Assessing the undrained strength cross-anisotropy of three tailings types

2022 ◽  
Vol 12 (1) ◽  
pp. 1-24
Author(s):  
D. Reid ◽  
R. Fanni ◽  
A. Fourie
Keyword(s):  
Principal Stress ◽  
Stress Ratio ◽  
Additional Data ◽  
Layered Materials ◽  
Engineering Practice ◽  
Published Data ◽  
Shear Tests ◽  
Undrained Strength ◽  
Cross Anisotropy ◽  
Current Engineering

The cross-anisotropic nature of soil strength has been studied and documented for decades, including the increased propensity for cross-anisotropy in layered materials. However, current engineering practice for tailings storage facilities (TSFs) does not appear to generally include cross-anisotropy considerations in the development of shear strengths. This being despite the very common layering profile seen in subaerially-deposited tailings. To provide additional data to highlight the strength cross-anisotropy of tailings, high quality block samples from three TSFs were obtained and trimmed to enable Hollow Cylinder Torsional Shear tests to be sheared at principal stress angles of 0 and 45 degrees during undrained shearing. Consolidation procedures were carried out such that the drained rotation of principal stress angle that would precede potential undrained shear events for below-slope tailings was reasonably simulated. The results indicated the significant effects of cross-anisotropy on the undrained strength, instability stress ratio, contractive tendency and brittleness of each of the three tailings types. The magnitude of cross-anisotropy effects seen was generally consistent with previous published data on sands.

scholarly journals Numerical simulation on the simultaneous stress interference of parallel multiple hydraulic fractures

2021 ◽  
pp. 014459872110019
Author(s):  
Weiyong Lu ◽  
Changchun He
Keyword(s):  
Principal Stress ◽  
Hydraulic Fracture ◽  
Stress Ratio ◽  
Fracture Network ◽  
Hydraulic Fractures ◽  
Fracture Spacing ◽  
Induced Stress ◽  
Minimum Principal Stress ◽  
Fracturing Process ◽  
Stress Ratios

During horizontal well staged fracturing, there is stress interference between multiple transverse fractures in the same perforation cluster. Theoretical analysis and numerical calculation methods are applied in this study. We analysed the mechanism of induced stress interference in a single fracture under different fracture spacings and principal stress ratios. We also investigated the hydraulic fracture morphology and synchronous expansion process under different fracture spacings and principal stress ratios. The results show that the essence of induced stress is the stress increment in the area around the hydraulic fracture. Induced stress had a dual role in the fracturing process. It created favourable ground stress conditions for the diversion of hydraulic fractures and the formation of complex fracture network systems, inhibited fracture expansion in local areas, stopped hydraulic fractures, and prevented the formation of effective fractures. The curves of the maximum principal stress, minimum principal stress, and induced principal stress difference with distance under different fracture lengths, different fracture spacings, and different principal stress ratios were consistent overall. With a small fracture spacing and a small principal stress ratio, intermediate hydraulic fractures were difficult to initiate or arrest soon after initiation, fractures did not expand easily, and the expansion speed of lateral hydraulic fractures was fast. Moreover, with a smaller fracture spacing and a smaller principal stress ratio, hydraulic fractures were more prone to steering, and even new fractures were produced in the minimum principal stress direction, which was beneficial to the fracture network communication in the reservoir. When the local stress and fracture spacing were appropriate, the intermediate fracture could expand normally, which could effectively increase the reservoir permeability.

Confound it: latent lessons from the Mwanza trial of STD treatment to reduce HIV transmission

2003 ◽  
Vol 14 (3) ◽  
pp. 179-184 ◽  
Author(s):  
David Gisselquist ◽  
John J Potterat
Keyword(s):  
Sexually Transmitted Disease ◽  
Hiv Transmission ◽  
Additional Data ◽  
Transmitted Disease ◽  
Published Data ◽  
Hiv Incidence ◽  
Syndromic Management ◽  
Sexually Transmitted ◽  
Safe Injection ◽  
Injection Safety

In 1995, an international team reported that improved syndromic management of sexually transmitted disease (STD) in Mwanza, Tanzania, had reduced HIV incidence by 38% in intervention compared to control communities. However, the team has not addressed confound: project interventions might have reduced HIV transmission during health care through provision of syringes and benzathine (replacing short acting) penicillin and through interactions with a coeval safe injection initiative. Mwanza's success in lowering HIV incidence is a puzzle, since it was achieved with only minor reductions in observed STD prevalence. Despite incomplete analyses, reports from Mwanza have encouraged expansion of STD treatment. However, should success be attributed to injection safety rather than to decreased STD prevalence — an hypothesis that fits published data — expanded STD treatment without attention to injection safety could, ironically, increase rather than decrease HIV incidence. To control for confound, additional data and analyses from the Mwanza study are warranted.

