Friction Angle Research Articles

Modified Mohr–Coulomb criterion for nonlinear strength characteristics of rocks

AbstractThe classical Mohr–Coulomb criterion has an extremely wide range of applications in the field of engineering geology, while it cannot accurately characterize rock failure under high confining stresses. Therefore, a nonlinear modification is implemented based on the Mohr–Coulomb criterion for achieving wider usage in all stress environments. The cohesion and internal friction angle are firstly calculated by regression based on the triaxial experiments of diorite and other typical rocks in different confining stress ranges, and the variation modes of cohesion and internal friction angle are then formalized and integrated into the classical Mohr–Coulomb criterion. Using the experimental results of 435 triaxial compression tests in existing publications, the predictions of the modified criterion are compared with those of the previous nonlinear criteria, which show that the predicted values of the modified criterion are in good agreement with the measured strength. Compared with the previous nonlinear criteria, the modified criterion has a wider application range and always maintains a higher accuracy.

Numerical investigation of granular column-improved soils using the direct shear test

The granular columns treatment is widely used in the weak soils. The present paper focuses on the numerical modeling of a direct shear test on granular columns in soils. The finite difference code Fast Lagrangian Analysis of Continua in 3 Dimensions (FLAC3D) was used in this research work, to evaluate the equivalent properties of granular column-improved soils with different diameters of the columns, and different plan configurations. The results of these numerical tests are discussed in terms of increases the shear load-strength and decreases the horizontal displacement due to the variation of arrangements, Young's modulus and the friction angle of the granular columns. Different types of failures observed in the granular columns. Bending failure mode is the main in the granular column with large values of Young's modulus and the friction angle when subjected a lateral load.

A pressure-sensitive rheological origin of high friction angles of granular matter observed in NASA–MGM project

Abstract An abnormally high peak friction angle of Ottawa sand was observed in (National Aeronautics and Space Administration) NASA–(Mechanics of Granular Materials) MGM tests in microgravity conditions on the space shuttle. Previous investigations have been unsuccessful in providing a constitutive insight into this behavior of granular materials under extremely low effective stress conditions. Here, a recently proposed unified constitutive model for transient rheological behavior of sand and other granular materials is adopted for the analytical assessment of high peak friction angles. For the first time, this long-eluded behavior of sand is attributed to a hidden rheological transition mechanism, that is not only rate-sensitive, but also pressure-sensitive. The NASA–MGM microgravity conditions show that shear-tests of sand can be performed under abnormally low confining stress conditions. The pressure-sensitive behavior of granular shearing that is previously ignored is studied based on the μ(I) rheology and its variations. Comparisons between the model and the NASA microgravity tests demonstrate a high degree of agreement. The research is highly valid for pressure-sensitive and rate-dependent problems that occur during earthquakes, landslides, and space exploration.

Study on soil pressure of loose soil in cohesive soil tunnel considering soil arch effect

Soil pressure in clay formation tunnels is closely related to soil arch effect and the development of slip surfaces. Firstly, numerical simulation software is used to simulate the actual situation of tunnel excavation, and the change rule of the slip-cracking surface of cohesive soil is analyzed. Secondly, based on the numerical simulation results and the ellipsoid theory, the pressure formula of Terzaghi loose Earth is modified considering that the principal stress trace is catenary. Finally, the calculation results are compared with the finite element calculation results to verify the rationality of the formula in this paper. The relationship between the internal friction angle, cohesion force c, eccentricity ε, looseness coefficient β, and the pressure of loose Earth is further studied. The results show that there is a gap between the sliding crack angles with or without dilatancy angle and it will affect the development form of soil arch. The slip angle decreases gradually with the increase of the buried depth ratio H/D and becomes stable when the buried depth ratio H/D≥3. Compared with deep-buried tunnels, the increase of internal friction angle in the shallow-buried tunnel is more conducive to reducing the overlying soil pressure. The loose soil pressure decreases with the increase of eccentricity ε and loose coefficient β, and the influence of eccentricity ε on loose soil pressure is significantly greater than that of loose coefficient β. Therefore, the change of eccentricity ε should be paid close attention in the project.

