Crack Dip Angle Research Articles

Research on triaxial compressive mechanical properties and damage constructive model of post-thawing double-fractured quasi-sandstones with different angles

Joints and fractures lead to different failure mechanisms in rock masses under different environments. The mechanical properties and failure mechanisms of rocks with fissures are key problems in rock mass engineering. Parallel double-fracture quasi-sandstone specimens with different dip angles were prepared and subjected to triaxial compression tests after a single freeze-thaw cycle. Pore development, crack propagation, damage evolution, and failure characteristics were analysed. Combined with the strength distribution theory of microelements and the static elastic modulus theory, a damage constitutive model of double-fracture quasi-sandstone under freeze-thaw cycles and loads was established. This study explored the pore development, fracture propagation, damage evolution, and failure characteristics of fractured sandstone after thawing. The results showed that the compression wave velocity of the thawed specimens decreased, the nuclear magnetic resonance (NMR) T2 curve shifted to the right, and the frost heave force promoted the development of the internal porosity in the specimens. With an increase in the crack dip angle, peak stress, expansion stress, cohesion and internal friction angle, the specimen showed a ‘U’ shaped change trend, compression cracks, and rock bridge penetration rate after failure decreased, and mixed failure of tension and shear gradually changed into shear failure. When the dip angles were 30° and 60°, the double fractured quasi-sandstone had larger total damage and more obvious brittle failure characteristics.

Mechanical Properties of Rock Specimens Containing Pre-Existing Cracks with Different Dip Angles Based on Energy Theory and Cohesive Element Method

To investigate the influence of the crack dip angle on the strength of rock specimens, uniaxial compression tests were conducted on granite specimens containing pre-existing cracks. The strain energy evolution during the loading process was analyzed, and the loading-induced cracking process was simulated using the cohesive element method. Both the experimental and numerical results indicate that cracks significantly impact the plastic-yielding stage of the stress–strain curve more than the initial and elastic deformation stages. When the crack dip angle is less than 45°, the stress concentration near the crack is significant, which is an important factor affecting the strength and elastic strain energy distribution of rock specimens. When the crack dip angle is greater than 45°, the degree of stress concentration decreases, and the uniformity of the elastic strain energy distribution and the possibility of crack bifurcation increase. Combining the energy theory with the cohesive element method helps comprehensively understand the initiation, propagation, and coalescence of microcracks near pre-existing crack tips. These research results can provide a reference for geotechnical engineering design and structural stability assessment.

Experimental Study on Mechanical Characteristics of Prefabricated Fractured Sandstone Samples under Uniaxial Cyclic Compression

The loading-unloading physical and mechanical characteristics of fractured coal-bearing strata are greatly affected by fracture occurrence. In order to study the physical and mechanical response characteristics of fractured rock under cyclic compression, this paper takes prefabricated fractured sandstone samples with different dip angles as the object, and uses uniaxial cyclic loading and unloading test to study the influence of crack dip angle on sample strength, failure mode and crack propagation law. The results show that with the increase of crack inclination angle, the cyclic loading and unloading peak strength and elastic modulus of the sample increase significantly, and the peak strain decreases first and then increases. During the cyclic loading process, the area of the hysteresis loop gradually decreases, the slope gradually increases, the energy con-sumed by the hysteresis loop gradually decreases, the cumulative plastic deformation increases, and the curve shape presents a “concave” type; when it is 15 ° and 30 °, the cracks at the crack tip are wing cracks. When it is 45 °, the cracks at the crack tip are secondary inclined cracks and wing cracks. When it is 60 °, 75 ° and 90 °, the cracks at the crack tip are secondary coplanar cracks and wing cracks. With the increase of fracture dip angle, the number of cycles and peak strength at failure are increasing.

Experimental study on strength and failure characteristics of mortar specimens with prefabricated cracks under uniaxial and triaxial stress

Cracks in rock masses have adverse effects on their mechanical characteristics and the stability of rock mass engineering. For this experiment, uniaxial compression and true triaxial compression unloading tests were conducted on mortar specimens. The strength of the specimens was the lowest when the dip angle of the crack was 45°. Under uniaxial compression, the failure mode was mainly tensile failure. With an increase in the crack dip angle of the specimens, the types of cracks changed from shear to tensile cracks. Under true triaxial compression, the confining pressure considerably increased the strength and deformation characteristics of the specimens and weakened the influence of the crack dip angle on the strength. The failure mode when the crack dip angle was 15° was mainly tensile. The failure mode when the crack dip angles were 45° and 75° was mainly tensile–shear composite. With the increase in the crack dip angle, the failure degree of the specimens was more severe. Under the triaxial unloading confining, the failure mode was mainly shear. Compared with uniaxial compression, the failure degree of the specimens was more severe under true triaxial compression and true triaxial unloading. The innovation of this experiment is the use of a special mold to prepare specimens. We recommend that scholars conduct experimental and numerical simulation studies on different crack geometries.