Cumulative Damage in Fatigue under Multiaxial Stress Conditions

1974 ◽  
Vol 188 (1) ◽  
pp. 423-430 ◽  
Author(s):  
D. L. Mcdiarmid
Keyword(s):  
Experimental Investigation ◽  
Aluminium Alloy ◽  
Principal Stress ◽  
Stress Ratio ◽  
Uniaxial Stress ◽  
Cumulative Damage ◽  
Stress Conditions ◽  
Multiaxial Stress ◽  
Stress Ratios ◽  
Damage Criteria

Previous investigations into cumulative damage fatigue under uniaxial stress are discussed in conjunction with the parameters relevant to the present experimental investigation. The results of two-level block programme tests on 2L65 aluminium alloy at four values of constant principal stress ratio and at several combinations of two different principal stress ratios are presented and discussed with reference to cumulative damage criteria developed for the case of uniaxial fatigue stress.

scholarly journals Determination of Equivalent Mohr-Coulomb Criterion from Generalised Hoek-Brown Criterion

2021 ◽  
Author(s):  
Qingqing Yang ◽  
Fei Cai
Keyword(s):  
Principal Stress ◽  
Least Squares Method ◽  
Method Comparison ◽  
Friction Angle ◽  
Engineering Practice ◽  
Shear Strength Parameters ◽  
Strength Parameters ◽  
Coulomb Criterion ◽  
Minor Principal Stress

Abstract A new analytical solution is presented for determining equivalent Mohr-Coulomb (MC) shear strength parameters over an arbitrary interval of minor principal stress σ3 from the generalised Hoek-Brown (HB) criterion using least squares method. Comparison with several published examples demonstrates that the proposed solution had a capacity to accurately determine equivalent MC parameters over a given interval of σ3, as well as instantaneous MC parameters by using a very small interval of σ3. EMC parameters depended heavily on the interval of σ3, which highlighted the importance of intervals of σ3. A calculation case shows that the equivalent internal friction angle and cohesion over the interval of σ3 from tension cut-off σcut−off to maximum minor principal stress σ3max were approximately 12% smaller and 10.3% larger than those over an interval from tensile strength to σ3max, respectively. The proposed solution offers great flexibility for the application of the HB criterion with existing methods based on the MC criterion for rock engineering practice.

Representing Product Architecture

2003 ◽  
Author(s):  
Mike J. Van Wie ◽  
Palani Rajan ◽  
Matthew I. Campbell ◽  
Robert B. Stone ◽  
Kristin L. Wood
Keyword(s):  
Conceptual Design ◽  
Dynamic Process ◽  
Product Architecture ◽  
Engineering Practice ◽  
Architecture Design ◽  
Transformation Of Function ◽  
Validation Experiment ◽  
Design Factors ◽  
Current Engineering ◽  
Current Practices

Product architecture is the transformation of function to layout. Like much of conceptual design, it is a highly dynamic process whereby engineers must consider a deluge of information in terms of both function and form. One shortcoming of current engineering practice is the absence of representations or abstractions used to aid in developing, refining, and exploiting alternative layout solutions. The purpose of this paper is to present a representation for product architecture that sufficiently captures the design factors relevant to product architecture design which are not taken into account in current practices. An example is given to illustrate the technique, and results of a validation experiment are shown.