BACK ANALYSIS AND STABILITY PREDICTION OF SURROUNDING ROCK DURING EXCAVATION OF THE SHUANGJIANGKOU UNDERGROUND POWERHOUSE

The underground powerhouse of the Shuangjiangkou hydropower station is one of the largest caverns under construction in China, and its stability during construction is crucial for safe construction. To study the stability of the surrounding rock during excavation, the displacement and stress of the surrounding rock were monitored by multi-point displacement meters and bolt stress meters. Based on the monitoring data, the elastic modulus, Poisson’s ratio, friction angle, and cohesion of surrounding rock were inversely analyzed by the PSO-BP algorithm. Then, the back-analyzed parameters were used to simulate the subsequent excavations and predict the stability of surrounding rock during the following construction. The analysis results show that the surrounding rocks were generally stable during the initial four stages of excavation, and the main factors affecting their stability were blasts and unfavorable geological structures, including the lamprophyre vein and the F1 fault. These unfavorable geological structures also significantly decrease the mechanical parameters of surrounding rock as demonstrated by back analysis, and the stability prediction results show that the omnibus bar cave and the tailrace tunnel were at the greatest risk of instability during the subsequent excavations. This study provides a practical analysis for engineering excavation of the underground caverns.

Numerical investigation on the fracture and mechanical behaviors of marble containing two parallel fissures under triaxial compression conditions using FDEM

This paper aims to investigate the fracture and mechanical behaviors of fissured marble under triaxial compression. The two-dimensional models of marble with two parallel fissures and various rock bridge angles were established, and then the numerical simulations considering the effect of confining pressure were performed with the finite-discrete element method. The brittle-ductile transition and stress multi-peak characteristics are presented with the increase of the confining pressure. The characteristic strain, stress, and elastic strain energy exhibit various trends with the increment of the rock bridge angle, whilst increasing trend with the increment of the confining pressure. The cohesion presents the variation of first increasing and then decreasing with the increase of the rock bridge angle, and the friction angle presents the opposite trend to the cohesion. The proposed strength model can reflect the evolutions of the cohesion and the friction angle considering the effect of confining pressure and rock bridge angle. The elastic strain energy has the trends of nonlinear increase and fluctuation in the pre-peak and post-peak phases, respectively. The variation of kinetic energy is induced by the internal local fracture during the progressive failure. The failure pattern transforms from the tensile failure to the shear failure with the increase of the confining pressure. The coalescence behavior of cracks at the rock bridge can be classified into four modes.

Study on active earth pressure of narrow backfill of balance weight retaining wall under translational displacement mode

The balance weight retaining wall is a kind of gravity retaining wall. However, the theoretical results of the earth pressure are relatively few. The failure modes of backfill soil under different factors such as width to depth ratio of fill soil and rock inclination angle were studied by finite element limit analysis. Based on differential element methods and wedge limit equilibrium method, the active earth pressure calculation formula of balance weight retaining wall under translational displacement mode was derived. According to the parameter analysis, the interface friction resistance escalates alongside the rise in the boundary friction angle. The active earth pressure resultant force of the retaining wall increases with the increase of the width to depth ratio of filling, and decreases with the increase of the friction angle of filling. The design of counterweight retaining wall can benefit from the scientific basis and technical reference offered by the research findings.

Effects of microbially induced calcite precipitation on static liquefaction behavior of a gold tailings sand

