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1.
压缩作用下岩石内部细观裂纹扩展导致岩石产生损伤,其对岩石变形、强度等力学特性有着重要影响;然而,岩石内部裂纹扩展与剪切特性（黏聚力、内摩擦角及剪切应力）动态演化关系很少被研究。基于裂纹扩展机制推出的岩石应力-应变本构模型,并结合摩尔-库仑失效准则,推出了在岩石应力-应变关系峰值应力（对应岩石压缩强度）状态时,本构模型细观力学参数与岩石黏聚力、内摩擦角及剪切强度之间的状态关系。然后,引入岩石应力-应变本构关系塑性变形阶段服从摩尔-库仑屈服准则的力学流动规律,进而将已推出的应力-应变关系峰值状态点所满足的细观力学参数与黏聚力、内摩擦角关系,推广到岩石进入塑性变形后,岩石内部裂纹扩展（或应变）与黏聚力、内摩擦角及剪切应力动态演化的理论关系。随着裂纹扩展或应变增加,黏聚力、内摩擦角及剪切应力先增大,达到一个峰值点后减小,该结果与应力-应变本构曲线变化趋势相对应。通过试验结果验证了所提出理论结果的合理性。并讨论了初始裂纹之间摩擦系数对黏聚力、内摩擦角及剪切应力随裂纹扩展或应变演化规律的影响。  相似文献   

2.
李晓照  邵珠山  戚承志 《岩土力学》2019,40(11):4249-4258
岩石内部细观裂纹的存在,对压缩作用下岩石剪切断裂的宏观现象有着重要的影响。然而,能够通过解析解阐释细观裂纹几何特性、围压等影响因素对压缩作用下剪切断裂面角度变化趋势的研究很少。基于Ashby模型中提出的裂纹尖端应力强度因子,提出了一种改进的考虑裂纹角度影响的应力强度因子表达式。利用该改进的应力强度因子表达式,推出了一个可以预测岩石峰值强度的裂纹扩展、应变与应力之间的本构关系。结合本构关系的峰值强度与摩尔-库仑失效准则,得到了岩石损伤与内摩擦角、黏聚力、剪切强度及失效断裂面角度之间的理论关系;讨论了围压、裂纹尺寸、角度及摩擦系数对岩石宏观剪切断裂面角度的影响,通过试验结果验证了模型合理性。结果表明：随着损伤增大,内摩擦角、黏聚力及剪切强度不断减小;随着围压增大、摩擦系数增大和初始裂纹尺寸减小,剪切断裂面角度不断增大;随着裂纹角度增大,剪切断裂纹面角度先减小后增大。  相似文献   

3.
This paper presents a theoretical approach to evaluate the uncertainties and the correlation of the shear strength parameters c and t (cohesion and friction coefficient), obtained in direct shear tests. The analysis is based on the hypothesis that the soil is statistically homogeneous, with shear strength normally distributed having an expected resistance which is linearly dependent on the effective normal stress. With regard to the scatters of the population of the shear strength, two further statements have been formulated for the standard deviation: (1) a constant value, independent of the effective normal stresses and (2) a value which is linearly dependent on the normal effective stresses as a consequence of a constant coefficient of variation. The investigation shows that the strength parameters are negatively correlated and the coefficient of correlation and the coefficients of variation of cohesion and friction angle are highly dependent on the number of shear tests and the normal stresses used in the tests.  相似文献   

4.
This paper presents a new analytical criterion for brittle failure of rocks and heavily over-consolidated soils. Griffith’s model of a randomly oriented defect under a biaxial stress state is used to keep the criterion simple. The Griffith’s criterion is improved because the maximum tensile strength is not evaluated at the boundary of the defect but at a certain distance from the boundary, known as half of the critical distance. This fracture criterion is known as the point method, and is part of the theory of critical distances, which is utilised in fracture mechanics. The proposed failure criterion has two parameters: the inherent tensile strength, σ 0, and the ratio of the half-length of the initial crack/flaw to the critical distance, a/L. These parameters are difficult to measure but they may be correlated with the uniaxial compressive and tensile strengths, σ c and σ t. The proposed criterion is able to reproduce the common range of strength ratios for rocks and heavily overconsolidated soils (σ c/σ t = 3–50) and the influence of several microstructural rock properties, such as texture and porosity. Good agreement with laboratory tests reported in the literature is found for tensile and low-confining stresses.  相似文献   

