Low Fines Content Research Articles

A particle packing model for sand–silt mixtures with the effect of dual-skeleton

The study of particle packing models for binary mixtures is important in the field of granular materials, from both theoretical and practical perspectives. A number of particle packing models have been developed for predicting packing density (or void ratio) of a binary mixture. However, the measured results and the predicted values do not always agree with each other, particularly in the range of fines content between 25 and 50%. It is postulated herein that the discrepancies between the measured results and the predicted values are primarily due to the incorrect assumptions used in the existing models. In the existing models, the packing density is determined from one of the following two assumed mechanisms of particle mixing: (1) the mixed packing has a dominant large-particle skeleton and the small particles fill the voids of the large-particle skeleton, or (2) the mixed packing has a dominant small-particle skeleton and the large particles are embedded in the small-particle skeleton. It is obvious that the first assumed mechanism is only applicable for mixtures with low fines content, whereas the second assumed mechanism is only applicable to mixtures with high fines content. Therefore, the predictions from existing models are unsuitable for mixtures with medium fines content, such as a mixture of fines content between 25 and 50%. In this study, a 3-D discrete element simulation is carried out to show that, for a mixture of medium fines content, the packing structure has a dual-skeleton, which is neither dominated by a large nor small-particle skeleton. Then, we postulate that, in the mixed packing, both mechanisms can take place: filling of small particles and embedment of large particles. The concepts of “dual-skeleton index” and “index size” are proposed to account for the interactive effects of filling and embedment. Based on this postulation, we develop an analytical method, which has the capability of predicting minimum void ratio for sand–silt mixtures with various fines contents. The developed model is then validated by the experimental results obtained from 16 types of sand–silt mixtures.

The Coupled Influence of Relative Density, CSR, Plasticity and Content of Fines on Cyclic Liquefaction Resistance of Sands

ABSTRACTIn this study, stress-controlled cyclic simple shear tests were performed on sand specimens with up to 10% silt or clay contents, and coupled effects of plasticity, fines content (FC), relative density (DR) and CSR (cyclic stress ratio) were investigated. The results demonstrated that for sands with low fines content, reasonable trends were obtained when the packing index control parameter was selected as DR. Also, clean sand specimens demonstrated highest liquefaction strength compared with that of sands with fines up to 10% FC. The effect of fines’ plasticity became apparent as the FC increases and CSR reduces in relatively denser specimens.

Effect of the minimum void ratio on the vertical intercept of the steady state line of non-plastic soils

The steady state line (SSL) plays a key role in understanding and modelling the mechanical response of soils. Accordingly, understanding how the SSL correlates to soil index properties is of primary importance. A previous study reported that the vertical location of the SSL (Γ1) in void ratio (e) versus mean effective stress (ρ') space is correlated to the minimum void ratio (emin). However, the correlation only included soils with narrow particle size distributions (PSD) and low fines content (FC). In the current study, published data corresponding to 30 non-plastic soils were re-processed to further explore the applicability of the r1-emincorrelation. The results indicate that the r1-emincorrelation is linear (R2 = 0.85) and valid regardless of the coefficient of uniformity (Cu), FC, and particle shape. The r1-emindataset presented herein was also compared to a previously published dataset, and good agreement was observed. It is proposed that the r1-emjncorrelation can be very useful to understand how the Γ1 of different non-plastic soils compare to one another, and to minimise the extent of triaxial testing required when characterising a soil deposit from an SSL standpoint. Limitations of the r1-emin correlation are also discussed.

Open Graded Asphalt Mixture Design for Environmentally Friendly Road

The road is an important infrastructure to support various economic development. By increasing the population, the constructions of road infrastructure are obviously required and cover more land use area, consequently narrowed the areas for water absorption into the land. Therefore, it is necessary to improve more environmentally friendly of road constructions, in this case is by using open graded asphalt. Open graded asphalt is the mixture of asphalt with low fine aggregate content to produce a high percentage of air voids, which expected to be able to absorb water into the land underneath. This observation uses laboratory experiment method. Materials that are used are natural gravel and the volcanic gravel, 60/70 asphalt penetration and stone dust filler. The tests performed for the samples are Marshall test, falling head water permeability, indirect tensile strength and unconfined compressive strength. The optimum bitumen content for each type of aggregate have been found to be 2.95% for natural gravel and 4.65% for volcanic gravel. Open graded asphalt porosity is 26.52% for natural gravel, whereas the volcanic gravel is 22.31%. The vertical and horizontal permeability for natural gravel are 1.25 cm/second and 0.92 cm/second, respectively. Whereas, for the volcanic gravel is 1.43 cm/second and 1.10 cm/second, respectively. Indirect tensile strength (ITS) value for natural gravel is 59.49 KPa whereas the volcanic gravel is 74.84 KPa. The unconfined compressive strength (UCS) value for natural gravel is 1070.63 KPa, whereas the volcanic gravel is 1120.69 KPa. It is concluded that the open graded porous asphalt is only compatible for low volume traffic road and need improvement to be able to be used as standard road.

