NP7.2

EDI
Non-linear Waves and Fracturing

Waves in the Earth’s crust are often generated by fractures in the process of their sliding or propagation. Conversely, the waves can trigger fracture sliding or even propagation. The presence of multiple fractures makes geomaterials non-linear. Therefore the analysis of wave propagation and interaction with pre-existing or emerging fractures is central to geophysics. Recently new observations and theoretical concepts were introduced that point out to the limitations of the traditional concept. These are:
• Multiscale nature of wave fields and fractures in geomaterials
• Rotational mechanisms of wave and fracture propagation
• Strong rock and rock mass non-linearity (such as bilinear stress-strain curve with high modulus in compression and low in tension) and its effect on wave propagation
• Apparent negative stiffness associated with either rotation of non-spherical constituents or fracture propagation and its effect on wave propagation
• Triggering effects and instability in geomaterials
• Active nature of geomaterials (e.g., seismic emission induced by stress and pressure wave propagation)
• Non-linear mechanics of hydraulic fracturing
• Synchronization in fracture processes including earhtquakes and volcanic activity

Complex waves are now a key problem of the physical oceanography and atmosphere physics. They are called rogue or freak waves. It may be expected that similar waves are also present in non-linear solids (e.g., granular materials), which suggests the existence of new types of seismic waves.

It is anticipated that studying these and related phenomena can lead to breakthroughs in understanding of the stress transfer and multiscale failure processes in the Earth's crust, ocean and atmosphere and facilitate developing better prediction and monitoring methods.

The session is designed as a forum for discussing these and relevant topics.

Convener: Arcady Dyskin | Co-conveners: Sergey Turuntaev, Elena Pasternak, Serge Shapiro
Presentations
| Fri, 27 May, 08:30–09:54 (CEST)
 
Room 0.94/95

Presentations: Fri, 27 May | Room 0.94/95

Chairpersons: Arcady Dyskin, Sergey Turuntaev, Elena Pasternak
08:30–08:36
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EGU22-567
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ECS
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Virtual presentation
Elizaveta Grebenshchikova, Victor Nachev, and Sergey Turuntaev

This work presents the numerical simulation results of porous-elastic-plastic materials' mechanical behavior, reproducing the filtration-capacitance properties of reservoir rocks. The authors perform numerical modelings of laboratory experiments conducted earlier at the Sadovsky Institute of Geospheres Dynamics of the Russian Academy of Science on an installation that allows conducting studies on fracture propagation under triaxial loading conditions. This work aims to study the dynamics of fracture propagation under various loading conditions using numerical modelings. For this purpose, we take into account the porous and elastoplastic properties of the medium under study.

The authors prepared a mathematical model to study the propagation trajectory and fracture shape of hydraulic fracturing in poroelastic plastic artificial materials: set a system of defining equations and fracture criteria. Then we prepared numerical models using a mechanical software package. We built a three-dimensional numerical elastoplastic model of the rock based on the geometry of the sample. Modeling includes setting a set of mechanical parameters: Young's modulus, Poisson's ratio, internal friction angle, dilatancy angle, and deformation criterion of failure. In the study, we used a ready-made physical and mathematical mechanical model depending on the pressure of Mohr-Coulomb and pore pressure. Next, a series of numerical mechanical calculations were performed using the extended finite element method.

As a result of numerical modeling using a software package, the authors obtain that in the poroelastic model of the sample, a plasticity zone appears in the region of the central well before the fracture begins to form. Then, as the fracture spreads, the plasticity zone along the fracture propagation path is preserved. Modeling the stress-strain state along the fracture trajectory shows asymmetric distributions of stresses, pressures, and porosity relative to the central well. Different pressure values caused it in the injection and production wells used in a laboratory experiment to create pore pressure. Also, it leads to the formation of different fracture lengths towards the production and injection wells, which we see during laboratory experiments.

