Initial Relative Density Research Articles

Laboratory study of shear strength response of Chlef natural sand: Effect of saturation

The study of the unsaturated soils is a very complex field to which several researches in laboratory and on site are directed these last years. An experimental study aims to quantify the influence of the Skempton coefficient B characterizing the degree of saturation on the behavior of the granular sand to the liquefaction resistance of sand. The study is based on undrained triaxial tests performed on natural Chlef sand carried out at an initial relative density Dr = 50% under a confining pressure of 50, 100 and 200 kPa for Skempton coefficient B = 10 to 92%. The results of the tests show that an increase of confining pressure leads to an increase of the shear stress of the samples. For the lower value of the degree of saturation results of our findings indicate an increase of the resistance to liquefaction; our results are in good agreement with others observed in several research projects conducted with other sands. The increase of Skempton coefficient B induces an increase of pore water pressure and a decrease of the shear strength. The pore pressure (u) increases with an exponential manner with the increase of the degree of saturation; while the residual shear strength (Rs) decreases with logarithmic manner with the increase of degree of saturation (B).

Distinct element analysis of the microstructure evolution in granular soils under cyclic loading

Granular soils exhibit very complex macroscopic mechanical responses when subjected to cyclic loading. To enhance the understanding of the cyclic behaviors of granular soils and provide significant insights into the constitutive modelling, this paper investigates the microstructure and its evolution under cyclic loading using distinct element method (DEM). A series of cyclic triaxial tests in drained conditions were numerically carried out on the DEM specimens with two different initial relative densities. At particle scale, both the coordination number and contact fabric were investigated to study the microstructure evolution of the granular soils. The simulations indicate that the evolutions of coordination number and contact fabric are highly dependent on the relative density and cyclic mode. A threshold value for the fabric anisotropy exists under cyclic loading, and once the threshold is reached, the internal structure of the specimen tends to be unstable, and the critical coordination number is reached at the specimen failure. The contact normal fabric tensor is always coaxial with the stress tensor under cyclic loading regardless of the sand relative density and cyclic model. Although there is no unique relationship between the contact normal fabric and stress, a uniqueness relationship between strong contact fabric and stress can be observed.

Investigation of basal friction effects on impact force from a granular sliding mass to a rigid obstruction

Understanding the behavior of rapid granular flow and quantifying the impact force from a granular sliding mass on a rigid obstruction provide useful information for risk assessment and engineering design against rapid flow-like landslides. Basal friction affects the governing mechanisms of rapid granular flow and consequently influences the impact force. This paper presents an experimental and analytical investigation on the effects of basal friction on flow front velocity and impact force from a granular sliding mass to a rigid obstruction. For the experimental investigation, the results of a series of 2-D flume tests with two different basal friction conditions at different inclination angles, sliding distances, and initial relative densities are presented and discussed. It is observed that increasing the basal friction angle induces more shearing within the sand mass and results in a more dominant spreading mechanism, a shallower flow profile, a lower flow front velocity, and a smaller dynamic impact force. For the analytical investigation, the static and dynamic force components are investigated individually and a method for calculating these forces is presented. In this approach, the static force is calculated using the limit equilibrium method and the dynamic force is calculated by considering the reflection of compression shock waves due to impact. This approach allows the material stiffness to be taken into account in the dynamic force calculation. Adding the static and dynamic force components, the instant value of the total impact force can be calculated and an excellent agreement is observed between the calculated and measured impact forces.

Effect of Selective Heating on Formability and Densification of Powder Metallurgy Preforms During Upsetting

In this work, a new method of selective heating is proposed to increase the deformation behaviour of cylindrical sintered aluminium preforms during the process. Initially, cold upsetting is carried out using 0.5 MN hydraulic press machine at 0.1 s−1 strain rate and the failure locations of the preforms are predicted for various initial relative densities with the aspect ratio of 1 during the deformation process. After the prediction of this failure location, various conditions of selective heating are attempted uniformly on the deformed preforms after a certain stage of deformation before the onset of the failure initiation, using portable gas cartridge at a different temperature and time to assess their consequence on formability behaviour. The detailed experimental results are evaluated for the formability of the selectively heated preforms under different variables such as flow stress, relative density, axial strain, formability stress index and stress ratio parameter. As a result, the initiation of failure and its progression can be delayed by selectively heating the samples before the onset of the failure initiation. Selective heating of the failure location may relieve the accumulated stresses and delay the onset of failure to a later strain level thereby increasing the formability of the metal.

