scholarly journals Biaxial Shear Crack Propagation Modes of Rock-Like Specimens with Prefabricated Fissures and Their Strength Characteristics

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Nai-Zhong Xu ◽  
Chang-Qing Liu ◽  
You-Jian Wang ◽  
Hong-Bin Dang
Keyword(s):  
Shear Strength ◽  
Crack Propagation ◽  
Shear Crack ◽  
Crack Coalescence ◽  
Strength Characteristics ◽  
Propagation Mode ◽  
Peak Shear Strength ◽  
Shear Cracks ◽  
Tensile Shear ◽  
Dip Angle

A biaxial shear test is performed on prefabricated, single-fissure type, cubic rock-like specimens by using the TZW-500 rock direct shear apparatus to study the shear strength characteristics, crack coalescence, and propagation modes of the specimens with different geometric parameters. Results show that the crack coalescence and propagation modes of the rock-like specimens with prefabricated fissures can be divided into four types, namely, single main shear crack coalescence mode, main shear crack coalescence and secondary tensile-shear crack propagation mode, main shear crack coalescence and secondary shear crack propagation mode, and main shear crack coalescence and secondary tensile crack propagation mode. All modes are affected by the dip angle α and length l of the prefabricated fissure. When the dip angle of the prefabricated fissure is α∈[0°, 20°) or (70°, 90°], the cracks center on shear failure, and most shear cracks propagate along one end of the prefabricated fissure. At α∈(30°, 50°), the cracks bear the tensile-shear combined action, and the shear cracks propagate along the two ends of the prefabricated fissure. The peak shear strength of the rock-like specimens with prefabricated fissures is also closely related to the dip angle α and length l of the fissure. With the increase in dip angle α of the prefabricated fissure, the peak shear strength of each rock-like specimen decreases initially then increases, and the peak shear strength curve presents a similar “U” shape. At α∈[30°, 60°], the peak shear strength is within the peak-valley interval. When the length l of the prefabricated fissure is increased, the peak shear strength experiences a gradual reduction. When l > 20 mm, the peak shear strength is greatly influenced by l, but the influence is minimal when l ≥ 20 mm. At the same dip angle α and fissure length of l ≥ 20 mm, the correlation between peak shear strength and fissure width b is low.

AE Characterization of Cracking Mode in Sandstone Uniaxial and Brazilian Tests

2014 ◽  
Vol 910 ◽  
pp. 35-39
Author(s):  
Xiao Hu Zhang ◽  
De Chao Liu ◽  
Xiao Long Ren
Keyword(s):  
Acoustic Emission ◽  
Shear Crack ◽  
Shear Mode ◽  
Shear Cracks ◽  
Compression Tests ◽  
Tensile Shear ◽  
Unstable Crack ◽  
Cracking Mode ◽  
Brazilian Splitting

Laboratory results from sandstone Brazilian splitting tests and uniaxial compression tests based on acoustic emission (AE) monitoring indicated that the acoustic emission parameters analysis method can be applied to analyse the characteristics of acoustic emission and to classify the crack modes in rock materials. It concluded that more than 99 per cent of the whole cracking signals in Brazilian tests were classified as tensile mode, and no shear cracks occurred. And more than 65 per cent of the AE signals in uniaxial tests were tensile-shear crack mode, along with about 30 percent of tensile mode and 5 percent of shear mode, and shear cracks only occurred in the unstable crack extension stages; tensile-shear cracks are the main crack modes in the crack stable extension stage.

scholarly journals Study on the Interaction of Collinear Cracks and Wing Cracks and Cracking Behavior of Rock under Uniaxial Compression

2018 ◽  
Vol 2018 ◽  
pp. 1-10 ◽  
Author(s):  
Chaolin Wang ◽  
Yu Zhao ◽  
Yanlin Zhao ◽  
Wen Wan
Keyword(s):  
Uniaxial Compression ◽  
Inclination Angle ◽  
Shear Crack ◽  
Crack Coalescence ◽  
Crack Interaction ◽  
Shear Cracks ◽  
Collinear Cracks ◽  
Wing Crack ◽  
Cracking Behavior ◽  
Initiation And Propagation