Influence of coefficient of uniformity and base sand gradation on static liquefaction of loose sands with silt

When occurred on site static or flow type liquefaction could result in catastrophic consequences due to its sudden occurrence with large strains. Presented here is an experimental study based on monotonic undrained triaxial compression tests conducted on three clean sands and their mixtures with three different non-plastic silts at three different fines contents (≤25%). The results demonstrate that base sand gradation has significant influence on the static liquefaction potential of clean and silty sands. It was observed that clean sands become more liquefiable as their mean grain size got smaller and/or they became more uniform. However, it was found that the order of liquefaction resistance of the same base sands were reversed when they were mixed with silt (i.e. resulting silty sands become more liquefiable as the mean grain size of base sand got larger and/or base sand became relatively well graded). Possible reason for such a reversed behavior was hypothesized and then experimentally justified with extra tests. It was also found that the influence of base sand gradation on static liquefaction of loose specimens was most significant at low fines content (e.g. 5%) and almost erased at relatively high fines contents (e.g. 25%). In the last part of the study, the relationship between the normalized peak deviator stress (qpeak/σ‘3c) and coefficient of uniformity (CU) is discussed. It was shown that unlike clean sands, for which liquefaction potential decreases with increasing CU, the liquefaction potential of sand-silt mixtures reconstituted in the laboratory increases with increasing coefficient of uniformity (i.e. technically as they became more well graded). Two equations were proposed to represent the discussed relationship between qpeak/σ‘3c and CU; one for stable and temporarily liquefied specimens, the other for liquefied specimens. Finally, the applicability of these equations to other types of silty sands in literature was shown.

Proposed soil classification based on the experiences of soft-ground tunneling in Iran

An essential step in successful mechanized and conventional tunneling operations is a thorough characterization of ground conditions and identification of geological and geotechnical risks. In bored tunneling, this and other information is needed in order to select the appropriate tunnel boring machine (TBM) and to determine its technical specifications for proper soil conditioning and optimal TBM performance. In conventional tunneling, this information is also important for ensuring the correct choice of drilling method and minimizing drilling risk. The major geological risks in tunneling (New Austrian Tunneling Method [NATM] or mechanized) are stickiness and clogging of soils, soil abrasi veness, soils with low fine content or oversized grains, tunnel collapse and instability, groundwater fluctuation, mixed-face conditions, liquefaction, and soil movement. Experiences from both conventional and mechanized tunneling in Iran show that the potential for each geological hazard is higher in certain types of soils. As such, knowledge of the various soil types is important for predicting soil behavior and possible geological hazards. In this study, we present a simple and practical classification of soil types for the prediction of soil behavior and geological hazards in both conventional and mechanized tunneling. With this method, soils are classified based on two parameters. The first is soil grain distribution. For this purpose, tests were conducted on soil samples from the test pit and geotechnical boreholes, and the percentage of particles remaining above a no. 4 sieve and those passing through a no. 200 sieve were calculated for each sample. The second parameter is the consistency index, which is estimated from the Atterberg limits. The soils were classified into ten groups based on these two parameters, and soil behavior and geological hazards for each class were then predicted based on Iranian tunneling experiences. Finally, the real soil behavior and geological hazards in the Qom tunnel were analyzed to determine the accuracy of the predictions. The results showed that the predictions were largely comparable to actual conditions. These results were then directly used for preliminary and permanent lining design and recommendations for soil conditioning, as well as for structural design of the different stations.

Hydraulic drag of dense beds consisting of particles of different shape

Formulas derived by different researchers for the hydraulic drag of a dense bed consisting of particles of different type (balls, pellets, particles of arbitrary shape) are compared. Similarities in the dependence on the temperature and filtration rate are sought in terms of the reduced hydraulic drag coefficient. The dependence of the hydraulic drag on the porosity is practically unaffected by the shape of the particles. A formula is recommended for the hydraulic drag of a pellet bed with natural packing, with a low content of fines. On that basis, the energy losses in the bed itself and in the whole gas–air channel of roasting machines may be determined.

