Apparent Friction Coefficient Research Articles

Effect of curing stress on the interface property of cement-treated dredged mud and geogrid

The cement-treated dredged mud mixture is suitable for backfill in earthwork projects because of its high water content and flowability. Incorporating geogrid can enhance the mixture’s tensile strength. Constructing with cement-treated mud at greater heights generates curing stress, affecting the interface with geogrid. Pullout tests were performed to analyze the impact of curing stress, water content, and cement content on the interface performance. Results showed similar pullout force-displacement curves regardless of curing stress, indicating strain-softening behavior. Higher water content resulted in decreased pullout forces, while higher cement content led to increased pullout forces. Samples under curing stress exhibited increased peak pullout forces ranging from 2% to 70% compared to samples without curing stress. The rate of increase in pullout force because of curing stress decreased with higher water or cement contents. Curing stress influenced the interface friction angle in specimens with water contents 1.5 and 2 times the liquid limit. It significantly affected the interface cohesion in samples with water contents 2.5 times the liquid limit. Samples subjected to curing stress demonstrated a higher apparent friction coefficient, with an average increase ranging from 4% to 43%, which decreased with higher water content and lower cement content, regardless of curing stress.

Flow front mobility of rock avalanches as a function of flow volume, grain size, channel width, basal friction and flow scale

The ability to predict the mobility of rock avalanches is necessary when designing strategies to mitigate the risks they pose. A popular mobility indicator of the flow front is the Heim’s apparent friction coefficient μH\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\mu }_{H}$$\\end{document}. In the field, μH\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\mu }_{H}$$\\end{document} shows a decrease in value as flow volume V increases. But this correlation has been a mystery as to whether it is due to a causal relationship between V and mobility since: (1) field data of μH\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\mu }_{H}$$\\end{document} do not collapse onto a single curve because typically widely scattered and (2) laboratory experiments have shown an opposite volume effect on the center of mass mobility of miniature flows. My numerical simulations confirm for the first time the existence of a functional relationship of scaling parameters where μH\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\mu }_{H}$$\\end{document} decreases as V increases in unsteady and nonuniform 3D flows. Data scatter is caused by μH\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\mu }_{H}$$\\end{document} that is affected by numerous other variables besides V. The interplay of these variables produces different granular regimes with opposite volume effects. In particular, μH\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\mu }_{H}$$\\end{document} decreases as V increases in the regime characterized by a relatively rough subsurface. The relationship holds for large-scale flows that, like rock avalanches, consist of a very large number of fine clasts traveling in wide channels. In these dense flows, flow front mobility increases as flow volume increases, as channel width increases, as grain size decreases, as basal friction decreases and as flow scale increases. Larger-scale flows are more mobile because they have larger Froude number values.

Evaluation of the Wear Properties and Corrosion Resistance of 52100 Steel Coated with Ni/CrC by Cold Spraying

Coatings deposited by the cold particle gas spray method have shown significant potential for enhancing the properties of metals. We investigated the wear characteristics and corrosion behavior of 52100 steel coated with a mixture of Ni/chromium carbide (Ni/CrC) particles. These coatings exhibited high density and were devoid of cracks, closely adhering to the substrate’s surface. Microscratch resistance testing revealed strong resilience, with the apparent friction coefficient exhibiting multiple peaks as the displacement varied. The determination of the friction coefficient, utilizing linear and rotational sliding tests, displayed a brief transition period. This occurred as the apparent contact area expanded until it reached an equilibrium state, with the large asperities being smoothed out and the remaining particles on the sliding track acting as an abrasive material, resulting in higher friction coefficient values. Electro-corrosion tests confirmed the near-intact condition of the deposited layer. Few compounds were detected in the electrolyte solution, resulting in significantly lower oxidation in the layer compared to the base material.

Scaling behavior of granular columns collapse on erodible-inclined surfaces

This paper explores the effects of slope angle, initial column aspect ratio, and interparticle friction coefficient on the mobility and erodibility of granular columns collapsing on an erodible-inclined layer before spreading and depositing on a nonerodable-horizontal surface using Discrete Element Method. The numerical results showed that the column collapse with higher aspect ratio or smaller friction coefficient induces larger normalized kinetic energy, leading to larger granular masses out the inclined region and longer runout distance. The slope angle, on the other hand, shows trivial impacts on the kinetic energy and apparent friction coefficient. Remarkably, these physical quantities are nontrivially behaved by a new dimensionless number that incorporates the initial column aspect ratio, inclination angle, and interparticle friction coefficient. These findings may significantly complement the better understanding of the behavior of natural disaster events such as landslides, rock and snow avalanches, or pyroclastic flows on complex surfaces.