Electrically-activated reactive synthesis (EARS) and electro-annealing of Ni/CNT-Al nanocomposite powders

The present paper discusses the electrically activated reactive synthesis (EARS) of Ni/CNT-Al nano-composite powders. The effect of initial relative green density (RGD) on reaction characteristics and resultant microstructure has been investigated in addition to post reaction electro-annealing. Results show that a relative density of 0.67 RGD resulted in the highest combustion temperature and lowest product porosity, while detrimental cracking was observed at the higher RGDs during EARS. Post reaction electro-annealing was also found to promote homogenization and sintering of as-reacted products. Microhardness values as high as ∼250 HV are reported following electro-annealing.

Influence of particle size and gradation on shear strength–dilation relation of granular materials

Upon close scrutiny of data reported in the literature, taking into account particle-scale characteristics to optimize the precision of the well-known empirical Bolton’s equations and imposing particle-size limits on them is recommended. The present paper examines the potential influence of particle size and grading on the shear strength–dilation relation of granular materials from the results of 276 symmetrical direct shear tests. The applicability of physical symmetrical direct shear tests to interpret the plane strain frictional shearing resistance of granular materials has been widely discussed using the discrete element method (DEM) computer code SiGran. Sixteen different grain-size distribution curves of three different materials were tested at different normal pressures and initial relative densities. It is demonstrated that while the contribution of dilatancy to shear strength is not influenced by the variation in the coefficient of uniformity, Cu, in the investigated range, it significantly decreases with increasing mean particle size, D50. The coefficients of Bolton’s equations have been, therefore, adjusted to account for D50. A comparison of the predictions by the proposed empirical formulas with plane strain friction angle, [Formula: see text], and dilation angle, ψ, data from the literature shows that accounting for the grain size yields more accurate results.

Structural Properties Evaluation of Semisolid Extruded Al–Cu–Mg Powder Metallurgy Alloys

Structural properties evaluation of semisolid extruded Al–4Cu–xMg alloy preforms have been performed in the present investigation. Pressureless sintering of Al–4 wt% Cu with varying Mg (0, 0.25, 0.5, 0.75 and 1 wt%) powder mixture was performed in an inert atmosphere. The sintering behavior and mechanical properties of all alloys were investigated at different temperatures and compositions, respectively. The maximum density and hardness (647 MPa) were found in the Al–4Cu–0.5 Mg composition sintered at 550 °C. Semisolid extrusion was carried out on sintered Al–4Cu–0.5 Mg alloys having an Initial Relative Density of 80% and 90% to find the structure–property correlation due to deformation. Extrusion was carried out in between solidus (542.7 °C) and liquidus (662.8 °C) temperatures with different solid fractions, which were derived from the TG/DTA analysis. All experiments were performed with low extrusion ratio of 1.44, strain rate of 0.1 s−1 and die approach angle of 30°. Structure–property correlation study of extruded rod was performed at front end, middle part and rear end to understand the temperature and metal flow profiles during deformation process. There were no visible defects found in the demarcated samples. The presence of Al2Cu precipitate in the extruded alloy was identified by X-Ray diffractometer and scanning electron microscope with energy dispersive spectroscopy analysis. The microstructural evolution was observed in all the extruded bars by optical microscope. Micro-hardness of extruded samples was found to be 1001 MPa, which was almost two times of sintered sample.

