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It is generally accepted that the use of void ratio and bulk density as measures of soil8state have limitations in the case of gap-graded soils as the finer grains may not 9transmit stress. However, hitherto no one has systematically explored whether this 10issue also emerges for soils with continuous gradings. Building on a number of experimental and discrete element method (DEM) studies that have considered the idea of an effective void ratio for gap-graded or bi-modal soils, this contribution extends consideration of this concept to a broader range of particle size distributions. By exploiting high performance computers, this study considers a range of ideal isotropically compressed samples of spherical particles with linear, fractal and gap-graded (bimodal and trimodal) particle size distributions. The materials’ initial packing densities are controlled by varying the inter-particle coefficient of friction. The results show that even for soils with continuous particle size distributions, a significant proportion of the finer particles may not transmit stress and be inactive. Drawing on ideas put forward in relation to gap-graded soils, both a mechanical void ratio and mechanical bulk density that consider the inactive grains as part of the void space are determined. Even for the linear and fractal gradings considered here, the difference between the conventional measures and the mechanical measures is finite and density dependent. The difference is measurably larger in the looser samples considered. These data highlight a conceptual/fundamental limitation of using the global void ratio26as a measure of state in expressions to predict granular material behaviour

Coal fines are small coal particles produced during coal seam gas (CSG) production and may plug fluid flow paths, resulting in significant reduction in CSG productivity. This study aims to employ laboratory experiments to examine coal permeability variation induced by coal fines generation and migration during the dewatering stage. One coal sample from Bowen Basin, Australia, was tested under different pressure differences. The evolution of coal permeability and the amount of produced coal fines were monitored during the experiments. The pressure difference was increased from the initial 0.8 MPa to 1.5 MPa through 7 steps to investigate its impact on the characteristics of coal fines and the corresponding permeability change, and to obtain the critical velocities for a range of particle sizes. Every 5 mL effluent was collected and analysed in terms of particle size distribution and volume. The results revealed that for this sample, the sizes of coal fines ranged from 1 μm to 14 μm. Initially the coal permeability dropped dramatically due to excessive coal fines generation, with 74.1% reduction for the case of 0.8 MPa pressure difference, followed by gradual decline with fluctuations. It was observed that the production of large coal fine particles was accompanied by significant permeability fluctuations. This was attributed to the counteraction between formation damage (cleats plugging and coal fines settlement) and coal fines removal from the samples (widened cleats). Although no clear correlation between particle size and pressure difference was observed, the critical particle size was positively related to the flow velocity. The velocity followed parabolic fashion against the pressure difference. For this sample, keeping the differential pressure between 1.1-1.3 MPa can reduce the permeability damage induced by coal fines. This study delivers fundamental understandings of coal fines generation and migration behaviours during the dewatering stage, which can provide useful guidelines to implement effective dewatering strategies to minimize production loss induced by coal fines.

In this paper, the upgraded Anm model, which places multiple particles into a 3D unit cell, was used to study the microstructural properties of lunar soil simulant. A statistical analysis was performed to study the packing density and shape effects with a large number of modeled particles. The lunar soil simulant JSC-1a was developed to study simulant soil behaviors for large and medium scale engineering studies in support of future human activities on the Moon. Parameters such as particle size distribution, specific gravity, angle of internal friction, and cohesion have all been investigated. However, no research has been performed to explore the microstructural behaviors and their influences on the engineering properties as a whole. As such, Anm model can provide us a useful approach to investigate microstructural features of lunar simulant, e.g. charge contact, lofting, transport, stratification and adsorption. Thus the virtual JSC-1a microstructure can be used to study lunar soil handling, construction, excavation, and transportation. Furthermore, the uniform-thickness shell is a customized parameter to control the minimum inter-particle distances. Integrating this algorithm into individual particles packing, the Anm model can be used to create a virtual lunar regolith to investigate the particle contact charging properties at the individual particle scale. In general, this virtual lunar soil simulant model could provide a broad range of applications to lunar surface missions. It is a potential tool for modeling the behavior of the lunar soils, and accurately predicting the geotechnical properties of lunar soils for lunar base planning and construction.

