Assessing the undrained strength cross-anisotropy of three tailings types

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.

Analysis and Research of the High-Cycle Fatigue Fracture Mode Based on Stress Ratio and Residual Stress of Ti-6Al-4V

The content of titanium is about 0.63% in the earth’s crust, and it ranks 10th among all elements. The content of titanium is next to the metal elements of aluminum, iron and magnesium, iron, and magnesium; titanium alloys have low density, high specific strength (the ratio of tensile strength to density), wide working range (−253°C–600°C), and excellent corrosion resistance melting point; the chemical activity of titanium alloy is very high, and it easily reacts with hydrogen, oxygen, and nitrogen, so it is difficult to be smelted and processed, and the processing cost is high. Titanium alloys also have poor thermal conductivity (only 1/5 of iron and 1/15 of aluminum), small deformation coefficient, large friction coefficient, and other characteristics. They are widely used in aircraft fuselage, gas turbine, petrochemical, automotive industry, medical, and other fields for important parts.

On some uncertainties related to static liquefaction triggering assessments

Static liquefaction has been identified as the cause of several recent tailings storage facility (TSF) failures. Partially based on the investigations carried out, significant advances on the analysis of static liquefaction triggering have been made. This includes application of critical state-based models in a stress-deformation framework to identify if in situ conditions are approaching a level where triggering could occur. However, several important uncertainties remain. The current work investigates three of these uncertainties and their effect (both independently, and in conjunction) on the identification of static liquefaction triggering and slope failure: geostatic stress ratio K0, intermediate principal stress ratio, and principal stress angle from vertical. These uncertainties are examined through a series of numerical analyses of an idealised TSF. Various values of K0 are used to examine their effect on triggering, while different approaches to the potential effect of intermediate principal stress ratio and principal stress angle from vertical on instability are taken. This work shows that current state of knowledge in these areas is such that significant uncertainty seems unavoidable in attempting to identify exactly when a particular slope may undergo static liquefaction triggering. Experimental and in situ test programs that may be useful in reducing this uncertainty are outlined.

Effect of Shear/Axial Stress Ratio on Multiaxial Non-Proportional Loading Fatigue Damage on AISI 303 Steel

In this paper, we investigate the cyclic response of AISI 303 stainless steel subjected to non-proportional loads with different amplitude ratios between shear stresses and normal stresses. Based on the experiments, a relationship between the proportional reference load and a varied range of non-proportional loads was established. To achieve this objective, an experimental program was implemented to evaluate the non-proportional parameter Y. Then, the evolution of this parameter was analyzed with the number of cycles to failure and with the ratio between shear and normal stresses, finally, the evolution of the non-proportional parameter Y was mapped by two functions. The results show that the non-proportional response of the AISI 303 can be estimated using the two functions obtained. This allows the estimation of the relationship between non-proportional and proportional stresses as a function of the number of cycles to failure together with the relationship between shear and normal stresses. The results obtained have direct application in the evaluation of accumulated damage, assessed in real-time, resulting from variable amplitude loading spectra. This is of particular interest for the evaluation of structural health monitoring of structures and mechanical components.

Shear strength behaviour of liquefiable sand of petobo on treated by agarose under direct shear test

Liquefaction process is associated with the loss of the shear strength of the saturated loose sands caused by strong earthquakes. Due to mitigitation of liquefaction hazard, an appropriate mitigation of liquefaction using environmentally friendly methods is critical and becoming increasingly important and unavoidable. The laboratory investigation was carried out to study the shear strength behaviour of liquefiable sand of Petobo treated by agarose on different concentration 1%,3% 5%. A series of direct shear test were conducted under three level of vertical stress 10 kPa, 20 kPa, and 30 kPa on the specimen. It was found that the optimum content of agarose which can be considered is at 1%-3%, using stress ratio (τ/σv) analysis shows that stress ratio decreases with increasing the vertical stress on the same agar content. The implication this result that the application of this method must consider variation of material source and characteristic, and the suitable level of vertical stresses.

Small strain stiffness for granite residual soil: effect of stress ratio

Most previous studies have focused on the small strain stiffness of sedimentary soil while little attention has been given to residual soils with different properties. Most studies also neglected the effects of the deviator stress, which is extensively involved in civil engineering. This note considers the effects of the deviator stress on the small-strain stiffness of natural granite residual soil (GRS) as established from resonant column tests performed under various stress ratios. Although increasing the stress ratio results in a greater maximum shear modulus for both natural and remolded residual soils, remolded soil is more sensitive to changes in the stress ratio, which highlights the effects of soil cementation. The data herein offers new insights to understand the stiffness of residual soil and other weathered geomaterials.

Seawater Effect on Fatigue Behaviour of Notched Carbon/Epoxy Laminates

This paper studies the effect of seawater immersion on the fatigue behavior of notched carbon/epoxy laminates. Rectangular cross-section specimens with a central hole were immersed in natural and artificial seawater for different immersion times (0, 30 and 60 days), being the water absorption rate evaluated over time. After that, fatigue tests were performed under uniaxial cyclic loading using a stress ratio equal to 0.1. After the tests, the optical microscopy technique allowed the examination of the failure micro-mechanisms at the fracture surfaces. The results showed that saturation appeared before 30 days of immersion and that water absorption rates were similar for natural and artificial seawater. The S–N curves showed that the seawater immersion affects the fatigue strength, but there were no relevant effects associated with the type of seawater. Moreover, it was also clear that fatigue life was similar for long lives, close to 1 million cycles, regardless of the immersion time or the type of seawater. On the contrary, for short lives, near 10 thousand cycles, the stress amplitude of dry laminates was 1.2 higher than those immersed in seawater. The failure mechanisms were similar for all conditions, evidencing the fracture of axially aligned fibres and longitudinal delamination between layers.

Experimental Study on the Fracture Behaviors Effect of Stress Conditions on the Fracture of Shale by Super-Critical Carbon Dioxide

This paper examines the fracture propagation problems of supercritical carbon fracturing in low permeability shale. Acoustic emission monitoring and computerized tomography (CT) scanning methods were used to study the influence of initial stress ratios on crack initiation and propagation crack in fracturing experiments. The results show that crack initiation pressure and crack morphology are very different under different stress conditions. Under the condition of constant confining pressure, when the initial stress ratio λ = 1, cracks are mainly in a horizontal direction; while for an initial stress ratio of λ < 1, cracks are mainly in a vertical direction. With the decrease of λ, crack initiation pressure, reopening pressure, and fracturing liquid volume also decrease, and crack propagation is not as obvious. According to CT scanning results, the crack propagation direction is the same as the maximum principal stress, and fewer cracks are initiated with a smaller initial stress ratio. Based on the acoustic emission characteristics, the fracturing process (including crack initiation, propagation, and closure), can be divided into three stages: 1) the pressure accumulation in the wellbore, 2) Pump Closure; and 3) crack reopening. This study provides the basis for a reasonable selection of shale gas fracturing formation and geo-sequestration of greenhouse gas CO2.