Geotechnical characteristics of polystyrene treated sand

Many polymeric materials are recently used in geotechnical practice for enhancing the engineering properties of soils. Among the various polymers, this study aims at investigating the geotechnical properties of silica sand coated with polystyrene(PS), which is rarely studied in geotechnical engineering. The polystyrene coated sand was prepared by polymerizing styrene monomer on the surface of silanized sand with median diameter of 0.467 mm. Testing specimens were prepared at 3 different initial relative densities (30, 50 and 70%) by air pluviation. Comprehensive experiments, including one-dimensional compression test with bender elements and triaxial test, were performed to observe the change in geotechnical properties due to the coating of PS on sand surface. The results demonstrate that the adsorbed polymer plays different roles according to strain levels. At very small strain, the polymer on the sand surface may increase the interparticle contact area by applying additional adhesion force between soil particles, leading to an increase in Gmax. However, with an increase in strain level, the polymer will act as the lubricant between sand particles; therefore, the coated sand can show increased compression index and decreased friction angle.

Shear modulus and damping ratio of a nonplastic silt at large shear strains

Site response analyses and solution of dynamic soil-structure interaction problems need determination of variation of shear modulus and damping ratio with shear strain. Since many studies in literature concern evaluation of behavior of sands and silty sands, a series of cyclic triaxial tests were performed to determine the variation of shear modulus and damping ratio of a nonplastic silt with shear strain. Stress controlled cyclic triaxial tests on silt specimens of initial relative densities ranging among 30%, 50% and 70% were performed. Tests were carried out on identical samples under different CSR levels, and the confining pressure was selected as 100 kPa. Variation of shear modulus and damping ratio of silts with cyclic stress ratio amplitude, relative density and number of cycles were investigated. It was understood that soil relative density and cyclic stress ratio amplitude has a significant influence on shear modulus and damping ratio of silts. It was also observed that, as the cyclic stress ratio amplitude is increased, greater shear modulus and lower damping ratio values were obtained.

Експериментальне дослідження процесу подрібнення твердих побутових відходів під час зневоднення шнековим пресом

Experimental investigation of the milling process of solid domestic wastes during dewatering by the auger press is an urgent scientific and technical task as one of the components for solving the problem of creation of scientific and technical bases for designing highly efficient working bodies of machines for collecting and primary processing of solid domestic wastes. The purpose of the investigation is to determine the regression models of indicators of technological milling process of solid domestic wastes during dewatering in a garbage truck with the auger press from the main parameters of influence. The investigation used the method of analysis of literary sources, the method of sieve analysis, as well as the planning of the experiment by the Box–Wilson method of the second order. The analysis of literary sources on solid domestic wastes management confirmed the need for their milling. There has been conducted the experimental investigation of the milling process of solid domestic wastes during dewatering by the auger press. Adequate quadratic regression dependences of such indicators of the milling process as the residue on the sieve and the energy intensity of milling of solid domestic wastes were obtained from the main parameters of influence, such as average particle size, initial relative density of solid domestic wastes, diameter of the auger core at the last coil. The adequacy of the regression models was verified according to the Fisher criterion and the significance of the regression coefficients by the Student criterion. The obtained regression models can be used to create a methodology for engineering calculations of the parameters of machines and mechanisms for milling solid domestic wastes as a component of the scientific and technical basis of designing highly efficient working bodies of machines for the collection and primary processing of solid domestic wastes. The response surfaces of the target functions is constructed — the residue on the sieve and the energy intensity of milling of solid domestic wastes and their two-dimensional cross sections in the planes of the impact parameters, which allow to clearly illustrate the dependence of these target functions on the individual impact parameters.

Experimental study on mitigation of liquefaction-induced vertical ground displacement by using gravel and geosynthetics

BackgroundEarthquakes in liquefaction-prone areas are frequently followed by the settlement of surface structures due to subsoil liquefaction. This paper aims to study the influence of geosynthetics along with gravel usage to reduce the vertical soil displacement caused by liquefaction using a shake table equipment. This influence is analyzed by means of measuring soil acceleration, pore water pressures and vertical soil deformation due to the shaking process.ResultsResults of a series of 1-g shaking table tests which have been conducted in different initial relative densities which are 50% (loose sand conditions) and 90% (dense sand conditions) to evaluate the performance of proposed mitigation against settlement problem are presented. It is found that ground settlement reduced around 11.4 mm for loose sand conditions, from 20.9 mm in the case with no countermeasure (Case 1) to 9.5 mm in the Case reinforced with gravel and geosynthetics Type II (Case 4). Correspondingly, for dense sand states, the settlement decreased by about 1.8 mm, from 5.6 mm in the Case 1 to 3.8 mm in Case 4. Moreover, a differential settlement between loose sand and dense sand conditions decreased as well, around 9.6 mm, from 15.3 mm in the Case 1 to 5.7 mm in Case 4.ConclusionsBy conducted a series of shake table tests, it is confirmed that the vertical ground displacement decreased by the use of geosynthetics and gravel up to 54% and 32% for loose sand and dense sand states, respectively. Furthermore, test results also show that there is a decrease in the differential settlement between loose sand and dense sand conditions, around 62%.

