scholarly journals Аnalysis of methods of calculating road structures based by shear resistance in the soil

2021 ◽  
Vol 18 (5) ◽  
pp. 576-613
Author(s):  
A. S. Aleksandrov
Keyword(s):  
Shear Stress ◽  
Internal Friction ◽  
Classical Solution ◽  
Equivalent Stress ◽  
Friction Angle ◽  
Shear Resistance ◽  
Shear Stresses ◽  
Total Shear Stress ◽  
Coulomb Criterion ◽  
Total Shear

Introduction. Checking the soil of the subgrade and the layers of road pavement made of loosely cohesive materials by shear resistance is one of the three mandatory conditions for calculating road clothing according to strength criteria. The methodology for checking the soil of the subgrade and the sandy layers of the road pavement is constantly being modified, which is why changes concerning certain calculation details appear in each new version of the regulatory document. The purpose of this work is to analyze the advantages of the classical solution of A.M. Krivissky and to reveal the essence of the errors made in subsequent modifications of this calculation.Materials and methods. The analysis of solutions is carried out from the standpoint of compliance with the basics of mechanics. It is shown that the calculation of the total shear stress in the classical solution of A.M. Krivissky is performed in accordance with the principle of force superposition, which consists in calculating the components of the stress tensor from each force (time load and the own weight of the layer materials) separately, followed by summing the corresponding components. In this case, the active shear stresses from the temporary load and the own weight of the materials are calculated as the equivalent stress of the Mohr-Coulomb criterion. The calculation of these two components of the total shear stress is performed at the same value of the internal friction angle. Since the angle of inclination of the sliding surface to the main axes is determined by the sum or difference of 45 degrees and half of the internal friction angle, the tangential and normal stresses, which are components of the active shear stress, both from the temporary load and the own weight of the materials, are determined for the same shear surface rotated to the main axes at the same angle. In the current normative calculations, the active shear stresses from the temporary load and the own weight of the materials are determined at different angles of internal friction. This means that the active shear stresses from the temporary load and the own weight of the materials act on two different shear surface rotated to the main axes at different angles. Such stresses cannot be summed up or compared with each other. In addition to this error of the normative calculation methods, their other disadvantages are given.Results. As a result of a detailed analysis of the known modifications of the classical solution, obvious contradictions to the principles of continuum mechanics are established. As an alternative to modern calculation criteria for shear resistance, the article presents criteria for soil strength in which the shear stress exceeds the equivalent stress in the Mohr-Coulomb criterion. The principle of deducing formulas for calculating the first critical load and the total shear stress from the strength criteria under consideration is shown.Conclusion. Conclusions are drawn about the need to return to the classical solution obtained by specialists of the Leningrad School of the USSR, or to develop a fundamentally new solution based on a new plasticity condition in which the total shear stress exceeds the similar characteristic of the stress state of the original Mohr - Coulomb criterion.

scholarly journals Experimental Study on the Effects of Initial Shear Stress and Vibration Frequency on Dynamic Strength of Saturated Sands

2019 ◽  
Vol 2019 ◽  
pp. 1-9 ◽  
Author(s):  
Jian Zhang ◽  
Jiuting Cao ◽  
Sijie Huang
Keyword(s):  
Shear Stress ◽  
Internal Friction ◽  
Vibration Frequency ◽  
Stress Ratio ◽  
Dynamic Strength ◽  
Friction Angle ◽  
Cyclic Stress ◽  
Internal Friction Angle ◽  
Shear Stresses ◽  
Cyclic Stress Ratio

The cyclic triaxial system is used to investigate the effects of confining pressure, initial shear stress, cyclic stress ratio, and vibration frequency on the dynamic strength characteristics of saturated sand in the Wenchuan area. Results show that when the vibration frequency is constant, the dynamic strength of sand increases with the increase of the consolidation ratio. However, when the consolidation ratio exceeds a certain value, the dynamic strength of sand decreases or increases slowly. The dynamic internal friction angle first increases and then decreases with the increase of consolidation ratio, and the dynamic internal friction angle under different initial shear stresses differs by a maximum of about 12%. When the failure cycles are constant, the dynamic strength and the dynamic internal friction angle of the sand increase with the increase of vibration frequency, and the dynamic internal friction angle at different frequencies differs by a maximum of about 7%. When the cyclic stress ratio is constant, the higher the vibration frequency, the greater the cycles required to achieve the failure. As the cyclic stress ratio decreases, the influence of the vibration frequency on the failure cycles is gradually reduced.