Coming to Terms with Complexity—Mechanical Engineering 1986 and Beyond

1987 ◽  
Vol 201 (1) ◽  
pp. 11-19 ◽  
Author(s):  
Oscar Roith
Keyword(s):  
Mechanical Engineering ◽  
Engineering Practice ◽  
Engineering Profession ◽  
The Future ◽  
Current Engineering

The paper questions whether current engineering practice provides the engineering profession with the ability to adapt flexibly to the technological and economic challenge of the future and discusses some ways forward.

scholarly journals Numerical Investigation of a Hydrosplitting Fracture and Weak Plane Interaction Using Discrete Element Modeling

Water ◽  
2020 ◽  
Vol 12 (2) ◽  
pp. 535
Author(s):  
Shuaiqi Liu ◽  
Fengshan Ma ◽  
Haijun Zhao ◽  
Jie Guo ◽  
Xueliang Duan ◽  
...  
Keyword(s):  
Shear Stress ◽  
Principal Stress ◽  
Stress Ratio ◽  
Water Pressure ◽  
Maximum Shear Stress ◽  
Water Inrush ◽  
Discrete Element ◽  
Maximum Principal Stress ◽  
In Situ Stress

Water inrush caused by hydrosplitting is an extremely common disaster in the engineering of underground tunnels. In this study, the propagation of fluid-driven fractures based on an improved discrete element fluid-solid coupling method was modeled. First, the interactions between hydrosplitting fractures (HFs) and preexisting weak planes (WPs) with different angles were simulated considering water pressure in the initial fracture. Second, the influence of the in situ stress ratio and the property of WPs were analyzed, and corresponding critical pressure values of different interactions were calculated. Lastly, the maximum principal stress and maximum shear stress variation inside the pieces were reproduced. The following conclusions can be drawn: (1) Five different types of interaction modes between HFs and natural WPs were obtained, prone to crossing the WPs under inclination of 90°. (2) The initiation pressure value decreased with an increased in situ stress ratio, and the confining stress status had an effect on the internal principal stress. (3) During HFs stretching in WPs with a high elastic modulus, the value of the maximum principal stress was low and rose slowly, and the maximum shear stress value was smaller. Through comprehensive analysis, the diversity of the principal stress curves is fundamentally determined by the interaction mode between HFs and WPs, which are influenced by the variants mentioned in the paper. The analysis provides a better guideline for understanding the failure mechanism of water gushing out of deep buried tunnel construction and cracking seepage of high head tunnels.

Numerical Simulation on Fracture Formation on Surfaces of Bi-Layered Columnar Materials

2012 ◽  
Vol 446-449 ◽  
pp. 2929-2933
Author(s):  
Tian Hui Ma ◽  
Chun An Tang ◽  
Lian Chong Li ◽  
Zheng Zhao Liang ◽  
Yong Bin Zhang
Keyword(s):  
Principal Stress ◽  
Stress Ratio ◽  
Numerical Solutions ◽  
Process Analysis ◽  
Failure Process ◽  
Numerical Results ◽  
Numerical Code ◽  
Continuous Transition ◽  
Fracture Patterns ◽  
Fracture Formation

Parallel fracture formation on surfaces of bi-layered columnar materials like growing tree trunk has been previously studied numerically. In this paper, numerical results of a continuous transition from parallel to polygonal fracture patterns with principal stress ratio provides the clear convincing theoretical explanation for fracture spacing. We perform three-dimensional simulations of fracture growth in a bi-layered columnar model with an embedded heterogeneous layer under inner radial expansion and terminal tension by finite element approach. As a result of this expansion, the bark stretches until it reaches its limit of deformation and cracks. A novel numerical code, 3D Realistic Failure Process Analysis code (abbreviated as RFPA3D) is used to obtain numerical solutions. In this numerical code, the heterogeneity of materials is taken into account by assigning different properties to the individual elements according to statistical distribution function. Elastic-brittle constitutive relation with residual strength for elements and a Mohr-Coulomb criterion with a tensile cut-off are adopted so that the elements may fail either in shear or in tension. The discontinuity feature of the initiated crack is automatically induced by using degraded stiffness approach when the tensile strain of the failed elements reaching a certain value. Numerical results of a continuous transition from parallel to polygonal fracture patterns with principal stress ratio are obtained by varying simulation parameters, the thickness of the material layer. We find that, except for further opening of existing fractures after they are well-developed (saturation), new fractures may also initiate and propagate along the interface between layers, which may serve as another mechanism to accommodate additional strain for fracture saturated layers.

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