This paper presents some mechanical test results of a lunar soil simulant, FJS1, to clarify the effect of grain size distribution on bulk mechanical properties of lunar surface soil under low confining pressure. The samples used are the original FJS-1 imitating an average grading of lunar soil, two sieved FJS-1 samples, whose grain sizes are less than 0.1mm and from 0.1 to 0.4mm, respectively. First, the maximum and minimum void ratio tests of those samples revealed both pore-filling effect and inter-granular adhesion effect of fines. Next, according to small-scale triaxial compression tests and self-standing height tests, the internal friction angle ranges from 30 to 50 degrees, and the bulk cohesion is about 0-175(Pa) depending on the void ratio, which are consistent with the previous estimation of typical lunar soil. Finally, based on the experimental results, we propose a simple micromechanics model that describes the experimental results in a consistent manner.

Know-how from terrestrial geotechnical engineering may be applied for a variety of space problems such as the prediction of the soil mechanical response of extra-terrestrial soils, the exploration of near-surface planetary soil, and the movement of vehicles. Penetration testing constitutes a well-established method for the back-calculation of the soil properties. In an initial study, indentation of a rod into granular material placed within a mold has been investigated for variable density states. Regolith simulants, natural soils, and glass have been considered. The test results are presented and key features are elucidated showing that the sole use of the grain size distribution curve as a prediction tool within each subgroup is not appropriate. The effects of the rigid base and the rigid walls are clearly revealed in the response.

In Ontario, underground stormwater detention chamber systems (USDC) are a relatively new alternative to wet detention ponds for the detention and treatment of urban stormwater runoff. Few tools are available for designers to predict the removal of contaminants from USDC. A conceptual model was developed to fill this void and make USDC a more approachable solution to stormwater management. The Model for Underground Detention Sedimentation (MUDS) predicts the removal efficiency of total suspended solids through sedimentation based on the hydraulic properties of USDC. As runoff enters the USDC waves of particles are released, the pathline of these particles are tracked along vertical and longitudinal axes as they move through the USDC to determine whether a given diameter of particle is removed by sedimentation. Based on the particle size distribution and the density of the particles, the mass removal efficiency is determined. The model was found to adequately predict the hydraulics and treatment efficiency of USDC.

The effect of median particle size and breadth of particle sizes in clean sands on the SWCC and the van Genuchten parameters α and n is described. For uniform sands, the air entry suction increases (α decreases) and the steepness diminishes slightly (n decreases) for the drying SWCC as the particles become finer. Increasing the breadth of particle sizes also increases the air entry suction (lower α) and reduces the steepness (lower n) of the SWCC. Breadth of the particle size distribution has a larger effect on steepness and n of the SWCC, and median particle size has a larger effect on the air entry suction and α. Similar effects occur for the wetting SWCC, although the impact on the water entry suction is less than the impact on the air entry suction. The systematic effects of median particle size and breadth of particle sizes on the SWCC are captured in a pedotransfer function (PTF) to estimate α and n for clean sand based on d 60 and C u . Comparison with other SWCC data shows that α estimated with the PTF typically is within a factor of 2 of the actual α and n estimated with the PTF is within ± 2 of the actual n. These findings are applicable to α for sands with nonplastic fines provided the fines content is less than 20%, but apply to n only for sands with negligible fines content. A procedure to convert between van Genuchten and Brooks-Corey parameters for sands is also presented.

In this study, a series of rigid-wall downward erosion tests were conducted to investigate the mitigation effect of microbially induced calcite precipitation (MICP) on soil internal erosion. Sand-kaolin mixture was used in this study, which proves to be internally unstable in terms of particle size distribution. Binary mixture was prepared using dry tamping method. Bacteria and cementation solutions were injected into samples at several phases. For comparison, control samples without MICP treatment were prepared. All samples were subjected to downward seepage flow with incremental flow rates. Evolutions of hydraulic conductivity, effluent kaolin concentration, and total erosion mass were measured against hydraulic gradient and shear stress. Results confirmed that, with MICP treatment, both critical hydraulic gradient and shear stress were significantly increased and erosion mass was reduced under the same hydraulic conditions. © 2014 American Society of Civil Engineers.

