Correlation between the rock mass properties and maximum horizontal stress:A case study of overcoring stress measurements

Understanding the mechanical properties of the lithologies is crucial to accurately determine the horizontal stress magnitude.To investigate the correlation between the rock mass properties and maximum horizontal stress,the three-dimensional(3D)stress tensors at 89 measuring points determined using an improved overcoring technique in nine mines in China were adopted,a newly defined characteristic parameter C_(ERP)was proposed as an indicator for evaluating the structural properties of rock masses,and a fuzzy relation matrix was established using the information distribution method.The results indicate that both the vertical stress and horizontal stress exhibit a good linear growth relationship with depth.There is no remarkable correlation between the elastic modulus,Poisson's ratio and depth,and the distribution of data points is scattered and messy.Moreover,there is no obvious relationship between the rock quality designation(RQD)and depth.The maximum horizontal stress σ_(H) is a function of rock properties,showing a certain linear relationship with the C_(ERP)at the same depth.In addition,the overall change trend of σ_(H) determined by the established fuzzy identification method is to increase with the increase of C_(ERP).The fuzzy identification method also demonstrates a relatively detailed local relationship betweenσ_H and C_(ERP),and the predicted curve rises in a fluctuating way,which is in accord well with the measured stress data.

Granular behaviour under bi-directional shear with constant vertical stress and constant volume

This paper aims to investigate the role of bi-directional shear in the mechanical behaviour of granular materials and macro-micro relations by conducting experiments and discrete element method(DEM)modelling.The bi-directional shear consists of a static shear consolidation and subsequent shear under constant vertical stress and constant volume conditions.A side wall node loading method is used to exert bi-directional shear of various angles.The results show that bi-directional shear can significantly influence the mechanical behaviour of granular materials.However,the relationship between bidirectional shear and mechanical responses relies on loading conditions,i.e.constant vertical stress or constant volume conditions.The stress states induced by static shear consolidation are affected by loading angles,which are enlarged by subsequent shear,consistent with the relationship between bidirectional shear and principal stresses.It provides evidence for the dissipation of stresses accompanying static liquefaction of granular materials.The presence of bi-directional principal stress rotation(PSR)is demonstrated,which evidences why the bi-directional shear of loading angles with components in two directions results in faster dissipations of stresses with static liquefaction.Contant volume shearing leads to cross-anisotropic stress and fabric at micro-contacts,but constant vertical stress shearing leads to complete anisotropic stress and fabric at micro-contacts.It explains the differentiating relationship between stress-strain responses and fabric anisotropy under these two conditions.Micromechanical signatures such as the slip state of micro-contacts and coordination number are also examined,providing further insights into understanding granular behaviour under bi-directional shear.

Boulder-induced form roughness and skin shear stresses in a gravel-bed stream

Boulder spacing in mountain rivers and near-wake flow zones within the boulder array is very useful for fish habitat and growth of aquatic organisms.The present study aims to investigate how the boulder array and spacing influence the near-bed flow structures in a gravel-bed stream.Boulders are staggered over a gravel-bed stream with three different inter-boulder spacing namely(a)large(b)medium and(c)small spacing.An acoustic Doppler velocimeter was used for flow measurements in a rectangular channel and the results were compared with those acquired from numerical simulation.The time-averaged velocity profiles at the near-wake flow zones of boulders experience maximum flow retardation which is an outcome of the boulder-induced form roughness.The ratio of velocity differences associated to form and skin roughness and its positive magnitude reveals the dominance of form roughness closest to the boulders.Form roughness computed is 1.75 to 2 times higher than the skin roughness at the near-wake flow region.In particular,the collective immobile boulders placed at different inter-boulder spacings developed high and low bed shear stresses closest to the boulders.The low bed shear stresses characterised by a secondary peak developed at the trough location of the boulders is attributed to the skin shear stress.Further,the spatial averaging of time-averaged flow quantities gives additional impetus to present an improved illustration of fluid shear stresses.The formation of form-induced shear stress is estimated to be 17%to 23%of doubleaveraged Reynolds shear stress and partially compensates for the damping of time-averaged Reynolds shear stress in the interfacial sub-layer.The quadrant analysis of spatial velocity fluctuations depicts that the form-induced shear stresses are dominant in the interfacial sub-layer and have no significance above the gravel-bed surface.

