scholarly journals Simulation Study on Strength and Failure Characteristics for Granite with a Set of Cross-Joints of Different Lengths

2018 ◽  
Vol 2018 ◽  
pp. 1-10 ◽  
Author(s):  
Dawei Yin ◽  
Shaojie Chen ◽  
Xingquan Liu ◽  
Hongfa Ma
Keyword(s):  
Compressive Strength ◽  
Crack Propagation ◽  
Uniaxial Compressive Strength ◽  
Shear Failure ◽  
Tensile Failure ◽  
Failure Characteristics ◽  
Included Angle ◽  
Loading Direction ◽  
Joint Plane ◽  
Plane Direction

The strength and failure characteristics for granite specimen with a set of cross-joints of different lengths were studied using PFC2D software. The results show that when the included angle of α between the main joint and loading direction is 30° or 45°, no matter what the included angle of β between main and secondary joints is, the main joint controls crack propagation and failure of granite specimen, which occurs the shear failure propagating from main joint tips, and the corresponding uniaxial compressive strength is low. Meanwhile, the secondary joint is the key joint for crack propagation and failure at α of 0° and 90° except when β is 90°. The granite specimen occurs the shear failure propagating from secondary joint tips. And, the shear failure crossing upper tips of main and secondary joints is found at α of 0° or 90° and β of 90°. Their uniaxial compressive strengths are large. Also, the combined actions of main and secondary joints determine crack propagation and failure at α of 60° except when β is 90°. The granite specimen occurs the hybrid failure, including shear failure propagating from main joint tips and tensile failure propagating from main and secondary joints center or secondary joint tips. And, when α is 60° and β is 90°, the granite specimen occurs the shear failure along secondary joint plane direction, and its uniaxial compressive strength is small. Generally, when α or β is a fixed value, the uniaxial compressive strength firstly decreases and then increases with the increase of β or α. Additionally, when α is 60° and β>45°, the uniaxial compressive strength represents a decreasing trend. The uniaxial compressive strength at α and β between 30° and 60° is generally small. Finally, the microdisplacement field distributions of granite specimen were discussed.

scholarly journals Effects of Kaolin Addition on Mechanical Properties for Cemented Coal Gangue-Fly Ash Backfill under Uniaxial Loading

Energies ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3693
Author(s):  
Faxin Li ◽  
Dawei Yin ◽  
Chun Zhu ◽  
Feng Wang ◽  
Ning Jiang ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Compressive Strength ◽  
Elastic Modulus ◽  
Fly Ash ◽  
Uniaxial Compressive Strength ◽  
Shear Failure ◽  
Coal Gangue ◽  
Tensile Failure ◽  
Peak Strain ◽  
Local Shear

In this investigation, six groups of cemented coal gangue-fly ash backfill (CGFB) samples with varying amounts of kaolin (0, 10, 20, 30, 40, and 50%) instead of cement are prepared, and their mechanical properties are analyzed using uniaxial compression, acoustic emission, scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. The uniaxial compressive strength, peak strain, and elastic modulus of CGFB samples decreased with the kaolin content. The average uniaxial compressive strength, elastic modulus, and peak strain of CGFB samples with 10% amount of kaolin are close to that of CGFB samples with no kaolin. The contribution of kaolin hydration to the strength of CGFB sample is lower than that of cement hydration, and the hydration products such as ettringite and calcium-silicate-hydrate gel decrease, thereby reducing strength, which mainly plays a role in filling pores. The contents of kaolin affect the failure characteristics of CGFB samples, which show tensile failure accompanied by local shear failure, and the failure degree increases with the kaolin content. The porosity of the fracture surface shows a decreasing trend as a whole. When the amount of kaolin instead of cement is 10%, the mechanical properties of CGFB samples are slightly different from those of CGFB samples without kaolin, and CGFB can meet the demand of filling strength. The research results provide a theoretical basis for the application of kaolin admixture in fill mining.

scholarly journals Effect of Filling Interval Time on Long-Term Mechanical Strength of Layered Cemented Tailing Backfill

