Friction Angle Of Sand Research Articles

Estimation of Distribution Factor for Peak Penetration Resistance Prediction of Spudcan Foundations in Loose to Medium-Dense Sand Overlying Clay

A series of 3D finite element (FE) analyses were performed to estimate the peak penetration resistance of spudcan foundations in sand over clay soil profiles. Elasto-perfectly plastic models following Mohr–Coulomb and Tresca failure criteria were used for sand and clay layers, respectively. The coupled Eulerian–Lagrangian (CEL) approach was used to simulate the large deformation in soil that occurs during the spudcan penetration. The performance of the numerical model was validated against centrifuge test results. A parametric study with a broad range of strength parameters for sand and clay was performed. The numerical results were used to assess the influence of sand thickness (Hs), the diameter of spudcan (D), friction angle of sand, and undrained shear strength of clay (su). A wide range of su was utilized to predict the resistance both of the soft and stiff clays. The calculated peak resistances are compared with a published analytical model. It is demonstrated that the model highly overestimates the peak resistance for stiff clays, most likely because it was developed specifically for soft clays and, therefore, does not account for the influence of su. One of the parameters of the model is revised to account both for su. Comparisons highlight that the modified model is able to capture the simulated peak penetration resistance for both soft and stiff clays.

Numerical Analysis on the Sandy Slope Reinforced with Sand Bags

In recent decades, many expressways and railways have been construction in Western China. One of important projects is Menghua Railway as a major energy transportation line. Since most of its Contract I routine is located in Maowusu Desert, it seems the first choice is to utilize the sandy soil to construct the railway subgrade. The sand bag structure is explored as a reinforcement method for as railway sandy subgrade by numerical analysis. The Flac3D is selected as the calculation tool with its GeogridSEL structural element used to simulate the function of geotextile bag. It is assumed the geotextiles remain elastic in the calculation, and the failure occurs at the interface between geotextiles and surrounding soil. The results show that when bagged sand is used, the internal friction angle of sandy soil can be appropriately reduced, or a steeper slope can be used, but the friction angle between bagged sand and geotextile is required to be larger. At the same time, if the internal friction angle of sand is small, in order to obtain a smaller slope, geotextile is required to be subjected to a larger tensile stress.

Bearing capacity mechanisms for pipes buried in sand

This paper presents results of scaled physical model tests performed to measure the reaction developing on a rigid pipe buried in dry sand when the pipe is subjected to vertical downwards movement relative to its surrounding soil. The aim of this experimental study is to evaluate the efficacy of methods used to determine the properties of vertical bearing springs, an integral part of beam-on-nonlinear Winkler spring models used for the analysis of buried pipelines subjected to permanent ground displacements. We show that bearing capacity formulas used in practice to estimate the ultimate reaction developing on buried pipes may provide reasonably accurate estimates, provided that they are used together with sand friction angle values that account for the fact that granular materials do not obey an associative flow rule, and with bearing capacity factors compatible with the mode of sand failure observed in the tests. We also provide evidence suggesting that laying pipes in loose sand backfills does not have a beneficial effect on the reaction developing on the pipe, compared to medium dense sand, and we recommend against using loose sand material properties for the estimation of the properties of vertical bearing springs.

Experimental study on the pullout behavior of scrap tire strips and their application as soil reinforcement

The recycling and reuse of scrap tires is a popular area of study in sustainability-driven pavement development. However, several common methods of using scrap tires cannot take advantage of their residual performance. This study examines cutting scrap tires into strips and applying them for soil reinforcement. Pullout performance is an important index for evaluating geotechnical materials’ interface characteristics, but the pullout performance of scrap tires under multi-factor conditions has not been comprehensively studied. Pullout tests for single tire strips and tire strip meshes under different normal stresses were carried out to explore their interface characteristics. The results showed that the equivalent friction angle at the tire strip-sand interface is 68.1% to 71.5% greater than the internal friction angle of sand, indicating that there is an interlocking effect between the tire strip and the sand, which mobilizes pullout resistance to external tension. The processed mesh tire strip provides greater pullout resistance due to the bearing resistance of the transverse member. Comparing the experimental values of the transverse member end resistance to the calculated values from three failure models, the experimental values fall between the calculated values for the general shear failure mode and the modified punching shear failure mode. This study suggests the feasibility of processing scrap tires into strips and applying them as soil reinforcement.