How to cite: Grebenshchikova, E., Nachev, V., and Turuntaev, S.: Digital Modeling of the Mechanical Processes of Hydraulic Fracturing in Poro-Elastic-Plastic Artificial Materials, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-567, https://doi.org/10.5194/egusphere-egu22-567, 2022.

08:36–08:42
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EGU22-9747
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ECS
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Presentation form not yet defined
Vasily Riga and Sergey Turuntaev

Seismicity associated with fluid injection into the subsurface is one of the most important issues worldwide. Fluid injection near a fault could lead to seismic sliding of the fault and as a consequence to significant seismic events. In the presented research, we study the single fault behavior under the action of a single well injection near the fault. Various cases of fluid injection and friction properties of the fault are considered. To describe the friction on the fault we use two-parameter rate-and-state law. The fault has zones characterized by velocity-weakening and velocity-strengthening friction behavior. We analyze how injection rate and volume and parameters of the friction law influence the fault sliding dynamics and seismicity level. As the result, we get conditions that are favorable for the occurrence of noticeable seismicity and dependence of seismicity parameters on injection parameters.

How to cite: Riga, V. and Turuntaev, S.: Seismic sliding of the single fault under fluid injection , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9747, https://doi.org/10.5194/egusphere-egu22-9747, 2022.

08:42–08:48
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EGU22-13042
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Virtual presentation
Boris Gurevich, Alexey Yurikov, Konstantin Tertyshnikov, Maxim Lebedev, Roman Isaenkov, Evgenii Sidenko, Sinem Yavuz, Valeriya Shulakova, Julia Correa, Stanislav Glubokovskikh, Barry Freifeld, and Roman Pevzner

Due to their granular nature and presence of fluids, elastic moduli of most crustal rocks show a strong stress dependency. This means that the relationship between stress and strain is nonlinear, which should cause nonlinear wave phenomena. In particular, interaction of seismic waves of different frequencies should generate higher harmonics and combinational frequencies. Analysis of these effects in field data can potentially help find areas of anomalous nonlinear properties, such as fractured zones, mixed saturation or overpressure. To better understand the potential of nonlinear seismology, we observed and analyzed nonlinear seismic effects in field and laboratory experiments. The field experiment was performed using two seismic vibrators generating monochromatic signals of different frequencies. The wavefield was recorded with a fiber optic distributed acoustic sensing (DAS) cable cemented in a 900 m deep borehole. The signals recorded both on the surface and in the borehole show combinational frequencies, harmonics, and other intermodulation products of the fundamental frequencies. The laboratory experiment, which was designed to replicate the setup of the field experiment, shows similar nonlinear products of the fundamental frequencies. Furthermore, the nonlinear effects show a dependency on the saturating fluid. These tests confirm that nonlinear components of the wavefield propagate in a form of body waves, are likely to be generated in rock formations, and have the potential for reservoir fluid characterization.

How to cite: Gurevich, B., Yurikov, A., Tertyshnikov, K., Lebedev, M., Isaenkov, R., Sidenko, E., Yavuz, S., Shulakova, V., Correa, J., Glubokovskikh, S., Freifeld, B., and Pevzner, R.: Nonlinear seismic phenomena as recorded by distributed acoustic sensors, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13042, https://doi.org/10.5194/egusphere-egu22-13042, 2022.

08:48–08:54
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EGU22-11759
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ECS
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Presentation form not yet defined
Victor Nachev and Sergey Turuntaev

This work aims to study the propagation of fractures during hydraulic fracturing operations to determine the conditions that lead to the most extensive network of secondary fractures along with the main fractures at the microlevel. The occurrence and propagation of 3D fractures were studied, considering the granular composition and complex structure of elastic-plastic rock samples. The simulation allowed us to calculate fracture networks for various loading conditions. We propose a method that will enable us to calculate the pressure of hydraulic fracturing fluid injection into the formation from the obtained numerical conditions of loading and regional stress in the reservoir rock. Based on the results of numerical modeling and recalculation of the obtained loading conditions into the pressure of the injected fluid, geomechanical engineers will choose the necessary conditions that will provide the stress-strain states that lead to the most significant degree of fracturing of the formation.