This paper investigates the crack interaction, initiation, and propagation rules of rock-like materials containing two collinear cracks. Based on the Kachanov method, the formulations for stress intensity factors (SIFs) of two collinear cracks and two winged cracks are derived, respectively. The influences of bridge ligament and crack length on the crack interaction are analyzed theoretically. The results show that the propagation of a long crack is independent of crack interaction when d≥a2 and the same rule applies for a short crack when d≥a1. With the growth of wing cracks, the SIF of wings first remarkably decreases and then it tends toward a steady value. Subsequently, the propagation of collinear cracks and cracking processes under uniaxial compression are analyzed experimentally and numerically. Both the experimental results and simulation results demonstrate that shear cracks tend to initiate and propagate at higher inclination angle. The crack coalescence is affected by the inclination angle of bridge ligament. For increasing the inclination angle, the crack coalescence varies from wing crack failure to shear crack coalescence. As bridge ligament increases, the crack coalescence varies from shear crack coalescence to shear-wing crack coalescence and then to wing crack failure.

scholarly journals Modeling of Shear Crack Propagation in Rock Masses Using Mesh-Free LRPIM

2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Qingbo Li ◽  
Nengxiong Xu ◽  
Weifeng Wan ◽  
Yazhe Li
Keyword(s):  
Crack Propagation ◽  
Interpolation Method ◽  
Shear Crack ◽  
Propagation Path ◽  
Crack Model ◽  
Rock Masses ◽  
Shear Cracks ◽  
Elastic Plastic ◽  
Mesh Free ◽  
Point Interpolation Method

The modeling of shear cracks in materials is critical in various engineering applications, such as the safety analysis of concrete structures and stability analysis of rock slopes. Based on the idea of Goodman element, the elastic-plastic constitutive model of the shear cracks is derived, and the elastic-plastic analysis of shear crack propagation is realized in the local radial basis point interpolation method (LRPIM). This method avoids the loss of accuracy caused by the mesh in the analysis of fracture propagation, and the crack propagation of rock brittle material is simulated. The investigation indicates that (1) the LRPIM results are close to the FDM results, which demonstrates that it is feasible to analyze shear cracks in rock masses. (2) Compared with the results of the built-in oblique crack model, when the LRPIM is used to analyze crack propagation, the results are close to the experimental results, showing that the LRPIM can model shear crack propagation in a rock mass. (3) The propagation path using the LRPIM is not sufficiently smooth, which can be explained as the crack tip stress and strain not being sufficiently accurate and still requiring further improvement.

scholarly journals Distribution of Cracks in an Anchored Cavern Under Blast Load Based on Cohesive Elements

2021 ◽  
Author(s):  
Yi Luo ◽  
Chenhao Pei ◽  
Dengxing Qu ◽  
Xinping Li ◽  
Ruiqiu Ma ◽  
...  
Keyword(s):  
Crack Propagation ◽  
Side Wall ◽  
Blast Load ◽  
Shear Cracks ◽  
Cohesive Elements ◽  
Peak Displacement ◽  
Tensile Cracks ◽  
Crack Propagation Process ◽  
The Difference ◽  
Dip Angle