2016 ◽  
Vol 2016 ◽  
pp. 1-7 ◽  
Author(s):  
Shuai Cao ◽  
Wei-dong Song
Keyword(s):  
Compressive Strength ◽  
Mechanical Strength ◽  
Failure Modes ◽  
Shear Failure ◽  
Development Stage ◽  
Stability Control ◽  
Tensile Failure ◽  
Uniaxial Compression Test ◽  
Linear Elastic ◽  
Shear Mixing

To explore the influence that filling interval has on the mechanical strength of layered cemented tailing backfill (LCTB), uniaxial compression test is conducted on LCTB samples with a concentration of 70%, 72%, and 75% and a filling interval of 12 h, 24 h, 36 h, and 48 h. From the tests above, mechanical properties and failure modes of LCTB are acquired. The results are as follows: (1) The peak compressive strength of LCTB decreases as the filling interval increases, and it increases when the concentration grows with a certain length of filling interval. At the same time, the peak compressive strength and filling interval show polynomial distribution. (2) There are four stages during the loading process of cemented backfill specimen, that is, compression stage, linear elastic stage, crack extension stage, and undermines development stage. As the filling interval increases, CTB shows a failure mode of tensile failure-tensile shear failure transition-tensile and shear mixing destruction, which provides a theoretical basis for strength design and stability control of backfill.

scholarly journals Instability Process of Crack Propagation and Tunnel Failure Affected by Cross-Sectional Geometry of an Underground Tunnel

2019 ◽  
Vol 2019 ◽  
pp. 1-17 ◽  
Author(s):  
Xianjie Hao ◽  
Shaohua Wang ◽  
Duoxiang Jin ◽  
Bo Ren ◽  
Xiangyang Zhang ◽  
...  
Keyword(s):  
Crack Propagation ◽  
Large Scale ◽  
Shear Failure ◽  
Side Wall ◽  
Surrounding Rock ◽  
Physical Models ◽  
Tensile Failure ◽  
Circular Tunnel ◽  
Cross Sectional ◽  
Underground Tunnel

The process of crack propagation and tunnel failure is affected by the cross-sectional geometry of an underground tunnel. In order to quantify the effect of section shape on the process of crack propagation in deep tunnels under high ground stress conditions, a total of four physical models with two cross-sectional shapes and twelve stress levels were designed and several large-scale physical model tests were conducted. The results indicated that, when the vertical stress is 4.94 MPa, the length and depth of the cracks generated in the rock surrounding the horseshoe tunnel are about eight times that around a circular tunnel. The position where the circumferential displacement of the horseshoe tunnel begins to be stable is about two, to two and a half, times that around a circular tunnel. After the deep chamber was excavated, continuous spalling was found to occur at the foot of the horseshoe tunnel and microcracks in the surrounding rock were initially generated from the foot of the side wall and then developed upwards to form a conjugate sliding shape to the foot of the arch roof, where the cracks finally coalesced. Discontinuous spalling occurred at the midheight of the side wall of the circular tunnel after excavation, and microcracks in the surrounding rock were initially generated from the midheight of the side wall and then extended concentrically to greater depth in the rock mass surrounding the tunnel. Tensile failure mainly occurred on the surface of the side wall: shear failure mainly appeared in the surrounding rock.

scholarly journals Investigation of the anisotropic confinement-dependent brittleness of a Utah coal

2020 ◽  
Author(s):  
Bo-Hyun Kim ◽  
Gabriel Walton ◽  
Mark K. Larson ◽  
Steve Berry
Keyword(s):  
Compressive Strength ◽  
Unconfined Compressive Strength ◽  
Shear Failure ◽  
Confining Stress ◽  
Included Angle ◽  
Anisotropic Strength ◽  
Brittle Ductile Transition ◽  
The Given ◽  
Compressive Tests