5.
As soft rocks are likely to soften, slime and swell while contacting water, the existence of soft rocks is harmful for stability of surrounding rocks and supporting structures of tunnels. Through uniaxial and triaxial tests under dry condition and triaxial test with different moisture contents, the mechanical properties and failure modes of soft rocks were studied under conditions that the schistosity plane of the rock samples was vertical to, presented an oblique angle with, and paralleled to the loading direction. The results showed that peak strengths in natural and water-bearing states increased with increasing confining pressures, while those in water-bearing state were 40% lower than those in natural state. The samples were mainly subjected to ductile failure in both natural and water-bearing states while the samples in natural state exhibited a certain brittle failure characteristic in post-peak phase. With the increase of confining pressures, the post-peak curve gradually became gentle after certain brittle failure while the post-peak stresses had an insignificant change. In comparison, the samples in water-bearing state showed significant post-peak disparity, that is, exhibited strong ductile failure characteristic. Moreover, the fitting relationship between triaxial compressive strength and moisture of soft rocks can be expresses as σ 1 = Aω + B (A < 0, B > 0) while that between elasticity modulus and moisture can be expresses as E = Aω + B (A < 0, B > 0).  相似文献   

6.
By using the lower bound finite elements limit analysis, the pullout capacity of an inclined strip anchor plate embedded in a cohesionless soil medium has been computed with an inclusion of pseudo-static horizontal earthquake body forces. The variation of the pullout capacity factor (F γ ) with changes in horizontal earthquake acceleration co-efficient (α h ) has been computed by varying the inclination angle (β) of the anchor plate between 0° and 90°. The results clearly reveal that the pullout capacity factor (F γ ) decreases significantly with an increase in the value of α h . The reduction in the pullout resistance due to seismic forces (1) becomes much more extensive for a vertical anchor plate as compared to the horizontal anchor, (2) decreases generally with increases in the soil friction angle (?) and (3) increases with an increase in friction angle between soil and anchor plate (δ). The developments of the failure zone around the anchor plate were also examined by varying α h and β. The results obtained from the analysis compare well with the solutions reported in literature.  相似文献   

7.
Since cross-anisotropic sand behaves differently when the loading direction or the stress state changes, the influences of the loading direction and the intermediate principal stress ratio (b = (σ 2 ? σ 3)/(σ 1 ? σ 3)) on the initiation of strain localization need study. According to the loading angle (angle between the major principal stress direction and the normal of bedding plane), a 3D non-coaxial non-associated elasto-plasticity hardening model was proposed by modifying Lode angle formulation of the Mohr–Coulomb yield function and the stress–dilatancy function. By using bifurcation analysis, the model was used to predict the initiation of strain localization under plane strain and true triaxial conditions. The predictions of the plane strain tests show that the major principal strain at the bifurcation points increases with the loading angle, while the stress ratio decreases with the loading angle. According to the loading angle and the intermediate principal stress ratio, the true triaxial tests were analyzed in three sectors. The stress–strain behavior and the volumetric strain in each sector can be well captured by the proposed model. Strain localization occurs in most b value conditions in all three sectors except for those which are close to triaxial compression condition (b = 0). The difference between the peak shear strength corresponding to the strain localization and the ultimate shear strength corresponding to plastic limit becomes obvious when the b value is near 0.4. The influence of bifurcation on the shear strength becomes weak when the loading direction changes from perpendicular to the bedding plane to parallel. The bifurcation analysis based on the proposed model gives out major principal strain and peak shear strength at the initiation of strain localization; the given results are consistent with experiments.  相似文献   