Abstract To explore the distribution of cracks in anchored caverns under the blast load, cohesive elements with zero thickness were employed to simulate crack propagation through numerical analysis based on a similar model test. Furthermore, the crack propagation process in anchored caverns under top explosion was analysed and the distribution and mode of propagation of cracks in anchored caverns when a fracture with different dip angles was present in the vault were discussed. With the propagation of the explosive stress waves, cracks successively occur at the boundary of the anchored zone of the vault, arch foot, and floor of the anchored caverns. Tensile cracks are preliminarily found in rocks surrounding the caverns. In the case that a pre-fabricated fracture is present in the upper part of the vault, the number of cracks at the boundary of the anchored zone of the vault decreases, then increases with increasing dip angle of the pre-fabricated fracture. The fewest cracks at the boundary of the anchored zone occur if the dip angle of the pre-fabricated fracture is 45º. The wing cracks deflected to the vault are formed at the tip of the pre-fabricated fracture, around which tensile and shear cracks are synchronously present. Under top explosion, both the peak displacement and peak particle velocity in surrounding rocks of anchored caverns reach their maximum values at the vault, successively followed by the side wall and the floor. In addition, they show asymmetry with the difference of the dip angle of the pre-fabricated fracture; the vault displacement of anchored caverns is mainly attributed to the formation of tensile cracks at the boundary of the anchored zone generated due to tensile waves reflected from the free face of the vault. When a fracture is present in the vault, the peak displacement of the vault decreases while the residual displacement increases.

Shear strength characteristics of an unsaturated expansive clay

2006 ◽  
Vol 43 (7) ◽  
pp. 751-763 ◽  
Author(s):  
Tony LT Zhan ◽  
Charles WW Ng
Keyword(s):  
Shear Strength ◽  
Manganese Oxides ◽  
Matric Suction ◽  
Strength Characteristics ◽  
Water Volume ◽  
Silty Clay ◽  
Expansive Clay ◽  
Direct Shear ◽  
Peak Shear Strength ◽  
Direct Shear Tests

The shear strength characteristics of an expansive clay from China were studied by performing suction-controlled direct shear tests on both natural and compacted specimens. The tested soil was a silty clay with intermediate plasticity and medium expansion potential. A modified direct shear apparatus with a newly developed water volume indicator was used for this laboratory study. The experimental results clearly show that the dilatancy of the expansive clay increases with an increase in the applied suction for both the natural and compacted specimens. Matric suction contributes to the shear strength of the expansive clay via two different mechanisms: the contribution of capillary force to interparticle normal stress, and the effect of suction on soil dilatancy. As a result of the second mechanism, the contribution of suction to peak shear strength for the clay is more significant than that to post-failure shear strength, particularly at a high suction range. The contribution of suction to post-failure shear strength for the natural specimen is basically consistent with that for the compacted specimen. The higher peak shear strength and dilatancy for the natural specimen are related to the cementation effect of the iron and manganese oxides. The contribution of suction to shear strength for the compacted expansive clay is more significant than that for a compacted kaolin at suctions less than 100 kPa.Key words: expansive clay, matric suction, shear strength, dilatancy, direct shear test, water content.

Critical shear crack theory-based punching shear model for FRP-reinforced concrete slabs

2020 ◽  
pp. 136943322097814
Author(s):  
Xing-lang Fan ◽  
Sheng-jie Gu ◽  
Xi Wu ◽  
Jia-fei Jiang
Keyword(s):  
Shear Strength ◽  
Reinforced Concrete ◽  
Shear Crack ◽  
Concrete Strength ◽  
Weight Ratio ◽  
Punching Shear ◽  
Concrete Slabs ◽  
Crack Theory ◽  
Reinforced Concrete Slabs ◽  
Rc Slabs

Owing to their high strength-to-weight ratio, superior corrosion resistance, and convenience in manufacture, fiber-reinforced polymer (FRP) bars can be used as a good alternative to steel bars to solve the durability issue in reinforced concrete (RC) structures, especially for seawater sea-sand concrete. In this paper, a theoretical model for predicting the punching shear strength of FRP-RC slabs is developed. In this model, the punching shear strength is determined by the intersection of capacity and demanding curve of FRP-RC slabs. The capacity curve is employed based on critical shear crack theory, while the demand curve is derived with the help of a simplified tri-linear moment-curvature relationship. After the validity of the proposed model is verified with experimental data collected from the literature, the effects of concrete strength, loading area, FRP reinforcement ratio, and effective depth of concrete slabs are evaluated quantitatively.

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