How to cite: Nachev, V. and Turuntaev, S.: Investigation of 3D Fracture Propagation in Complex Reservoirs Rocks at Microscale, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11759, https://doi.org/10.5194/egusphere-egu22-11759, 2022.

08:54–09:00
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EGU22-8272
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Virtual presentation
Oleg Izvekov, Andrey Konyukhov, and Ivan Cheprasov

Complex structure of a skeleton of saturated porous medium can have a great influence on the processes of heat and mass transfer. 

There are various approaches to the description of  two-phase flow: direct numerical calculation of fluid flow in the pore space, multicontinuous models with the laws of mass exchange between continua, single-continuum models of non-equilibrium flow. In the family of isothermal non-equilibrium filtration models, the relative phase permeabilities and capillary pressure are functions not of current saturation but of their change history.

In this work we generalize the relaxation model of capillary nonequilibrium to the non-isothermal case. We introduce two internal thermodynamic parameters (capillary and thermal nonequilibrium) which depend on change history of saturation and temperature. In the model relative phase permeabilities and capillary pressure are functions of saturation, temperature, and current values of these internal parameters. Based on the analysis of the dissipation inequality, thermodynamically consistent kinetic equations for the evolution of these parameters are proposed. The parameters of the single-continuum model are clarified with double-porosity model of porous media with special structure. Structure of the penetration front of fluid hot (or cold) compared to the skeleton was investigated.

This work was supported by the Russian Foundation for Basic Research: grant N19-01-00592. 

 

How to cite: Izvekov, O., Konyukhov, A., and Cheprasov, I.: Modeling of capillary and thermal nonequilibrium flows in porous media, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8272, https://doi.org/10.5194/egusphere-egu22-8272, 2022.

09:00–09:06
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EGU22-2171
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ECS
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Virtual presentation
Kuan Jiang, Cheng-zhi Qi, and Ze-fan Wang

Pendulum-type wave is a kind of sign-alternating wave with discontinuous and nonlinear characteristics found in deep rock mass, which is different from the traditional continuum elastic waves. The dynamic engineering disasters such as rockbrusts and anomalously low friction phenomenon occur frequently in surrounding deep level tunnels rock mass, and the study of pendulum-type wave is of great significance for explaining the mechanism and prevention of these engineering disasters. The presence of multiple fractures makes geomaterials nonlinear. Therefore, it is unreasonable to use linear model to study pendulum-type wave in block-rock mass. With the consideration of the nonlinear deformation characteristics of deep rock mass, a nonlinear dynamic model of pendulum-type wave in block-rock mass is established by introducing hyperbolic elastic model of interlayers of geoblocks, and the time-domain characteristics, frequency-domain characteristics and the law of energy transfer are studied. Furthermore, the influence of initial geostress on pendulum-type wave propagation in nonlinear block-rock mass is studied. The research shows that the improved nonlinear model can not only shows the nonlinear deformation of block-rock mass, but also limits the maximum compression deformation of cracks between rock blocks. Under the action of strong impact loading, the acceleration amplitude of blocks far away from the impact point increases significantly, and is the largest, which is not conducive to the structure safety of rock mass. With the increase of impact loading, the frequency response of blocks tends to move to high-frequency domain, and the frequency center increases continuously. Kinetic energy and potential energy are constantly transformed to each other in block-rock mass, and in the free vibration stage, they are in inverse phase, i.e. when the kinetic energy reaches the maximum, the elastic potential energy is the minimum, and vice versa. Relative to the initial geostress, the hyperbolic elastic model can be grouped into three categories: low stress state, high stress state and ultra-high stress state. Under different initial geostress states, the dynamic response of the block-rock mass is very different. With the increase of initial geostress, the displacement amplitude decrease approximately exponentially. In ultra-high stress state, the displacement amplitude of rock blocks decreases by more than 95% compared with that without initial geostress. Therefore, we conclude that in the ultra-high stress state, the pendulum-type wave phenomenon will not occur in block-rock mass, and the wave propagation is close to the longitudinal wave. This paper provides a reference for further study on nonlinear pendulum-type wave in block-rock mass under the conditions of strong impact and high initial geostress.