8.
Circular failure is generally observed in the slope of soil, highly jointed rock mass, mine dump and weak rock. Accurate estimation of the safety factor (SF) of slopes and their performance is not an easy task. In this research, based on rock engineering systems (RES), a new approach for the estimation of the SF is presented. The introduced model involves six effective parameters on SF [unit weight (γ), pore pressure ratio (r u), height (H), angle of internal friction (φ), cohesion (C) and slope angle (\(\beta\))], while retaining simplicity as well. In the case of SF prediction, all the datasets were divided randomly to training and testing datasets for proposing the RES model. For comparison purposes, nonlinear multiple regression models were also employed for estimating SF. The performances of the proposed predictive models were examined according to two performance indices, i.e., coefficient of determination (R 2) and mean square error. The obtained results of this study indicated that the RES is a reliable method to predict SF with a higher degree of accuracy in comparison with nonlinear multiple regression models.  相似文献   

9.
Particle flow code (PFC2D) software was adopted to investigate the anchorage behaviour and the characteristics of crack initiation, propagation and coalescence of reinforced specimens containing a single fissure (RSCSF). The microscopic parameters of the specimens in the numerical simulation were first validated by experimental outcomes of intact specimens, while the microscopic parameters of the rock bolts were validated based on the results of the RSCSF tests. Then, the mechanical parameters as well as the failure modes in the physical experiments were compared with those derived by the numerical simulation; the results showed good agreement between the simulated macroscopic mechanical properties and failure modes and those obtained in the laboratory experiments. The peak strength, number of cracks and the failure mode varied considerably as the anchorage angle α and fissure angle β increased. Three types of stress–strain curves, types I to III, were obtained from the RSCSF. Shear cracks were observed for all three categories of curves, but the tensile cracks were dominant. The number of cracks and the rate of bond failures decreased as the curve changed from type II to type I to type III. RSCSF failure can be classified into three failure modes: (1) tip crack propagation mode, (2) midpoint crack propagation mode and (3) rock bolt crack propagation mode. These failure modes are primarily differentiated by relations between α and β, and the ratio UCSS/UCSI between the uniaxial compressive strength (UCS, σ max) of the RSCSF (UCSS) and the uniaxial compressive strength of the intact specimen (UCSI).  相似文献   

10.
Microbially induced calcite precipitation (MICP) is used increasingly to improve the engineering properties of granular soils that are unsuitable for construction. This shows MICP technique significant advantages such as low energy consumption and environmentally friendly feature. The objective of the present study is to assess the strength behaviour of bio-cemented sand with varying cementation levels, and to provide an insight into the mechanism of MICP treatment. A series of isotropic consolidated undrained compression tests, calcite mass measurement and scanning electron microscopy tests were conducted. The experimental results show that the strength of bio-cemented sand depends heavily on the cementation level (or calcite content). The variations of strength parameters, i.e. effective friction angle φ′ and effective cohesion c′, with the increase in calcite content can be well evaluated by a linear function and an exponential function, respectively. Based on the precipitation mechanism of calcite crystals, bio-clogging and bio-cementation of calcite crystals are correlated to the amount of total calcite crystals and effective calcite crystals, respectively, and contributed to the improvement in the effective friction angle and effective cohesion of bio-cemented sand, separately.  相似文献   

11.
The estimated undrained shear strength (su) is often not a unique value because it can be evaluated by various test types and/or procedures, such as different failure modes, shear strain rates, and boundary conditions. This study explores (1) the relationship between reference undrained shear strength and in situ shear wave velocity in terms of the effective overburden stress, and (2) the independent relationships to evaluate the undrained shear strength with special consideration of different directional and polarization modes (VH, HV, HH shear waves), which has not been reported. This evaluation is done via a worldwide database compiled from 43 well-documented geotechnical test sites associated with soft ground. Finally, new correlation models are proposed to estimate the undrained shear strength based on the in situ shear wave velocity as well as the plasticity index or the overconsolidation ratio. The application of the shear wave velocity–undrained shear strength relation is illustrated through two independent case studies. The proposed relationships are expected to contribute to reasonable estimates of undrained shear strength as well as offer practical guidance on even extrapolation beyond the data that is available to geotechnical engineers.  相似文献   