Abstract Changes of failure mechanism with increasing confinement, from extensional to shear-dominated failure, are widely observed in the rupture of intact specimens at the laboratory scale and in rock masses. In an analysis published in 2018, both unconfined and triaxial compressive tests were conducted to investigate the strength characteristics of 84 specimens of a Utah coal, including the spalling limits, the ratio of apparent unconfined compressive strength to unconfined compressive strength (UCS), the damage characteristics, and the post-yield dilatancy. These mechanical characteristics were found to be strongly anisotropic as a function of the orientation of the cleats relative to the loading direction, defined as the included angle. A total of four different included angles were used in the work performed in 2018. The authors found that the degree of anisotropic strength differed according to the included angle. However, the transition from extensional to shear failure at the given confinements was not clearly identified. In this study, a total of 20 specimens were additionally prepared from the same coal sample used in the previous study and then tested under both unconfined and triaxial compressive conditions. Because the authors already knew the most contrasting cases of the included angles from the previous work using the four included angles, they chose only two of the included angles (0° and 30°) for this study. For the triaxial compressive tests, a greater confining stress than the mean UCS was applied to the specimens in an attempt to identify the brittle-ductile transition of the coal. The new results have been compiled with the previous results in order to re-evaluate the confinement-dependency of the coal behavior. Additionally, the different confining stresses are used as analogs for different width-to-height (W/H) conditions of pillar strength. Although the W/H ratios of the specimens were not directly considered during testing, the equivalent W/H ratios of a pillar as a function of the confining stresses were estimated using an existing empirical solution. According to this relationship, the W/H at which in situ pillar behavior would be expected to transition from brittle to ductile is identified.

scholarly journals Failure Behaviour of Sandstone with a Preexisting Joint under Stepped Excavation

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Yinzhu Liu ◽  
Ping Cao ◽  
Liwen He ◽  
Qibin Lin
Keyword(s):  
Failure Modes ◽  
Shear Failure ◽  
Normal Load ◽  
Crack Coalescence ◽  
Tensile Failure ◽  
Type I ◽  
Failure Characteristics ◽  
Excavation Process ◽  
Spalling Failure ◽  
Shear Slip

Much geotechnical construction needs to be carried out under the condition of stepped excavation. However, there is still a lack of research on crack coalescence and failure modes of jointed rock mass under stepped excavation conditions. In order to simulate the stepped excavation test of the real project, the polylactic acid (PLA) material is selected as the filler for the excavation area. The stepped excavation tests are performed on sandstone specimens containing a preexisting joint under different normal load conditions. The dynamic stepped excavation of simulating excavate rock engineering is realised. The constant normal loads during the excavation process are determined to be 80 kN and 100 kN. The influence of the joint inclination on the failure characteristics of the excavation process is analysed. Four typical failure modes are summarised: (a) Mode I: crack coalescence of tensile failure; (b) Mode II: crack coalescence of mixed failure; (c) Mode III: without crack coalescence of mixed failure; (d) Mode IV: without crack coalescence of shear failure. Furthermore, the failure characteristics of the area above the excavation hole and the preexisting joint are analysed. The results show that there are three failure modes: (a) Type I: spalling failure; (b) Type II: shear slip failure; (c) Type III: shear slip and spalling mixed failure.

scholarly journals Long-term creep behavior of deep-buried marble under different confining pressures

2019 ◽  
Vol 23 (Suppl. 3) ◽  
pp. 653-660
Author(s):  
Ersheng Zha ◽  
Ru Zhang ◽  
Zetian Zhang ◽  
Li Ren ◽  
Wenju Zhang ◽  
...  
Keyword(s):  
Creep Behavior ◽  
Shear Failure ◽  
Confining Pressure ◽  
Tensile Failure ◽  
Creep Failure ◽  
Failure Characteristics ◽  
Underground Caverns ◽  
Confining Pressures ◽  
Term Creep

To explore the long-term creep behavior of deep rock, the long-term tri-axial creep mechanical behavior of the rock under different confining pressures has been carried out. The results show that the instantaneous strain and creep strain of the high confining pressure specimen are significantly higher than that of the low confining pressure specimen under high deviatoric stress. By analyzing the failure characteristics of different confining pressure specimens, it is found that with the increase of the confining pressure, the creep failure characteristics of the marble transforms from tensile failure to shear failure. These research results have certain reference significance for the long-term stability analysis of the deep underground caverns.