The role of rolling resistance in the rheology of wizarding quidditch ball suspensions

To elucidate the effect of particle shape on the rheology of a dense, viscous suspension of frictional, non-Brownian particles, experimental measurements are presented for suspensions of polystyrene particles with different shapes in the same solvent. The first suspension is made of spheres whereas the particles which compose the second suspension are globular but with flattened faces. We present results from steady shear and shear-reversal rheological experiments for the two suspensions over a wide range of stresses in the viscous regime. Notably, we show that the rheology of the two suspensions is characterised by a shear-thinning behaviour, which is stronger in the case of the suspension of globular particles. Since the shear-reversal experiments indicate an absence of adhesive particle interactions, we attribute the shear thinning to a sliding friction coefficient which varies with stress as has been observed previously for systems similar to the first suspension. We observe that the viscosity of the two suspensions is similar at high shear stress where small sliding friction facilitates particle relative motion due to sliding. At lower shear stress, however, the sliding friction is expected to increase and the particle relative motion would be associated with rolling. The globular particles attain a higher viscosity at low shear stress than the spherical particles. We attribute this difference to a shape-induced resistance to particle rolling that is enhanced by the flattened faces. Image analysis is employed to identify features of the particle geometry that contribute to the resistance to rolling. It is shown that the apparent rolling friction coefficients inferred from the rheology are intermediate between the apparent dynamic and static rolling friction coefficients predicted on the basis of the image analysis. All three rolling resistance estimates are larger for the globular particles with flat faces than for the spherical particles and we argue that this difference yields the stronger shear thinning of the globular particle suspension.

Microrollers flow uphill as granular media

Pour sand into a container and only the grains near the top surface move. The collective motion associated with the translational and rotational energy of the grains in a thin flowing layer is quickly dissipated as friction through multibody interactions. Alternatively, consider what will happen to a bed of particles if one applies a torque to each individual particle. In this paper, we demonstrate an experimental system where torque is applied at the constituent level through a rotating magnetic field in a dense bed of microrollers. The net result is the grains roll uphill, forming a heap with a negative angle of repose. Two different regimes have been identified related to the degree of mobility or fluidisation of the particles in the bulk. Velocimetry of the near surface flowing layer reveals the collective motion of these responsive particles scales in a similar way to flowing bulk granular flows. A simple granular model that includes cohesion accurately predicts the apparent negative coefficient of friction. In contrast to the response of active or responsive particles that mimic thermodynamic principles, this system results in macroscopic collective behavior that has the kinematics of a purely dissipative granular system.

Cohesive granular columns collapsing: Numerics questioning failure, cohesion, and friction

Simulations of the failure of cohesive granular steps with varying intensities of the contact adhesive force are presented. The simulations are compared with experimental and numerical studies of wet shear flows [Badetti et al., J. Rheol. 62, 1175–1196 (2018) and Khamseh et al., Phys. Rev. E 92, 022201 (2015)], computing the apparent friction coefficient. We observe consistent behaviors. We reproduce the dependence between the macroscopic cohesion and the contact adhesion [Rumpf, Chem. Ing. Tech. 42, 538–540 (1970) and Richefeu et al., Phys. Rev. E 73(5), 051304 (2006)] observed experimentally for sticky polymer-coated grains, as well as the range of friction explored [Gans et al., Phys. Rev. E 101, 032904 (2020)]. Focusing on the interface between moving and static materials, and assuming a linear failure, we infer the orientation of the failure plane with the horizontal. We disclose a nonmonotonous evolution with the intensity of the contact adhesion. Assuming an ideal Coulomb material allows for proposing an interpretation to this nonmonotonous behavior. Although the systems are past incipient failure, we consider an edge of material at equilibrium, for which the failure angle is related to the internal frictional properties of the material. In this framework, the nonmonotonous evolution of the failure orientation may hint at a cohesion-induced weakening mechanism, by which stronger contact adhesion involve weaker friction.