A method for extracting the preseismic gravity anomalies over the Tibetan Plateau based on the maximum shear strain using GRACE data

The occurrence of earthquakes is closely related to the crustal geotectonic movement and the migration of mass,which consequently cause changes in gravity.The Gravity Recovery And Climate Experiment(GRACE)satellite data can be used to detect gravity changes associated with large earthquakes.However,previous GRACE satellite-based seismic gravity-change studies have focused more on coseismic gravity changes than on preseismic gravity changes.Moreover,the noise of the north–south stripe in GRACE data is difficult to eliminate,thereby resulting in the loss of some gravity information related to tectonic activities.To explore the preseismic gravity anomalies in a more refined way,we first propose a method of characterizing gravity variation based on the maximum shear strain of gravity,inspired by the concept of crustal strain.The offset index method is then adopted to describe the gravity anomalies,and the spatial and temporal characteristics of gravity anomalies before earthquakes are analyzed at the scales of the fault zone and plate,respectively.In this work,experiments are carried out on the Tibetan Plateau and its surrounding areas,and the following findings are obtained:First,from the observation scale of the fault zone,we detect the occurrence of large-area gravity anomalies near the epicenter,oftentimes about half a year before an earthquake,and these anomalies were distributed along the fault zone.Second,from the observation scale of the plate,we find that when an earthquake occurred on the Tibetan Plateau,a large number of gravity anomalies also occurred at the boundary of the Tibetan Plateau and the Indian Plate.Moreover,the aforementioned experiments confirm that the proposed method can successfully capture the preseismic gravity anomalies of large earthquakes with a magnitude of less than 8,which suggests a new idea for the application of gravity satellite data to earthquake research.

Experimental and simulation study on shear stress-induced erythrocyte damage based on vortex oscillator

Background:Shear stress-induced erythrocyte damage,namely hemolysis,is an important problem in the development of blood-contacting medical devices such as mechanical circulatory support devices.Computational fluid dynamics simulation combined with hemolysis prediction models have been widely used to predict hemolysis.With the development of hemolysis prediction models,the new hemolysis prediction model requires more experimental data to verify.In addition,the difference of in vitro blood-shearing device also affect the accuracy of hemolysis prediction.Methods:To address these problems,a new in vitro blood-shearing device(vortex oscillator)was used to further verify the accuracy of the hemolysis prediction models,and to guide the optimal design of blood-contacting medical devices such as mechanical circulatory support devices.Firstly,the flow field information such as wall stress and velocity of the vortex oscillator under different speeds was analyzed.Secondly,different hemolysis prediction models were used to calculate hemolysis,and the predicted data was compared with the experimental data.Results and Conclusion:In this study,the flow field information inside the vortex oscillator at high rotational speeds was systematically investigated,and the prediction of hemolysis was carried out.The results showed that the predicted data of hemolysis was significantly different from the experimental data,which indicated that it was urgent to establish a standardized in vitro blood-shearing platform to provide a reference for accurate hemolysis prediction.

Maximum twin shear stress factor criterion for sliding mode fracture initiation

Previous researches on the mixed mode fracture initiation criteria were mostly focused on opening mode fracture. In this study, the authors proposed a new criterion for mixed mode sliding fracture initiation, which is the maximum twin shear stress factor criterion. The authors studied a finite width plate with central slant crack, subject to a far field uniform uniaxial tensile or compressive stress.

Shear behavior of coarse aggregates for dam construction under varied stress paths

Coarse aggregates are the major infrastructure materials of concrete-faced rock-fill dams and are consolidated to bear upper and lateral loads. With the increase of dam height, high confining pressure and complex stress states complicate the shear behavfor of coarse aggregates, and thus impede the high dam＇s proper construction, operation and maintenance. An experimental program was conducted to study the shear behavior of dam coarse aggregates using a large-scale triaxial shear apparatus. Through triaxial shear tests, the strain-stress behaviors of aggregates were observed under constant confining pressures： 300 kPa, 600 kPa 900 kPa and 1200 kPa. Shear strengths and aggregate breakage characteristics associated with high pressure shear processes are discussed. Stress path tests were conducted to observe and analyze coarse aggregate response under complex stress states. In triaxial shear tests, it was found that peak deviator stresses increase along with confining pressures, whereas the peak principal stress ratios decrease as confining pressures increase With increasing confining pressures, the dilation decreases and the contraction eventually prevails. Initial strength parameters （Poisson＇s ratio and tangent modulus） show a nonlinear relationship with confining pressures when the pressures are relatively low. Shear strength parameters decrease with increasing confining pressures. The failure envelope lines are convex curves, with clear curvature under low confining pressures. Under moderate confining pressures, dilation is offset by particle breakage. Under high confining pressures, dilation disappears.