Characterization of Shear Strength and Interface Friction of Organic Soil

2020 ◽  
Vol 857 ◽  
pp. 203-211
Author(s):  
Majid Hamed ◽  
Waleed S. Sidik ◽  
Hanifi Canakci ◽  
Fatih Celik ◽  
Romel N. Georgees
Keyword(s):  
Shear Stress ◽  
Shear Strength ◽  
Internal Friction ◽  
Moisture Content ◽  
Water Content ◽  
Friction Angle ◽  
Structural Materials ◽  
Organic Soil ◽  
Internal Friction Angle ◽  
Interface Friction

This study was undertaken to investigate some specific problems that limit a safe design and construction of structures on problematic soils. An experimental study was carried out to examine the influence of loading rate and moisture content on shear strength of organic soil. Influece of moisture content on interface friction between organic soil and structural materials was also attempted. A commonly used soil in Iraq was prepared at varying moisture contents of 39%, 57% and 75%. The experimental results showed that the increase in water content will decrease the shear stress and the internal friction angle. An increase of the shearing rate was found to decrease the shear stress and internal friction angle for all percetanges of water contents. Further, direct shear tests were carried out to detect the interface shear stress behavior between organic soil and structural materials. The results revealed that the increase in water content was shown to have significant negetavie effects on the interface internal friction and angle shear strength.

scholarly journals Three-Dimensional Combined Finite-Discrete Element Modeling of Shear Fracture Process in Direct Shearing of Rough Concrete–Rock Joints

2020 ◽  
Vol 10 (22) ◽  
pp. 8033
Author(s):  
Gyeongjo Min ◽  
Daisuke Fukuda ◽  
Sewook Oh ◽  
Gyeonggyu Kim ◽  
Younghun Ko ◽  
...  
Keyword(s):  
Friction Coefficient ◽  
Internal Friction ◽  
Fracture Process ◽  
Three Dimensional ◽  
Friction Angle ◽  
Discrete Element ◽  
Shear Resistance ◽  
Internal Friction Angle ◽  
Rock Joints ◽  
Joint Shear

A three-dimensional combined finite-discrete element element method (FDEM), parallelized by a general-purpose graphic-processing-unit (GPGPU), was applied to identify the fracture process of rough concrete–rock joints under direct shearing. The development process of shear resistance under the complex interaction between the rough concrete–rock joint surfaces, i.e., asperity dilatation, sliding, and degradation, was numerically simulated in terms of various asperity roughness under constant normal confinement. It was found that joint roughness significantly affects the development of overall joint shear resistance. The main mechanism for the joint shear resistance was identified as asperity sliding in the case of smoother joint roughness and asperity degradation in the case of rougher joint asperity. Moreover, it was established that the bulk internal friction angle increased with asperity angle increments in the Mohr–Coulomb criterion, and these results follow Patton’s theoretical model. Finally, the friction coefficient in FDEM appears to be an important parameter for simulating the direct shear test because the friction coefficient affects the bulk shear strength as well as the bulk internal friction angle. In addition, the friction coefficient of the rock–concrete joints contributes to the variation of the internal friction angle at the smooth joint than the rough joint.

Influence of turbulent shear stresses on the numerical blood damage prediction in a ventricular assist device

2019 ◽  
Vol 42 (12) ◽  
pp. 735-747 ◽  
Author(s):  
Benjamin Torner ◽  
Lucas Konnigk ◽  
Frank-Hendrik Wurm
Keyword(s):  
Shear Stress ◽  
Equivalent Stress ◽  
Volumetric Analysis ◽  
Turbulent Shear ◽  
Shear Stresses ◽  
Ventricular Assist ◽  
Damage Prediction ◽  
Blood Damage ◽  
Damage Models ◽  
Order Of Magnitude

