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 Failure Process Simulation of Interlayered Rocks under Compression

2018 ◽  
Vol 2018 ◽  
pp. 1-13
Author(s):  
Chi Yao ◽  
Sizhi Zeng ◽  
Jianhua Yang
Keyword(s):  
Shear Failure ◽  
Failure Process ◽  
Strength Criterion ◽  
Tensile Failure ◽  
Strength Anisotropy ◽  
Rigid Block ◽  
Bedding Planes ◽  
Typical Experiment ◽  
Confining Pressures ◽  
Spring Method

Anisotropy in strength and deformation of rock mass induced by bedding planes and interlayered structures is a vital problem in rock mechanics and rock engineering. The modified rigid block spring method (RBSM), initially proposed for modeling of isotropic rock, is extended to study the failure process of interlayered rocks under compression with different confining pressures. The modified rigid block spring method is used to simulate the initiation and propagation of microcracks. The Mohr–Coulomb criterion is employed to determine shear failure events and the tensile strength criterion for tensile failure events. Rock materials are replaced by an assembly of Voronoi-based polygonal blocks. To explicitly simulate structural planes and for automatic mesh generation, a multistep point insertion procedure is proposed. A typical experiment on interlayered rocks in literature is simulated using the proposed model. Effects of the orientation of bedding planes with regard to the loading direction on the failure mechanism and strength anisotropy are emphasized. Results indicate that the modified RBSM model succeeds in capturing main failure mechanisms and strength anisotropy induced by interlayered structures and different confining pressures.

scholarly journals The meso-fracturing mechanism of marble under unloading confining pressure paths and constant axial stress

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Linna Sun ◽  
Liming Zhang ◽  
Yu Cong ◽  
Yaduo Song ◽  
Keqiang He
Keyword(s):  
Shear Failure ◽  
Axial Stress ◽  
Confining Pressure ◽  
Particle Flow Code ◽  
Shear Cracks ◽  
Confining Pressures ◽  
Tension Cracks ◽  
Trial And Error Method ◽  
Unloading Confining Pressure ◽  
Fracturing Mechanism

AbstractFailure tests on marble during unloading confining-pressure under constant axial stress and simulations with the particle flow code were performed. The influence mechanism of the unloading rate of the confining pressure, initial unloading stress, and confining pressure on the failure characteristics of, and crack propagation in, marble was studied. By using the trial-and-error method, the conversion relationship between the unloading rates of confining pressures in laboratory tests and numerical simulations was ascertained. Micro-cracks formed in the unloading process of confining pressure are dominated by tension cracks, accompanied by shear cracks. The propagation of shear cracks lags that of tension cracks. As the confining pressure is increased, more cracks occur upon failure of the samples. The proportion of shear cracks increases while that of tension cracks decreases. The failure mode of samples undergoes a transition from shear-dominated failure to conjugated shear failure.

Long-term creep behavior of resin-based polymers in the construction industry

2019 ◽  
Vol 18 ◽  
pp. 60-65 ◽  
Author(s):  
Joerg Fischer ◽  
Patrick R. Bradler ◽  
David Schmidtbauer ◽  
Reinhold W. Lang ◽  
Roman Wan-Wendner
Keyword(s):  
Construction Industry ◽  
Creep Behavior ◽  
Term Creep

scholarly journals An Evaluation Method of Brittleness Characteristics of Shale Based on the Unloading Experiment

Energies ◽  
2019 ◽  
Vol 12 (9) ◽  
pp. 1779 ◽  
Author(s):  
Xiaogui Zhou ◽  
Haiming Liu ◽  
Yintong Guo ◽  
Lei Wang ◽  
Zhenkun Hou ◽  
...  
Keyword(s):  
Evaluation Method ◽  
Shear Failure ◽  
Confining Pressure ◽  
Shear Zones ◽  
Loading Path ◽  
Mechanical Parameters ◽  
Failure Characteristics ◽  
Unloading Rate ◽  
Uplift And Erosion ◽  
Unloading Effect

Shale reservoir has an initial unloading effect during the natural uplift and erosion process, which causes the shale brittleness to change, affecting the design of the fracturing scheme. To consider this, the axial compression loading and confining pressure unloading experiment of shale is carried out, and then the influence of unloading rate on the mechanical parameters, failure characteristics, and the brittleness of rock are analyzed. What is more, a new evaluation method of brittleness characteristics that take the unloading effect into consideration is proposed. The conclusions are as follows: (1) The unloading rate has a weakening effect on the mechanical parameters, such as the destructive confining pressure and the residual strength of the samples. (2) The failure characteristics of shale specimens are a single shear failure in an oblique section under low unloading rate, and multiple shear zones accompanied with bedding fracture under high unloading rate. (3) The brittleness of shale samples is well verified by the brittleness index B d 1 and B d 2 during the loading path; nevertheless, it has shortage at the unloading path. This paper proposes a new brittleness evaluation method which can consider the influence of the different unloading rates and unloading points. Furthermore, there is a nice characterization between the brittleness damage and this method.

