Comparison of shear strength of sand backfills measured in small-scale and large-scale direct shear tests (original) (raw)
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Bulletin of Engineering Geology and the Environment, 2001
The paper records the in¯uence of the shape and the percentage of gravel on the shear strength/frictional angle of sand and gravel mixtures using direct shear tests. The shear strength is mainly derived from the frictional forces developed due to sliding and interlock; they depend on the maximum particle size and shape, the uniformity coef®cient, density and the effective normal stress. As the size of material in a mixture is variable, the shear strength also depends upon the ratio of the specimen diameter to the maximum particle size. In this study, two different shapes of limestone were used, angular and rounded, and the maximum gravel size was 6.3 mm in diameter. Air-dried samples were used in the tests. It is concluded that the shape and percentage of gravel have an important in¯uence on the shear strength properties.
Determination of Shear Strength Values for Granular Backfill Materials Used by Wisconsin DOT
2007
This research was funded through the Wisconsin Highway Research Program by the Wisconsin Department of Transportation and the Federal Highway Administration under Project # 0092-05-08. The contents of this report reflect the views of the authors who are responsible for the facts and accuracy of the data resented herein. The contents do no necessarily reflect the official views of the Wisconsin Department of Transportation or the Federal Highway Administration at the time of publication. This document is disseminated under the sponsorship of the Department of Transportation in the interest of information exchange. The United State Government assumes no liability for its contents or use thereof. This report does not constitute a standard, specification or regulation.
Determination of the Effect of Soil Particle Size Distribution on the Shear Behavior of Sand
Journal of Advanced Engineering and Computation
Many geotechnical problems require the determination of soil engineering properties such as shear strength. Therefore, the determination of the reliable values for this parameter is essential. For this purpose, the direct shear test, as one of the oldest tests to examine the shear strength of soils, is the most common way in laboratories to determine the shear parameters of soil. There are far too many variables that influence the results of a direct shear test. In this paper, a series of 10 × 10 cm direct shear tests were carried out on four different poorly graded sands with different particle size distributions to determine their shear behaviors. Four different poorly graded sands with a different median diameter or medium value of particle size distribution (D50) (0.2, 0.53, 1.3, and 2.3 mm) has been selected, and about 40 direct shear tests were conducted. It was concluded that a soil’s friction angle is affected by coarse-grained material. Accordingly, sandy soils with bigger ...
Geological and Physical Factors Affecting the Friction Angle of Compacted Sands
Journal of Geotechnical and Geoenvironmental Engineering, 2008
This study evaluated the effects of physical characteristics and geologic factors on the shear strength of compacted sands from Wisconsin that are used as granular backfill for mechanically stabilized earth walls and reinforced soil slopes. Physical properties and shear strength were determined for 30 compacted sands collected from a broad range of geological deposits. Relationships between strength/deformation behavior, geologic origin, and physical properties were used to categorize the sands into four friction angle groups. Sands with the lowest friction angle are derived from weathering of underlying sandstones, and tend to be medium-fine, well-rounded, and poorly graded sands. Sands with the highest friction angle are from recent glacial activity and tend to be coarser grained, well-graded, and/or angular sands. A multivariate regression model was developed that can be used to predict friction angle ͑Ј͒ of compacted sands from comparable geological origins based on effective particle size ͑D 10 ͒, maximum dry unit weight ͑␥ dmax ͒, and Krumbein roundness ͑R s ͒.
Effects of particle characteristics on the shear strength of calcareous sand
2017
The paper presents a 3D analysis (3DA) to evaluate the particle shape and size of silica and calcareous sands. The particles of calcareous sand are found to be less spherical than those of silica and crushed calcareous sands. Furthermore, the results indicate that the average sphericity (SPH) holds an inverse relationship to the particle size. However, in each sample the larger particles have higher SPHs than the smaller particles. In addition, the 3DA yields smaller particles than the sieve analysis (SA). Owing to a variety of particle shapes, causing particle interlocking, especially for calcareous sand, the particles cannot pass through the sieves by their shortest dimension. This paper discusses the effects of particle characteristics on the shear strength properties. Although the calcareous sand shows higher peak and residual shear strength properties, it tends to reach a lower shear strength at a small shear strain and a lower dilation than the silica sand. Moreover, the findi...
Effect of Gravel Content on the Shear Behavior of Sandy Soils
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Most of the previous constitutive models used for investigation of the shear behavior of sandy soils have been developed without consideration of the oversize particles. The size of experimental samples is an important limitation in this case. In this research a laboratory study has been planned to investigate the shear strength of sandy soils containing different gravel contents. The tests conducted using a large scale direct shear apparatus with a 300 mm ×300 mm shear box. All the tests have been performed on dry samples in drained condition. The gravel contents of 20, 40 and 60 percent were used in sample preparation. The tests conducted in three different densities of 35, 60 and 85 percent and three different surcharges of 1.5, 3 and 4.5 kg/cm 2 . It was observed that the increase in gravel content and relative density results to an increase in the shear strength and dilation of the mixture. The gravel particles are floating in sandy soil matrix in lower gravel contents. As a result the shear behavior is mainly controlled by the sandy matrix behavior. However, as the gravel content increases in sandy soil, the non floated state of the gravel controls the behavior of sand-gravel mixture.
Influence of Particle Morphology on the Friction and Dilatancy of Sand
Journal of Geotechnical and Geoenvironmental Engineering, 2018
The shear strength of granular materials is influenced by many factors that include particle morphology, gradation, mineralogy, fabric, material density, applied stresses, boundary conditions and loading path. In recent years, 3D imaging techniques such as computed tomography enabled researchers to quantify sand particle morphology based on 3D images of particles. This paper presents an experimental investigation of the influence of particle morphology (i.e., surface texture, roundness, form, and sphericity), specimen density, and initial mean stress on the shear strength properties of dry specimens of silica sands and glass beads. Spherical glass beads as well as three other sands (with different morphologies) with grain sizes between US sieve #40 (0.42 mm) and sieve #50 (0.297) where tested at 15, 50, 100, and 400 kPa confining pressures under axisymmetric triaxial compression. The influence of particle morphology on stress-strain response, volume change behavior as well as peak state and critical state (CS) friction, and dilatancy angles was examined. The triaxial test results of Toyoura and Hostun RF sands collected from the literature was included in the analyses. Simple statistical models capable of predicting the peak and CS friction angles as well as dilatancy angle by providing particle surface texture, roundness, sphericity, relative density and initial mean stress as input parameters were developed. The results show that morphology parameters highly influence dilatancy angle, CS and peak state friction angles.
Early Age Mechanical Behavior and Stiffness Development of Cemented Paste Backfill with Sand
2012
Rapid delivery of backfill to support underground openings attracted many mines to adopt paste backfilling methods. As a precaution to prevent liquefaction and to improve the mechanical performance of backfills, a small portion of a binder is added to the paste to form the cemented paste backfill (CPB). Recently, adding sand to mine tailings (MT) in CPB mixes has attracted attention since it enhances the flow and mechanical characteristics of the pastefill. This thesis investigates the effects of adding sand to CPB on the undrained mechanical behavior of the mixture (CPBS) under monotonic and cyclic loads. Liquefaction investigations took place at the earliest practically possible age. Beyond this age, the present research focused on characterizing the evolution of stiffness and obtaining the values of the stiffness parameters that could be useful for designing and modeling backfilling systems.The liquefaction investigation involved monotonic compression and extension triaxial tests...