Loose tailings are susceptible to static liquefaction during which they lose a substantial amount of their strength. This study examines a sustainable technique known as Microbially-Induced Calcite Precipitation (MICP) to improve the static liquefaction resistance of gold mine silty sand tailings. These materials were enriched with Sporosarcina pasteurii, consolidated in a direct simple shearing apparatus, and subjected to several injections of a cementation solution. Calcified tailings were then sheared under constant-volume and constant vertical stress conditions to evaluate their undrained and drained shearing behaviors. Results showed that bio-mineralization can prevent the occurrence of static liquefaction in tailings by reducing their contraction tendency. This is demonstrated by the strong strain-hardening behaviors of the treated tailings specimens compared to the strain-softening and undrained strength loss in specimens of the untreated tailings. Substantial increases in the tailings undrained and drained shear strengths (by up to 30 - 50 kPa), improvements (by up to 5 MPa) in their tangent moduli, and more than 5° rise in their friction angles are observed in the direct simple shear tests following MICP-treatment. The critical state line of tailings is also found to be steeper and shifted to denser void ratios following MICP treatment. These changes reduce liquefaction susceptibility of tailings and enhance their resistance against static liquefaction. Post-treatment acid dissolution further indicates that CaCO3 contents of about 4% to 11% precipitated in the treated specimens. This amount decreases with increasing specimens void ratio. Changes in the microstructural fabric of the cemented tailings particles are also characterized using scanning electron microscopic (SEM) images and X-ray diffraction (XRD) analyses.

Grain size effect on the anisotropic shear behavior of sand–textured geomembrane interface

A set of direct shear tests was conducted to investigate the effects of sand mean grain size and geomembrane surface roughness on the shear behaviour of the sand–geomembrane interface. Four types of sands with different mean grain sizes were used and the interfaces included a smooth geomembrane (SGM) and four textured ones with different asperity characteristics. The samples were prepared in a direct shear box at five sedimentation angles. The experimental results showed that the peak friction angle of the soil–textured geomembrane interface was dependent on the mean grain size, inherent anisotropy and surface roughness of the geomembrane. The shear strength of sand–textured geomembranes was two to three times larger than that of the sand–SGM interface. The peak and residual friction angles of sand-SGM interface occurred at sedimentation angle of 72° while it was 108° for sand-TGM interfaces. An increase in mean grain size increased the shear strength of the sand–textured geomembrane interface; while a reverse condition occurred for the sand–SGM interface. The shear strength occurred at larger horizontal displacement as mean particle size increased and the effect of relative roughness on peak friction angle increased with increase in mean grain size.

ViT-Based Image Regression Model for Shear-Strength Prediction of Transparent Soil

The direct-shear test is the primary method used to test the shear strength of transparent soil, but this experiment is complex and easily influenced by experimental conditions. In order to simplify the process of obtaining the shear strength of transparent soil, an image regression model based on a vision transformer (ViT) is proposed in this paper; this is used to recognize the shear strength of the soil based on images of transparent-soil patches. This model uses a convolutional neural network (CNN) to decompose the transparent-soil images into multiple image patches containing high-order features, utilizes a ViT for feature extraction, and designs a regression network to facilitate the transfer of information between the abstract image features and shear strength. This model solves the problem of boundary blurring and difficult-to-identify features in speckle images. To demonstrate the effectiveness of the proposed model, different parameters related to transparent soil were obtained by controlling the particle size of fused quartz sand and the content of aerosol; in addition, the friction angle and cohesive force of the transparent soil under different proportions were measured using direct-shear tests, serving as two datasets. The results show that the proposed method achieves correlations of 0.93 and 0.94 in the two prediction tasks, thus outperforming existing deep learning models.

Analysis of Off-Road Tire Cornering Characteristics by Using Advanced Analytical Techniques

ABSTRACT This paper focuses on analysis of the cornering characteristics of an off-road truck tire running under several operating conditions over different soils. The finite element analysis (FEA) method is used to model the Goodyear RHD 315/80R22.5 truck tire, and the smoothed-particle hydrodynamics (SPH) method is used to model the soil. The goal of this research is to provide a virtual testing environment in Pam-Crash software as an alternative to actual tests for FEA and SPH analyses of rolling tire interactions on deformable terrains. The study on the effects of different operating parameters on the cornering performance combined with the sensitivity study can be of interest to tire engineers or vehicle engineers because they provide insight into the design and real-time behavior of a vehicle. Tire and soil models are validated using experimental data and published measurements, showing good agreement. The tire–soil interaction is investigated under different tire conditions, such as longitudinal speed, inflation pressure, vertical load, and slip angle, and under various soil characteristics, such as cohesion, internal friction angle, and rut depth. Cornering force, self-aligning moment, and overturning moment are studied as the fundamental cornering characteristics that affect truck lateral stability and control. Owing to the excessive computational demands posed by the FEA-SPH tire–soil models, we propose unique mathematical relationships for estimating the cornering characteristics of free-rolling as well as driven truck tires in an efficient manner. The genetic algorithm (GA) technique is used to develop relationships between the cornering parameters and operating conditions. We conclude that the identified mathematical relationships could provide very good estimations of the cornering characteristics under a broad range of operating conditions and soils. The GA equations will ultimately be implemented into a full vehicle model to evaluate the full vehicle performance.