Particle morphology is essential to understand and define the mechanical behavior of cohesionless soils. Shear strength of cohessionless soil depends on its various morphological characteristics such as size, shape, surface texture etc. However, there are limited studies available in the literature on the influence of particle size and shape on the shear strength behavior of soil. Moreover, most of the geotechnical soil classification systems including the USCS donot take particle shape into consideration. Therefore, the true role of particle shape on soil behavior remains uncertain. Therefore, the present study attempts to investigate the influence of the particle size and shape on the shear strength of cohesionless soils. The paper describes the effect of particle size and shape on the shear strength of four cohesionless soils including two rock quarry dust.

This paper presents the results from an experimental study of the flexural behavior of a lightly stabilized granular material subjected to different freeze-thaw (f-t) cycles. A granular base material with a reconstituted particle size distribution, stabilized using cement-flyash in a ratio of 3:1 with two different binder contents of 1.5% and 3%, was used to make beam specimens that were molded at an optimum moisture content (OMC) and cured for 28 days. Their flexural properties, such as modulus of rupture (MOR) and flexural modulus, were determined using monotonic third-point loading test after they were subjected to different numbers of f-t cycles. The MOR and flexural modulus values decreased dramatically (by more than 40% of the initial value) after the first f-t cycle and then continued to decrease slightly with increasing numbers of f-t cycles as the moisture content gradually decreased. The relationship between the moisture content and MOR after different f-t cycles showed a different trend than that after different post-compaction moisture content. It is expected that this degradation was caused by the possible expansion of the ice lenses during the freezing phase and changes in the soil matrix.

It has been well established that the mechanical behavior of unbound aggregate materials is strongly influenced by the shape of the particles and the complete grain size distribution (i.e., gradation). This paper presents the use of an image-aided discrete element method (DEM) approach to realistically model the micromechanical interactions of aggregate particles including size and shape effects. A realistic unbound aggregate model is developed from previous studies to simulate triaxial compression tests based on the DEM approach and the innovative use of membrane elements surrounding the cylindrical aggregate specimen in the DEM model. To calibrate the DEM model, six different types of aggregates were used to prepare samples of twenty-one unbound aggregate blends at the same gradation and voids content but different crushed percentages. The shape properties of flatness and elongation, surface texture and angularity were quantified by imaging then correlated to strength and permanent deformation characteristics obtained from triaxial testing. The experimental test results are utilized to determine required parameters for the discrete element model by minimizing the differences between DEM-simulated triaxial shear strength results and experimental ones. It is found that the developed DEM model is not only capable of reproducing the typical shear strength behavior of different unbound aggregate materials with varying shape properties, but also has the potential for optimizing the selection of size and shape properties of various unbound aggregates to achieve desired shear strength (or rutting resistance) and hydraulic behavior for open-graded permeable aggregate base.

The geotextile industry research and development is growing at a fast rate and new products of variable specifications are now available for earthworks and design engineers. The nature of the material as a filter and the engineering properties of the materials used made it possible to explore a wide range of application. The polypropylene is non-biodegradable and can stand aggressive chemical exposure when placed inside a soil media. This research is conducted on a polypropylene geotextile material locally manufactured in order to gauge the retention capacity for a range of opening sizes. Tests were carried out using an erosion plate subjected to controlled flow for a specific period of time. Erosion loss is computed for different products and different soil material. The results were viewed in relation to the soil grain size distribution and the geotextile material physical properties. The data provides helpful guide for the design of erosion control system using typical geotextile material.

Warm mixture asphalt has been used worldwide aiming to save energy and reduce emissions without decreasing in-service performance. In this paper, the influences of conventional physical properties of warm asphalt rubber (WAR) are studied by orthogonal test, analysis of variance (ANOVA), and range analysis for three factors (crumb rubber modifier [CRM] particle size, CRM content, and warm asphalt additive [WAA]), and levels. The results show CRM particle size is the main factor on the effect of nearly all the investigated indexes, especially temperature susceptibility of WAR binders, and the performance of WAR containing 60 meshes is very close with that of 80 meshes. The impact of content of CRM comes second. Besides penetration index, the other performances improve as the content of CRM increases. The high content of WAA is favorable to high temperature and temperature sensitivity as well as bad to low-temperature performance slightly.