Analytical solution for the effective elastic properties of rocks with the tilted penny-shaped cracks in the transversely isotropic background

Seismic prediction of cracks is of great significance in many disciplines, for which the rock physics model is indispensable. However, up to now, multitudinous analytical models focus primarily on the cracked rock with the isotropic background, while the explicit model for the cracked rock with the anisotropic background is rarely investigated in spite of such case being often encountered in the earth. Hence, we first studied dependences of the crack opening displacement tensors on the crack dip angle in the coordinate systems formed by symmetry planes of the crack and the background anisotropy, respectively, by forty groups of numerical experiments. Based on the conclusion from the experiments, the analytical solution was derived for the effective elastic properties of the rock with the inclined penny-shaped cracks in the transversely isotropic background. Further, we comprehensively analyzed, according to the developed model, effects of the crack dip angle, background anisotropy, filling fluid and crack density on the effective elastic properties of the cracked rock. The analysis results indicate that the dip angle and background anisotropy can significantly either enhance or weaken the anisotropy degrees of the P- and SH-wave velocities, whereas they have relatively small effects on the SV-wave velocity anisotropy. Moreover, the filling fluid can increase the stiffness coefficients related to the compressional modulus by reducing crack compliance parameters, while its effects on shear coefficients depend on the crack dip angle. The increasing crack density reduces velocities of the dry rock, and decreasing rates of the velocities are affected by the crack dip angle. By comparing with exact numerical results and experimental data, it was demonstrated that the proposed model can achieve high-precision estimations of stiffness coefficients. Moreover, the assumption of the weakly anisotropic background results in the consistency between the proposed model and Hudson's published theory for the orthorhombic rock.

Research on crack evolution law and mechanical analysis of three cracked rock masses subjected to compression load

Rocks containing various types of cracks may undergo microcrack expansion and connection under compressive load, which leads to rock fracture under different loading conditions, posing a significant threat to the stability of underground tunneling. Therefore, studying the mechanical response of rocks with different types of cracks is of great importance for controlling the stability of underground mining projects. In this study, we conducted compression tests on three cracked rock samples with different crack types, using an electro-hydraulic servo universal testing machine. We investigated the effect of crack dip angle on the compressive strength, stress–strain curve, and failure pattern of the three cracked rocks, and examined the fracture morphology of the specimens using an industrial camera and the digital image correlation (DIC) technique. To verify the test results, we constructed a parallel bond model in the discrete element method PFC2D to describe the compression process, and compared the peak strength, damage results, and crack number curves. We also investigated the effect of in-situ stress on the mechanical characteristics of the rock by applying in-situ stress values based on the successful PFC2D model. Our research findings revealed that the weakening effect of cracks parallel to the loading direction on the strength of rock is smaller than that of cracks perpendicular to the loading direction. During the compression process, stress concentration phenomena appear first at the crack tip, and the specimen eventually undergoes tensile splitting-type damage. Furthermore, the compressive strength of the three cracked rock samples tends to increase first and then decrease with the application of in-situ stress. These results provide valuable insights into the behavior of cracked rocks and can be utilized to improve the stability of underground mining projects.

Experimental Study on the Charge Signal Time-Frequency Characteristics during Fracture Process of Precracked Syenogranite under Uniaxial Compression

During the process of rock deformation and failure, a significantly large number of charge signals are generated as a result of fracture appearance and crack expansion. The generation of charge signal is the comprehensive embodiment of the coal-failure behavior. The study of charge signal in the process of fractured-rock deformation and failure is of great significance to the prediction of rock dynamic disasters such as tunnel-engineering stability, slope instability and earthquake. In this work, a surveillance system utilizing charge induction is employed to extract precursory information related to the instability and failure of precracked syenogranite. The results reveal a significant influence of fractures on the strength of syenogranite specimens and the number of charge-induction signal events. The position of the charge signal generated is related to the crack dip angle. Furthermore, with the increase of the crack inclination, the number of events and the amplitude and power value of the charge-induced signal increase and reach the maximum in the instability-failure phase. The syenogranite specimen has a relatively large value, medium correlation, or even high correlation charge-induction signal in the phase of rack propagation, which can make an early warning of the deformation and failure risk of syenogranite; with the increase of the fracture degree, the charge-induction signal with large values and high correlations gradually increases.