Numerical simulation and experimental study on seafloor sampling of an anchor-type mud collector based on SPH-FEM coupling method

Marine sediments are important for research in scientific fields such as marine geology, environmental testing of waters, marine biology and seabed resource exploration. Among them, mud miner is an important way to obtain sediments. However, due to the complexity of the marine environment, the seabed sampling operation is a relatively difficult and complicated project. The structural design of the sampler, the operation mode, and the interaction between the sampler and the sediment affect the sampling effect, which leads to the low efficiency of the sampler operation. In order to investigate the main factors affecting the drag force of the sampler during seafloor sampling, this paper takes a simple and portable anchor-type mud collector surface sediment sampler as a study. This paper introduces the mechanical structure and working principle of an anchor-type mud collector, establishes a mechanical model of the mud collector seafloor sampling process and derives the main factors affecting the dragging force: internal friction angle; the horizontal angle of the bi-directional shaft rod; undercut angle [Formula: see text] of bottom cover and dragging speed. A FEM-SPH method based on the coupling of the finite element method (FEM) and the smooth particle hydrodynamics method (SPH) was proposed to simulate the dynamic process of mud collector subsea sampling, and the mechanical data of fine sand and clay were obtained through land-based experiments. Based on the comparison between experimental data and numerical simulation data, the simulation validity of the FEM-SPH method was verified. The results show that the drag force of the clay was greater than that of the fine sand in the experiment of cutting the lower cover of the mud collector into the fine sand and clay, the internal friction angle of the clay is greater than that of the fine sand; with the increase in horizontal inclination angle and the decrease in undercut angle, the dragging force gradually increased; The dragging speed ranged from 0.2 to 0.6 m/s, with an increase in the mass of clay and fine sand collected with increasing speed, resulting in a gradual increase in dragging force. This paper provides a new method to study the force of the mud collector, provides a theoretical method to reduce the intensity and difficulty of manual work in the sampling process and increase the efficiency of sampling.

Estimating Max moment and shear exerted on contiguous piles subjected to earthquake using ANN.

Recently the usage of Contiguous piles in many different aspects of construction projects are become more common. Determination of the shear force and moment values exerted on the contiguous piles require extensive analysis and calculations especially when earthquake is to be encountered. ANN mathematical models for calculating this value combining 144 input sets that represent height of excavated (H), ratio of H to the depth of embedment (D), unit weight of retained soil ( ) and angle of internal friction ( ) is presented in this paper. The mathematical models obtained show acceptable regression and deviation. It was found that both shear and moment values subjected on the piles are decreases with the decrease of ( ) and increases with the increase of ( ). The height of excavation (H) was found as the most important input parameter that affects the output values of the models

Introducing a New Classification System for Estimating Non-cemented Alluvial Bimsoils Friction Angle

Introducing a New Classification System for Estimating Non-cemented Alluvial Bimsoils Friction Angle

Study on Shear Characteristics of Herbs Plant Root–Soil Composite System in Beiluhe Permafrost Regions under Freeze–Thaw Cycles, Qinghai–Tibet Highway, China

