scholarly journals Research on the Development Mechanism of Postpeak Cracks in Sandstone under Different Confining Pressures

2019 ◽  
Vol 2019 ◽  
pp. 1-10
Author(s):  
Jihua Zhang ◽  
Lianguo Wang ◽  
Yun Dong ◽  
Yadong Chen ◽  
Yang Jiang ◽  
...  
Keyword(s):  
Probability Density ◽  
Water Inrush ◽  
Confining Pressure ◽  
Ct Images ◽  
Surrounding Rock ◽  
Internal Crack ◽  
Geometrical Parameters ◽  
Stress Levels ◽  
Confining Pressures ◽  
Development Mechanism

Water inrush happens occasionally during deeper roadways excavation. It is mainly due to the lack of understanding in the formation and development mechanism of cracks and its spatial distribution pattern under ground stress. In view of this, this paper used different stress levels to represent the fracture state of different parts of the surrounding rock of the deep roadway; CT detection technique is used to scan the fractured sandstone in the postpeak state; and the CT images under different confining pressures are thus obtained. The geometrical parameters such as area, length, and width of the crack are used to describe the distribution patterns based on CT images processing technique and statistical principle. These patterns are then analyzed under varying postpeak stress levels and confining pressures. The result shows that, as the area, length, and width of the cracks get larger, number of cracks increases with decreasing stress level; at different stress levels, sandstone crack area probability density, crack length probability density, and crack width probability density form exceptional, linear, and Gaussian distribution, respectively. The amount of confining pressure affects the size of cracks and the extent of expansion. This means that the higher the confining pressure is, the easier the internal crack will be penetrated and expanded and the bigger the cracks are, and the number of cracks gets lesser. Such research results can be used to describe the propagation and evolution law of cracks under different stress states of postpeak rock, which also provide an important basis for further analysis of its permeability and the stability of roadway surrounding rock.

scholarly journals Experimental Study on Mechanical Properties of Deep Buried Granite under Different Confining Pressures

2020 ◽  
Vol 2020 ◽  
pp. 1-10
Author(s):  
Jun Zhao ◽  
Tan Zhang
Keyword(s):  
Cyclic Loading ◽  
Confining Pressure ◽  
Surrounding Rock ◽  
Underground Engineering ◽  
Failure Characteristics ◽  
Deformation And Failure ◽  
Cyclic Loading And Unloading ◽  
Confining Pressures ◽  
Crack Damage Stress ◽  
Loading And Unloading

Brittle failure of hard rock poses a serious threat to the stability of surrounding rock in deep underground engineering. In order to study the deformation and failure characteristics of deep buried granite under high confining pressure cyclic loading and unloading, MTS815 electro-hydraulic servo rock test system was used to conduct cyclic loading and unloading tests under confining pressures of 15 MPa, 35 MPa, 45 MPa, and 55 MPa, and the corresponding stress-strain curves and deformation failure characteristic curves were obtained. The experimental results show the follows: (1) under the same confining pressure, the peak strength, crack initiation stress, crack damage stress, and Poisson’s ratio of the specimens under cyclic loading and unloading are larger than those under conventional triaxial loading and unloading, and the unloading elastic modulus is smaller than that, under conventional triaxial compression; (2) the results show that, under different confining pressures, the granite samples show obvious brittle failure characteristics, the elastic modulus and crack initiation stress increase first and then decrease with the confining pressure, the peak strength and crack damage stress of the samples increase linearly with the confining pressure, and Poisson’s ratio increases first and then remains unchanged with the confining pressure; (3) under the two kinds of stress conditions, the macroscopic failure of the samples is mainly shear failure. The deformation and failure law of granite samples revealed in this study has significant reference value for the selection of rock mass mechanical model of surrounding rock stability of underground engineering, the formulation of surrounding rock support countermeasures, and the evolution law of mechanical parameters with damage variables.

scholarly journals Progressive failure mechanical behaviour and response characteristics of sandstone under stress-seepage coupling

