Pre-existing Fissures Research Articles

Experimental investigation on mechanical, acoustic, and fracture behaviors and the energy evolution of sandstone containing non-penetrating horizontal fissures

Flaws are the weakest part of rock mass, which directly determine the stability of underground engineering. Existing investigations on the mechanical behaviors of flawed rock mainly emphasize on the geometric parameters of the fissure, such as inclination, width, and length, but few works have been conducted on the effect of fissure location on rock properties. This study explores the influences of two fissure layouts (distance between horizontal single fissure and specimen end, and horizontal double fissures spacing) on the sandstone properties under uniaxial compression. The properties studied include strength and deformation, failure mode, acoustic emission (AE) characteristics, and energy evolution. The findings indicated that pre-existing fissures significantly reduced the rock's strength, elastic modulus, and peak strain, and the rock's mechanical properties decreased as the distance between the horizontal single fissure and the specimen end decreased and as the double fissures spacing increased. Furthermore, it was observed that intact specimens mainly underwent shear failure and the flawed rocks under uniaxial compression experienced splitting failure or both. The flawed specimens presented multiple higher AE counts before the peak stress, corresponding to crack initiation, propagation and coalescence, which were distinctly distinct from the intact specimen. The energy evolution characteristics of the fissured sandstone reflected their damage process. The findings are promising to improve the understanding of mechanical mechanisms and energy evolution of flawed rock engineering.

Particle Flow Analysis on Mechanical Characteristics of Rock with Two Pre-Existing Fissures

Many research results show that under any stress state the rock mass is most likely to crack, swell, bifurcate, and infiltrate from the fissure tip, resulting in rock engineering instability and failure. In order to study the influence of double fissure angles on rock mechanical characteristics, five rock numerical models with different fissure angles were established by numerical simulation software. Uniaxial compression tests were carried out, and the variation characteristics of rock stress, strain, failure, microcrack, and acoustic emission (AE) were recorded. The test results show that: With increases in the fissure angles, the elastic modulus of rock increased, while the peak strength decreased first and then increased. The number of microcracks in rock was greater at 15° and 75° than at other angles. The microcracks in rock were mainly tensile cracks, and relatively few were shear cracks. The angles of microcracks were mostly concentrated between 0 and 180°, most of which were between 60 and 110°. The failure of rock was relatively light when the fissure angle was15° or 75°, but it produced more and smaller fragments, and the failure was the most serious when the fissure angle was 30°. The angles of the fissures affected the maximum number of AE events, the strain values for the initial AE event, and the maximal AE event. This research can provide some reference for disasters caused by rocks with pre-existing fissures.

Experimental Study of Rock-like Materials with Two Unequal Parallel Preexisting Fissures under Uniaxial Compression

Fissures substantially impact the engineering stability of rock masses, making research on rock masses with preexisting fissures essential for engineering activities. The development of specimens with different preexisting fissure types was examined in this study. Three different types of specimens with preexisting fissures can be broadly categorized: specimens with few preexisting fissures, specimens with multiple preexisting fissures, and specimens with preexisting fissures and other flaws. Uniaxial compression tests of specimens with preexisting fissures of two unequal lengths were conducted, and the influence of preexisting fissure angle, the distance between the two fissures and fissure length on the peak strength and coalescence mode of specimens were analyzed. A large preexisting fissure length significantly influenced the peak strength and coalescence, and the uniaxial compressive strength (UCS) values of the rock-like materials decreased. In contrast, increasing the long preexisting fissure length influenced the crack propagation and coalescence more extensively in the case of a long preexisting fissure. The preexisting fissure angle and two preexisting fissure distances had a negligible effect on the UCS values of the rock-like materials. However, with increasing long preexisting fissure length, the short preexisting fissure was subject to crack propagation and coalescence.

Three-dimensional failure behavior and cracking mechanism of rectangular solid sandstone containing a single fissure under triaxial compression