12.
The rock mass failure process can be divided into several distinct deformation stages: the compaction stage, elastic stage, stable failure stage, accelerated failure stage, and post-peak stage. Although each stage has been well studied, the relationship among the stages has not been established. Here, we establish two models which are the Strain model Q and Energy density model S by using the renormalization group theory and investigate the mechanical relationship between the volume dilatant point and peak stress point on the rock stress-strain curve. Our models show that the strain ratio (ε f /ε c ) and energy ratio (E f /E c ) at the volume dilatant point and peak stress point are solely functions of the shape parameter m. To verify our models, we further studied the failure process of rock specimens through several uniaxial compression experiments and found that the relationship between ε f /ε c or E f /E c and m shares a notably similar pattern to that from our theoretical model. However, the ε f /ε c and E f /E c values in our experiments are slightly smaller than those predicted by the models. In brief, we demonstrate that our models can be used to predict the failure process of the laboratory-scale hard brittle rock samples.  相似文献   

13.
Based on a laboratory study of drained direct shear tests of remoulded, pre-cut and polished specimens and drained ring shear tests of uncut and remoulded specimens of slip surface materials of five landslide soils, significant correlations of the mobilized shear strength parameters, cohesion (c, c r) and internal friction angle (Φ, Φr), are proposed. The investigated soils consisted of the slip surface material belonging to tuffaceous clay, mudstone, loess and siltstone. Most of the previous studies on residual shear strength measured by reversal direct shear and ring shear devices have obtained significantly different results using the two devices, even when pre-cut and polished specimens were used in the direct shear device. In this study, the residual shear strength values of remoulded specimens measured by a ring shear device are shown to significantly correlate with the drained large displacement shear strength values of remoulded specimens, which were measured using pre-cut and polished specimens in a direct shear device. The correlation between the cohesion measured in the two shear devices is expressed by the linear relationship, $ {c_{\text{r}}} = 0.{7394}c - {6}.{6857} $ , while the correlation between the friction angle measured in the two devices is expressed by the linear relationship, $ {\Phi_{\text{r}}} = {1}.0{852}\Phi - {6}.0{247} $ . The proposed linear correlations for effective cohesion (c′) and effective friction angle (Φ′) have yielded significant coefficients of determination within an effective normal stress range of 30–150?kN/m2.  相似文献   

14.
Pile reinforcement mechanism of soil slopes   总被引：1，自引：1，他引：0  
Stabilizing piles are widely used as an effective and economic reinforcement approach for slopes. Reasonable designs of pile reinforcement depend on the understanding of reinforcement mechanism of slopes. A series of centrifuge model tests were conducted on the pile-reinforced slopes and corresponding unreinforced slopes under self-weight and vertical loading conditions. The deformation of the slope was measured using image-based analysis and employed to investigate the pile reinforcement mechanism. The test results showed that the piles significantly reduced the deformation and changed the deformation distribution of the slope, and prevented the failure occurred in the unreinforced slope. The pile influence zone was determined according to the inflection points on the distribution curves of horizontal displacement, which comprehensively described the features of the pile–slope interaction and the characteristics of reinforced slopes. The concepts of anti-shear effect and compression effect were proposed to quantitatively describe the restriction features of the piles on the deformation of the slope, namely the reduction in the shear deformation and the increase in the compression deformation, respectively. The pile reinforcement effect mainly occurred in the pile influence zone and decreased with increasing distance from the piles. There was a dominated compression effect in the vicinities of the piles. The compression effect developed upwards in the slope with a transmission to the anti-shear effect. The anti-shear effect became significantly dominated near the slip surface and prevented the failure that occurred in the unreinforced slope.  相似文献   