Potential Role of Volcanic Glass‐Smectite Mixtures in Slow Earthquakes in Shallow Subduction Zones: Insights From Low‐ to High‐Velocity Friction Experiments

AbstractVolcanic glass and its mixture with smectite are commonly observed in shallow parts of subduction zones. As volcanic glass layers often act as glide planes in submarine landslides, and because its alteration product, smectite, is one of the frictionally weakest geological materials, the frictional characteristics of volcanic glass‐smectite mixtures are important for fault slip behavior in shallow parts of subduction zones. We performed a series of friction experiments on volcanic glass‐smectite mixtures with different smectite contents from 0% to 100% at various velocity conditions from 10 μm/s to 1 m/s under an effective normal stress of 5 MPa and pore pressure of 10 MPa. In general, apparent friction coefficients negatively depend on the smectite content at any velocity tested. We found that samples with smectite contents of 15%–30% showed a drastic slip‐weakening behavior at intermediate velocities of 1–3 mm/s. Finite element method modeling shows that thermal pressurization does not contribute to the observed weakening behavior. The critical nucleation length estimated from the slip‐weakening behavior is approximately 1–10 km, which is large enough to prevent the slip to accelerate to seismic slip velocity. Therefore, gouges with minor amount of clay, such as subducting volcanic ash layers, may contribute to the occurrence of the slow earthquakes at shallow depths in subduction zones.

Machinability appraisal of nitronic-50 under dry environment using uncoated carbide inserts

ABSTRACT Nitrogen strengthened austenitic stainless steels are uneasy to machine. 22-13-5 stainless steel better known as Nitronic-50 is also not an exception. The current study deals with such an investigation where Nitronic-50 has been machined under varied cutting speeds, feeds and depths of cut and its machinability has been tried to be adjudged on the basis of cutting forces, apparent coefficient of friction, tool-tip temperature, chip reduction coefficient, flank wear width, chip morphology and surface roughness. It is seen that while using higher cutting speed-lower feed-higher depth of cut combination, tangential cutting forces were 18.83% and 29.57%, apparent coefficient of friction was 9.48% and 12.90%, tool-tip temperature was 11.02% and 22.31%, flank wear was 41.25% and 29.91%, and surface roughness was 22.91% and 24.27% lesser as compared to the higher values obtained with higher cutting speed-higher feed-higher depth of cut and intermediate cutting speed-higher feed-higher depth of cut combinations, respectively.

Discrete element investigation of the mobility of granular mass flows

The gravitational flows of granular materials are omnipresent in industrial processes such as handling and transportation of material and in natural events such as landslides, rock and snow avalanches; however, their mobilities remain elusive due to the arbitrary slope geometry and the sliding volume. By means of three-dimensional discrete element simulations, this paper investigates the flow mobility characterized by its energy evolution, run-out distance, and movement of the center of mass of granular materials collapse on an inclined-upstream region, then plunge and deposit on a horizontal-downstream region. A specific case of numerical simulation is first compared with a theoretical prediction published previously to validate the capability of this numerical approach for simulating the mobility of granular flows. Based on this theoretical validation, a series of numerical experiments is generated by varying a broad range of values of the inclination angle of the inclined-upstream surface and the volume of granular blocks. The results show that the kinetic energy increases significantly with increasing the inclination angle but slightly increases with the volume of granular materials changing along the inclined direction. In which, the rate of reaching the peak values of the vertical and horizontal kinetic energies on the upstream and downstream regions, respectively, increases linearly with increasing the inclination angle. More interestingly, the flow mobility enhances with increasing the sliding volume, represented via the increase of the run-out distance and the decrease of the apparent friction coefficient which is defined as a ratio of the total drop and horizontal movement of the center of mass. Remarkably, the run-out distance of the flows can be nicely scaled by the maximum kinetic energy in the whole process and in horizontal region. These findings robustly declare the origins of the run-out distance from the spreading stage of granular materials in the downstream area and strongly provide evidence for describing the mobility of granular flows on the complex surface.

Surface integrity evaluation in ecological nanofluids assisted grinding of Inconel 718 superalloy

Surface integrity is an important term that describes the surface behaviour of a ground component. Grinding is defined as a finishing operation that has high specific energy consumption. High heat generation while grinding, adversely affects the surface integrity of the ground surfaces. With the development of advanced materials such as superalloys, this process is widely used in bulk machining for making critical components used in dynamic loading. Therefore, it becomes necessary to investigate the surface integrity of the ground components, as their surface integrity primarily determines their performance and durability. The purpose of this work is to enhance the grinding performance of Inconel 718, a difficult-to-grind material, by employing silver and zinc oxide (ZnO)-based ecological nanofluids in a minimum quantity lubrication (MQL) mode. The grinding parameters such as wheel speed and table speed are kept constant with variations in the grinding infeed. The grinding performance in terms of grinding forces, apparent coefficient of friction, surface roughness and residual stresses on the ground surfaces have been investigated. Skewness, kurtosis and the Abbott–Firestone curve have also been analysed using two-dimensional and three-dimensional plots for an in-depth study of ground surface behaviour. The finding suggests that ZnO-based nanofluid outclass the silver-based nanofluid using MQL mode in terms of reduced grinding forces and favourable residual stress. Therefore, it appears as the potential grinding environment for the improved grinding performance of Inconel 718.