scholarly journals Experimental Investigation of Unloading-Induced Red Sandstone Failure: Insight into Spalling Mechanism and Strength-Weakening Effect

2020 ◽  
Vol 2020 ◽  
pp. 1-16
Author(s):  
Yong Luo ◽  
Fengqiang Gong ◽  
Dongqiao Liu
Keyword(s):  
Shear Failure ◽  
Hard Rock ◽  
Confining Pressure ◽  
Tensile Failure ◽  
Compression Tests ◽  
Failure Characteristics ◽  
Red Sandstone ◽  
Confining Pressures ◽  
Unloading Rate ◽  
Rock Tunnels

To study the effect of excavation unloading on hard rock failure, a series of true-triaxial compression tests, biaxial compression tests, and true-triaxial unloading compression tests (two different unloading rates) at different confining pressures was conducted on red sandstone cube samples. The strength and failure characteristics and their relationship for red sandstone unloading at different unloading rates and confining pressures were analyzed. Based on the test results, the effects of the unloading rate and confining pressure on the strength and failure characteristics of hard rock were explored, and a reasonable explanation for unloading-induced spalling in hard rock tunnels was presented. The results show the stress-strain curve of highly stressed red sandstone exhibits a stress step during unloading, and the higher the unloading rate, the lower the stress level required for a stress step. The rock strength-weakening effect induced by unloading was confirmed. The mechanical properties of red sandstone become more unstable and complicated after unloading. After the red sandstone is unloaded to a two-dimensional stress state, with increasing confining pressure, the strength increases first and then decreases; the failure mode changes from a low-confining pressure tensile-shear failure to a high-confining pressure tensile failure; and the geometries of the slabs change from large thick plates and wedges to medium- and small-sized thin plates. At equal confining pressures, the higher the unloading rate, the lower the strength (i.e., the strength-weakening effect is more pronounced), the thinner the slab, and the lower the confining pressure required for the failure mode to change from tensile-shear failure to tensile failure. The unloading rate and confining pressure affect the strength and failure characteristics by affecting the crack initiation type and propagation direction in hard rock. For deep hard rock tunnels with high unloading rate and axial stress, neglecting the effects of unloading rate and axial stress will lead to a dangerous support design. For deep hard rock ore, if the maximal horizontal principal stress exceeds the critical confining pressure, the mining surface should be perpendicular to the direction of the minimal horizontal principal stress. The results of this study are of great engineering significance for guiding deep hard rock tunnel construction and mining.

scholarly journals Mechanical Anisotropy and Failure Characteristics of Columnar Jointed Rock Masses (CJRM) in Baihetan Hydropower Station: Structural Considerations Based on Digital Image Processing Technology

Energies ◽  
2019 ◽  
Vol 12 (19) ◽  
pp. 3602 ◽  
Author(s):  
Yingjie Xia ◽  
Chuanqing Zhang ◽  
Hui Zhou ◽  
Chunsheng Zhang ◽  
Wangbing Hong
Keyword(s):  
Rock Mass ◽  
Crack Propagation ◽  
Structural Characteristics ◽  
Jointed Rock ◽  
Hydropower Station ◽  
Defect Structures ◽  
Failure Characteristics ◽  
Included Angle ◽  
Baihetan Hydropower Station ◽  
Columnar Joints

The columnar joints in Baihetan hydropower station are primary tensile joints since they were formed during the process of lava condensation. Understanding the influence of columnar jointed rock mass (CJRM) on the mechanical response and failure modes is the basis for designing of associated engineering works. Hence, the structural characteristics of Baihetan CJRM were analyzed by carrying out a geological survey at first. Three groups of numerical models capable of reflecting the structural characteristics of CJRM were then established to analyze the mechanical and failure characteristics. The results in this study showed that: (1) Irregularity of columnar basalt restricted crack propagation on columnar joints and also led to stress concentration in the distorted parts, and thus, damage of basalt columns; (2) when the included angle between direction of concentrated defect structures in CJRM and uniaxial stress was large, the defect structures can prevent crack propagation on columnar joints, and the failure of defect structure can cause the overall failure of the rock mass; and (3) under the condition of same columnar structure and included angle, the peak strength of models with microcracks and structural plane was low and the irregular shape of columnar joints decreased the anisotropy of mechanical parameters.