15.
The objective of this study was to evaluate the effect of mine tailings composition on shear behavior and shear strength of co-mixed mine waste rock and tailings (WR&T). Crushed gravel was used as a synthetic waste rock and mixed with four types of tailings: (1) fine-grained garnet, (2) coarse-grained garnet, (3) copper, and (4) soda ash. Co-mixed WR&T specimens were prepared to target mixture ratios of mass of waste rock to mass of tailings (R) such that tailings “just filled” interparticle void space of the waste rock (i.e., optimum mixture ratio, R opt). Triaxial compression tests were conducted on waste rock, tailings, and mixed waste at effective confining stresses (\(\sigma_{\text{c}}^{{\prime }}\)) ranging from 5 to 40 kPa to represent stresses anticipated in final earthen covers for waste containment facilities. Waste rock and co-mixed WR&T specimens were 150 mm in diameter by 300 mm tall, whereas tailings specimens were 38 mm in diameter by 76 mm tall. Shear strength was quantified using effective stress friction angles (?′) from undrained tests: ?′ for waste rock was 37°, ?′ for tailings ranged from 34° to 41°, and ?′ for WR&T mixtures ranged from 38° to 40°. Thus, shear strength of co-mixed WR&T was comparable to waste rock regardless of tailings composition. Shear behavior of WR&T mixtures was a function of R and tailings composition. Tailings influenced shear behavior for R < R opt and when tailings predominantly were silt. Shear behavior was influenced by waste rock for R ≥ R opt and when tailings predominantly were sand or included clay particles.  相似文献   

16.
Laboratory measurements are required to study geophysical properties of the subsurface because of lacking direct observation of Earth’s crust. In this research, compressional (P) and shear (S) wave velocity measurements have been conducted on cylindrical specimens of Quartz-micaschist cored using rock blocks taken from the zinc and lead Angouran mine, Zanjan, northwest of Iran. Cylindrical rock specimens were prepared from the blocks by coring in 0°, 30°, 45°, 60°, and 90° into the foliation direction. P- and S-wave velocities were measured along the cylindrical specimens with different foliation orientations. Percent variations of the P- and S-wave velocities (Thomsen’s anisotropic parameters ε and γ) and constant dynamic modulus of test results have been determined. Percent variations of the P-wave velocity (ε) increase with an increase of the foliation angle with respect to the propagating waves direction by a parabolic function as it shows P-wave velocity differences up to a maximum value of 50 %. Thomsen’s anisotropic parameter of γ has also the same function with the foliation angle. Meanwhile, foliation orientation has a much greater influence on ε than γ for foliation angle from 45° to 90° as \( \frac{\varepsilon }{\gamma } \) ratio increases with an increase of foliation angle. Values of dynamic elastic modulus (E), Poisson’s ratio (ν), shear modulus (μ), bulk modulus (K), and Lamé’s constant (λ) increase with the increase of foliation angle with the parabolic function. The results show that dynamic elastic modulus, Poisson’s ratio, shear modulus, bulk modulus, and Lamé’s constant have anisotropic behavior in relation with the foliation orientation.  相似文献   

17.
Theoretical absorption-line profiles and radial-velocity curves for tidally deformed optical stars in X-ray binary systems are calculated assuming LTE. The variations in the profile shapes and radial-velocity curve of the optical star are analyzed as a function of the orbital inclination of the X-ray binary system. The dependence of the shape of the radial-velocity curve on the orbital inclination i increases with decreasing component-mass ratio q = m x /m v . The integrated line profiles and radial-velocity curves of the optical star are calculated for the Cyg X-1 binary, which are then used to estimate the orbital inclination and mass of the relativistic object: i < 43° andm x = 8.2–12.8 M⊙. These estimates are in good agreement with earlier results of fitting the radial-velocity curve of Cyg X-1 using a simpler model (i < 45°, m x = 9.0–13.2 M⊙).  相似文献   