Effect of past history on liquefaction resistance of level ground in shaking table test

In recent years, many researchers have discovered that using relative density as a single index parameter, cannot be correlated well with liquefaction resistance. In general, it is also governed by past-liquefaction history. To study the effect of liquefaction history on liquefaction resistance of level ground in more detail, a series of shaking table tests was performed on loose and dense silica sand models. Small base acceleration was implemented on loose models and then increased up to 1000 gal. Ground motion, behaviour and relative density change during each liquefaction stage were monitored. The results showed that liquefaction history can greatly affect future liquefaction resistance. After being subjected to repeated liquefaction, loose sand models stopped liquefying at 1000 gal with a relative density of approximately 80%, regardless of the initial acceleration. However, the dense sand model with initial relative density of 80% subjected to the initial acceleration of 700 gal continuously liquefied until reaching a relative density of nearly 100% at 1000 gal.

Shear modulus of sand–tyre chip mixtures

This paper presents experimental results on the shear modulus of sand–tyre chip (STCh) mixtures. A series of bender element tests was carried out on specimens of sand mixed with varying proportions of tyre chips (TCh). Tests were carried out on STCh mixtures at a constant initial relative density of 50% for different initial effective confining pressures. The bender element test results indicate that the maximum shear modulus of the STCh mixtures increases with effective confining pressure and decreases with the gravimetric proportion of TCh, which ranged from 23 to 138 kPa and 0 to 40%, respectively. However, the strain-controlled cyclic triaxial test results show that the shear modulus at large shear strains decreases with increasing single-amplitude shear strain as a function of the proportion of TCh in the mixture. The lower the proportion of TCh, the larger the degradation observed. The modified Hardin and Drnevich mathematical formulation adequately captures the variation in shear modulus of the STCh mixtures for a wide range of shear strain amplitudes.

On the influence of platy shell particles on the cumulative deformations in sand under drained high-cyclic loading

Mixtures of a fine sand with platy shell fragments have been tested under drained monotonic and high-cyclic loading. The content (0 to 40 %) and the size of the platy shell particles in the mixtures were varied. Comparative tests have been also performed on a mixture containing 40 % coarse sand and gravel particles instead of the shells. In the cyclic tests different stress amplitudes, initial relative densities and average stresses have been tested on the various mixtures. The strain accumulation rates were found to increase with growing content of shell particles. This can be primarily attributed to the more well-graded grain size distribution curves of the sand-shell mixtures. Particle breakage effects were almost absent in the cyclic tests as demonstrated by sieve analysis. Dependencies between the parameters of a high-cycle accumulation (HCA) model and the content of shell particles are analyzed. Amongst others, an extraordinary low dependence of the strain accumulation rate on strain amplitude (parameter Campl<1) has been observed for larger amounts of shell particles in the mixtures.

Drained analyses of cylindrical cavity expansion in sand incorporating a bounding-surface model with state-dependent dilatancy

• Governing differential equations of the cylindrical cavity expansion problem are solved as an initial value problem . • Rigorous definitions of the invariant stresses permit the examination of the effect of k 0 value. • Model parameters that are of paramount importance for the cylindrical cavity expansion analyses are presented. This paper presents a semi-analytical drained solution for cylindrical cavity expansion in sand. By introducing an auxiliary variable, defined as the ratio of the original position to the current position of a material particle, the governing differential equations of the cylindrical cavity expansion problem can be transformed into a group of first-order ordinary differential equations. These equations are solved as an initial value problem by incorporating a bounding-surface model with state-dependent dilatancy. This approach does not require the division of the material around the cavity into an elastic zone and a plastic zone. The state-dependent dilatancy model employed in this study allows the investigation of the effects of the initial relative density and mean normal stress of the sand, whereas the rigorous definitions of the invariant stresses permit the examination of the effect of the initial ratio of the horizontal stress to the vertical stress. Moreover, the model parameters that are of paramount importance for the cylindrical cavity expansion analyses are determined via comprehensive parametric studies.