In actual rock engineering, fissures play an important role in determining the mechanical parameters of rock mass, whereas it is very difficult to construct fissures in cylindrical specimens. Therefore, the pre-fissured rectangular rock specimens were constructed innovatively. Moreover, a series of triaxial compression experimental results on the failure mechanical behavior of rectangular solid sandstone specimens containing a single fissure were reported. The lateral strain in different directions was monitored and the experimental results show that elastic modulus and axial strain increase non-linearly with confining pressure, and the average Poisson’ s ratio parallel to fissure (μ2) is larger than that vertical to fissure (μ3). The cohesion, Hoek-Brown parameters of peak strength show similar trends with that of crack damage threshold to the fissure angle (α), and the parameters of the peak strength are larger than those of crack damage threshold. However, the internal friction angles of the peak strength and crack damage threshold are almost equal. Based on the geometries and properties of cracks, ten typical crack types are identified. Cracks vertical to pre-existing fissures occur in specimens under uniaxial compression, whereas cracks parallel to pre-existing fissures occur under triaxial compression. Finally, X-ray micro-computed tomography (CT) observations are conducted to analyze the internal damage mechanism of sandstone specimens with respect to various fissure angles. Reconstructed 3-D CT images indicate obvious effects of confining pressure and fissure angle on the crack system of sandstone specimens. This research elucidates the fundamental nature of rock failure under triaxial compression.

Mechanical Behaviors and AE Characteristics of Brittle Coal Specimens with Different Fissure Angles

Uniaxial compression tests were performed on coal specimens with five fissure angles to study the mechanical behaviors and acoustic emission (AE) characteristics of fractured coals. AE and video monitoring techniques were used to examine crack propagation in the fractured specimens. The stress–strain curves, mechanical properties, and cracking processes at different fissure angles were analysed. The AE counts and dominant frequency characteristics, during the failure processes of the specimens, were investigated. In addition, five types of AE signals were classified according to the AE spectral frequency analysis, and low-frequency–high-energy signals were used to accurately predict the brittle fracture processes of the fractured specimens. Finally, a comparison with sandstone specimens revealed the influence of primary cracks on the strength of brittle coal specimens containing preexisting fissures under uniaxial compression. The test results are helpful to elucidate the mechanical behavior and failure mechanism in underground engineering, such as hydraulic slotting in mines.

Undrained monotonic and cyclic behavior of a stiff fissured overconsolidated clay

Due to their geological history, highly overconsolidated stiff clays often contain fissures which can induce strength degradation and structural anisotropy. The aim of this paper is to deepen our knowledge on the monotonic and cyclic behavior of this type of clay. For this purpose, a series of laboratory tests on overconsolidated Merville clay samples were carried out to analyze the influence of the fissure orientation and amplitude on its behavior. Clay samples were scanned by X-ray tomography (CT) and scanning electron microscope (SEM) to obtain a representation of the structure at the micro scale completed by observations of fissure networks within intact specimens. Specimens tested at the same effective confining pressure had different shear strengths due to the influence of the amount and orientation of pre-existing fissures. The value of the shear strength of horizontally drilled specimens was found higher than that of vertically drilled specimens. This anisotropic behavior was mainly the result of preferential orientation of the fissures within the clayey material. The results of one-way and two-way cyclic tests demonstrated also the strong influence of pre-existing fissures on the cyclic behavior. As for the monotonic shear strength, the cyclic resistance of a fissured clay is mainly governed by the intensity and the orientation of pre-existing fissures within the specimens.

Reconstruction of active surface deformation in the Rishi Ganga basin, Central Himalaya using PSInSAR: A feedback towards understanding the 7th February 2021 Flash Flood

Active surface deformation, displacement pattern, and erosional variability is estimated using the geomorphologically sensitive morphometry along with the Persistent Scatterer Interferometric Synthetic Aperture Radar (PSInSAR) technique using the Sentinel-1Adata (119 images) acquired between 07- 02-2017 and 10-02-2021. The average velocities for this dataset are estimated to be between ±11 mm/y. The Raunthi River catchment from where the flood was triggered is undergoing ~8 mm/y subsidence and ~10 mm/y uplift. Compared to this the basin wide deformation (Rishi Ganga basin) is estimated to be around ±10 mm/y with commulative ground displacement of around ±45 mm. The times series analysis suggests an increase in the ground displacement by around 5 mm/y and seems to be responsible for the expansion of pre-existing cracks in the vicinity of the Vaikrita Thrust (VT) and subsequent failure of the northern face of Nandi Peak on 7th February 2021. The Global Positioning System (GPS) derived strain distribution pattern indicate a relatively higher accumulation of strain (>0.35µ strain/y). The normalized steepness index (ksn) variation along the longitudinal section of Rishi Ganga and Raunthi River sub-basin in Central Himalayan region shows anomalous increase at the glacio-fluvial transitional processes. Moreover, the χ profiles as well as planform plots shows anomalously lower values within the Raunthi River sub-basin when compared with the Rishi Ganga basin. Based on the lower values of χ it is observed that Raunthi River sub-basin is undergoing high erosion which can be caused by the presence of sheared lithology and incision of the relict glacial and paraglacial sediments. We negate the suggestion that abrupt rise in the temperature was the major triggering mechanism for the recent disaster, instead it is the sheared lithology and pre-existing fissure developed because of differential uplift and subsidence in Raunthi River that led to the wedge failure and subsequent flash flood. Had the climate was the major driver of the recent tragedy ?, it should have impacted multiple hanging glaciers in the Rishi Ganga valley. Therefore, the study calls for detailed geomorphological, structural and glaciological investigation in regions dominated by glacial and paraglacial processes in the strategic regions of the Himalaya. Towards this, the state of art PSInSAR technique seems to provide fast and reliable detection of terrain instability/stability along with identification of potential areas of slope failures in near future in the glacial and preglacial zones.