The blood damage prediction in rotary blood pumps is an important procedure to evaluate the hemocompatibility of such systems. Blood damage is caused by shear stresses to the blood cells and their exposure times. The total impact of an equivalent shear stress can only be taken into account when turbulent stresses are included in the blood damage prediction. The aim of this article was to analyze the influence of the turbulent stresses on the damage prediction in a rotary blood pump’s flow. Therefore, the flow in a research blood pump was computed using large eddy simulations. A highly turbulence-resolving setup was used in order to directly resolve most of the computed stresses. The simulations were performed at the design point and an operation point with lower flow rate. Blood damage was predicted using three damage models (volumetric analysis of exceeded stress thresholds, hemolysis transport equation, and hemolysis approximation via volume integral) and two shear stress definitions (with and without turbulent stresses). For both simulations, turbulent stresses are the dominant stresses away from the walls. Here, they act in a range between 9 and 50 Pa. Nonetheless, the mean stresses in the proximity of the walls reach levels, which are one order of magnitude higher. Due to this, the turbulent stresses have a small impact on the results of the hemolysis prediction. Yet, turbulent stresses should be included in the damage prediction, since they belong to the total equivalent stress definition and could impact the damage on proteins or platelets.

scholarly journals Properties of Some Selected Soil under Mymensingh District in Bangladesh

1970 ◽  
Vol 4 (1) ◽  
pp. 149-154
Author(s):  
Md. Tohidul Islam ◽  
Md. Serazul Islam ◽  
Md Nurul Hoque
Keyword(s):  
Shear Stress ◽  
Internal Friction ◽  
Moisture Content ◽  
Physical Properties ◽  
Key Words ◽  
Friction Angle ◽  
Soil Samples ◽  
Plasticity Index ◽  
Standard Methods ◽  
Different Soils

This paper elucidated an attempt to determine the physical properties of some selected soils at different location under Mymensingh districts. The properties of soils were determined using standard methods. Field moisture content was more or less similar for all the locations. The dry unit weights of selected seven soils for Bangladesh Institute of Nuclear Agriculture (BINA), Valuka, Muktagacha, Trisal, Madhupur, Chorkhai and Shomvoganj sites were found to be 17.61, 16.50, 17.00, 17.50, 15.50, 16.40 and 16.20 kN/m3, respectively while the specific gravities were found as 2.67, 2.66, 2.68, 2.70, 2.69, 2.72 and 2.65, respectively also the values of plastic limits of soils were found to be 16.00, 17.00, 15.50, 18.50, 16.00, 17.20 and 14.00 percent, respectively whereas the plasticity index values were 16.25, 14.50, 15.00, 17.00, 18.00, 13.60 and 15.50 percent, respectively for the above locations. The liquid and plastic limits varied for all the locations but the plasticity index values were found more or less similar for all the soil samples. The friction angles were found more or less similar while cohesion varied for different locations. The properties of soils thus obtained can be used for soils of these areas of Bangladesh. A relation between the gradations with plasticity indices of different soils was also characterized. Key words: Dry unit weights, plastic limits, plasticity index, shear stress and internal friction angle.

scholarly journals Mechanism for initiating secondary currents in channel flows

2009 ◽  
Vol 36 (9) ◽  
pp. 1506-1516 ◽  
Author(s):  
Shu-Qing Yang
Keyword(s):  
Shear Stress ◽  
Secondary Flow ◽  
Flow Region ◽  
Streamwise Velocity ◽  
Vortex Center ◽  
Duct Flow ◽  
Secondary Currents ◽  
Total Shear Stress ◽  
Underlying Mechanisms ◽  
Total Shear

This study investigates the underlying mechanisms that initiate secondary flow in developing turbulent flow along a corner. This is done by theoretical examination of the total shear stress, which is the time-averaged product of instantaneous streamwise velocity U and the velocity Vn normal to the interface. The study shows that lines of zero total shear stress exist in the flow region, which delineate the region of secondary flow. Therefore, the flow region is dividable and eight vortices occur in a duct flow. The theoretical and experimental results show that the division line, separating the neighboring secondary currents in a corner, is not always identical to the bisector of the corner, but deviates from the corner bisector if the aspect ratio is b/h ≠ 1. By simplifying Reynolds equation in the near-bed region, we find that theoretically a lateral variation of streamwise velocity initiates the wall-tangent flow that drives the vortex in the region bounded by zero total shear stress. A simplified method for estimating the vortex center, near-bed secondary velocity, and shape of secondary currents has been proposed, and a good agreement between the measured and predicted features is achieved.