Effective elastic properties and S-wave anisotropy for rocks containing any oriented penny-shaped cracks in transversely isotropic background

Fractures have a significant influence on rock elastic properties. The existing elastic models for cracked medium mainly consider the crack dip angle. In this work, based on the previous transversely isotropic (TI) background and arbitrary dip crack model, a theoretical model is derived using the Bond transform matrix to quantify the effects of any oriented penny-shaped cracks on the elastic properties of rocks with a TI background. Based on this model, the effects of crack orientation on rock elastic properties are studied. Particularly, a special case with random crack orientation is investigated by using the spherical averaging of the crack compliance matrix with any orientations. Furthermore, the S-wave anisotropy for rocks containing multiple crack sets also is analyzed. The results indicate that the crack orientation has a great influence on rock elastic properties. Especially, the rock elastic properties indicate nonlinear changes with crack azimuth angles when cracks are inclined with respect to the TI background isotropic plane. The randomly oriented cracks decrease the overall rock elastic moduli but have little effect on rock anisotropy. For rocks containing multiple crack sets, parallel crack sets have great effects on the S-wave anisotropy, whereas the effects of orthogonal crack sets are negligible. Using this model, a complete workflow for the inversion of fracture properties using field data measured by acoustic logging is introduced. To explain the effect of crack azimuth angle, the crack density is inverted without considering crack orientation, only considering crack dip angle, and considering both crack dip and azimuth angles. The results indicate that the inversion results considering the crack dip and azimuth angles are in good agreement with the resistivity imaging results. This work provides the theoretical basis for fracture properties inversion for rocks with a TI background.

Analysis on fracture mechanics theory of roof cutting instability mechanism with large mining height face in shallow coal seam

The roof in a fully-mechanized face of a shallow coal seam with large mining height is prone to form a combined cantilever—articulated rock beam structure. When the support resistance is insufficient, the articulated rock beam will sink. This will make the combined cantilever beam rotate and fracture. It is then easy to induce the sliding and instability of the articulated rock beam, which results in large-scale roof cutting and the support crushing. Taking the combined cantilever beam structure as the main research object, and considering the mining damaged characteristics of cantilever beam rock stratum, the rock beam was regarded as a finite plate model with an edge crack of arbitrary dip angle. In addition, a fracture mechanics model controlled by a set of structural planes was established, the instability conditions of rock beam and the main control factors were analyzed, and the method of determining the support resistance were discussed. The results show that the cantilever beam rotates and fractures. This causes a chain reaction of the rock beam that leads to fracture. The combined cantilever beam then loses stability with the increase of the length of the crack length and the crack dip angle, and therefore it is easier to penetrate the cantilever beam and cause roof instability. The necessary condition for rock beam instability was crack activation, and the sufficient condition was the airfoil branch crack propagate through the rock beam. The influence degree of each parameter on the support resistance was thus determined: crack length a > crack dip angle β > rock thickness h > weighting interval l. The theoretical analysis results were proven to be reasonable by an in situ monitoring example of no. 22,310 working face in the Daliuta coal mine, China. On this basis, the reasonable value of support resistance was obtained. The conclusions of this research provide a new method for researching the roof instability mechanism. They are also conducive to the green and sustainable development of mines.

Failure characteristics of concrete pipes with pre‐existing cracks

AbstractUrban ground subsidence accidents have become frequent in recent years, mainly due to cracked concrete sewer pipes. Based on the discrete element method (DEM), the process from crack‐initiation to the formation of penetrating macrocracks were investigated and crack‐initiation load and failure load were calculated. The results showed that numerical results were in good agreement with the experimental results, thus verifying the effectiveness of the DEM calculation results. The crack‐initiation load and failure load of concrete pipes varied when different parameters were involved. The diameter of pipe had the greatest impact on the crack‐initiation load and failure load, followed by the crack position. The crack dip angle did not show any significant influence on the failure load. The crack depth significantly affected the deformation characteristics prior to crack initiation. The diameter of pipe and crack depth had a minor impact on the failure mode of concrete pipes. However, the crack dip angle determined the path of crack propagation while the crack position determined the crack initiation location and failure mode of the concrete pipes.