Relation between the Friction Angle of Sand at Triaxial Compression and Triaxial Extension and Plane Strain Conditions

The strength of sand is usually characterized by the maximum value of the secant friction angle. The friction angle is a function of deformation mode, density, and stress level and is strongly correlated with dilatancy at failure. Most often, the friction angle is evaluated from results of conventional compression tests, and correlation between the friction angle of sand at triaxial compression and triaxial extension and plane strain conditions is a vital problem of soil mechanics. These correlations can be obtained from laboratory test results. The failure criteria for sand presented in literature also give the possibility of finding correlations between friction angles for different deformation modes. The general stress-dilatancy relationship obtained from the frictional state concept, with some additional assumptions, gives the possibility of finding theoretical relationships between the friction angle of sand at triaxial compression and triaxial extension and plane strain conditions. The theoretically obtained relationships presented in the paper are fully consistent with theoretical and experimental findings of soil mechanics.

Review of torque models for offshore helical piles

Helical (or screw) piles, sometimes defined as anchors, are a piled system consisting of one or multiple helices welded along the shaft. Piles are installed by applying a torque to the shaft. The pile is rotated into the soil and the rate of advancement should be an amount equal to the pitch for each rotation in order to minimize the disturbance of the original soil. Torque is maybe the most important parameter to be assessed during pile installation. In fact, torque and uplift capacity are directly proportional. Generally, torque depends on the soil conditions and on the geometrical features of the pile. Torque increases with sand density, installation depth, friction angle of sand, pile shaft and helix diameters. The geometry of the pile has a strong influence on the torque, the larger the helix-to-shaft ratio is, the larger the torque will be. In offshore applications helical piles are being considered as a valid alternative. However, one of the issues is still related to the assessment of the installation torque values. Several torque models have been considered and critical evaluated. Some simple comparisons among selected torque models have been also done and discussed.

Sand–concrete interface response: The role of surface texture and confinement conditions

Sand–concrete interface direct shear tests were used to investigate the effects of surface roughness, surface waviness, mean sand diameter and relative density on interface strength and behavior under different confinement conditions. Extreme concrete surface textures, including smooth, rough and rough–wavy textures, were reproduced. Surface plowing was assessed via image analysis, laser scanning and extended multifocal micrographs. The experimental results showed that smooth concrete surfaces exhibited high values of interfacial–to–internal friction angle ratios, ranging 88–90%, due to the angular shape of sand particles. The rough concrete surfaces generated higher interface strength than smooth concrete surfaces; however, the interface strength was still inferior to the surrounding sand strength. Surface plowing, which identified a mixed shear plane at the sand–concrete interface, was developed as particles were detached from the surface, thus inhibiting the interface friction angle from reaching the sand friction angle. Higher sand–concrete interface strength was achieved as surface waviness increased, and interface friction angles greater than the surrounding sand friction angle were reached. Under a constant normal stiffness condition, significantly high interface strength is achieved due to the increase of the current normal stress, which was directly influenced by the initial normal stress, stiffness, surface roughness, mean sand diameter and relative density; surface waviness did not have a marked effect on the normal stress variation. Based on these results, multiple regressions were proposed to estimate the sand–concrete interface strength by the interfacial–to–internal friction angle ratio and the effect of the constant normal stiffness condition.

Three-dimensional analysis of vertical square anchor plate in cohesionless soil

ABSTRACTVertical anchor plates are often provided to increase the performance of various geotechnical engineering structures such as sheet pile walls, bulkheads, bridge abutments and offshore structures. Hence, the safe design of such structures needs a better understanding of the 3D behaviour of the anchor plate. This paper presents and discusses the results obtained from a series of 3D finite-difference analyses of vertical square anchor plate embedded in cohesionless soil. The 3D model is found to closely predict experimental pullout load–displacement relationship. The failure mechanism observed in the numerical model is found to be very similar to the failure reported in experimental studies. For a given embedment depth, the stiffness of the breakout factor–displacement response substantially reduces with increase in anchor plate size. However, the ultimate reduction in anchor capacity is found to approximately 8% with an increase in anchor size from 0.1 to 1 m. Numerical analysis reveals that at deeper embedment depth, the friction angle of sand is the critical parameter in enhancing the performance of anchor plate. The obtained 3D model results are then compared with the published results and are found to be reasonably in good agreement with each other.