Activation Energy and Mechanism of the Molybdenum Disilicide Sintering Process

This paper presents dilatometric analysis data for the sintering of off-the-shelf molybdenum disilicide (MoSi2) powder prepared by magnesiothermic synthesis. We have obtained continuous shrinkage curves for MoSi2 powder compacts with an initial relative density of 70% at different heating rates: 5, 10, 20, and 30°C/min. From a quantitative analysis of densification curves for the compacts, the activation energy for the initial stage of sintering has been determined to be Q = 695 kJ/mol. It has been shown that the dominant process in the initial stage of MoSi2 powder sintering is volume diffusion from grain boundaries and surfaces.

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.

Improvement of Coarse Sand Engineering Properties by Microbially Induced Calcite Precipitation

This paper investigates the effectiveness of microbially induced calcite precipitation method in improving the strength and stiffness of coarse sands using treatments based on a four-phase percolation technique. An increase of biochemical treatment cycles was associated with increased deposition of calcium carbonate (CaCO3) and consequently an increase in compressive strength. Furthermore, the bio-cemented coarse sand retained reasonable porosity and permeability, which should allow dissipation of pore water pressure if required. The results also establish a correlation between the strength gained and stiffness of the bio-cemented coarse sand with the increase in the amount of deposited CaCO3, initial relative density and dry density. Scanning electron microscopy and electron dispersive spectroscopy analysis indicate that the inter-structure of the bio-cemented coarse sand tend to change in morphology based upon the number of biochemical treatments used.

El potencial de licuefacción de las mezclas arena-limo bajo Cargas estáticas

DOI: 10.7764/RDLC.17.2.196 As a part of an on-going research program on the mechanical instability of granular soils in our laboratory, defined contents of sand and silt in soil mixtures are studied through the triaxial apparatus, full range of initial relative density states (loose, medium and dense) are experimented and analyzed. In this work, the investigated soil is collected from different depths of Kharouba coastal region in the province of Mostaganem (Lat: 35.96° N; Long: 0.1° E). It consists mainly of sand with a low percentage fraction of non-plastic silt, below 30%. The coastal region of Mostaganem (Kharouba) is very close to the harbor and it experiences a significant seismic activity, then it would be very susceptible to the phenomenon of liquefaction under static or dynamic loads, hence the importance and relevance of this study which introduces the identification parameters of this instability due to liquefaction. Undrained triaxial tests under monotonic loading are carried out in the laboratory on saturated reconstituted samples. These results are presented and analyzed. New parameters for assessing the influence of fines content and density state on the behavior of heterogeneous soils (sand-silt) will be introduced to the liquefaction. New correlations expressing the undrained critical shear with these new parameters will be deducted for full range of initial relative density (loose, medium and dense) for design purpose.

Determination of Minimum Void Ratio of Crushed Rock Sand Using a Vibrating Table Test

The use of crushed rock sand in construction projects has recently increased. Because the crushed rock sand has not undergone any weathering processes, it has a higher breakage potential than that of natural sand. This experimental investigation aims at developing a reliable method for the determination of the minimum void ratio (emin) of crushed rock sand using a vibrating table test. The minimum void ratios of one natural sand (Toyoura sand) and five commercially available crushed sands were measured using both vibrating table and pluviation tests. Additionally, the vibrating table tests were repeatedly conducted on the same soil specimen to measure both the emin and relative breakage as a function of the number of retests. The results of this study demonstrate that a vibrating table test induces noticeable breakage of the tested crushed sands, regardless of the initial relative densities and operating frequencies of a vibrating table. Therefore, the extrapolating method, which determines the emin of the artificial sand as the y-intercept in the relation between emin and relative breakage, is suggested in this study, and the determined emin values using the suggested method are compared with the measured emin using pluviation tests.