2021 ◽  
Vol 18 (2) ◽  
pp. 1-19
Author(s):  
Zhixiang Song ◽  
Junwen Zhang
Keyword(s):  
Mechanical Behaviour ◽  
Pressure Effect ◽  
Axial Strain ◽  
Water Inrush ◽  
Confining Pressure ◽  
Permeability Model ◽  
Triaxial Loading ◽  
Seepage Pressure ◽  
Confining Pressures ◽  
Confining Pressure Effect

Abstract Conventional triaxial loading tests with different confining pressures and stress-seepage coupling tests on sandstone with different confining pressures and seepage pressures were conducted. A permeability model considering strength and strain was established, which better characterized the progressive deformation mechanical behaviour of sandstone under stress-seepage coupling. The results showed the following. (i) The confining pressure not only affects the peak strength of sandstone but also affects the axial deformation under conventional triaxial loading conditions. (ii) Compared with the seepage pressure effect, the degree of the confining pressure effect on the strength of sandstone was weaker, but the degree of that on the axial, radial and volumetric deformations of sandstone was stronger under stress-seepage coupling. (iii) With increasing confining pressure, the axial strain of sandstone decreased, while the corresponding radial and volumetric strains showed progressively increasing evolution characteristics under identical seepage pressures and different confining pressures. With increasing seepage pressure, the axial strain continuously decreased, while the corresponding radial and volumetric strains showed the progressive evolution characteristic of first increasing and then decreasing under identical confining pressures and different seepage pressures. (iv) Compared with the confining pressure effect, the degree of the seepage pressure effect on the permeability progressive evolution law of sandstone was weaker under stress-seepage coupling. The research conclusions could enrich the theories for the prevention and control of water inrush accidents in coal mines.

scholarly journals Analysis of Tunnel Water Inrush Considering the Influence of Surrounding Rock Permeability Coefficient by Excavation Disturbance and Ground Stress

2021 ◽  
Vol 11 (8) ◽  
pp. 3645
Author(s):  
Helin Fu ◽  
Pengtao An ◽  
Long Chen ◽  
Guowen Cheng ◽  
Jie Li ◽  
...  
Keyword(s):  
Permeability Coefficient ◽  
Water Pressure ◽  
Water Inrush ◽  
Surrounding Rock ◽  
Water Inflow ◽  
Calculation Error ◽  
External Water Pressure ◽  
Ground Stress ◽  
External Water ◽  
Inflow Prediction

Affected by the coupling of excavation disturbance and ground stress, the heterogeneity of surrounding rock is very common. Presently, treating the permeability coefficient as a fixed value will reduce the prediction accuracy of the water inflow and the external water pressure of the structure, leading to distortion of the prediction results. Aiming at this problem, this paper calculates and analyzes tunnel water inflow when considering the heterogeneity of permeability coefficient of surrounding rock using a theoretical analysis method, and compares with field data, and verifies the rationality of the formula. The research shows that, when the influence of excavation disturbance and ground stress on the permeability coefficient of surrounding rock is ignored, the calculated value of the external water force of the tunnel structure is too small, and the durability and stability of the tunnel are reduced, which is detrimental to the safety of the structure. Considering the heterogeneity of surrounding rock, the calculation error of water inflow can be reduced from 27.3% to 13.2%, which improves the accuracy of water inflow prediction to a certain extent.

Mechanical behaviour of powders using a medium pressure flexible boundary cubical triaxial tester

2003 ◽  
Vol 217 (3) ◽  
pp. 233-241 ◽  
Author(s):  
F Li ◽  
V M Puri
Keyword(s):  
Shear Modulus ◽  
Mechanical Behaviour ◽  
Triaxial Compression ◽  
Three Dimensional ◽  
Volumetric Strain ◽  
Confining Pressure ◽  
Alumina Powder ◽  
Medium Pressure ◽  
Mean Pressure ◽  
Confining Pressures