On wear mechanisms and microstructural changes in nano-scratches of fcc metals

Sliding and scratching are fundamental tribological phenomena which affect the surface and surface-near zones of materials. To clarify ongoing tribological and microstructural mechanisms, a thorough analysis of three fcc materials (aluminium, austenitic steel and copper) was performed via nano-sliding and scratching at different load levels. Nanoindentation was used to evaluate the phases’ mechanical properties, namely hardness H, Young’s modulus E and the ratios H/E (yield strain) and H³/E2 (resistance against plastic indentation), which proved to be good measures to understand the abrasive wear behaviour. Electron backscatter diffraction (EBSD) measurements and focused ion beam (FIB) cross-sections of the scratches provided deeper insight into the degree of deformation and deformation induced phase changes.Results show a distinct influence of the materials’ mechanical parameters and phase changes on the deformation and wear mechanisms, and the thereby entailed apparent coefficient of friction (FT/FN). The mechanical properties were a key factor for a change in wear mechanism from sliding to ploughing to chipping. The thresholds were investigated for the three materials and increase from Aluminium to Copper to Austenite with H³/E2 being a good descriptor of the necessary contact pressures entailing changes of the wear mechanism.

A tribological characterisation of Ti-48Al-2Cr-2Nb and Ti-6Al-4V alloys with dry, flood, and MQL lubricants

The development of cutting tools requires the knowledge of tribological phenomena at the tool – workpiece contact area. This knowledge is in dearth particularly for difficult-to-cut alloys like gamma titanium aluminide (gamma – TiAl alloys). Therefore, this article is an attempt to plug the gap and aid the development of cutting tools for gamma – TiAl alloys. To this end, friction, adhesion, and coating wear between AlTiSiN coated cemented carbide tool and Ti-48Al-2Cr-2Nb (Near lamellar), Ti-48Al-2Cr-2Nb (Duplex), and the most used titanium alloy of Ti-6Al-4V (alpha – beta) were experimentally derived. A Pin-on-Cylinder (PoC) tribometer with contact conditions corresponding to commercial machining conditions was used with dry, flood(EML), and two MQL lubricants. Additionally, the heat generated and partitioned between the pin and workpiece was quantified to assess the thermal exposure to the coatings. The results showed that Ti-6Al-4V had approximately 50% higher apparent friction coefficient than the Ti-48Al-2Cr-2Nb alloys. Interestingly, the friction coefficients of Ti-48Al-2Cr-2Nb alloys were nearly consistent across the entire test matrix. Notably, the change in the microstructure from near lamellar to duplex did not elicit any qualitative or quantitative change in the friction profile of Ti-48Al-2Cr-2Nb alloys. The contact pressure proved to be the statistically significant property influencing friction evolution inversely for Ti-6Al-4V alloy and directly for Ti-48Al-2Cr-2Nb alloys. The results showed higher probability of coating wear in dry conditions as opposed to the flood and MQL lubricants.

Analysis of material removal process when scratching unidirectional fibers reinforced polyester composites

AbstractIn this study, the micromechanical scratch behavior of unidirectional glass fiber reinforced polyester (GFRP) using several wear conditions was highlighted. Single-indenter scratch tests (SSTs) were carried out on GFRP composite material perpendicular (SST⊥) and parallel (SST//) to fiber direction. Damage modes dominating the material removal process (MRP) and friction exhibit significant sensitivity to both attack angle and normal load. From findings, damage modes and apparent friction coefficient substantially accentuate when increasing the attack angle. The inspections of the damage state at different testing conditions using a scanning electron microscope (SEM) reveal the dominating modes governing the MRP through the different phases. The response surface methodology (RSM) was adopted to develop a mathematical model based on the measured data. The RSM approach was found very promoting for predicting friction evolution versus attack angle and normal load. The proposed model reveals good ability not only in predicting apparent friction coefficient but also in detecting separately its ploughing and adhesive component. To emphasize the correlation between friction coefficient and MRP, the wear maps have been drawn up.