Liquefaction of cargo in a bulk carrier can cause the cargo to shift, which in turn can cause a ship to list and eventually can cause the ship to capsize. When liquefaction occurs, a material undergoes a transition from a solid to a liquid state and, in general, it is caused by the pore water pressure increasing above the total stress and overcoming the effects of cohesion, i.e. shear strength becomes negligible. In this paper, a number of iron ore samples, representing loosely the range of iron ore cargos from around the world, are characterised and tested. The grain size distribution and particle density were determined along with the tests which are prescribed by the International Maritime Solid Bulk Cargoes (IMSBC) code to assess the liquefaction potential: the Proctor/Fagerberg test, the penetration test and the flow table test. It is found that the results from these test methods correspond reasonably well, however they are not applicable for all ore types and the conditions at which the tests are performed do not correspond with the conditions encountered in the ship. Therefore one cannot quantify the risk of liquefaction based on the results of these tests alone, and further investigations on the liquefaction mechanism and the factors which influence this process are required. Part of these investigations have shown that the liquefaction behaviour is strongly linked to the grain size distribution, both in terms of particle size and grading. It is anticipated that the permeability, compaction and water retention behaviour are also of influence in determining liquefaction potential and are governed, in part, by the grain size distribution. Examples of these properties are presented, although the experimental programme is still ongoing.

The present study was undertaken to compare angularity, texture, and flat and elongated (F&E) particles of three different types (namely, granite, rhyolite, and limestone) of coarse aggregates. An aggregate imaging system (AIMS) manufactured by Pine Instruments Inc., was used to measure the shape parameters of the aggregates. Comparison of shape parameters was performed by plotting the distribution of different types of angular particles (i.e., rounded, sub-rounded, subangular, and angular), texture particles (i.e., polished, smooth, low, medium, and high roughness) and F&E particles (maximum to minimum dimension ratio = 5:1 and 3:1). In addition, analysis of variance (ANOVA) was conducted to compare the mean of the shape parameters. Results show that no significant difference exists in angularity of different types of aggregates. However, texture was found to be significantly different for the three types of aggregates considered in this study. It was observed that the granite aggregates have the highest texture followed by the limestone and the rhyolite aggregates. The study indicates that aggregates can have same angularity but can differ significantly in texture. The distribution of F&E particles shows that three aggregates had less than 10% and 20% of particles with maximum to minimum dimension ratios 5:1 and 3:1, respectively. It is expected that present study will be helpful in understanding the shape parameters for different types of aggregates.

High temperatures can be very damaging to clays forming part of natural slopes. High temperatures cause cracking of the clays. The cracking is the result of evaporation and shrinkage. The present study deals with the formation and evolution of cracks in clays as result of high temperatures. At the beginning of the desiccation process of a clay, few cracks form. As time passes, these original cracks interconnect producing the complete fragmentation of the clay. At the end of the fragmentation process, the clay is formed of clay fragments of different sizes. This study uses the fractal dimension concept from fractal theory to measure the particle size distribution of the fragments. The fractal analysis was conducted on bentonite clay samples desiccated in the laboratory and on the giant desiccation polygons found in clays forming part of the Great Basin Playas in the United States. These giant desiccation polygons have three very distinctive shapes: regular random, irregular random, and orthogonal polygon. The level of fragmentation of the clays was measured by the fragmentation fractal dimension. The fragmentation fractal dimension was found to be equal to 2.21 for the regular random polygons, 1.96 for the irregular random polygons, and 3.89 for the orthogonal desiccation polygons. The effect of the level of fragmentation on the stability of shallow failures that the desiccated clay areas could develop is also analyzed in this study.

Impinging rocket plumes from spacecraft interact with the lunar regolith surface and release a high velocity particle-spray that is potentially hazardous to surrounding surface structures and surface architecture. Experiments performed at NASA-KSC and the University of Florida provide data on the cratering of a particle bed composed of lunar soil simulant JSC-1A by a turbulent subsonic jet of gas. Cratering experiments were also performed on beach sand, which has a narrower particle size distribution than JSC-1A. JSC-1A contains a wide particle size distribution with a high number of fine particles (20% by volume less than 35 μm). JSC-1A is highly compressible and contains much rougher and more angular particles than beach sand. The differences in the particle properties between JSC-1A and beach sand leads to stark differences in the cratering of the two materials. The cratering of beach sand results in a dual crater shape consisting of a conical outer crater and a paraboloid inner crater. While the jet is impinging on the sand, the crater grows logarithmically with time and the outer crater cycles between the angle of repose and angle of failure as particles are ejected from the inner crater onto the outer crater. The JSC-1A crater is similar to a scour hole in shape, which grows deeper over time, with large chunks of material being eroded by the jet. The growth rate of the crater of JSC-1A is highly dependent on the bulk bed density of the JSC-1A. For the same jet velocity the cratering rate of a bed of JSC-1A with a higher bulk density (more compact) was slower than a bed with a lower bulk density (less compact). Even for a lower jet velocity, the less compact bed can crater faster than the more compact bed. The cratering of a sieved fraction of JSC-1A in the absence of fine particles is studied by sieving to a particle size range of 150 to 425 μm. The cratering of sieved JSC-1A is more similar to the cratering of beach sand than to unsieved JSC-1A indicating that the presence of fine particles in unsieved JSC-1A is the cause for its atypical cratering behavior. 36 Earth and Space 2012 © ASCE 2012