A medium pressure (<21 MPa) flexible boundary cubical triaxial tester was designed to measure the true three-dimensional response of powders. In this study, compression behaviour and strength of a microcrystalline cellulose powder (Avicel® PH102), a spray-dried alumina powder (A16SG), and a fluid-bed-granulated silicon nitride based powder (KY3500) were measured. To characterize the mechanical behaviour, three types of triaxial stress paths, that is, the hydrostatic triaxial compression (HTC), the conventional triaxial compression (CTC), and the constant mean pressure triaxial compression (CMPTC) tests were performed. The HTC test measured the volumetric response of the test powders under isostatic pressure from 0 to 13.79MPa, during which the three powders underwent a maximum volumetric strain of 40.8 per cent for Avicel® PH102, 30.5 per cent for A16SG, and 33.0 per cent for KY3500. The bulk modulus values increased 6.4-fold from 57 to 367MPa for Avicel® PH102, 3.7-fold from 174 to 637 MPa for A16SG, and 8.1-fold from 74 to 597MPa for KY3500, when the isotropic stress increased from 0.69 to 13.79 MPa. The CTC and CMPTC tests measured the shear response of the three powders. From 0.035 to 3.45MPa confining pressure, the shear modulus increased 28.7-fold from 1.6 to 45.9MPa for Avicel® PH102, 35-fold from 1.7 to 60.5MPa for A16SG, and 28.5-fold from 1.5 to 42.8MPa for KY3500. In addition, the failure stresses of the three powders increased from 0.129 to 4.41 MPa for Avicel® PH102, 0.082 to 3.62 MPa for A16SG, and 0.090 to 4.66MPa for KY3500, respectively, when consolidation pressure increased from 0.035 to 3.45MPa. In addition, the shear modulus and failure stress values determined from the CTC test at 2.07, 2.76, and 3.45MPa confining pressures are consistently greater than those from the CMPTC test at the same constant mean pressures. This observation demonstrates the influence of stress paths on material properties. The CTT is a useful tool for characterizing the three-dimensional response of powders and powder mixtures.

Influence of cyclic load input on the mechanical properties of a sensitive soil from Orleans, Ontario

1980 ◽  
Vol 17 (4) ◽  
pp. 498-508 ◽  
Author(s):  
R. N. Yong ◽  
D. Taplin ◽  
G. Wiseman
Keyword(s):  
Mechanical Properties ◽  
Laboratory Test ◽  
Dynamic Loading ◽  
Cyclic Strain ◽  
Peak Stress ◽  
Confining Pressure ◽  
Constant Load ◽  
Deviatoric Stress ◽  
General Terms ◽  
Stress Levels

The importance of disturbance and remoulding to the alteration of mechanical properties of sensitive soils has been well documented in the geotechnical literature both in terms of laboratory and field behaviours. Man-made transient dynamic input such as dynamite blasting, heavy vehicles, and train movement have been suspected of being capable of causing a reduction in the in situ strength parameters of sensitive clays. A laboratory test program was undertaken to determine whether dynamic loading at peak stress levels below normal failure strength caused similar changes in the mechanical properties, and specifically to quantify the phenomena.In order to simulate highly overconsolidated conditions most of the tests were carried out under conditions of no confining pressure, although supplemental data were obtained from consolidated undrained tests. Some of the variables examined in this program were confining pressure, mean deviatoric stress, cyclic deviatoric stress, cyclic strain, number of applications, frequency, and reference strength. In order to compare the effect of dynamic input with the long-term creep phenomena, a simultaneous constant load program was undertaken.In general terms, the study indicates that under the prestated laboratory test conditions no major reduction in peak strength was found under dynamic loading, and that failure would occur at comparative stress levels under dead-load conditions, but required a greater time. In addition, examination of the sample after failure revealed that any remoulding of the sample appeared to be restricted to the area adjacent to the shear zone.

scholarly journals Experimental Study on the Creep Characteristics of Coal Measures Sandstone under Seepage Action

Processes ◽  
2018 ◽  
Vol 6 (8) ◽  
pp. 110 ◽  
Author(s):  
Ziheng Sha ◽  
Hai Pu ◽  
Ming Li ◽  
Lili Cao ◽  
Ding Liu ◽  
...  
Keyword(s):  
Creep Deformation ◽  
Deformation Rate ◽  
Confining Pressure ◽  
Test System ◽  
Stability Control ◽  
Surrounding Rock ◽  
Natural State ◽  
Saturation State ◽  
Creep Characteristics ◽  
Coal Measures