Ambivalent role of fine particles on the stability of a humid granular pile in a rotating drum

We have studied the influence of fine particles on the stability of a granular medium in a rotating drum. The stability diagram of this system was established as a function of the drum rotation speed, fine particle content and relative humidity. Four regimes were observed. At low fine content, an avalanching regime is encountered at low rotation rate, and a continuous flow regime at high rotation rate. At high fine content, a stick–slip regime at the drum wall is seen at low rotation rate and a continuous sliding regime at high rotation rate. The influence of fines is ambivalent. At low fine content, they fluidize the pile and decrease its stability, by granular lubrication. At high fine content, they solidify the pile and increase its stability, by jamming the grain assembly. The enhancement of humidity increases the stability for high fine content, but has no effect for low fine content.

종이 기저귀로부터 재생된 fluff 펄프와 그 수초지 특성 분석

ABSTRACT The purpose of this study is to examine the reusability of the fluff pulp recycled from paper diaper. To do this, the physical and optical properties of each handsheet made from these fluff pulp sample as well as the properties of the fiber recycled from paper diaper were analyzed and compared with those of non-recycled diaper fluff pulp samples and conventional pulp samples. These comparisons show that the characteristics of fiber such as length, width, curl, kink of the pulp recycled from paper diaper were sim-ilar to those of non-recycled diaper fluff pulp as well as to those of commercial pulp. The fine content of recycled diaper fluff pulp was lower than that of other pulp samples, while the ash content of the former was higher than that of the latter. Furthermore, it was also found that the bulk of handsheets made from the recycled fluff pulp was higher than that of other pulp samples, while the formation of the former was worse than that of the latter. The mechanical properties of the handsheet sample made from the recycled diaper fluff pulp was higher than those of the unused diaper fluff pulp and was lower that those of com-mercial fluff pulp and softwood tissue pulp handsheet. But, it was higher than that of hardwood tissue pulp handsheet. The optical properties of recycled diaper fluff pulp handsheet was lower than those of each handsheet samples made from other pulps due to its low fine content.

Influence of fine particles on the stability of a humid granular pile.

We have investigated by rotating drum experiments the influence of a small amount of fine particles on the stability of a granular heap. The fine particles are shown to have a strong and ambivalent influence. For low fine particle content, the heap destabilizes by avalanches, and the fine particles tend to fluidize the heap. In contrast, for high fine particle content, they increase the cohesion of the heap, which destabilizes through stick-slip at the drum wall. We interpret and model the fluidification in the avalanching regime, which we show is independent of humidity, by granular lubrication considerations, whereas the stick-slip behavior, highly dependent on humidity, is understood by a solid friction model.

Grain size distribution of soils within the Cordillera Blanca, Peru: An indicator of basic mechanical properties for slope stability evaluation

This paper presents results of a study on the mechanical properties of sandy and gravely soils within the Cordillera Blanca, Peru. The soils were divided into groups according to their origin (glacial, fluvial, or debris flow). The grain size distribution of forty three soil samples was used to classify the soils according to the scheme of the Unified Soil Classification System (USCS). These distributions have then been used to estimate shear strength and hydraulic properties of the soils. There are clear differences between the soils which reflect their divergent origins. The glacial soils normally fit within one of two distinctive groups according to the proportion of fines (Group A, 7%-21.5%; Group B, 21%-65%). The estimation of shear strength at constant volume friction angle and peak shear strength of the glacial sediments with low content of fines was made using published data relating to the measured shear strength characteristics of soils with similar origins and grain size distributions. The estimated values were supported by measurements of the angle of repose taken from fourteen samples from two moraines and by shear tests on samples from one locality. The results of the grain size distribution were also used to estimate the average hydraulic conductivity using the empirical Hazen formula which results were verified by field infiltration tests at two localities.

Effects of Fines Content on Hydraulic Conductivity and Shear Strength of Granular Structural Backfill

For cast-in-place abutments and retaining walls, structural backfill is preferred to be free-draining, which generally implies less than 5% fines content. This fines content is expected to eliminate the need to design for hydrostatic pressures. The availability of high-quality structural backfill with naturally low fines content is declining. This situation warrants an evaluation of whether granular backfill materials with greater than 5% fines content could be successfully used in practice. Flexible wall, hydraulic conductivity tests on a granular structural backfill with 0%, 5%, 10%, 15%, 20%, and 25% nonplastic fines content were conducted at 41, 83, and 124 kPa (6, 12, and 18 psi) confining pressures followed by consolidated drained triaxial compression tests for obtaining associated drained shear strength parameters of these gradations. The 15.2-cm (6-in.) diameter specimens were prepared at optimum moisture content and 95% of maximum standard Proctor density. To enable a comparison with respect to modified Proctor maximum densities, modified Proctor tests were also performed for all base soil–fines content mixtures. The experimental results were compared with relevant studies found in the literature. This research indicates that a nonplastic fines content up to 10% may be justified in structural backfill specifications for retaining walls and abutments.