In this paper, the hydration of geosynthetic clay liners (GCL) from underlying subsoils is described. GCL specimens with difference in the type and connection of geotextiles were placed in contact with subsoils that vary in soil grain size distribution and initial moisture contents under simulated field conditions. The rate and degree of hydration of GCLs are well shown to be dependent on the GCL type, grain size distribution, and the initial moisture content of the subsoil. The field exposure conditions such as external loading and thermal cycles are also shown to affect the rate of hydration of the GCL as well as the maximum moisture content attained.

As attention has shifted to the use of monitored natural attenuation to remediate sites contaminated with chlorinated solvents, optical spectroscopic methods have gained attention as a potential means to enable long-term monitoring. However, previous field research has shown that a number of geoenvironmental factors adversely influence the quality of in-situ optical spectroscopic measurements, including the presence of (non-target) fluorophores, presence of multiple chemical compounds, and the hydrogeological environment of the site. The purpose of this study was to evaluate and characterize the influence of turbidity on the capability of a Time Resolved Raman Spectroscopy (TRRS) system to observe chlorinated solvents in aqueous samples via laboratory tests conducted on liquid standards of trichloroethylene. Key issues investigated included turbid constituent particle size, mineralogy, and turbidity level. Samples were created by doping aqueous chlorinated solvent samples with fine silica flour and Namontmorillonite ranging from 0.02-2μm, with the ultimate aim of understanding how variations in turbidity influence TRRS measurement. Preliminary data indicate that turbidity and particle size consistently influence optical spectroscopic measurements of the TCE contaminant in aqueous solution, with a general trend of exponential decreases in SNR with linear increases in turbidity. Overall, a loss in SNR of ~50% was observed at a turbidity value of ~40 NTU. This observation indicates that absolute Raman intensity in turbid media likely needs to be corrected for the influence of suspended particulate materials in solutions.

A field study was performed to document the benefit of a punched and drawn polypropylene triaxial geogrid. The triaxial geogrids have triangular apertures and increased rib thickness as compared to many geogrids with square apertures. These fundamental changes to the geogrid structure, coupled with high junction efficiency, gives greatly improved aggregate confinement and interaction, leading to improved structural performance of the mechanically stabilized layer (MSL). The project consisted of the widening of La Media Road as part of the Highway 905 improvements. La Media Road and Highway 905 typically experience heavy truck traffic loads from the Mexico/U.S. border crossing. The subgrade material beneath La Media Road is comprised of clayey sand and clayey sand with gravel. Additionally, cobbles ranging up to about 8 inches in diameter were observed on the surface of the subgrade. R-Values of 21 and 24 were determined for the subgrade material. Laboratory testing included grain size analysis, Atterberg limits, maximum density, optimum moisture content and R-Value tests. The field-testing consisted of 5-inch diameter plate load tests on the subgrade and at various levels of the pavement cross-section. Results of plate load testing indicate that the triaxial geogrid increased the modulus of the mechanically stabilized section relative to the conventional unbound aggregate pavement section. The measured improvement of the MSL sections ranged between 27% and 52% greater than the 30% thicker unbound aggregate conventional design section.