Experimental Study on the Bed Shear Stress Under Breaking Waves

The object of present study is to investigate the bed shear stress on a slope under regular breaking waves by a novel instrument named Micro-Electro-Mechanical System （MEMS） flexible hot-film shear stress sensor. The sensors were calibrated before application, and then a wave flume experiment was conducted to study the bed shear stress for the case of regular waves spilling and plunging on a 1 ： 15 smooth PVC slope. The experiment shows that the sensor is feasible for the measurement of the bed shear stress under breaking waves. For regular incident waves, the bed shear stress is mainly periodic in both outside and inside the breaking point. The fluctuations of the bed shear stress increase significantly after waves breaking due to the turbulence and vortexes generated by breaking waves. For plunging breaker, the extreme value of the mean maximum bed shear stress appears after the plunging point, and the more violent the wave breaks, the more dramatic increase of the maximum bed shear stress will occur. For spilling breaker, the increase of the maximum bed shear stress along the slope is gradual compared with the plunging breaker. At last, an empirical equation about the relationship between the maximum bed shear stress and the surf similarity parameter is given, which can be used to estimate the maximum bed shear stress under breaking waves in practice.

Wave-current bottom shear stresses and sediment re-suspension in the mouth bar of the Modaomen Estuary during the dry season

On the basis of the measurement data pertaining to waves, current, and sediment in February 2012 in the mouth bar of the Modaomen Estuary, the Soulsby formulae with an iterative method are applied to calculating bottom shear stresses （BSS） and their effect on a sediment resuspension. Swell induced BSS have been found to be the most important part of the BSS. In this study, the correlation coefficient between a wavecurrent shear stress and SSC is 0.86, and that between current shear stresses and SSC is only 0.40. The peaks of the SSC are consistent with the height and the BSS of the swell. The swell is the main mechanism for the sediment re-suspension, and the tidal current effect on sediment re-suspension is small. The peaks of the SSC are centered on the high tidal level, and the flood tide enhances the wave shear stresses and the SSC near the bottom. The critical shear stress for sediment re-suspension at the observation station is between 0.20 and 0.30 N/m2. Tidal currents are too weak to stir up the bottom sediment into the flow, but a WCI （wave-current interaction） is strong enough to re-suspend the coarse sediment.

Research on Measurement of Bed Shear Stress Under Wave-Current Interaction

The movement of sediment in estuary and on coast is directly restricted by the bed shear stress. Therefore, the research on the basic problem of sediment movement by the bed shear stress is an important way to research the theory of sediment movement. However, there is not a measuring and computing method to measure the bed shear stress under a complicated dynamic effect like wave and current. This paper describes the measurement and test research on the bed shear stress in a long launder of direct current by the new instrument named thermal shearometer based on micro-nanotechnology. As shown by the research results, the thermal shearometer has a high response frequency and strong stability. The measured results can reflect the basic change of the bed shear stress under wave and wave-current effect, and confirm that the method of measuring bed shear stress under wave-current effect with thermal shearometer is feasible. Meanwhile, a preliminary method to compute the shear stress compounded by wave-current is put forward according to the tested and measured results, and then a reference for further study on the basic theory of sediment movement under a complicated dynamic effect is provided.