An Improved Form of 2D SPH Method for Modeling the Excavation Damage of Tunnels Containing Random Fissures

The excavation damage of deep tunnels is one of the most important factors contributing to the failure of tunnel structures. In order to investigate the influence of tunnel shapes and fissure geometries, the kernel function in the traditional SPH method has been improved, which can realize the brittle fracture characteristics of particles and can be called the Improved Kernel of Smoothed Particle Hydrodynamics (IKSPH-2D). Meanwhile, the random fissure generation method in IKSPH has been put forward. Different tunnel shapes, fissure geometries, and locations are considered during the simulation of tunnel excavation, and results show that (1) the typical “V”-shaped shear damage zones appear after the tunnel excavation, which is consistent with engineering practice. Meanwhile, tunnel excavation also has an “activating” effect on the preexisting fissures. (2) The stability of circular-shaped tunnel is the best, while horseshoe shaped tunnel is worse, and the “U”-shaped tunnel is the worst. (3) Fissures with small and large dip angles have the greatest influence on the stability of tunnel excavation. With the increase of fissure numbers and lengths, the tunnel tends to be instable. (4) The IKSPH method gets free from traditional grids in FEM, which can dynamically reflect the fracture processes of tunnel excavation. Meanwhile, developing 3D IKSPH parallel program will be the future directions.

Crack Evolution and Failure Modes of Shale Containing a Pre-Existing Fissure under Compression.

To investigate the crack evolution of Longmaxi shales with a single prefabricated fissure, a CCD (charge coupled device) camera and AE (acoustic emission) monitoring equipment were employed. On the basis of real-time CCD photographs and AE events, a real-time crack evolution process in fissured shale specimens under uniaxial compression was investigated. The crack initiation angle and extension angle were calculated, the relationship between the crack initiation stress, strength, and crack angle was compared, and the proportion of tensile and shear cracks at different stages of the whole compression process was briefly analyzed. The results demonstrate that, with the increase in fissure angle (α), the weakening ability of the prefabricated fissure to uniaxial compressive strength and crack initiation stress was reduced. The initial cracks and secondary cracks always appeared at the tip of the pre-existing fissure in the form of tensile cracks for α = 30–90°. The crack initiation angle and expansion angle increased first and then decreased rapidly with α increasing. Furthermore, the ultimate failure modes were mixed tensile and shear failure when α = 0–90°. The crack evolution of the fissured shale was progressive, but the final failure of the fissured specimen occurred rapidly. Furthermore, the appearance of the cracks, stress drops, and AE counts had good consistency in time.

An experimental study on failure mechanical behavior and cracking mechanism of rectangular solid sandstone containing two non-coplanar fissures under conventional triaxial compression

Fissures are generally existing in engineering rock mass, and cracking pattern observed in specimens with multiple fissures is analogous to the pattern obtained in specimens with two fissures, whereas the cracking coalescence of real rock specimen under triaxial compression have rarely been investigated. Therefore, thirty fissured rectangular specimens containing two non-coplanar fissures with different ligament angles were prepared to perform triaxial compression in this work, and the stress-strain curves, strength and deformation parameters, ultimate failure modes and Acoustic Emission (AE) characteristic were investigated. The experimental results indicate that pre-existing fissures have a significant effect on the stress-strain curves, more stress drops were observed before and after the peak strength, whereas confining pressure cannot reduce stress-drop. Cohesion (C) of peak strength and damage threshold has different trend with ligament angle (β), and the C of the peak strength is larger than that of the damage threshold. Pre-existing fissures have more effect on damage threshold than peak strength; cracks are easier to initiate in fissured specimen. It is easier to coalesce when ligament angle is parallel to the maximum principal stress, and cracks are easier to expand in width direction than that in thickness direction. The coalescence of the two non-coplanar fissures is classified as five typical modes, and the CT result shows that crack distribution in depth direction is similar. Crack classification by AE parameter and k-mean method can reflect the cracking process in a certain extent. It is more drastic when shear crack initiates, and tensile crack propagates in a stable way.