The seepage action of underground water accelerates the deformation of roadway surrounding rock in deep mines. Therefore, the study of creep characteristics of surrounding rock under seepage action is the basis for the stability control of roadway surrounding rock in deep water-rich areas. In this paper, a seepage-creep coupling test system for complete rock samples was established. Combined with a scanning electron microscopy (SEM) test system, the seepage-creep law of coal measures sandstone and the damage mechanism were revealed. The study results showed that the maximum creep deformation of sandstone under natural and saturation state decreased gradually with the increase of confining pressure, and the maximum creep deformation under saturation state was greater than the corresponding value under natural state when the confining pressure was same. When the confining pressure was constant, the creep deformation, the constant creep deformation rate and the accelerated creep deformation rate of sandstone increased rapidly with the increase of infiltration pressure. With the change of time, the change of permeability parameters went through three cycles; each cycle was divided into two stages, slow change stage and rapid change stage, and the rate of variation increased with the increase of the seepage pressure. Based on the macroscopic and microscopic characteristics of sandstone rupture, the connection between macroscopic and microscopic mechanism on sandstone rupture was established. The results in this paper can provide a theoretical basis for stability control of roadway surrounding rock in water-rich areas.

scholarly journals Research on Microscopic Evolution Laws of Sandstone Deformation and Failure Based on the Particle Discrete Element Method

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Zhiwei Cai ◽  
Tongqing Wu ◽  
Jian Lu ◽  
Yue Wu ◽  
Nianchun Xu
Keyword(s):  
Shear Crack ◽  
Rock Fracture ◽  
Confining Pressure ◽  
Particle Flow Code ◽  
Shear Cracks ◽  
Deformation And Failure ◽  
Fracture Development ◽  
Confining Pressures ◽  
The Law ◽  
Microcrack Growth

The fracture of sandstone is closely related to the condition of internal microcracks and the fabric of micrograin. The macroscopic mechanical property depends on its microscopic structures. However, it is difficult to obtain the law of the microcrack growth under loading by experiments. A series of microscopic sandstone models were established with particle flow code 3D (PFC3D) and based on the triaxial experiment results on sandstones. The experimental and numerical simulations of natural and saturated sandstones under different confining pressures were implemented. We analyzed the evolution of rock deformation and the rock fracture development from a microscopic view. Results show that although the sandstones are under different confining pressures, the law of microcrack growth is the same. That is, the number of the microcracks increases slowly in the initial stage and then increases exponentially. The number of shear cracks is more than the tensile cracks, and the proportion of the shear cracks increases with the increase of confining pressure. The cracking strength of natural and saturated sandstones is 26% and 27% of the peak strength, respectively. Under low confining pressure, the total number of cracks in the saturated sample is 20% more than that of the natural sample and the strongly scattered chain is barely seen. With the increase of the confining pressure, the effect of water on the total number of cracks is reduced and the distribution of the strong chain is even more uniform. In other words, it is the confining pressure that mainly affects the distribution of the force chain, irrespective of the state of the rock, natural or saturated. The research results reveal that the control mechanism of shear crack friction under the different stress states of a rock slope in the reservoir area provides a basis for evaluating the stability of rock mass and predicting the occurrence of geological disasters.

Uplift behaviour of tapered piles established from model tests

2000 ◽  
Vol 37 (1) ◽  
pp. 56-74 ◽  
Author(s):  
M Hesham El Naggar ◽  
Jin Qi Wei
Keyword(s):  
Load Transfer ◽  
Compressive Loading ◽  
Compressive Load ◽  
Tensile Load ◽  
Confining Pressure ◽  
Cohesionless Soil ◽  
Uplift Capacity ◽  
Experimental Modelling ◽  
Confining Pressures ◽  
Load Tests