Fracture Mechanism of Crack-Containing Strata under Combined Static and Harmonic Dynamic Loads Based on Extended Finite Elements

Based on the existing research results, a theoretical fracture model of strata under the compound impact of static and harmonic dynamic load is improved, and the fracture characteristic parameters (stress intensity factor, T-stress, and fracture initiation angle) under the two far-field stress are determined according to the crack dip angle. Additionally, the effects of harmonic dynamic load on the distribution of the stress field and the fracture characteristic (the crack initiation angle, the fracture degree, the number of fracture units, and the fracture area) are further calculated and discussed by theoretical model solution, extended finite element simulation, and the secondary development of the simulation module, respectively. The research results show that the far-field stress, stress intensity factor, and T-stress vary in harmonic form with time under the compound impact of static and harmonic dynamic loads. The frequency of dynamic load affects the number of reciprocal fluctuations of stress intensity factor and T-stress as well as the crack initiation time, but has less influence on the crack initiation angle and fracture degree. While the amplitude of dynamic load affects the stress intensity factor, the extreme value of T-stress and fracture characteristics of the crack. This study has theoretical guiding significance for parameters’ optimization and realization of resonance impact drilling technology.

Oblique Crack Propagation of Brittle Rock under Uniaxial Compression and Its Influencing Factors

With the development of infrastructure in China, the slope rock mass is affected by external forces such as roads. Tunnel excavation will cause a series of engineering problems, which are essentially caused by the instability caused by the propagation of internal cracks in the rock mass. At the same time, in practical engineering, the rock mass is formed through long-term geological structure, and its internal cracks have a variety of properties. Based on granite samples as the research object, two different angles of sample shapes, cylindrical and circular, are prefabricated. The uniaxial compression test is studied to analyze the law of inclined crack propagation in rock under uniaxial compression. Combined with the theory of fracture mechanics, the influence mechanism of crack inclination and sample shape on crack propagation in rock mass is discussed. The test results show that under uniaxial compression, the stress-strain curves of granite samples can be divided into four stages: compaction, elasticity, plasticity, and residual deformation. For the cylindrical sample, the crack initiation occurs at the tip. The compressive strength of the sample decreases with the increase in the prefabricated crack angle, and the crack initiation angle increases with the increase in the prefabricated crack angle. The fracture of the sample changes from shear slip failure to split shear failure of the penetrating rock mass with the increase in the crack angle. For the disk sample, the crack initiation location gradually increases from the tip to the middle with the increase in the crack angle, and the crack initiation angle increases with the increase in the crack angle. The peak load of the sample decreases first and then increases with the increase in the crack angle and is the minimum at 60°. The fracture mode of the sample is mainly tensile failure. When the crack dip angle is between 30° and 60°, the tensile and shear composite failure of the sample occurs, and the influence mechanism of crack dip angle and sample shape on the crack propagation path is analyzed. The research results have important theoretical significance for engineering design, construction, and stability maintenance.

Numerical and experimental investigation on hydraulic fracturing for offshore wind turbine rock-socketed pile foundation construction

Rock-socketed pile is one of the important foundation forms for offshore wind turbines, however, the construction of rock-socketed piles is very difficult. In this work, we propose to use hydraulic fracturing to pre-crack the rock foundation seabed around the piles to assist the construction of rock-socketed piles. Understanding the propagation mechanism of hydraulic fractures is the theoretical basis for hydraulic fracturing of rock seabed. Using mortar specimens containing single internal cracks and corresponding numerical simulations, hydraulic fracturing tests were carried out to study the influences of pre-existing crack characteristics and in situ stress on hydraulic fracture propagation behavior. The mortar specimens showed a tensile-shear failure mode under confining stress in hydraulic fracturing tests, and a macro-fracture penetrated the upper and lower ends of the specimens. Quantitative analysis of hydraulic fracture propagation behavior shows that under the comprehensive influences of the pre-existing crack angle and the stress, it is relatively easy to obtain good engineering results by selecting the pre-existing crack dip angle of 45°∼60° for directional hydraulic fracturing, and the increase of in-situ stress will improve the stability and deflection capacity of the cracks in the seabed.