Mathematical Model and Experiment Validation of Fluid Torque by Shear Stress under Influence of Fluid Temperature in Hydro-viscous Clutch

The current design of hydro-viscous clutch（HVC） in tracked vehicle fan transmission mainly focuses on high-speed and high power. However, the fluid torque under the influence of fluid temperature can not be predicted accurately by conventional mathematical model or experimental research. In order to validate the fluid torque of HVC by taking the viscosity-temperature characteristic of fluid into account, the test rig is designed. The outlet oil temperature is measured and fitted with different rotation speed, oil film thickness, oil flow rate, and inlet oil temperature. Meanwhile, the film torque can be obtained. Based on Navier-Stokes equations and the continuity equation, the mathematical model of fluid torque is proposed in cylindrical coordinate. Iterative method is employed to solve the equations. The radial and tangential speed distribution, radial pressure distribution and theoretical flow rate are determined and analyzed. The models of equivalent radius and fluid torque of friction pairs are introduced. The experimental and theoretical results indicate that tangential speed distribution is mainly determined by the relative rotating speed between the friction plate and the separator disc. However, the radial speed distribution and pressure distribution are dominated by pressure difference at the lower rotating speed. The oil film fills the clearance and the film torque increases with increasing rotating speed. However, when the speed reaches a certain value, the centrifugal force will play an important role on the fluid distribution. The pressure is negative at the outer radius when inlet flow rate is less than theoretical flow, so the film starts to shrink which decreases the film torque sharply. The theoretical fluid torque has good agreement with the experimental data. This research proposes a new fluid torque mathematical model which may predict the film torque under the influence of temperature more accurately.

ANALYSIS OF SHEAR STRESS DISTRIBUTION IN HONEYCOMB AIRCRAFT WING STRUCTURE SUBJECTED TO (S.T.) TORQUE

Using the method of elasticity, an analytical approach is developed to analyze the shear stress in a honeycomb wing structure with a large aspect ratio under the condition of free torsion. The formulas of shear stress, warping and angle of twist are derived. These formulas are both useful and convenient from the point of view in the structure design.

Microstreaming velocity field and shear stress created by an oscillating encapsulated microbubble near a cell membrane

Sonoporation mediated by microbubbles is being extensively studied as a promising technology to facilitate gene/drug delivery to cells. However, the theoretical study regarding the mechanisms involved in sonoporation is still in its infancy.Microstreaming generated by pulsating microbubble near the cell membrane is regarded as one of the most important mechanisms in the sonoporation process. Here, based on an encapsulated microbubble dynamic model with considering nonlinear rheological effects of both shell elasticity and viscosity, the microstreaming velocity field and shear stress generated by an oscillating microbubble near the cell membrane are theoretically simulated. Some factors that might affect the behaviors of microstreaming are thoroughly investigated, including the distance between the bubble center and cell membrane（d）, shell elasticity（χ）, and shell viscosity（κ）. The results show that（i） the presence of cell membrane can result in asymmetric microstreaming velocity field, while the constrained effect of the membrane wall decays with increasing the bubble-cell distance;（ii） the bubble resonance frequency increases with the increase in d and χ, and the decrease in κ,although it is more dominated by the variation of shell elasticity; and（iii） the maximal microstreaming shear stress on the cell membrane increases rapidly with reducing the d, χ, and κ. The results suggest that microbubbles with softer and less viscous shell materials might be preferred to achieve more efficient sonoporation outcomes, and it is better to have bubbles located in the immediate vicinity of the cell membrane.

Effects of bottom shear stresses on the wave-induced dynamic response in a porous seabed:PORO-WSSI (shear) model

When ocean waves propagate over the sea floor,dynamic wave pressures and bottom shear stresses exert on the surface of seabed.The bottom shear stresses provide a horizontal loading in the wave-seabed interaction system,while dynamic wave pressures provide a vertical loading in the system.However,the bottom shear stresses have been ignored in most previous studies in the past.In this study,the effects of the bottom shear stresses on the dynamic response in a seabed of finite thickness under wave loading will be examined,based on Biot＇s dynamic poro-elastic theory.In the model,an ＂u-p＂ approximation will be adopted instead of quasi-static model that have been used in most previous studies.Numerical results indicate that the bottom shear stresses has certain influences on the wave-induced seabed dynamic response.Furthermore,wave and soil characteristics have considerable influences on the relative difference of seabed response between the previous model（without shear stresses） and the present model（with shear stresses）.As shown in the parametric study,the relative differences between two models could up to 10% of p0,depending on the amplitude of bottom shear stresses.