Experimental Study on Failure Behaviour of Ligaments Between Strike-Inconsistent Fissure Pairs Under Uniaxial Compression

Aiming at the fact that discontinuities in rock mass exhibit different orientations, uniaxial compression tests of resin specimens containing a strike-inconsistent fissure pair were carried out to investigate the failure behaviour of the ligaments. Combined with computerized tomography scanning technology, cracking behaviour and ligament failure pattern were revealed. The failure characteristics and mechanical properties of specimens were studied. The results indicate that the primary cracks generally initiate at a local point of the pre-existing fissure tip, then integrate into a wavy-shaped crack, and develop into a large wrapping crack over time. With the variation of fissure deflection angle, the ligament exhibits three failure patterns: spalling failure, coalescence of cracks at the proximal end and incoherence at the distal end, and torsional failure. The crack initiation stress generally exhibits an increasing trend as fissure deflection angle increases. Peak stress and strain difference are closely related to fissure deflection angle and failure pattern. The mechanical properties of specimens with parallel fissure deflection are the most affected by the fissure deflection angle, followed by those with steep fissure deflection, and those with gentle fissure deflection are minimally affected.

Mechanical Mechanism and Propagation Law of Fissure‐Tip Cracks of Large‐Size Rock Specimens with Two Precut Fissures

The rock is a kind of geological medium with damages of different degrees including fissures, faults, joints, and other structural defects. Many underground rock engineering projects, such as mining and tunnel excavation, can break the three‐dimensional stress balance state of rock mass and make it subject to two‐dimensional or even one‐dimensional stress, thus inducing stress concentration which leads to rapid failure. In order to investigate the failure law of the rock mass with such defects under two‐dimensional stress, based on the similarity theory, we first prepared rocklike specimens with fissures featuring actual mechanical properties and then systematically analyzed the fissure‐tip crack propagation and specimen failure law and mechanical mechanism under two‐dimensional stress in view of the stress field theory. The results demonstrate that with the increase of load, the microcracks developed and propagated gradually, during which a number of branch paths were generated from the fissure tips of the specimens; the upper and lower cracks were connected first due to the main crack propagation, forming a sliding surface which caused the failure of the specimens, and the strengths of the specimens also fluctuated according to the different combinations of the fissure dip angles and rock bridge dip angles. In view of acoustic emission (AE), we calculated and obtained the spatial positions of stress peaks in each direction at the fissure tips; through comparison and analysis, the angle corresponding to the negative angle peak of the maximum circumferential tensile stress and the maximum radial tensile stress is basically the same as the angle of the main crack propagation direction generated from the preexisting fissure; it can be inferred that the tensile stress is the main stress inducing crack initiation and specimen failure, which is consistent with the physical characteristics of rock (resistant to compression but not tension). This may serve as a guidance for judging the direction along which new cracks are generated in a rock mass with double structural planes.

Influence of a preset fissure on clay behavior under uniaxial compression

Under compression, the flaws in soils will not only weaken the mechanical properties of soils, but also affect the strain localization of soils. In order to study the influence of flaws on the behavior of soils under compression, the uniaxial compression tests of clays with different inclination and position fissures were carried out, and the two-dimensional numerical analysis was also discussed based on the damage plasticity model. Analyzing the results of the uniaxial compression test and simulation of the intact and fissured clays, the following conclusions can be drawn: (1) The 60-degree fissure located on the upper position of the right edge of the clay has the greatest influence on the failure form and damage energy of clays, which can reduce the compression strength by 30% compared with that of the intact clay. (2) The numerical method based on the damage plasticity model can basically simulate the compression behavior of clays containing a pre-existing fissure and reproduce the failure characteristics of clays. (3) The preset fissure has obvious influence on the evolution of maximum principal stress in the area with serious damage, but less on the shear stress. And in the area with slight damage, the effect on the maximum principal stress and shear stress is very weak.