How to cite: Jiang, K., Qi, C., and Wang, Z.: Theoretical Research on the Pendulum-type Wave in Nonlinear Block-rock Mass Based on Hyperbolic Elastic Model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2171, https://doi.org/10.5194/egusphere-egu22-2171, 2022.

09:06–09:12
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EGU22-5669
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Virtual presentation
Sergey Turuntaev and Evgeny Zenchenko

It has been proposed that rock fracturing can be obtained by the powerful and fast pressure discharge at some boundary of the rock (fracture, borehole). The fracturing related with rapid pore pressure discharge looks as a “fracturing wave”.  Laboratory experiments allow to evaluate the main characteristics of the phenomena and to estimate conditions for the fracturing. Experimental data on the fracturing process were obtained with the help of transparent pressure-drop setup (plexiglass tube with length 455 mm, inner diameter 60 mm, wall thickness 5 mm) using the weak-cohesive porous samples made from the sand wetted by glycerol. The tube ends were closed by brass covers equipped by pressure transducers. Additionally, nipples for the air pumping and decompression were mounted at one of the covers. The pressure was increased by air pumping in up to 0.35 MPa, then the pressure was released through solenoid valve with flow section 15 mm. Decompression rate was controlled by the diaphragms with different diameters: 2.8, 3.0, 3.4, 4.0, 4.8 mm. To observe the fracturing, high-speed camera with frame rate 1200 frames per second was used. The dependencies of maximum depth of the fracture formations and mean distance between the fractures on decompression rate were obtained. It was found that the number of fractures and the last fracture depth grow with the pressure drop rate, while the inter-fracture distance decreases.

How to cite: Turuntaev, S. and Zenchenko, E.: Experimental study of saturated porous medium fracturing by abrupt pressure drop, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5669, https://doi.org/10.5194/egusphere-egu22-5669, 2022.

09:12–09:18
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EGU22-3242
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Virtual presentation
Giang D. Nguyen, Rupesh Verma, and Murat Karakus

Specimens of quasi-brittle materials under Brazilian disc testing usually fracture abruptly, with load carrying capacities dropping almost instantly from peak to zero. This abrupt failure in a split second is known due to the excess storage of strain energy at peak load that is released through the creation of new fracture surfaces and in the form of kinetic energy. This kind of dynamics and bursting is hard or impossible to control in laboratory testing using direct vertical displacement. We present our innovative technology, registered as an innovation patent in Australia, to control the dynamic splitting of Brazilian disc specimens so that the failure process is not abrupt, indicated by the snapback load-vertical displacement responses. Thanks to the use of lateral strain to control the loading, the time to complete the whole fracturing process increases significantly from a split second to a few hours, sufficient to enable advanced instrumentation using image-based techniques.  Acoustic Emission (AE) is used to monitor the fracturing process to make sure that the snapback response observed is not unloading. The proposed technology has been applied with largely success to a wide range of quasi-brittle materials, including sandstone, granite, and even 3D-printed rock-like materials with inherent weak discontinuities. This presentation reports the obtained results and challenges in controlling the dynamic splitting of Brazilian disc specimens using the proposed technology.

How to cite: Nguyen, G. D., Verma, R., and Karakus, M.: Controlling dynamic splitting of Brazilian disc specimens using Adelaide University Snapback Indirect Tensile test (AUSBIT), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3242, https://doi.org/10.5194/egusphere-egu22-3242, 2022.