A new analytical solution for calculation the displacement and shear stress of fully grouted rock bolts and numerical verifications

In presence of difficult conditions in coal mining roadways, an adequate stabilization of the excavation boundary is required to ensure a safe progress of the construction. The stabilization of the roadways can be improved by fully grouted rock bolt, offering properties optimal to the purpose and versatility in use. Investigations of load transfer between the bolt and grout indicate that the bolt profile shape and spacing play an important role in improving the shear strength between the bolt and the surrounding strata. This study proposes a new analytical solution for calculation displacement and shear stress in a fully encapsulated rock bolt in jointed rocks. The main characteristics of the analytical solution consider the bolt profile and jump plane under pull test conditions. The performance of the proposed analytical solution, for three types of different bolt profile configurations, is validated by ANSYS software. The results show there is a good agreement between analytical and numerical methods. Studies indicate that the rate of displacement and shear stress from the bolt to the rock exponentially decayed. This exponential reduction in displacement and shear stress are dependent on the bolt characteristics such as: rib height, rib spacing, rib width and grout thickness, material and joint properties.

Wall shear stress in intracranial aneurysms and adjacent arteries

Hemodynamic parameters play an important role in aneurysm formation and growth. However, it is difficult to directly observe a rapidly growing de novo aneurysm in a patient. To investigate possible associations between hemodynamic parameters and the formation and growth of intracranial aneurysms, the present study constructed a computational model of a case with an internal carotid artery aneurysm and an anterior communicating artery aneurysm, based on the CT angiography findings of a patient. To simulate the formation of the anterior communicating artery aneurysm and the growth of the internal carotid artery aneurysm, we then constructed a model that virtually removed the anterior communicating artery aneurysm, and a further two models that also progressively decreased the size of the internal carotid artery aneurysm. Computational simulations of the fluid dynamics of the four models were performed under pulsatile flow conditions, and wall shear stress was compared among the different models. In the three aneurysm growth models, increasing size of the aneurysm was associated with an increased area of low wall shear stress, a significant decrease in wall shear stress at the dome of the aneurysm, and a significant change in the wall shear stress of the parent artery. The wall shear stress of the anterior communicating artery remained low, and was significantly lower than the wall shear stress at the bifurcation of the internal carotid artery or the bifurcation of the middle cerebral artery. After formation of the anterior communicating artery aneurysm, the wall shear stress at the dome of the internal carotid artery aneurysm increased significantly, and the wall shear stress in the upstream arteries also changed significantly. These findings indicate that low wall shear stress may be associated with the initiation and growth of aneurysms, and that aneurysm formation and growth may influence hemodynamic parameters in the local and adjacent arteries.

Symmetric Equations for Evaluating Maximum Torsion Stress of Rectangular Beams in Compliant Mechanisms

There are several design equations available for calculating the torsional compliance and the maximum torsion stress of a rectangular cross-section beam, but most depend on the relative magnitude of the two dimensions of the crosssection(i.e., the thickness and the width). After reviewing the available equations, two thickness-to-width ratio Independent equations that are symmetric with respect to the two dimensions are obtained for evaluating the maximum torsion stress of rectangular cross-section beams. Based on the resulting equations, outside lamina emergent torsional joints are analyzed and some useful design Insights are obtained. These equations, together with the previous work on symmetric equations for calculating torsional compliance, provide a convenient and effective way for designing and optimizing torsional beams in compliant mechanisms.

Wall shear stress in portal vein of cirrhotic patients with portal hypertension

AIM To investigate wall shear stress(WSS) magnitude and distribution in cirrhotic patients with portal hypertension using computational fluid dynamics. METHODS Idealized portal vein(PV) system models were reconstructed with different angles of the PV-splenic vein(SV) and superior mesenteric vein(SMV)-SV. Patient-specific models were created according to enhanced computed tomography images. WSS was simulated by using a finite-element analyzer, regarding the blood as a Newtonian fluid and the vessel as a rigid wall. Analysis was carried out to compare the WSSin the portal hypertension group with that in healthy controls.RESULTS For the idealized models, WSS in the portal hypertension group(0-10 dyn/cm2) was significantly lower than that in the healthy controls(10-20 dyn/cm2), and low WSS area(0-1 dyn/cm2) only occurred in the left wall of the PV in the portal hypertension group. Different angles of PV-SV and SMV-SV had different effects on the magnitude and distribution of WSS, and low WSS area often occurred in smaller PV-SV angle and larger SMV-SV angle. In the patient-specific models, WSS in the cirrhotic patients with portal hypertension(10.13 ± 1.34 dyn/cm2) was also significantly lower than that in the healthy controls(P < 0.05). Low WSS area often occurred in the junction area of SV and SMV into the PV, in the area of the division of PV into left and right PV, and in the outer wall of the curving SV in the control group. In the cirrhotic patients with portal hypertension, the low WSS area extended to wider levels and the magnitude of WSS reached lower levels, thereby being more prone to disturbed flow occurrence.CONCLUSION Cirrhotic patients with portal hypertension show dramatic hemodynamic changes with lower WSS and greater potential for disturbed flow, representing a possible causative factor of PV thrombosis.