Ultimate Uplift Capacity of Bell-Shaped Anchor in River Sand Using Finite Element Software “ABAQUS”

A 2-dimensional axisymmetric finite element analysis has been carried out to determine the ultimate uplift capacity of bell-shaped anchor embedded in river sand. Seven types of belled anchors with varying bell diameter (0.125 m–2.0 m) have been chosen in the present investigation. Anchor has been considered as a linear elastic material and the sand as an elasto-plastic material. General purpose finite element software ABAQUS has been used for the finite element analysis. Results obtained from the numerical analysis have shown that increase in the embedment depth (H) to bell diameter (D) ratio increases the values of ultimate uplift capacity of anchor irrespective of friction angle, ϕ and anchor diameter. In the present study, the scale effect is found to have a large influence on the calculated breakout factor (Fq) irrespective of the values of H/D ratio of anchor and also friction angle of sand. Based on the data obtained in the present numerical analysis, a non-linear power model has been developed for estimating Fq in terms of H/D ratio and tanϕ. The developed power model has been found to be very much useful within the range of H/D ratio from 0.5 to 5.0 and the range of ϕ from 32° to 43°.

Estimating in situ relative density and friction angle of nearshore sand from portable free-fall penetrometer tests

The friction angle of sand in the nearshore zone of Cannon Beach, Yakutat, Alaska, was estimated from the deceleration measured by a portable free-fall penetrometer (PFFP) at 72 test locations. A correlation between the relative density and PFFP’s maximum deceleration was developed from controlled PFFP deployments into sand of different relative densities. Two approaches were tested: (i) a correlation between relative density and friction angle and (ii) bearing capacity theory. For the former, laboratory vacuum triaxial tests were performed to adjust an existing correlation between relative density and friction angle for the tested nearshore sediments. In situ peak friction angles were then determined using this adjusted correlation and estimates of relative densities. The resulting in situ relative density and friction angle varied between 32%–88% and 44°–56°, respectively. Two bearing capacity–based methods suitable for shallow penetrations were tested. For this approach, equivalents of static cone resistance were determined from the measured decelerations considering the strain rate effect. A range of empirical strain rate coefficients K = 0.1–1.5 were tested. A K value between 0.2 and 0.4 yielded matching results between the two approaches. The estimated friction angles agreed well with expected values and may be applied to problems of sediment transport or early site assessment.

Finite-Element Limit Analysis of Strip and Circular Skirted Footings on Sand

The lower- and upper-bound theorems of the limit analysis have been used in conjunction with finite elements and second-order cone programming (SOCP) for determining the bearing capacity of strip and circular skirted footings on sand. The analysis follows the Mohr-Coulomb’s yield criterion and the associated flow rule; sand is not usually considered to obey this rule, but the results of using it are discussed. The friction angle of sand was varied between 30 and 45°, and the depth (Ds) of the skirt increased from 0.25 to 2B; here B implies: (1) the width of a skirted strip footing, and (2) the diameter of a circular skirted footing. The results are expressed in terms of the bearing capacity ratio (BCR): the ratio of the bearing capacities of a skirted footing to that of the surface footing, with the same value of B but without any skirt element. The results reveal that the magnitude of the BCR increases quite extensively with an increase in the value of Ds/B. The skirted footing was found to be especially quite advantageous for loose sand. With the same Ds/B, the BCR for a circular skirted footing was found to be substantially greater than that for the strip skirted footing.