Engineering geological investigations of mechanized tunneling in soft ground: A case study, East–West lot of line 7, Tehran Metro, Iran

The essential requirements of a successful TBM tunneling operation are the complete characterization of the ground and the thorough identification of geological and geotechnical risks. These besides other information are needed for selecting the right TBM and determining its technical specifications for proper soil conditioning and for achieving the optimum TBM performance. This paper concentrates on a methodology for engineering geological investigations and geotechnical ground characterization, which is important for successful application of mechanized tunneling methods in soft alluvial sediments along the East–West section of line 7 of the Tehran Metro. Geotechnical considerations related to tunneling with a soft ground TBM are described in detail, including the site investigation program, project-specific soil grouping system, distribution of soil types, geological–geotechnical risks (oversize grains, clogging, soil abrasiveness, fine grain content, permeability and groundwater fluctuation) and the engineering geological subsurface model. The encountered soil materials have been divided into four categories according to physical characteristics and engineering properties. In this study, the characteristics of the ground and the hydrogeological regime indicate that an EPB-TBM is rather a slurry-TBM. Although the engineering geological conditions of the ground along the tunnel are favorable for EPB-TBM, stickiness of fine-grained soils, abrasiveness of soils, existence of coarse-grained soils with low fine content and groundwater fluctuations are the most important risks for applying mechanized tunneling method in this specific project.

A preliminary investigation into the physical and chemical properties of biomass ashes used as aggregate fillers for bituminous mixtures

Fly and bottom ashes are the main by-products arising from the combustion of solid biomass. Since the production of energy from this source is increasing, the processing and disposal of the resulting ashes has become an environmental and economic issue. Such ashes are of interest as a construction material because they are composed of very fine particles similar to fillers normally employed in bituminous and cementitious mixtures. This research investigates the potential use of ash from biomass as filler in bituminous mixtures. The morphological, physical and chemical characteristics of 21 different ashes and two traditional fillers (calcium carbonate and “recovered” plant filler) were evaluated and discussed. Leaching tests, performed in order to quantify the release of pollutants, revealed that five ashes do not comply with the Italian environmental re-use limits. Experimental results show a wide range of values for almost all the investigated properties and a low correlation with biomass type in terms of origin and chemical composition. Furthermore, sieving and milling processes were found to improve the properties of the raw material in terms of grading and sample porosity. The effectiveness of these treatments and the low content of organic matter and harmful fines suggest that most of the biomass ashes investigated may be regarded as potential replacements for natural filler in bituminous mixtures.

Discussion of the paper: Effect of physical parameters on static undrained resistance of sandy soil with low fines content

Discussion of the paper: Effect of physical parameters on static undrained resistance of sandy soil with low fines content

Effect of Crushed Rock Layer Width on Natural Convection Cooling of Highway Embankment in Permafrost Regions

For the construction of the proposed Qinghai-Tibet Express Highway in permafrost regions, it will be necessary to use the new technique of cooling the ground temperature by the coarsely crushed rock layer with a low fines content. The heat convection governing equations based on airflow function in variable permeability porous crushed rock layer are derived. Comparison of the cooling capability of winter-time natural convection in the crushed rock highway embankments with various widths of crushed rock layer and an air-permeable side slope surface were studied using a finite element method. The result indicates that the cooling capability of natural convection within the crushed rock highway embankment with a crushed rock layer width of 12 m is stronger than that with a crushed rock layer width of 10 m. Under the same temperature and pressure boundaries, the storage of cold energy in the foundation soils below the wider crushed rock highway embankment due to natural convective heat transfer is larger than that below the narrower one.

