quantitatively evaluated the effect of nonlinear flow resistance on heat extraction feasibility, revealing that energy conversion rates in highly heterogeneous fractures can be up to 452 times lower than in less heterogeneous ones. This highlights the pivotal role of flow resistance in heat extraction feasibility. Our findings are instrumental for understanding and predicting the hydrodynamic heat transfer within fractured geothermal reservoirs and analogous hydro-thermal systems. [ABSTRACT FROM AUTHOR]

Fluid flow in rock fractures is described by Darcy's law and its nonlinear extension, the Forchheimer equation in form of a quadratic polynomial. Since the nonlinearity of the Forchheimer equation, determining its key coefficient of inertial permeability (i.e., the quadratic coefficient representing inertial losses) requires a series of flow tests under different hydraulic gradients. However, how to choose the volumetric flux range for deriving inertial permeability is never scrutinized. Here we report a seemly irrational dependency of inertial permeability on volumetric flux range by massive direct numerical simulations of fluid flow in rock fractures. This variation presents traceability and is closely related to the evolution of microscale eddies and macroscale flow regimes. A concept of global inertial permeability is thus proposed from this traceable variation, which can reproduce the whole flow regime in rock fractures. Two parametrized criterion models are subsequently established for calculating global inertial permeability using the lowest cost and ensuring its accuracy: one in terms of minimum Reynolds number for practical purposes, and the other in terms of minimum eddy volume ratio for mechanistic interpretation. Further discussions indicate that the proposed global inertial permeability is of great importance to non-Darcian flow prediction and flow regime assessment. Moreover, the parameterized criterion models in the form of power-law function for determining global inertial permeability, drawn from 2D fracture simulations, can apply to 3D fractures and large-scale fractured rock aquifers. The findings and results in this study are of great significance for accurately evaluating the hydraulic conductivity of rock fractures, especially at relatively high flow rates, and are useful for many geophysical and industrial applications. • Variation of inertial permeability with flow ranges is manifested which results from evolving eddies and flow regime. • Global inertial permeability referring to stable value of the variation is proposed to reproduce the whole flow regime. • Practical and mechanistic criterion models for determining global inertial permeability are both established. [ABSTRACT FROM AUTHOR]

Earthquake-induced rock slope failure is one of the most destructive geohazards, posing serious threats to human lives and properties. The potential hazard of a rock slope, under the loading of earthquakes, can be assessed from its failure and runout characteristics, which are however affected by inherent fractures. To simulate the randomness of these inherent fractures, the discrete fracture network (DFN) modeling technique that is based on the Monte Carlo simulation (MCS) is often employed. It is worthwhile noting that different realizations of DFN can be sampled from different MCSs; however, only one realization of DFN is considered and studied in the conventional analysis. There exist differences between the arbitrarily selected DFN and true DFN; as such, the conventional deterministic analysis could cause uncertainty in DFN modeling and the potential hazard of a rock slope cannot be accurately evaluated. In such a circumstance, this paper proposes a probabilistic analysis of earthquake-induced failure and runout behaviors of fractured rock slopes, in which multiple realizations of DFN that are systematically generated with MCS are taken as inputs to the discrete element method (DEM) modeling of slope behaviors, thus, the uncertainty induced by DFN modeling can be explicitly considered and evaluated. [ABSTRACT FROM AUTHOR]

Dynamic behavior and failure mechanism of slope during earthquake are hot topics in geotechnical engineering community. In Tianshui area, Northwest of China, the deformation features of loess-mudstone slopes induced by earthquakes are still not well understood. The current study aims to discuss the dynamic behavior of the slope under earthquake, by performing a series of centrifuge shaking table tests and numerical simulations. The results are processed for PGA amplificatory effect study and to evaluate the earthquake induced deformation mechanism. Better agreement is obtained between the results of numerical simulations and centrifuge tests. The results indicated that the acceleration response of the loess-mudstone slope showed several amplifying characteristic: the height effect, lithologic effect and surface effect. It also proves that the displacements in the loess layer are much larger than mudstone. As the input amplitude increased, the shear plastic zone developed along a further slide surface. Tension plastic zone mainly occurred at the crest. Roughly, the regions of earthquake induced deformation state increased with the increase in amplitude of earthquake wave. Deformations occurred at the upper part of the slope. Tensile cracks evolved on the crest and the upper part of slope in loess layer, moreover, failures occurred at slope surface, and only slight deformation at slope toe. Deformations with continuous shear cracks and slope surface upheavals developed at the middle part of slope. [ABSTRACT FROM AUTHOR]