Impact force to a rigid obstruction from a granular mass sliding down a smooth incline

The impact force to a rigid obstruction from a granular mass sliding down a smooth incline provides insights into the solid-like and fluid-like behaviors of granular avalanches and useful information for risk assessment and engineering design against landslides. In this study, a series of 2-D flume tests were performed to systematically investigate the effects of inclination angle, sliding distance, and initial relative density on the flow front velocity and impact force on a rigid obstruction. The experimental results show that for inclination angles smaller than the critical state friction angle of sand, an increase in the sliding distance and/or initial relative density results in smaller impact forces; for higher inclination angles, the trend is reversed. Based on the experimental results, an analytical equation is proposed to estimate the flow front velocity and an empirical approach is presented to estimate the maximum impact force based on elastic solid and hydrodynamic methods. The proposed equations are found to provide more accurate predictions for the maximum impact force than similar equations in the literature.

Upper Bound Analysis of the Effect of Footing Roughness on Nγ and the Failure Mechanism of a Strip Footing

The effect of footing roughness on the bearing capacity factor Nγ and failure mechanism of a strip footing on pure sand were examined using an upper bound finite element method with rigid translatory moving elements (UBFEM-RTME). The analysis was performed with different combination values of the footing–sand friction angle (δ) and the sand friction angle (ϕ). The magnitude of Nγ is found to continuously increase with increasing δ/ϕ and ϕ. The obtained failure mechanism primarily consists of a completely curved trapped wedge and a mesh-like failure zone, with the exception of the case where δ/ϕ = 0. The sizes of the failure zone and the curved wedge, briefly by four introduced geometric parameters, increase with an increase in δ/ϕ and ϕ. The values of δ/ϕ exhibit a particularly pronounced effect on Nγ and associated failure mechanism, especially for high values of ϕ with small values of δ/ϕ. The present results match quite well with those results available in the literature.

Relation between the critical state friction angle of sands and low vertical stresses in the direct shear test

In this study, the critical state friction angle in a direct shear box was tested at vertical effective stresses between 4 kPa and 150 kPa for seven sands of different origins. The results show a stress dependency on the angle of friction at low vertical stresses, and that the critical state friction angle decreases with increase in the vertical effective stress. The largest drop occurs for vertical effective stresses between 4 kPa and 50 kPa and varies between 4° and 10° depending mostly on the shape of the sand particles and the difference in the extreme void ratios.

A Simple Method for Assessing the Peak Friction Angle of Sand at Very Low Confining Pressures

Abstract This article presents a simple experimental method that may be used to assess the peak friction angle of sand at very low effective confining pressures (i.e., <10 kPa). Soil strength at very low confining pressures is important to a variety of geotechnical problems, including small-scale 1-g physical modeling and micro-gravity environments. It is often very difficult to assess friction angles at very low confining pressures in conventional element tests because some factors, such as specimen self-weight and machine friction, become significant. Currently, there are no published methods available to measure the peak friction angle of sands below a mean effective stress at failure of about 6 kPa. To address this need, a simple tilt test method is proposed that involves preparing a soil to a specified relative density within a steel mold and then tilting the mold to induce a shallow slope failure. Based on infinite slope analysis, the tilt angle at which the slope fails is equal to the peak friction angle. A modified stress-dilatancy relationship is also proposed that can be calibrated for a specific soil using a combination of tilt test and triaxial test data. This relationship can be used to predict peak friction and dilation angles over the low stress range.

Determination of the presence of microstructure in a soil using a seismic dilatometer

This article shows an approach for investigating the presence of microstructure in a soil based on the results obtained by seismic dilatometer (SDMT). Three main parameters are considered: intermediate dilatometer test (DMT) parameters material index (ID) and horizontal stress index (KD) and small strain stiffness (G0) obtained by shear wave velocity (Vs) measurements. The approach is engineering-oriented since it is simple, fast, inexpensive, and based directly on in situ measurements. We found that with increasing microstructure (cementation and aging) the ratio of measured to estimated G0 increases, which could be used to improve interpretation of empirically determined geotechnical parameters from DMT results. Applications of a DMT-based, CPT-based and Vs-based correlations for determination of effective peak friction angle of sands, with and without presence of microstructure, are evaluated. Finally, we propose an approach to reducing the influence of microstructure on K0–KD correlation in a clay.