Hydro-mechanical coupling behaviors in the failure process of pre-cracked sandstone

The interaction of cracks and water significantly affects the fracture mechanism of rocks. In this study, laboratory tests were conducted using sandstone samples containing a single fissure to explore the hydro-mechanical behaviors in the failure process of pre-cracked rocks. The internal crack characteristics were also analyzed using X-ray CT scanning. The results show that the confining pressure has the greatest effect on the mechanical properties (e.g., strengths, elastic modulus, and Poisson's ratio), followed by the fissure inclination and water pressure. At a lower fissure inclination, the confining pressure may control the type main cracks that form, and an increase in the water pressure increases the number of anti-wing cracks and the length of wing cracks and branch cracks. However, the fracture behaviors of samples with a higher fissure inclination are only slightly affected by the confining pressures and water pressures. The effect of fissure inclination on the internal crack area is reduced with the propagation from the fissure tips to the sample ends. The fissure inclination mainly affects the value of permeability but not affect the trend. The impact of pre-existing fissure on permeability is smaller than that of confining pressure and water pressure.

Numerical assessment of the effects of end-restraints and a pre-existing fissure on the interpretation of triaxial tests on stiff clays

Conventional laboratory triaxial tests apply axisymmetric boundary conditions to a cylindrical sample which has an axisymmetric geometry. For a homogeneous sample this implies that the deformed shape of the sample should maintain an axisymmetric geometry during the test. Consequently, the sample should deform in a barrelling mode and if slip planes develop they should define a cup and cone-like failure surface. However, in many triaxial tests such behaviour is not observed, especially as failure is approached when a planar slip surface develops. Such a deformation mode is not axisymmetric. One reason for this behaviour is that a fissure pre-exists in the sample. Employing hydro-mechanically coupled three-dimensional finite-element analyses, this paper investigates the influence of a single fissure in a triaxial sample of stiff clay on its behaviour throughout the test, focusing on the fissure position, orientation, strength and stiffness, in conjunction with the sample's end-restraints (rough or smooth). The effects are quantified in terms of the sample's overall stiffness and strength, indicating that the presence of a fissure can affect the very small strain stiffness, and that it has a significant effect on the strength of the sample, demonstrating that the conventional methods used to interpret laboratory tests may give unconservative results. The results also show a significant effect of the conditions at the top and bottom surfaces of the sample, where in particular the lateral restraint and rough ends introduce ‘bending’ in the sample.

Experimental Investigation on Drying and Wetting of GMZ Bentonite Using X-Ray Tomography and Volumetric Digital Image Correlation Technique

To investigate the shrinking and swelling properties of Gao-Miao-Zi (GMZ) bentonite, which has been considered as engineering barriers for high-level radioactive nuclear waste disposal in China, drying and wetting tests were carried out. The microstructure of the material at each hydric state was recorded using X-ray tomography (X-CT). The 3D images of the material were analyzed using digital volume correlation (DVC) technique, and the full-field strains at mesoscale (i.e., in the order of clay aggregate) during drying and wetting were quantified. The results show that the GMZ bentonite exhibits notable swelling characteristics during wetting and the swelling strain of the material is up to 8% at mesoscale. The full-field strain in 3D of the material is heterogeneous, anisotropic, and irreversible during drying and wetting. The corresponding deformation mechanisms are discussed. Two different swelling mechanisms were also identified: traction occurs in the interface between the matrix and inclusions during swelling; pre-existing fissure closes during swelling.

Experiment and peridynamic simulation on cracking behavior of red sandstone containing a single non-straight fissure under uniaxial compression

It is widely accepted that the strength, deformability, and failure behaviors of rock material are strongly influenced by widespread natural fissures. Research focusing on the crack initiation, propagation, and coalescence behavior in fissured rock material is important to ensure the reliability and predictability of rock engineering. However, the types and forms of pre-existing fissures are complex and variable; thus, mechanical experiments have rarely been conducted on rock samples containing non-straight prefabricated open fissures. In this research, the strength, deformability, and failure behaviors of sandstone samples containing a single non-straight fissure were systematically investigated by a series of uniaxial compression experiments and numerical simulations. First, the influence of the fissure angle (α) on the strength and deformation characteristics of red sandstone containing a single non-straight fissure was evaluated. Then, the ordinary state-based peridynamics model was used to investigate the fracture behavior of red sandstone specimens with respect to various α values. The results indicate that for α = 0°–15° and 75°–90°, tensile cracks first initiated from the convex points of the prefabricated fissure, and the crack initiation position transferred from the convex point to the tip of the prefabricated fissure for α = 30°–60°. In addition, for the α = 0°–90°, the cracks initiated in the form of tensile cracks, and the ultimate failure modes were mixed tensile and shear failure. Secondary cracks always appeared in the form of shear crack. Moreover, for α ≥ 75°, fewer cracks were initiated before the peak strength was reached; afterward, the crack initiations were more prolific, and more acoustic emission counts were observed.