• Flow behaviors are associated with fracture heterogeneity and the filling conditions. • Filling particles result in two competing mechanisms impacting flow regime in fractures. • Fracture walls confining the fluid flow significantly reduce the media permeability. • A semi-empirical model for predicting water flow in filled fractures is proposed. Fluid flow through filled rock fractures is relevant to numerous engineering applications and geophysical processes. However, a proper understanding of the flow behaviors in filled fractures is still far from being completed. To investigate the fluid flow in a rough-walled fracture filled with a porous medium, we systematically compare the micro- and macroscopic flow behaviors within filled fractures and corresponding open fractures and porous media based on a series of pore-scale simulation results. We find that the filling medium has a dual role in altering the flow regime, as the filling particles can not only cut the flow domain into several pore channels and thus limit the generation of large-span eddies, but also force the fluid to flow around them and promote the generation of local eddies. Compared with porous media, the fluid flow within filled fractures is confined by fracture walls, which greatly alters the media permeability and the flow nonlinearity therein. By introducing the hydraulic radius and Darcy-Weisbach equation, we develop a new semi-empirical model to estimate the fluid flow through filled fractures using phenomenological coefficients of corresponding open fractures and porous media. The proposed model, satisfying dimensional consistency, shows high fidelity in predicting water flow through filled fractures. More importantly, this model can be successfully reduced to the typical form of the Forchheimer equation applied to open fractures and porous media. The results and findings are expected to be useful in predicting and evaluating the fluid flow in complex geological setting. [ABSTRACT FROM AUTHOR]

• Solute transport in fractures with slip BC was studied by pore-scale simulations. • Effect of slip BC on solute transport was manifested over the entire flow regime. • Influencing mechanisms of slip BC were elucidated under different flow regimes. Fundamental understanding of solute transport behaviors in rock fractures is of great importance to many hydrogeological processes. The fate of fluid-borne solutes is inherently linked to fluid flow process in rock fractures, which is usually theoretically and numerically analyzed under the assumption of classic no-slip boundary condition. However, fluid slippage at rock surfaces is possibly present in some geological environments, such as hydrophilicity change in rock surfaces exposed to organic substances, or the immobile wetting film covering rock surfaces. These situations would induce a non-zero velocity at the boundary walls for flowing fluid, i.e., fluid slippage, which leads to a violation of the no-slip assumption. Nonetheless, the effect of slippery boundary on fluid-borne solute transport is poorly understood for rock fractures. This study systematically investigated the slippery boundary effect on solute transport in rough-walled rock fractures under different flow regimes. A series of pore-scale simulation results showed that the slippery boundary has a profound influence on both microscale and macroscale solute transport behaviors in rock fractures. Such an influence became more significant with increasing hydraulic gradient, accompanied by the flow regime transitioning from Darcy to non-Darcian. For Darcy flow regime, the slippery boundary exerted its influence on solute transport by altering velocity distribution pattern in rock fracture; while for non-Darcian flow regime, the enlarged eddy volume and promoted mass transfer process by the slippery boundary profoundly affected solute transport behaviors. Further discussion indicated that the predictive models with parameters estimated from the conventional no-slip boundary condition cannot directly apply to the slip one. Moreover, the effect of slippery boundary would possibly have an impact on larger-scale fractured rock aquifers which requires further verification. The results and findings enrich the understanding of solute transport in fractured rocks where the slippery boundary is prevalently present, and contribute to developing predictive models for complex geological environments. [ABSTRACT FROM AUTHOR]