Study of Robustness of Self-Compacting Concretes Made with Low Fines Content

Viscosity-modifying admixtures (VMAs) are often used to increase the robustness of self-compacting concretes (SCCs); however, concretes produced in this way require a higher cement or additions content than those made with additional limestone filler and thus are less attractive from the point of view of economics and sustainability. In light of this, the objective of this paper was to study the robustness of a SCC made with VMAs and low filler content and to determine whether it was comparable to a commercial SCC, with high limestone filler content and less cement. Three types of SCCs with water/cement (w/c) = 0.6 were produced with water contents varying between −7.5% and +7.5%. A linear regression model was constructed from the experimental data for each of the properties analyzed so as to provide an easy method of calculating the acceptable percentage of water-content variation in concrete that satisfies certain robustness requirements. This model provides a comparison of the different types of SCCs and thus assists the concrete producer to select the appropriate mixes. The results show that variations in flowability and compressive strength due to changes in water content were very similar in the three concrete types considered in this study. However, when filler was replaced by VMA, the material’s cohesive properties (viscosity and segregation resistance) showed improvement. In the SCC made with additional limestone fines, slump flow spread time T50 and V-funnel time were the properties that contributed the most to reducing the material robustness. It was also observed that segregation resistance and compressive strength do not play a significant role in the robustness of SCCs under consideration.

Evaluation of Liquefaction Potential Index Along Western Coast of South Korea Using SPT and CPT

For South Korea, liquefaction potential along the western coast has not been widely assessed because South Korea is considered to be a low seismic hazard. However, recent earthquake events and historical records indicate that the seismic hazard of South Korea should not be ignored. Moreover, as artificial fills are extensively used along the western coast for development, liquefaction evaluation of the soils in this area is necessary. In this paper, we present: (1) the seismic characteristics of the study area; (2) procedures for evaluating liquefaction potential, focusing on the liquefaction potential index (LPI) approach; and (3) LPI distributions at several representative locations along the western coast of South Korea under various seismic scenarios. The liquefaction potential index represents the liquefaction potential over the upper 20 m of a boring or sounding. Using cone penetration test (CPT) and standard penetration test (SPT) data from two coastal sites, we compare and discuss CPT-based and SPT-based LPI values, particularly values computed in nonplastic, silt-rich soils. In these soils, it appears that the CPT yields lower liquefaction resistance, resulting in large LPI values. Finally, discussion and suggestions are provided for CPT- and SPT-based liquefaction assessment of low plasticity and high fines content soils.

Effect of Gradation and Cement on the Properties of Soil-Cement Mixtures

Eight non-plastic soils with different gradation are used for this research to study the appropriate choice of soil-cement mixture for a earth and rock-fill dam construction project. The properties of soil-cement materials are influenced by several factors, including type and proportion of soil, cementitious materials, water content, compaction, uniformity of mixing, curing conditions, and age of the compacted mixture. Based on the experimental results, the maximum dry density will increase with an increase in cement content for soils with low fines content. However, no significant variation was noticed for soils with higher fines content. For given cement content, the maximum density of soil-cement mixture also has a positive correlation with the average grain size, D50, and uniformity coefficient of gradation, Cu. Based on USBR criteria and experimental results, a minimum of 11% of cement content are suitable for soil-cement application on the dam construction. Coarser grain soils are more applicable than finer grain soils to soil-cement construction.

Effect of Mixing Fine Sand on the Drained Shear Strength of Completely Decomposed Granite Soil

Experimental test results presented in this paper were from a series of triaxial compression tests studied under drained conditions for Completely Decomposed Granite (CDG) soil mixed with fine sand content of (0, 10, 20, 30, and 40%). The CDG soil showed high compressibility during isotropic consolidation, probably due to the use of the moist tamping method and the effect of weathering degree on the soil structure. The tests results produced a unique Critical State Line (CSL) in the e-lnp plane, and these lines were parallel for each mixture and moved downward with increasing fine sand content. The fine sand content, at which the intergranular void ratio of the CDG-fine sand mixture became equal to emax for plain CDG soil, was named as Transition Fine Sand Content (TFSC), which occurred at 20-30% fine sand content. Normalization of the critical state stresses showed that for the samples with low P/Pc between 0.58 and 0.65 (i.e. the CDG soil mixed with fine sand), the stress paths moved directly towards the critical state without passing through the boundary surface of the soil mixture, which revealed the impact of the fine sand addition to the CDG soil structure, reflecting an improvement in the soil strength behavior by developing a strong interlocking among the particles of the mixture. It was also observed that a small portion of stress paths could pass through the boundary of Hvorslev surface in the case of low fine sand content (≤ 10 %) and the boundary of Hvorslev surface observed clearly in the case of plain CDG soil. The friction angle increased at steady state from 28- 32.6, and the cohesion decreased from 15 to 8.3 kN/m 2 with increasing fine sand content. A comparison of critical state parameters and strength properties between weathered granite CDG soil from Malaysia and Hong Kong were also made and summarized in this study.