Effect of Various Lateral Boundaries on Bearing Capacity of Soilbag

Soilbags, namely geotextile bags filled with soil or soil-like materials, are commonly used in improving the bearing capacity of traditional earthworks. The paper aims to examine the effect of various lateral boundaries on the maximum bearing capacity of soilbag under vertical loading. In this research, the maximum bearing capacity of soilbag with lateral semi-circular boundary was examined using the analytical method. Then, the maximum bearing capacity of soilbag with lateral semi-elliptical boundary was presented. The result showed that by increasing of the semi-elliptical eccentricity and internal friction angle of sand, the vertical bearing capacity of soilbag increased under external loads.

Lateral Response of Contiguous Pile Wall Subjected to Staged Excavation: Physical and Numerical Investigations

In this paper, the lateral response of a contiguous pile wall retaining system under staged excavation is investigated using physical modelling. The effect of pile stiffness on pile wall deformation is studied by changing the diameter of pile. Numerical simulation of the physical response of the pile wall is studied using the finite element program PLAXIS-3D. Results of the finite element (FE) analysis are in good agreement with the experimental results. Sensitivity analysis is carried out to evaluate the effect of unit weight and friction angle of sand on the lateral response of the pile wall. It is found that with increase in the unit weight of sand, the deformation of pile wall increases and with increase in the friction angle of sand, the deformation of pile wall reduces. Experiments were performed on the sand to evaluate the unit weight, friction angle, Young’s modulus and Poisson’s ratio of sand corresponding to the four different values of the relative density (i.e. Dr = 15, 35, 65 and 85%). The response of the pile wall under stage excavation with change in the relative density of sand is studied by performing FE analysis. It is found that with increase in the relative density of sand, the deformation of pile wall reduces. The interpretation of modulus of elasticity of sand from the modulus of subgrade reaction evaluated from the plate load test is also presented. Based on the results of the FE analysis, it is noted that the finite element method (FEM) can be used for the real-time simulation of the lateral response of the pile wall systems.

Peak punch-through capacity of spudcan in sand with interbedded clay: numerical and analytical modelling

The presence of a thin soft clay layer inside a bed of sand may significantly reduce the bearing capacity of the sand layer, imposing a risk of punch-through failure. In this paper, finite element (FE) simulations are reported using a hardening soil (HS) model for sand. The FE model has been verified against centrifuge tests involving loose and dense sand layers overlying clay soil. The effects of sand stiffness, foundation roughness, sand friction angle, undrained clay strength, clay strength nonhomogeneity, and sand and clay layer geometries on the foundation peak capacities have been studied. Punch-through failure is initiated with an inclined sand plug being sheared and pushed into the underlying soft clay. During punch-through, the clay layer fails due to significant radial squeezing. Existing analytical models do not capture the combined failure mechanism of sand shearing and clay radial squeezing. A new analytical model is developed to estimate the peak punch-through capacity of a spudcan in sand with an interbedded clay layer, showing improved performance over the current industry guidelines.

Effect of granulated rubber on shear strength of fine-grained sand

Review of the literature related to the mixture of shredded tire and sand shows that, despite of the increase in shear strength due to addition of tire chips, granulated rubber causes reduction in shear strength of sand. In this study, the shear behavior of mixtures of fine-grained sand and 1–5 mm granulated rubber is investigated. Sixty direct shear tests were conducted on sand–granulated rubber mixtures with various rubber contents (0%, 5%, 10%, 20% and 30%) at different relative densities (50%, 70% and 90%) and different normal stresses (34.5 kPa, 54.5 kPa, 74.5 kPa and 104.5 kPa). The obtained results show that the granulated rubber improves the shear strength of fine-grained sand at medium relative density and low normal stress. The degree of improvement in shear strength is a function of rubber content, relative density and normal stress. The results show that at relative density of 50%, by adding 5% granulated rubber, the internal friction angle of sand increases from 35.1° to 39.2°. However, at relative densities of 70% and 90%, addition of granulated rubber to sand decreases its internal friction angle. The results also indicate that the behavior of sand becomes more ductile with increasing granulated rubber content. Adding granulated rubber leads to greater yielding strain and less tangent stiffness of sand. The maximum dilation angle decreases with the decrease in granulated rubber content. The stress ratio of sample at critical state (ψ = 0°) decreases with increasing granulated rubber content.