In order to study the root–soil composite system shear characteristics under the action of freeze–thaw cycles in the permafrost regions along the Qinghai–Tibet Highway (QTH) from the Beiluhe–Tuotuohe (B-T) section, the slopes in the permafrost regions along the QTH from the B-T section were selected as the object of the study. The direct shear test of root–soil composite systems under different amounts of freeze–thaw (F-T) cycles and gray correlations were used to analyze the correlation between the number of F-T cycles, water content, root content, and the soil shear strength index. The results show that the cohesion of the soil in the area after F-T cycles exhibits a significant stepwise decrease with an increase in F-T cycles, which can be divided into three stages: the instantaneous stage (a decrease of 46.73–56.42%), the gradual stage (a decrease of 14.80–25.55%), and the stabilization stage (a decrease of 0.61–2.99%). The internal friction angle did not exhibit a regular change. The root–soil composite system showed significant enhancement of soil cohesion compared with soil without roots, with a root content of 0.03 g/cm3 having the most significant effect on soil cohesion (increasing amplitude 65.20–16.82%). With an increase in the number of the F-T cycles, while the water content is greater than 15.0%, the greater the water content of the soil, the smaller its cohesion becomes. Through gray correlation analysis, it was found that the correlation between the number of F-T cycles, water content, root content, and soil cohesion after F-T cycles were 0.63, 0.72, and 0.66, respectively, indicating that water content had the most significant impact on soil cohesion after F-T cycles. The results of this study provide theoretical support for further understanding the variation law of the shear strength of root–soil composite systems in permafrost regions under F-T cycles and the influencing factors of plant roots to enhance soil shear strength under F-T cycles, as well as for the scientific and effective prevention and control of retrogressive thaw slump in the study area, the QTH stretches across the region.

Исследование технологического процесса подбора валка уборочно-транспортным агрегатом

The article is devoted to the design of the harvesting and transport unit (HTU), which is the main component of the complex of machines for harvesting loose hay. HTU is considered as a single-circuit system functioning as a result of the joint work of the picker and loader with the assembly chamber. The analysis of mathematical models of the processes of selection, loading and mass collection makes it possible to develop structural elements of the working bodies of the HTU. To check the operability of the technological scheme, the processes of selecting a roll by two types of pickers are considered: drum in combination with a chain-slat conveyor and canvas with spring fingers, an analysis of the mathematical model of this process is carried out. According to the results of the analysis, it was found that the chain-slat conveyor works satisfactorily in combination with a drum picker and provided that the ratio is fulfilled when its angle of inclination is less than the friction angle of the hay-straw mass. By studying the process of selecting a roll with a linen picker, the relationship between the agrotechnically permissible speed of the HTU movement with the step of the spring fingers arrangement was obtained. It is established that the condition of continuity of the

An Artificial Neural Network Method for Forecasting the Stability of Soil Slopes

Artificial neural network (ANN) methods, based on sophisticated models, have been developed recently that can predict slope stability. In this study, we have developed a genetic algorithm (GA) based on ANN to assess the stability of soil slope. Firstly, an ANN-based genetic algorithm was trained for nonlinear input-output mapping of the slope. A total of 190 soil slopes with unique values of shear strength properties (friction angle, cohesion, and unit weight), geometric parameters (slope angle and slope height), and corresponding factor of safety (FS) have been collected to give a neural network training dataset. Then, a three-layer neural network model is established based on GA. The prediction and performance ability of the established model is assessed using the correlation coefficient (R2). By the outcomes, the trained ANN model with the R2 value of 0.98 is reliable, valid, and simple for evaluating the soil slope stability and estimating the FS. Additionally, the proposed neural network model is applied to a case of soil slope from prior studies. Findings show that the developed ANN model can be versatile in studying the stability of soil slopes.

Pre- and post-failure behaviour of a dike after rapid drawdown of river level based on material point method

The rapid drawdown of river level is very detrimental to the stability of dikes. In this paper, the entire slope failure process of a real dike with sandy soil interlayer after rapid river drawdown is accurately reproduced using the material point method (MPM). The analysis of pre-failure behaviour, in combination with field test results, reveals the triggering mechanism of such dike slope failure, demonstrating that the presence of sandy soil interlayer is the leading cause of dike instability. By tracking the response of the dike slope from failure initiation to runout termination, the failure mode of the dike slope with sandy soil interlayer is identified as a progressive and retrogressive failure mode, with shallow and deep-seated slip surfaces appearing successively. Parametric studies indicate the friction angle, cohesion, dilatancy, and permeability of the sandy soil play significant roles in dike slope stability. A relationship between the permeability of sandy soil and the maximum sliding displacement is also found. In the face of rapid river drawdown, river-facing slope surface protection is the most effective protection measure for such dike slopes with sandy soil interlayer, while traditional riprap protection at the slope toe has a limited protecting effect.