09:18–09:24
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EGU22-9482
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ECS
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Virtual presentation
Hongyu Wang, Arcady Dyskin, Elena Pasternak, and Phil Dight

Rock samples tested in uniaxial compression tests are often observed to have spallation failure at the lateral surface of the sample caused by buckling of layers developing parallel to the direction of loading. These layers are caused by extensive crack growth. Yet, the experiments show that extensive crack growth in real 3D situations requires the presence of intermediate compressive principal stress (biaxial loading). We check the hypothesis that the intermediate principal stress is generated by the direct contact with metal loading platens, where the “frictional” boundary conditions are developed at the sample ends, creating non-uniform stress distributions near the sample ends. By the use of the finite element method (FEM), we analyse the stress distributions at the immediate lateral surface of the cylindrical sample in uniaxial compression in the polar coordinate system. It is found that near the ends the sample is actually biaxially loaded: the circumferential stress could be induced to play the role of the intermediate principal stress. The sizes of the zones and the maximum magnitude of the circumferential stress depend upon the friction coefficient and the Poisson’s ratio of the rock. The biaxial load ratio is defined by the ratio between the circumferential compressive stress and the axial stress. Comparing the biaxial load ratio determined in numerical models with the critical biaxial load ratio inducing extensive crack growth, the spallation of rock samples in uniaxial compression tests can be interpreted from a new perspective.

How to cite: Wang, H., Dyskin, A., Pasternak, E., and Dight, P.: Local biaxial loading induced by end friction in uniaxial compression, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9482, https://doi.org/10.5194/egusphere-egu22-9482, 2022.

09:24–09:30
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EGU22-10978
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Virtual presentation
Broadus Jeffcoat-Sacco, Arcady Dyskin, Elena Pasternak, Phil Dight, and Hongyu Wang

Growth of internal cracks in compression is a primary mechanism of catastrophic rock failures.  Since the cracks are internal, only indirect methods are currently available for investigation and monitoring of failures of this kind.  In order to understand the fundamentals of 3D (internal) crack growth in compression, special physical models using transparent polymer prisms with embedded penny-shaped flaws were performed.  A biaxial stress field was applied, to simulate conditions near the face or walls of deep tunnels.  Previously, such experiments were conducted within a fully-enclosed polyaxial testing machine, preventing observation of the growing crack itself.  Recent experiments at UWA utilized a plane-strain restraint device, which develops the secondary principal stress (σ2) by limiting the lateral expansion that would otherwise result from the imposition of the primary principal stress (σ1).  This device leaves clear line-of-sight to the sample free face, allowing visual observation and the installation of other instrumentation. 

As expected, the biaxial stress field resulted in growth of an extensive, nearly planar crack, parallel to the σ12 plane.  Growth of this crack was observed using high-speed video.  The crack surface morphology shows similarity to many natural and excavation-induced fractures in geomaterials.  This similarity justifies the usage of the transparent materials for investigating rock failure. Furthermore, the observed morphological features can be linked to specific events in the crack growth process.

In addition, experiments incorporated acoustic emission sensors, both on the sample, and in the air near the sample.  Two categories of vibration were observed at the sample’s rear free face: a short-duration wavelet, representing the crack initiation, and a long-duration high-amplitude “ringing” waveform.  The “ringing” was also observed in air (as audible sound) and in video (as movement of the whole sample). The observed vibrations could be utilized for monitoring dangerous rock failures.

How to cite: Jeffcoat-Sacco, B., Dyskin, A., Pasternak, E., Dight, P., and Wang, H.: Oscillations induced by crack growth in compression and morphology of fracture surface, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10978, https://doi.org/10.5194/egusphere-egu22-10978, 2022.

09:30–09:36
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EGU22-1586
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ECS
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Virtual presentation
Rui Xiang Wong, Elena Pasternak, and Arcady Dyskin

Asymmetric friction refers to different friction forces that resist sliding in opposing directions. Asymmetric friction can for instance be induced by an anisotropic block with an anisotropy axis inclined to the direction of sliding progressing in a constraint environment, (Bafekrpour et al., 2015). This study examines a Burridge-Knopoff-type model of multiple blocks connected through springs. Each block is connected to an external oscillating surface through a leaf spring; some blocks slide with asymmetric friction, while others experience conventional symmetric friction. Asymmetric friction favours slip in the direction of low friction. This increases spring forces to counteract the slip within the assembly, creating regions of tension and compression. When this model represents geological faults, regions of tension and compression can produce fractures oriented normal (in the tensile phase) or parallel (in the compressive phase) to the sliding surface.