scholarly journals Long-Term Creep Behavior Prediction of Sol-Gel Derived SiO2- and TiO2-Wood Composites Using the Stepped Isostress Method

Polymers ◽  
2019 ◽  
Vol 11 (7) ◽  
pp. 1215 ◽  
Author(s):  
Ke-Chang Hung ◽  
Tung-Lin Wu ◽  
Jyh-Horng Wu
Keyword(s):  
Creep Behavior ◽  
Creep Resistance ◽  
Flexural Modulus ◽  
Sol Gel ◽  
Untreated Wood ◽  
Behavior Prediction ◽  
Inorganic Composites ◽  
Sol Gel Process ◽  
Term Creep

In this study, methyltrimethoxysilane (MTMOS), methyltriethoxysilane (MTEOS), tetraethoxysilane (TEOS), and titanium(IV) isopropoxide (TTIP) were used as precursor sols to prepare wood-inorganic composites (WICs) by a sol-gel process, and subsequently, the long-term creep behavior of these composites was estimated by application of the stepped isostress method (SSM). The results revealed that the flexural modulus of wood and WICs were in the range of 9.8–10.5 GPa, and there were no significant differences among them. However, the flexural strength of the WICs (93–103 MPa) was stronger than that of wood (86 MPa). Additionally, based on the SSM processes, smooth master curves were obtained from different SSM testing parameters, and they fit well with the experimental data. These results demonstrated that the SSM was a useful approach to evaluate the long-term creep behavior of wood and WICs. According to the Eyring equation, the activation volume of the WICs prepared from MTMOS (0.825 nm3) and TEOS (0.657 nm3) was less than that of the untreated wood (0.832 nm3). Furthermore, the WICs exhibited better performance on the creep resistance than that of wood, except for the WICMTEOS. The reduction of time-dependent modulus for the WIC prepared from MTMOS was 26% at 50 years, which is the least among all WICs tested. These findings clearly indicate that treatment with suitable metal alkoxides could improve the creep resistance of wood.

scholarly journals Cracking Behaviors and Mechanical Properties of Rock-Like Specimens with Two Unparallel Flaws under Conventional Triaxial Compression

2019 ◽  
Vol 2019 ◽  
pp. 1-15 ◽  
Author(s):  
Huilin Le ◽  
Shaorui Sun ◽  
Chenghua Xu ◽  
Liuyang Li ◽  
Yong Liu
Keyword(s):  
Mechanical Properties ◽  
Inclination Angle ◽  
Failure Modes ◽  
Shear Failure ◽  
Triaxial Compression ◽  
Confining Pressure ◽  
Critical Value ◽  
Tensile Failure ◽  
Rock Bridge ◽  
Bridge Length

Flaws existing in rock masses are generally unparallel and under three-dimensional stress; however, the mechanical and cracking behaviors of the specimens with two unparallel flaws under triaxial compression have been rarely studied. Therefore, this study conducted comprehensive research on the cracking and coalescence behavior and mechanical properties of specimens with two unparallel flaws under triaxial compression. Triaxial compressive tests were conducted under different confining pressures on rock-like specimens with two preexisting flaws but varying flaw geometries (with respect to the inclination angle of the two unparallel flaws, rock bridge length, and rock bridge inclination angle). Six crack types and eleven coalescence types in the bridge region were observed, and three types of failure modes (tensile failure, shear failure, and tensile-shear failure) were observed in experiments. Test results show that bridge length and bridge inclination angle have an effect on the coalescence pattern, but the influence of bridge inclination angle is larger than that of the bridge length. When the confining pressure is low, coalescence patterns and failure modes of the specimens are greatly affected by flaw geometry, but when confining pressure rose to a certain level, the influence of confining pressure is larger than the effect of flaw geometry. The peak strength of the specimens is affected by flaw geometry and confining pressure. There is a critical value for the bridge length. If the bridge length is larger than the critical value, peak strengths of the samples almost keep constant as the bridge length increases. In addition, as the bridge inclination angle increases, there is an increase in the probability of tensile cracks occurring, and with an increase in the confining pressure, the probability of the occurrence of shear cracks increases.

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