scholarly journals An Experimental Study of the Uniaxial Failure Behaviour of Rock-Coal Composite Samples with Pre-existing Cracks in the Coal

2019 ◽  
Vol 2019 ◽  
pp. 1-12 ◽  
Author(s):  
Shaojie Chen ◽  
Yao Ge ◽  
Dawei Yin ◽  
Huisan Yang
Keyword(s):  
Crack Propagation ◽  
Composite Structure ◽  
Shear Failure ◽  
Progressive Failure ◽  
Strain Curve ◽  
Composite Sample ◽  
Compression Tests ◽  
Failure Characteristics ◽  
Splitting Failure ◽  
Composite Samples

Many hazards encountered during coal mining can be caused by the instability and failure of the composite structure of the coal seam and the surrounding rock strata. The defects present in the coal affect the structural stability of the composite structure. In this study, uniaxial compression tests were conducted on sandstone-coal composite samples with pre-existing cracks in the coal, combined with tests performed with an acoustic emission (AE) device and a digital video camera. The strength, macrofailure initiation (MFI), and failure characteristics of composite samples, as influenced by the coal’s pre-existing cracks, were analysed. The coal’s pre-existing cracks were shown to reduce the strength, promote the occurrence of MFI, and affect the failure characteristics of the samples. Vertical penetration cracks had much more pronounced effects on strength and MFI occurrence, especially vertical penetration cracks that penetrated through the centre of the coal. Horizontal penetration cracks had a much reduced effect on strength and MFI occurrence. The MFI caused a step shape in the stress-strain curve accompanied with a peak energy index signal and occurred around the original coal cracks. The MFI models predominantly exhibited crack initiation from the pre-existing coal cracks and surface spalling caused by crack propagation. The intact composite sample failure presented as an instantaneous failure, whereas the composite samples containing the pre-existing cracks showed a progressive failure. The failures of composite samples occurred predominantly within the coal and displayed an X-typed shear failure accompanied by a small splitting failure. Both the coal and sandstone were destroyed in the composite sample with vertical penetration cracks through the centre of the coal. Failure of the coal occurred through a splitting failure accompanied by a small X-typed shear failure, while the sandstone showed a splitting failure induced by crack propagation in the coal.

scholarly journals Numerical Investigation on the Evolution of Mechanical Properties of Rock Affected by Micro-Parameters

2020 ◽  
Vol 10 (14) ◽  
pp. 4957
Author(s):  
Haoyu Rong ◽  
Guichen Li ◽  
Dongxu Liang ◽  
Changlun Sun ◽  
Suhui Zhang ◽  
...  
Keyword(s):  
Compressive Strength ◽  
Uniaxial Compressive Strength ◽  
Stress Ratio ◽  
Three Dimensional ◽  
Particle Flow Code ◽  
Parameter Calibration ◽  
Failure Characteristics ◽  
Failure Patterns ◽  
Response Characteristics ◽  
Bond Model

Investigating the micro-parameters of rock is vital for understanding the macro-properties of rock, such as the uniaxial compressive strength (UCS), Young’s modulus, failure patterns, etc. In this paper, based on the experimental results of rock material, a parallel-bond model in three-dimensional particle flow code (PFC3D) was applied to investigate the effects of the joint action of bond stiffness ratio and bond stress ratio on macro-properties of rock. The uniaxial compressive strength, stress–strain relationships, and failure characteristics, as well as underlying compression and failure mechanisms, in the process of parameter calibration, were systematically studied. The results indicated that the interaction of several micro-parameters would obviously change the response characteristics of the macro-properties of the model. The mechanism of the effects of various micro-parameters on the macro-properties of the model was further revealed. The change of the micro-parameters would change the strength and stress state of the bond between particles. The research results could promote the understanding of the failure mechanism of rock and improve the efficiency of micro-parameter calibration and the accuracy of calibration results.

Sign in / Sign up

Export Citation Format

Share Document