Pullout behaviour of polymeric strips embedded in mixed recycled aggregate (MRA) from construction & demolition (C&D) waste – Effect of type of fill and compaction

Recycling and reusing construction and demolition (C&D) waste is the pressing priority, and the use of such non – conventional structural fill in reinforced soil structures (RSS) is gaining momentum. However, the utilisation of mixed recycled aggregate (MRA) from processed C&D waste as structural fill with polymeric strips (PS) and the effect of poorly compacted structural fill on the pullout interaction is not reported. This research presents the viability of using MRA as a structural fill for reinforced soil structures, appraising the physical, mechanical and electrochemical properties of MRA and the pullout behaviour of polymeric strips embedded in MRA at different relative densities in a large-scale pullout box. The results for MRA were compared with those obtained using locally available coarse and fine sands. The test results showed that MRA was alkaline (pH < 9) and had good mechanical properties and shear strength suitable for reinforced soil structures. Pullout testing results exhibited high values of the interface apparent coefficient of friction (μS/GSY) under dense conditions and a 70–80% reduction in loose conditions. The present study reinforces the viability of using MRA as an alternative structural fill with PS and highlights the effect of construction variability on μS/GSY.

Experimental investigation of the frictional behavior of single glass fiber filament

Fiber friction behaviors are crucial for understanding the ubiquitous frictional damage phenomena in the manufacturing and service processes of multiscale textile reinforcements. This paper investigates the influence of relative velocity and applied load on the frictional behavior between a solitary glass fiber filament and a metal roller. The results of piecewise regression analysis indicate that the apparent coefficient of friction initially decreases with relative velocity, followed by an increase, and subsequently decreases again until stabilizing at higher velocity. Specifically, the maximum values of the coefficient of static friction are observed within the relative velocity range of 1.26–1.68 mm/s, while that of dynamic friction occurs within the range of 0.84–3.94 mm/s; the coefficient of friction reaches stable values within the relative velocity range of 7.87–15.71 mm/s. Under four different tension conditions, the stable values for the coefficient of static friction are 0.336, 0.308, 0.321, and 0.281, while the coefficient of dynamic friction are 0.291, 0.269, 0.273, and 0.232 respectively. Furthermore, the relationship between the coefficient of friction and the applied load reveals that the coefficient of friction decreases as the load increases. Finally, quantitative investigation reveals a strong coupling characteristic between the velocity dependency and load dependency of the apparent coefficient of friction.

Frictional sliding of infilled planar granite fracture under oscillating normal stress

This paper investigates the frictional behavior of the infilled rock fracture under dynamic normal stress. A series of direct shear tests were conducted on saw-cut granite fractures infilled with quartz using a self-developed dynamic shear apparatus, and the effects of normal load oscillation amplitude, normal load oscillation period and sliding velocity were studied. The test results reveal that the shear response can be divided into three stages over a whole loading-unloading process, characterized by different time spans and stress variations. Generally, a smaller oscillation amplitude, a longer oscillation period and a fast shear velocity promote the stability of the friction system, which is also confirmed by the Coulomb failure criterion calculated based on the observed periodic apparent friction coefficient. The dynamic strengthening/weakening phenomenon is dependent on the oscillation amplitude and product of sliding velocity and oscillation period (vT). Also, the rate and state friction law incorporating the parameter α that characterizes the normal stress variation is employed to describe the dynamic friction coefficient but exhibits an incompetent performance when handling intensive variation in normal stress. Finally, the potential seismicity induced by oscillating normal stress based on the observed stress drop is analyzed. This work helps us understand the sliding process and stability evolution of natural faults, and its benefits for relative hazard mitigation.