The constrained modulus (Ms) of soil has been used to predict the deflection and the buckling potential of buried flexible pipe. Since the constrained modulus (Ms) of soil increases with depth, Ms could have significant value in calculations for deep burial conditions. The standard laboratory test used to determine the constrained modulus is limited to sand size particles and smaller for practical reasons. Gravel size crushed rock is a desirable material for buried pipe support. However, large scale tests to measure strength properties of gravel particles are impractical because of the expense and lack of standard procedures for cohesionless soils. Thus, only presumptive values of the constrained modulus (Ms) for crushed rock are available. As discussed in a companion paper (Gemperline and Gemperline 2011), a large-scale confined modulus laboratory test was developed to quantify Ms values for gravel size particles. The test was performed on different clean, uniform samples of crushed rock. Each sample was tested at low, medium, and high densities. The tests were incrementally loaded to a pressure simulating about 150 feet of fill. . The stress-strain curve was found to be linear with load, resulting in a constant value of constrained modulus for each soil at a specific density. The constrained modulus was also found to be directly dependent on placement density. The constrained modulus ranged between approximately 2000 lb/in 2 and 10,000 lb/in 2 . The low density tests had constrained modulus values between 2000 lb/in 2 and 4000 lb/in 2 . The high density tests had constrained modulus values between 5000 lb/in 2 and 10,000 lb/in 2 . The constrained modulus values representing compacted crushed rock compare favorably with published empirical and presumptive values. The constrained modulus values representing dumped conditions are 200 to 400 percent higher than published empirical and presumptive values. Higher Ms values may be possible using rounded to sub-rounded particles with a wider range of particle sizes. Further testing should verify this assumption.

Replacing cement with recycled clay-brick-powder could reduce carbon dioxide (CO2) emission, enhance conservation of natural resources, and decrease the cost of waste disposal sites. This paper studied the effect of recycled brick-powder on mortar mechanical properties, including flow, compressive strength, and flexural strength. Three level of cement replacement ratio (10%, 20%, and 30%) and four different average particle size of clay-brick-powder (0.3mm, 0.1mm, 0.06mm, and 0.04mm) were considered. Total 13 mixes, including one normal cement mortar as reference, were tested. The water/cement ratio (W/C) and sand ratio were kept constant for all mixes. Testing results showed that recycled clay-brick-powder could be used as partial replacement of cement in mortar without reducing its properties. Compared with normal cement mortar, samples with 10% of 0.1mm and 0.06mm clay-brick-powder had similar or even higher mechanical properties. The effect of clay-brick-powder on the flow and compressive strength depended on its replacement level and average particle size. Generally, compressive strength decreased as the replacement level and average particle size increased. However, mortar with and without clay-brick-powder had similar flexural strength.

With the survey data of land subsidence in Su-Xi-Chang area, the authors found the deformation in the pumped aquifers cannot be neglected, even which is comparable with the adjacent aquitards. A series of lab high pressure compression tests on Suzhou aquifer sand from five different depths using costume-made setup were used to verify the compressibility of the aquifer sand. The test results show that the compression index of aquifer sand is close to some kinds of clay. With the comparison of the grain size distribution before and after testing, it can be concluded that the permanent rearrangement of sand grains is partly responsible for the sand compression.

A two-dimensional Particle Flow Code (PFC2D) was applied to simulate sand liquefaction behavior induced by cyclic loading. The numerical sample was prepared with 4061 discs with its particle size distribution similar to Fujian Standard sand. Based on the theory of strain-controlled undrained cyclic triaxial test, a constant volume numerical test was carried out under cyclic loading with uniform strain amplitude. The macroscopic responses of the sample were obtained and the variation of average coordination number under cyclic loading was analyzed. The effects of cyclic strain amplitude and confining pressure on liquefaction resistance were further analyzed in numerical simulations. It was found that the numerical tests reproduced the general characteristics of liquefaction behavior of saturated sand under cyclic loading. The effects of cyclic strain amplitude and confining pressure on the liquefaction resistance of the numerical sample were comparable with reported experimental results.

This paper examines the critical state parameters of clays typical to the physiographic regions of Kentucky, a state located in the southeastern United States. The critical state model is unique due to the fact that it links the soil consolidation characteristics with shear strength properties allowing prediction of soil behavior at various loading states. The critical state strength parameters for the clays are presented and well-established engineering material property correlations are translated into critical state representation, particularly those correlations that relate consolidation index and recompression index to liquid limit and specific gravity. The Kentucky clay soil parameters are then compared to these representations. Finally, new relationships correlating critical state parameters to consistency limits and particle size analysis are presented.