Timeliness of collinear crack propagation in rock mass

There are a large number of non-penetrating collinear cracks in the rock slope of an open-pit mine. The timeliness of cracks in the rock mass is a problem that cannot be ignored in terms of slope engineering safety. Based on the superposition principle and fracture mechanics, the stress intensity factor of the rock mass crack tip with collinear fractures under biaxial compression was calculated in this study. A mechanical model of rock mass crack propagation with collinear fractures under constant load was established according to the Charles equation. The effects of loading time, crack penetration rate, and crack dip angle on crack propagation along the direction of the rock bridge were analyzed theoretically. The variations in crack propagation with time in the rock mass were examined using a LS-DYNA creep numerical model. The results show that the fracture growth rate changes in three stages over time, progressing through a stable stage, a decreasing stage, and an abrupt stage. A higher crack penetration rate and a larger crack inclination angle cause a higher rock bridge penetration rate in the rock mass. When the crack penetration rate exceeds 74% or the fracture inclination angle is about 60°, the crack expansion directly enters the abrupt stage, and the rock bridge is penetrated. The theoretical analysis results are in close agreement with the numerical results of this work, which validates the proposed age expansion mechanical model for rock masses with non-penetrating collinear fractures.

Mechanical Characteristics and Damage Evolution Law of Sandstone with Prefabricated Cracks Under Cyclic Loading

To study the damage evolution laws of red sandstone samples with prefabricated cracks under cyclic uniaxial compression, physical tests were conducted. In this research, the stress–strain curve characteristics, failure process characteristics, strength, and deformation properties of the cracked sandstone specimens were studied under different cracked geometric parameters (α, β) and cyclic loads. The experimental results revealed that the elasticity modulus, deformation modulus, residual strength, and peak strength increased linearly with the number of loading cycles. Additionally, the failure modes of the samples transition from brittle failure under a small number of loading cycles to ductile failure under a high number of loading cycles. The elastic modulus and peak strength of all the specimens under cyclic loading showed a “strengthening” phenomenon. With increasing crack dip angle (α), the peak strength and crack initiation stress first increased and then decreased. However, with the increase in the crack bridge inclination angle (β), the peak strength and crack initiation stress first decreased and then increased. By using the fitting analysis of the damage evolution equation, it was proven that the damage variable method is suitable for describing the damage evolution characteristics of cracked sandstone.

Analysis of Crack Initiation and Propagation Thresholds of Inclined Cracks under High-Pressure Grouting in Ordovician Limestone

Control of the grouting pressure within the critical grouting pressure for crack propagation in Ordovician limestone can not only ensure grout penetration length, but also prevent the risk of creating an artificial water channel. Based on the fracture mechanics theory, a formula was proposed to calculate the critical grouting pressure of mixed mode I-II cracks in Ordovician limestone. The necessary conditions for tilted crack opening, the rationality of the existing empirical value of the maximum allowable grouting pressure was investigated based on the mechanical model. The RFPA2D-Flow numerical simulation software was used to evaluate the deduced theory. The research results show that the deduced theoretical calculation formula of the critical grouting pressure agrees with the numerical simulation results; when the mixed mode I-II fracture initiation occurs, the grouting pressure exceeds the perpendicular stress of the overlying rock; the greater the density of the overlying rock mass, the greater the value of grouting pressure for fracture initiation; when the side pressure coefficient was ≥1, crack dip angle increased and the grouting pressure for fracture initiation tended to decrease; and the empirical grouting pressure at the maximum allowable grouting pressure is 2.0–2.5 pw, which will not cause propagation and failure of the existing crack.

Fracture behavior and acoustic emission characteristics of sandstone samples with inclined precracks

Sandstone samples with precracks of different dip angles were collected from a coal mine roof and subjected to uniaxial compression tests, and acoustic emission (AE) and scanning electron microscopy (SEM) were used to study how the crack dip angle affected the fracture mechanism. In the precracked sandstone samples, as the dip angle between the crack line and loading direction decreased, so did the peak stress and its completion time. The SEM observations revealed a fracture transition from tensile cleavage to shear slip, which was manifested by a microstructure change from aggregate to staggered. According to energy conversion, a decreased crack dip angle results in gradually decreasing total and dissipative peak energies, whose variation amplitudes at different stages are consistent with those of the peak stress of the samples. The decreased crack dip angle lowered the stress required to trigger the first appearance of AE energy peaks and ring-down counts, as well as shortening the period before the occurrence of the first AE peak signal. However, the AE energy and ring-down count during the failure stage after the stress peak increased gradually. A stepped increase was observed in the AE ring-down count curves, with each step corresponding to a jump in the stress-strain curve. From the characteristics of the AE signal of the fracture of a precracked rock sample, the occurrence of joints or faults in the rock mass can be reasonably inferred. This is expected to provide a new method and approach for predicting coal and rock dynamic disasters.