Velocity spectra produced by the model excited by an external oscillating surface reveal that the presence of asymmetric friction creates spectra with a frequency falloff of 1/f2, where f is the frequency. This is in contrast with the case of only symmetric friction blocks where oscillations result in velocity spectra with a frequency falloff of 1/f.

Recent triaxial compression of rock samples have shown slip events over shear fracture produce velocity spectra with frequency falloff that approximates 1/f2(Beeler et al., 2020). Using the results found from the model, a hypothesis on the mechanism that produces the 1/f2falloff is proposed: the shear fracture in the compression test is produced by formation of vertical micro-cracks within the rock samples. This effectively creates an anisotropic material with axes of symmetry inclined to the shear fracture, which explains the 1/f2spectra.

Acknowledgement. EP and AVD acknowledge support from the Australian Research Council through project DP210102224.

References

BAFEKRPOUR, E., DYSKIN, A., PASTERNAK, E., MOLOTNIKOV, A. & ESTRIN, Y. 2015. Internally architectured materials with directionally asymmetric friction. Scientific reports, 5, 10732-10732.

BEELER, N. M., MCLASKEY, G. C., LOCKNER, D. & KILGORE, B. 2020. Near‐Fault Velocity Spectra From Laboratory Failures and Their Relation to Natural Ground Motion. Journal of geophysical research. Solid earth, 125, n/a.

How to cite: Wong, R. X., Pasternak, E., and Dyskin, A.: The abnormal 1/f2 spectral falloff caused by asymmetric friction, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1586, https://doi.org/10.5194/egusphere-egu22-1586, 2022.

09:36–09:42
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EGU22-4550
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Virtual presentation
Elena Pasternak and Arcady Dyskin

Growth of real fractures is characterised by interruptions and local overlapping caused by rock heterogeneities. The interruptions and loci of overlapping can work as bridges distributed all over the fracture that connect opposite surfaces of the fracture [1]. These bridges constrain the crack opening and thus mitigate the dependence of the Mode I stress intensity factor of the fracture length (radius). In the case of hydraulic fractures, constraining the opening also affects the fluid (e.g. fracturing fluid) flow through the fracture.

The effect of bridges can be characterised by a characteristic length – the constriction length. When the fracture size is small compared to the constriction length, the fracture behaves similarly to a conventional Model I crack of the same configuration. Alternatively, when the fracture size is much greater than the constriction length both the  average fracture opening and the Mode I stress intensity factor become constant. This restricts the ability of the fracture to growth in unstable manner or dynamically.

The effect of constriction is even more pronounced in the case when the fracture gets open in the displacement-controlled mode. In this case the dependence of the stress intensity factor of disc-like fracture on the fracture radius is no longer monotonic. The stage of decrease of the stress intensity factor with the fracture radius leads to the emergence of stable fracture growth when increase in the displacement is required to maintain fracture propagation. It is important that without taking the constriction into account the corresponding stage of stable fracture propagation can be taken for the effect of rock heterogeneity.

The theory developed is essential for predicting and monitoring growth of Mode I fractures, in particular hydraulic fractures.

  • He, J., Pasternak, E. and A.V. Dyskin, 2020. Bridges outside fracture process zone: Their existence and effect. Engineering Fracture Mechanics, 225, 106453.

Acknowledgement. The authors acknowledge support from the Australian Research Council through project DP190103260.

How to cite: Pasternak, E. and Dyskin, A.: Growth of fractures with constricted opening, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4550, https://doi.org/10.5194/egusphere-egu22-4550, 2022.