18.
We present the results of our CCD photometric and moderate-dispersion spectroscopic observations of the binary system V4641 Sgr, which contains a black hole of mass ≈9.5M⊙ and a normal B9III star. The photometric light curve reveals an ellipticity effect with very high amplitudes in V and R, 0.40m and 0.37m, and the color curve shows that the surface temperature is nonuniform. All this testifies to tidal distortion of the normal star's surface due to the massive companion and to a high inclination of the orbit to the line of sight. In June and July 2002, during quiescence, we obtained data during three flares with amplitudes up to 0.26m. In particular, spectroscopic observations were acquired near the time of the black hole's inferior conjunction. One hour before conjunction, a depression by EW=0.5 Å was observed in the red wing of the Hα absorption line, interpreted as absorption by gas flowing in the direction from the observer toward the normal star. This flow is apparently associated with a rarefied gas disk around the black hole, and the conjunction grazes the stellar surface if the orbital inclination is close to 70.7°. The maximum velocity along a circular Keplerian orbit is 650 km/s at a distance of R=0.15–0.20a from the black hole (where a is the component separation). Thus, we find the mass of the black hole to be M BH =7.1–9.5M⊙, confirming the model of Orosz et al. (2001).  相似文献   

19.
It is essential to determine the shear strength parameters c and φ on the sliding surface for stability evaluation and engineering design of a landslide. In this study, a new parameter back analysis method is proposed by combining the 2D/3D upper bound method of limit analysis and reliability theory to accurately determine the shear strength parameters for a 3D slope with a single failure surface. The proposed reliability back analysis method overcomes the shortcomings of the traditional deterministic analysis method of slope stability that cannot take into account the randomness and uncertainty of geotechnical parameters. Based on the reliability theory, two methods were studied: first-order reliability method (implemented by spreadsheet and Matlab, called spreadsheet method and constrained optimization method, respectively, in this paper) and Monte Carlo simulation. The optimized values of c and φ were obtained by establishing only one balance equation with the consideration of the pore water pressure or other complex conditions, which can solve the problem of the back analysis of strength parameters for a single 3D sliding surface condition. The correlation research showed that the negative correlation between c and φ greatly affected the back analysis results, and the reliability index values were conservative without considering such a negative correlation. A case study for the back analysis of shear strength parameters is conducted based on a practical landslide model with a broken line slip surface slope in Zhuquedong village, Luxi town, Xiangxi County, Hunan Province, China, and a suggestion for the selection of landslide cross section is presented. The results show that the back analysis results determined by the reliability theory coincide well with the survey and experimental results. The proposed method is found to be more accurate and effective in determining the values of shear parameters than that of the traditional deterministic inversion method.  相似文献   

20.
Subcritical crack growth plays an important role in evaluating the long-term stability of structures in rocks. By applying the constant-displacement-relax method, two groups of test specimens that one immersed in groundwater and the other in air were tested to get the parameters of subcritical crack growth in double torsion test. The relations of the stress intensity factor K I versus the subcritical crack growth velocity V were obtained under the two different environments, and the behavior of subcritical crack growth was also analyzed. The results showed: the relations of lg K I  ? lg V accorded with linear rules, which is in good agreement with Charles theory; Compared with specimens in nature state, the lg K I  ? lg V curves of saturated water specimens locate top left comer of those of air specimens. The slope of curve is smaller, and the intercept is bigger, which shows that the water–rock interaction speeds up the subcritical crack growth. And A increases 2.9 × 1018 folds but n decreases from 85.12 to 40.83 because of the water–rock interaction. Meanwhile, the fracture toughness K IC also decreases obviously from 2.55 in air to 2.26 in water due to water rock interaction. The testing results provide a basis for time-dependence of rock engineering stability.  相似文献   

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