Investigation of Energy and Damage Evolutions in Rock Specimens with Large‐Scale Inclined Prefabricated Cracks by Uniaxial Compression Test and AE Monitoring

To explore the energy dissipation mechanism and damage evolution characteristics of rock specimens under compressive loading, we performed the acoustic emission (AE) testing under uniaxial compression in intact rock specimens and those with large‐scale prefabricated cracks. The basic mechanical properties of both types of specimens were analyzed comprehensively, and the evolution patterns of strain energy indicators (total strain, elastic, and dissipative energies) in rock specimens before the peak on the stress‐strain curve were identified. We further revealed the effect of the prefabricated crack dip angle, which controlled the surplus energy conversion of the following peak deformation and failure in the rock specimens. Using the modified equation of rock specimen damage evolution characterized by the AE energy and examining the fracture surface morphology via the scanning electron microscopy (SEM), the AE distribution law for rock specimen damage was revealed. An increase in the prefabricated crack dip angle was shown to reduce the peak stress and strain of rock specimens, which experienced a transition from the tensile and splitting failure mode to shear and slip one. Cracked rock specimens exhibited strain energy accumulation at the elastic deformation stage of the stress‐strain diagram and rapid energy consumption at the plastic stage. By contrast, the intact rock specimens had a smoother energy evolution pattern. As the prefabricated crack dip angle increased, the dissipated and surplus strain energies’ shares increased. Moreover, the first peak of the AE energy occurred earlier, and the stress needed for its occurrence decreased as the dip angle increased. According to the damage evolution equation for rock specimens, their damage process can be subdivided into the initial damage, stable damage increase, and the accelerating damage increase stages. An increase in the prefabricated crack dip angle accelerated the damage accumulation in rock specimens. The locking effect of the sawtooth‐like structures on the fracture surface was less conspicuous, and the fracture surface roughness increased. Thus, microcracks gradually developed, and rock specimens became more susceptible to sudden unstable failure.

Experimental Study on Mechanical Properties of Prefabricated Single‐Cracked Red Sandstone under Uniaxial Compression

This paper aims at the phenomenon of the fractured rock column in underground engineering which is prone to collapse when subjected to ground pressure. Uniaxial compression test and particle flow code (PFC2D) are used to analyze the influence of crack dip angle on the mechanical properties, crack propagation, and the failure mode of red sandstone. From the results, it is observed that the stress–strain curve of the precracked red sandstone can be divided into five stages, and there is a critical stress value in the stage of accelerated crack propagation and unstable fracture of the rock sample. Further, the peak strength, maximum strain, and the elastic modulus of the precracked red sandstone increase with the increase of crack dip angle, and the ultimate failure mode of rock sample changes from the “ladder” type failure to slope uneven failure. Furthermore, from PFC2D simulation, it is found that the tensile microcracks contribute more towards the failure of rock samples than the shear cracks. The contact force chain is very weak at the places where the precracks and macroshear planes are formed. This indicates that the original contact force is weakened due to particle fracture. Therefore, the bearing capacity of the precracked rock samples decreases with the increase in load. From the simulation results, it is found that the displacement at the shear plane of the rock sample is large, and the shear dilatation occurs. With the increase in load, the specimen falls off and is ejected. This is due to the weakening of the contact force between the internal particles. Thereafter, it fractures to produce microcracks, which gradually converge, thus providing a prerequisite for the transformation of elastic strain energy into kinetic energy.

Experimental Study on Axial Compression of Concrete with Initial Crack under Hydrostatic Pressure

The axial compression test of concrete with different initial cracks under hydrostatic pressure is carried out. The fracture propagation is analyzed based on the bearing state as well as the apparent phenomena of the specimens, and the failure modes and morphologies are further elaborated. The test results show that with the increase of the hydrostatic pressure, the peak strength growth rate of different crack dip angle specimens tends to be larger or smaller. The development of the hydrostatic pressure leads to the remarkable growth of the plasticity of initially cracked post-peak plastic specimens. Due to the influence of the crack inclination angle, various rates of variation of the elastic modulus after strain softening are detectable. Under the combinational effects of the crack inclination angle and the hydrostatic pressure, the failure modes of the concrete with different initially inclined cracks are different, leading to fracturing failure and shearing shear failure. The crack propagation morphologies of the initially cracked specimens are also dissimilar. With the increase of the hydrostatic pressure as well as the inclination angle of cracks, the crack propagation pattern gradually changes from I-shaped cracks to II-typed cracks, even I-II composite cracks would appear.