Experimental Investigation of Interface Characteristics between Geogrid and Coarse-Grained Soil in a Seasonally Frozen Area

In seasonally frozen soil regions, the influence of temperature change on reinforced-soil engineering cannot be ignored. In particular, the mechanical properties of the reinforced-soil interface have an important impact on the overall stability and long-term service performance of reinforced soil engineering. To explore the interface characteristics and reinforcement mechanism between geogrids and coarse-grained soil under negative temperatures, this paper takes the typical coarse-grained soil in Xinjiang as the material and carries out a direct shear test of the reinforcement–soil interface under different normal stresses, water contents and temperatures. The curve characteristics of the shear displacement-shear stress, the change trend of the peak shear stress and the formation mechanism between the geogrid and coarse-grained soil interface under freezing and nonfreezing conditions are thoroughly analyzed. The formation mechanism of the dilatancy characteristics of the reinforced-soil interface is explained by combining the Mohr-Coulomb strength criterion and apparent friction coefficient. It is concluded that the trend of the shear displacement-shear stress curve between the geogrid and coarse-grained soil interface under the nonfreezing state and freezing state is basically the same. In a state of low normal stress, the curve has no obvious peak, which is closer to the ideal elastic-plastic double linear model. In a state of high normal stress, the curves have more obvious peaks, and the curve type is closer to the elastic-strain softening type. In the nonfreezing state, the shear strength of the reinforcement–soil interface has a great correlation with the water content, which is different in the freezing state. The main sources of the difference are the cementation of pore ice in the soil skeleton in the frozen state, the improvement of the strength of the soil particles themselves, and the further interlocking effect of the geogrid on the soil. In comparison with the reinforced coarse-grained soil under the nonfrozen state, the shear strength under the frozen state is significantly improved. In comparison with coarse-grained soil reinforced by geogrids in the nonfreezing state (0 °C), the shear strength of the frozen state (−5 °C) is significantly improved. Under normal stresses of 40 kPa, 60 kPa, and 80 kPa, when the water content is 2%, the corresponding peak shear stress increases by 19.39%, 21.71% and 11.34%, respectively. When the water content is 4.5%, the corresponding peak shear stress decreases by 29.98%, 16.17%, and 13.83%. When the water content is 7%, the corresponding peak shear stress decreases by 50.85%, 18.64%, and 21.96%. The apparent friction coefficient between the geogrid coarse-grained soil interface in the nonfrozen state and frozen state decreases with increasing normal stress. With the decrease in temperature, the dilatancy phenomenon of the reinforced soil composite is more obvious. The research results can provide a reference for the construction of reinforced engineering in seasonal frozen soil areas.

Pullout behavior of a bearing polymeric strap under monotonic and cyclic tensile loads

Soil-reinforcement interaction consists of three factors including frictional resistance, shear strength of the soil and passive resistance. In the ordinary polymeric strap (PS) reinforcement, only frictional resistance contributes to pullout resistance. In this study, in order to develop passive resistance in the soil, a number of angles as transversal elements were attached to PS reinforcement, which is called bearing polymeric strap (BPS). The post-cyclic pullout behaviour of the BPS is evaluated using a large-scale pullout apparatus adopting multistage pullout (MSP) test and one-stage pullout (OSP) test procedures. The results show that a spacing-to-high ratio of angles equal to 3.33 gives the maximum pullout resistance. MSP tests were performed on the BPS with an optimum arrangement to evaluate the influence of various factors including cyclic tensile load amplitude, load frequency and number of load cycles, and also the influence of vertical effective stress on the pullout resistance and the peak apparent coefficient of friction mobilized at the soil-BPS interface. Moreover, for BPS system with a single isolated transverse member, the bearing capacity factor Nq was calculated using equations based on three failure modes and it was found that the Nq calculated in the punching shear failure mode makes the best prediction.

Study on Interface Interaction between Uniaxial Geogrid Reinforcement and Soil Based on Tensile and Pull-Out Tests

The interaction between reinforcement and soil is a key problem in the application of geosynthetics as reinforcement in geotechnical engineering. In this study, tensile and pull-out tests on a uniaxial geogrid were carried out using self-designed tensile and pull-out test equipment. The tensile test evaluated the tensile load–strain characteristics of a geogrid. Under the condition of lateral confinement, the tensile force and secant tensile stiffness of the geogrid increased with an increase in the normal stress when the strain was constant, and the secant tensile stiffness decreased with a decrease in the tensile rate. The stiffness coefficient was used to quantitatively describe the change in the stiffness of the reinforcement. Using the pull-out test, the variation laws of the pull-out force of the geogrid under different normal stresses and different longitudinal rib percentages were obtained. When the geogrid was broken, the pull-out force of the same type of geogrid was not significantly different under different normal stresses. With an increase in the longitudinal rib percentage, the pull-out force of the geogrid under the same normal stress gradually increased, and the apparent friction coefficient was obtained by analysis. The results of the apparent friction coefficient obtained by the analytical method in accordance with French specifications (NF P94-270-2020) are relatively safe compared to the experimental values.