Tapered piles have a substantial advantage with regard to their load-carrying capacity in the downward frictional mode. The uplift performance of tapered piles, however, has not been fully understood. This paper describes the results of an experimental investigation into the characteristics of the uplift performance of tapered piles. Three instrumented steel piles with different degrees of taper were installed in cohesionless soil and subjected to compressive and tensile load tests. The soil was contained in a steel soil chamber and pressurized using an air bladder to facilitate modelling the confining pressures pertinent to larger embedment depths. The results of this study indicated that the pile axial uplift capacity increased with an increase in the confining pressure for all piles examined in this study. The ratios of uplift to compressive load for tapered piles were less than those for straight piles of the same length and average embedded diameter. The uplift capacity of tapered piles was found to be comparable to that of straight-sided wall piles at higher confining pressure values, suggesting that the performance of actual tapered piles (with greater length) would be comparable to that of straight-sided wall piles. Also, the results indicated that residual stresses developed during the compressive loading phase and their effect were more significant on the initial uplift capacity of piles, and this effect was more pronounced for tapered piles in medium-dense sand.Key words: tapered piles, uplift, axial response, load transfer, experimental modelling.

Numerical Analysis of Faults on Deep-Buried Tunnel Surrounding Rock Damaged Zones

2011 ◽  
Vol 90-93 ◽  
pp. 74-78 ◽  
Author(s):  
Jun Hu ◽  
Ling Xu ◽  
Nu Wen Xu
Keyword(s):  
Numerical Analysis ◽  
Mechanical Response ◽  
Progressive Failure ◽  
Process Analysis ◽  
Failure Process ◽  
Water Inrush ◽  
Surrounding Rock ◽  
Factors Affecting ◽  
Rock Failure Process ◽  
Tunnel Instability

Fault is one of the most important factors affecting tunnel instability. As a significant and casual construction of Jinping II hydropower station, when the drain tunnel is excavated at depth of 1600 m, rockbursts and water inrush induced by several huge faults and zone of fracture have restricted the development of the whole construction. In this paper, a progressive failure progress numerical analysis code-RFPA (abbreviated from Rock Failure Process Analysis) is applied to investigate the influence of faults on tunnel instability and damaged zones. Numerical simulation is performed to analyze the stress distribution and wreck regions of the tunnel, and the results are consistent with the phenomena obtained from field observation. Moreover, the effects of fault characteristics and positions on the construction mechanical response are studied in details. Some distribution rules of surrounding rock stress of deep-buried tunnel are summarized to provide the reasonable references to TBM excavation and post-support of the drain tunnel, as well as the design and construction of similar engineering in future.

scholarly journals Analysis on Water Inrush Process of Tunnel with Large Buried Depth and High Water Pressure

Processes ◽  
2019 ◽  
Vol 7 (3) ◽  
pp. 134 ◽  
Author(s):  
Weimin Yang ◽  
Zhongdong Fang ◽  
Hao Wang ◽  
Liping Li ◽  
Shaoshuai Shi ◽  
...  
Keyword(s):  
High Pressure ◽  
Model Test ◽  
Water Pressure ◽  
Water Inrush ◽  
High Water ◽  
Surrounding Rock ◽  
Karst Cave ◽  
Tunnel Excavation ◽  
Pressure Water ◽  
High Water Pressure

In order to explore the catastrophic evolution process for karst cave water inrush in large buried depth and high water pressure tunnels, a model test system was developed, and a similar fluid–solid coupled material was found. A model of the catastrophic evolution of water inrush was developed based on the Xiema Tunnel, and the experimental section was simulated using the finite element method. By analyzing the interaction between groundwater and the surrounding rocks during tunnel excavation, the law of occurrence of water inrush disaster was summarized. The water inrush process of a karst cave containing high-pressure water was divided into three stages: the production of a water flowing fracture, the expansion of the water flowing fracture, and the connection of the water flowing fracture. The main cause of water inrush in karst caves is the penetration and weakening of high-pressure water on the surrounding rock. This effect is becoming more and more obvious as tunnel excavation progresses. The numerical simulation results showed that the outburst prevention thickness of the surrounding rock is 4.5 m, and that of the model test result is 5 m. Thus, the results of the two methods are relatively close to each other. This work is important for studying the impact of groundwater on underground engineering, and it is of great significance to avoid water inrush in tunnels.

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