Research on Designing Optimum Asphalt Aggregate Ratio of Asphalt Mixture by Mechanical Index Method

2012 ◽  
Vol 204-208 ◽  
pp. 1586-1592
Author(s):  
Hong Mei Li ◽  
Wen Fang Liu
Keyword(s):  
Shear Stress ◽  
Surface Layer ◽  
Internal Friction ◽  
Bond Strength ◽  
Asphalt Mixture ◽  
Friction Angle ◽  
Good Effect ◽  
Mechanical Index ◽  
Index Method ◽  
Better Than

The article designed optimum asphalt aggregate ratio of asphalt mixture by mechanical index method, the purpose of the mechanical index method is that the bond strength and internal friction angle of asphalt mixture can reach a best balance, the shear stress reaches the maximum, so the results have a good effect for preventing rut. The research indicated that the surface layer performance of asphalt mixture which designed by the mechanical index method is better than by the traditional Marshall method, so the mechanical index method is a simple and effective method.

scholarly journals Ricochet of Spheres on Sand of Various Temperature

2018 ◽  
Vol 68 (2) ◽  
pp. 150 ◽  
Author(s):  
Yoon Keon Kim ◽  
Woo Chun Choi
Keyword(s):  
Shear Stress ◽  
Kinetic Energy ◽  
Internal Friction ◽  
Initial Conditions ◽  
Fem Analysis ◽  
Friction Angle ◽  
Internal Friction Angle ◽  
Depth Of Penetration ◽  
Safety Distance ◽  
Sand Temperature

The debris generated by the explosion of a building or ammunition is flown far away through the ricochet phenomenon. The debris contains a very large amount of energy, and a risk factor surrounding it may be applied. The safety distance from debris is set from experiments or FEM analysis. The ricochet of debris is affected not only by the initial conditions of the debris, but also by the conditions of the medium. In this paper, the effect of sand temperature on the ricochet of sphere projectiles was investigated through experiments and FEM, by measuring the shear stress and internal friction angle when the sand temperature increases. As the temperature of the sand increases, the shear stress and the internal friction angle decrease, and the penetration depth of the projectile increases. As the depth of penetration becomes longer, the kinetic energy is lost more by the friction force with the sand and, the sphere projectile speed decreases more. This is mainly caused by the energy loss of the projectile, so the kinetic energy of the ricocheted projectile is reduced. Therefore, when setting the optimized inhabited building distance (IBD), the conditions of the medium should be taken into account.

Drag and shear stress partitioning in sparse desert creosote communities

1997 ◽  
Vol 34 (11) ◽  
pp. 1486-1498 ◽  
Author(s):  
V. E. Wyatt ◽  
W. G. Nickiing
Keyword(s):  
Shear Stress ◽  
Velocity Ratio ◽  
Surface Shear Stress ◽  
Surface Shear ◽  
Empirical Constant ◽  
Drag Coefficients ◽  
Stress Partitioning ◽  
Total Shear Stress ◽  
Shear Stress Partitioning ◽  
Total Shear

Most research to characterize the wind-erosion susceptibility and the degree of surface roughness required to suppress erosion on erodible surfaces has been empirical. However, a recently proposed shear velocity ratio model attempts to place shear stress partitioning in an entirely theoretical framework. The purpose of this study was to directly measure components of shear stress in a sparsely vegetated environment in order to evaluate the model. For the field study, new instrumentation was developed to measure drag on a creosote shrub, and Irwin sensors were modified to measure surface shear stress in the field. Simultaneous measurements of total shear stress and surface shear stress were taken at four sites of different roughness densities, in the Eldorado Valley, Nevada. Results indicate that porous shrubs had greater drag coefficients (Cd = 0.485) than did solid elements (sphere Cd = 0.3) and are more effective at protecting a surface. Values of β, the ratio of element to surface drag coefficients, were therefore higher than previously published values. Surface and total shear stress scaled consistently with each other at a range of wind speeds, and varied according to the roughness density of the surface. Shear stress partitioning values agreed well with previously published field data and some wind-tunnel data. The theoretical model predicted the results successfully when m = 0.16, where m is an empirical constant that accounts for the difference in average stress and the maximum surface stress in initiating erosion. The wide applicability of the model is likely due to the inclusion of the adjustable m, which accommodates all values of β and σ (ratio of roughness element basal area to frontal area).

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