09:42–09:48
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EGU22-4482
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Virtual presentation
Arcady Dyskin and Elena Pasternak

Stress field in geomaterials is not uniform; in particular due to the presence of spatial fluctuations. These are induced under external loading due to multiple randomly located heterogeneities and small-scale defects/fractures or by fluid transport. Stress fluctuations can be a form of residual stresses caused for instance by phase transformation (e.g. magma solidification), or as a result of strong seismic events. Subsequently, the stress field can be represented as a superposition of slowly changing large scale stress and small scale self-equilibrating spatial stress fluctuations (random stress field with zero average).

At the first glance, the field of spatial stress fluctuation taking alone is not supposed to cause any large scale development of fractures considered as linear objects (fracture opening linearly depending upon the applied load) since the average stress is zero. However, often the fractures are not independent of the stress field but produced in the zone where the stress fluctuations exhibit high tensile stress. The fracture initial size is of the order of the characteristic size of the zone of high tensile stress, that is the correlation length of the random field of stress fluctuations. The fracture will then be able to propagate further. The simplest model of such a fracture is a disc-like crack opened in the centre by a pair of concentrated forces with magnitude equal to the total force of the tensile stress in that zone [1].

Model [1] predicts the extensive fracture growth to be stable that is further increase in its size would require increase in the concentrated forces that is increase in the amplitude of stress fluctuations. In the case when the stress fluctuations represent residual stress, it is not possible as the residual stress can only decrease [2]. Yet, self-equilibrating residual stresses can cause macroscopic failure. This requires a new paradigm of crack/fracture growth in self-equilibrating field of stress fluctuations. To this end we accept that (1) the fracture opening is bilinear such that the local compressive stress just closes the fracture and hence cannot equilibrate the corresponding local tensile stress; (2) the fracture growth is not planar as passing through zones of compression is not possible leading to local overlapping.

The simplest model that accommodates the above features of fracture growth is a fracture with distributed bridges (fracture with constraint opening represented as a crack with Winkler layer [4]). We show that such a fracture will exhibit unstable growth forming a mechanism of both breakage due to residual stress and large (e.g. geological) scale fracture formation.

  • Dyskin, A.V. 1999. On the role of stress fluctuations in brittle fracture. J. Fracture, 100, 29-53.
  • Dyskin V. and E. Pasternak, 2019. Residual strain mechanism of aftershocks and exponents of modified Omori’s law. J. Geophys. Research: Solid Earth, 10.1029/2018JB016148.
  • He, J., E. Pasternak and A.V. Dyskin, 2020. Bridges outside fracture process zone: Their existence and effect. Engineering Fracture Mechanics, 225, 106453.

Acknowledgement. The authors acknowledge support from the Australian Research Council through project DP210102224.

How to cite: Dyskin, A. and Pasternak, E.: Fractures in geomaterials driven by spatial stress fluctuations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4482, https://doi.org/10.5194/egusphere-egu22-4482, 2022.

09:48–09:54
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EGU22-2006
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ECS
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Highlight
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Virtual presentation
Yuxin Ban, Qiang Xie, Xiang Fu, and Aiqing Wu

A meter-level direct shear test system and a true triaxial test system were designed by placing the traditional test apparatus into sealed cabins subjected to high water pressure. The influences of three-dimensional seepage water pressure on the shear and compression deformation of rock mass in Xiluodu Hydropower Station were studied. The test results showed that the changes in water pressure caused obvious shear deformation of the interlayer dislocation zone and tensile deformation and reduction in the triaxial compression strength of the fractured rock mass. The effect of water pressure on shear displacement and tensile displacement had a hysteresis effect. This was consistent with deformation data collected through field monitoring. The deformation mechanism in the reservoir valley was the coupling of the stress and seepage fields caused by reservoir impoundment. The effective stress was reduced, the mechanical parameters were weakened, and the change of the initial stress field led to the slightly overall shear slip and tensile deformation of the bank slope.

How to cite: Ban, Y., Xie, Q., Fu, X., and Wu, A.: A Hydro-Mechanical Coupling Test System for Simulating Rock Masses in High Dam Reservoir Operations , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2006, https://doi.org/10.5194/egusphere-egu22-2006, 2022.