Laboratory characterization of clay fouled rubber-coated ballast with and without geogrid

The utilization of rubber-coated ballast (RCB) aims to enhance the energy dissipation capacity and decrease the rate of deterioration of ballasted tracks, leading to reduced maintenance costs. Ballast fouling can affect the ballast's drainage properties, shear strength, deformation, and resilience that may ultimately lead to track misalignment. In this context, in the present study, the drainage and shear characteristics of RCB and RCB-conventional ballast mix are evaluated for various levels of clay fouling. The results of permeability tests indicated that the hydraulic conductivity (k) of RCB is more than that of conventional ballast. For example, the k of RCB is 71% higher than that of conventional ballast (fouling content = 50%). However, the k of ballast decreased significantly with the increase in the content of clay fouling. The results from the direct shear tests revealed that both RCB and RCB50% perform poorly in terms of peak friction angle (φ) when compared to conventional ballast. With the addition of clay fines, a further reduction in the shear strength is observed. For instance, the φ of unreinforced RCB, RCB50%, and conventional ballast decreases by 18.5%, 14.2%, and 10.4%, respectively, with the increase in fouling content from 0% to 50%. However, in case of geogrid-reinforced RCB50%, the peak friction and dilation angles are found to be relatively higher as compared to unreinforced conventional ballast in both clean and fouled conditions. The results of cyclic tests demonstrated that the deformation of both unreinforced and geogrid-reinforced RCB-conventional ballast samples increased while the resilience modulus (Mr), damping ratio (Dr), and ballast breakage index (BBI) decreased with the increase in fouling content. Moreover, the inclusion of geogrid significantly reduced the extent of deformation and particle breakage but enhanced the Mr and Dr when compared to unreinforced ballast. The various test results suggest that the geogrid-reinforced RCB50% performs better than unreinforced conventional ballast under both clean and clay fouling conditions. For geogrid-reinforced RCB50%, the volumetric strain (εv) and BBI are reduced by 9.7% and 69.5%, while Mr and Dr are improved by 5.75% and 176.5% as compared to unreinforced conventional ballast (fouling content = 20%). Additionally, empirical relations are developed to predict the vertical strain (ε1), lateral strain (ε3), Mr, Dr, and BBI of RCB-conventional ballast mix under clean and clay-fouled conditions.

Numerical Investigation into Factors Affecting Stability of Opencast Coal Mine's Rise Side Highwall Slope

Open-pit coal mining accounts for 93% of India's total coal production, playing a significant role in meeting the nation's substantial energy needs. The success of an open-pit mine hinges on maintaining the steepest and deepest slopes that remain stable over the mine's lifespan. However, slope failure is a complex issue influenced by numerous factors. In the context of openpit coal mines, the rise side highwall involves cutting through a rock mass containing various elements like an unconsolidated weathered mantle of sandstone, sandy clay, clay, carbonaceous shale and coal. Some opencast mines within the Godavari Valley Coal Field (GVCF), India have encountered significant pit slope failures. This paper uses a numerical modelling approach aimed at effectively assessing the stability of the rise side highwall, leveraging available geotechnical data from one of GVCF's largest opencast coal mines. The research investigates the impact of seven detrimental factors on slope stability, including dynamic loading due to blasting, employing a methodical One-Factor-At-A-Time (OFAT) approach. The study utilises Rocscience Phase2 version 9.0, a Finite Element Method (FEM) based numerical modelling software to gauge the sensitivity of each factor on the Factor of Safety (FoS). The numerical modelling results indicate that there is a linear decrease in FoS corresponding to the reduction in cohesion and an exponential increase in the FoS as the angle of internal friction rises. Furthermore, the analysis reveals significant impacts on the FoS due to groundwater and seismic loading from the blasting. This approach aims to comprehensively analyse and understand the intricacies of slope stability in the specific context of open-pit coal mining.