In search of potential earthquake source regions in the Chinese mainland in the light of ambient shear stress field

Earth media are incomplete media.There exist many cracks in it. The achievements of fracture mechanics showthat the strength of the incomplete materials will be much lower than that of the complete materials. We consider that earthquake occurrence is the result of unstable propagation of a crack in crust media in proper conditionand the earthquake rupture is the phenomenon of a failure by fast fracture under applied low shear stress. It hasalready been explained by fracture mechanics.The occurrence of failure by fast fracture is necessarily associated with the presence of high level concentration of local stress and strain. The elastic/plastic stress analysis in cracked pieces by Dugdale indicates that thestate of stress at the tip of a crack takes a very important role to crack propagation. A plastic zone has necessarilyformed in the tip of a crack due to stress concentration. Therefore, the dislocations st the tip of a crack are naturally a plastic displacement, rather than elastic one. The plastic displacement, where τ0 is appliedshear stress which is equivalent to initial or tectonic shear stress when the quake occurs, a is the half length of acrack, It is the rigidity,τy is the yield stresses in shear. The main seismic dislocations take place exactly at theends of the crack where the plastic zone had been formed. SO, a critical assumption is adopted, i. e. we assumethe dislocation D(1,,t) as formula (5) in text. The maximum earthquake dislocation, whereL is the fault length. If p is taken the value in the upper crust, μ=33 GPa; and τy is taken the average valuegiven from laboratories,τy= 30 MPa. Thus, according to observation values of Dmax and L, using the formula,one can estimate the initial shear stresses for large earthquakes. Computations show that the initial shear stressesfor large earthquakes all over the world are about 5-20 MPa which have some differences between regions.We further research the characteristics of source spectra and have derived the dependent relation of bodywave magnitude mb on the shear stress τ0 and seismic moment M, as formula (11)in text. Thus, the formulaprovides a POssibility of computation of large amount of tectonic shear stress values from seismic data. We consider that the tectonic shear stress field is a main factor which controls the earthquake occurrence. The regions withhigh tectonic shear stress values are considered to be prone to occur great earthquakes (Ms>6) and called earthquake hazard regions. Based on this criterion, τ0 values for all earthquakes with mb≥3. 8 all over China since1987 have been computed, and the great earthquake hazard regions with magnitude ranges have been zoned inthe Chinese mainland.During April 1992 -January 31, 1994, there were 9 Ms≥6 earthquakes which occurred in the Chinesemainland, 8 earthquakes of the 9 had fallen into the regions delineated by us prior to the earthquake occurrence,with only one failure. This new approach as a method for medium--term prediction of strong earthquakes hasbeen proved by practice to be an efficient one.It has good physical bases and bright prospect and worth furtherresearch. Received February 7,1994 1 Accepted February 10, 1995.Contribution No. 95A0061, Institute of Geophysics,SSB, China.

Analysis on Interface Shear Stress of Thermally InsulatedOcean Pipelines Under Installation

It has been proved that the thermally insulated ocean pipeline has advantages over the conventional pipe-in-pipe pipeline. The risk of using the thermally insulated pipeline is that the exterior layers covering the steel pipe may be. pulled off if the shear stress on the interface induced by the pullout fore from the tensioner is greater than the binding fore between two neighboring layers during installation. This paper develops a procedure to calculate the shear stress on the interface. The binding force between two neighboring layers can be determined with full scale model tests. The safety of the thermally insulated pipe under installation can then be checked by comparison of the interface shear stress with the binding force.