Experimental Study of Mechanical and Permeability Behaviors During the Failure of Sandstone Containing Two Preexisting Fissures Under Triaxial Compression

Rock masses are typical inhomogeneous geological materials that contain many fissures and cracks. The coupling effect of the crack propagation and seepage evolution in rocks is very important to the safety of rock engineering. However, hydromechanical coupling behavior during the failure of fissured rocks has rarely been investigated. In this research, hydromechanical coupling tests are performed to fully explore the behaviors in strength, deformation, permeability and failure mode of sandstone samples with two preexisting fissures. The experimental results show that the ratio of crack initiation threshold/peak strength, the ratio of crack damage threshold/peak strength and the value of the elastic modulus decrease by at most 31.8%, 12.2% and 18.4% due to the existence of the two fissures, while the Poisson’s ratio increases by at most 45.6%. Furthermore, the values of permeability before the sudden increase stage range from 2.1% to 17.6% of the maximum permeability value. The influence of bridge length and angle on permeability is more significant under lower confining pressure or higher water pressure. Five failure modes are observed in the double-fissure samples under hydromechanical coupling conditions. Additionally, the “wing cracks + indirect coalescence” failure mode is generated only when the ligament length is shorter than the fissure length. The corresponding strength is lower than that for other failure modes. CT images show that the expansion of cracks inside the samples is more restricted than that at the surface of the samples, especially near the rock bridge region. The effects of failure modes on the mechanical and permeability properties, from greatest to least, are as follows: crack initiation threshold, peak strength, crack damage threshold, elastic modulus, Poisson’s ratio and permeability. This research is contributed to analyze the stability of water-bearing rocks in underground caverns with many preexisting fissures.

Treatment of humeral condylar fractures and humeral intracondylar fissures in cats with patellar fracture and dental anomaly syndrome.

ObjectivesThe aim of this study is to describe the treatment and outcome of humeral condylar fractures and humeral intracondylar fissures in cats with patellar fracture and dental anomaly syndrome (PADS) and to provide advice on how to manage these cases in practice.MethodsData were collated on cats with PADS that were reported to have sustained humeral fractures or had fractures or fissures of the humerus identified on radiographs. The details of the fractures were recorded in addition to any treatment and outcome information.ResultsOf the 207 cases reported with PADS, 18 cats (8.7%) were found to have humeral condylar fractures, none of which was known to have resulted from significant trauma. Where treatment occurred, it involved the placement of transcondylar positional or lag screws. In some cases additional implants, including supracondylar bone plates and screws or Kirschner wires (K-wires), were used. Follow-up data revealed that only two cats were euthanased owing to the presence of the humeral fractures, with at least eight achieving some degree of recovery of function.Conclusions and relevanceThese humeral fractures all have the characteristics of stress insufficiency fractures, being simple isolated fractures that are short oblique, with increased radio-density at the fracture line and occurring following minimal or no trauma. Humeral intracondylar fissures were identified in two cats and it is possible that some of the other fractures may have occurred secondary to pre-existing fissures. To our knowledge, no prior reports exist of fissures in cats that do not meet the criteria for PADS. Surgical repair primarily consisted of the placement of transcondylar lag or positional screws with, in some cases, adjunct implants such as bone plates and screws or K-wires. Though there were insufficient data to determine the prognosis for these fractures in the long term, unlike patellar fractures, many of these fractures will heal if treated appropriately.

Investigation of the Effect of Fissure Angle and Temperature on the Strength and Deformation of Rock-like Material

In order to investigate the effect of fissure and temperature on deep-seated rock, uniaxial compression experiments were conducted on rock-like material with different fissure angle at different temperatures. We investigated the influence of fissure angle and temperature on strength and the influence of fissure on failure mode of the rock. Also, we simulated the uniaxial compression experiment of rock-like material with ABAQUS. The results of experiments and simulations confirmed that the strength of rock-like material decreased with increasing temperatures and the strength decreased first then increased with increased fissure angle. The crack initiation started from the tips of the pre-existing fissure and we could speculate via the simulation that the reason of the crack initiation was stress concentration on fissure tips.