High Fines Content Research Articles

The effects of small particles on soil seismic liquefaction resistance: current findings and future challenges

The natural and artificial sand soils always incorporate other small particles, which makes the soil liquefaction resistance difficult to predict. The particle size may change from 10−5 m (e.g., fine particles) to 10−8 m (e.g., ultrafine particles), and the soil behaviors change dramatically when such particles are present. Newly reported soil liquefaction cases involving fine particles provide great challenges to seismic design codes. To make it clear, this paper reviewed effects of small particles on soil liquefaction in three different types. The non-low plastic fines (5–75 μm), clay particles (0.1–5 μm), and ultrafine particles (1–100 nm) are discussed, respectively. Many scholars found that liquefaction resistance decreased at first but increased as fine particles (non-low plastic fines or clay particles) were added. This phenomenon can be attributed to the lubrication effect of fine particles. However, when particles in nanometer scale, the strong bond between particles and hydration adsorption of nano-suspension improve liquefaction resistance. There are still many challenges to understanding the roles of small particles in liquefaction, for example, determining relative density for a high fine content, determining particle shape effect (e.g., aspect ratio, flatness, and particle roundness), as well as the long-term reinforcement performance of ultrafine particles. In engineering practice, it suggests that the seismic design codes address the effects of non-plastic fines in laboratory tests. As for some new liquefaction mitigation methods by ultrafine particles, we believe that the standard penetration test may not be appropriate to evaluate soil improvement effect, because the test results cannot reflect the properties change of pore water.

Pullout Resistance of Tapered Metal Straps in Fills with High Fines Contents

AbstractMechanically stabilized earth-retaining walls (MSEWs) have been widely used in construction and transportation projects. Most codes and guidelines require that the soil used as backfill for...

Investigation of the short-term behaviour of silty sand stabilized by colloidal silica

Injection in soils using traditional materials, such as cement grout, has its inherent problems and has not shown the potential for further development in industrial applications. Accordingly, application of novel materials for injection in soils with considerable content of fines for stabilizing and even making them impermeable is suggested. Among different stabilizers that are injectable in soils with fine, colloidal silica seems very suitable due to its very low viscosity, nontoxicity in the nature, and adjustability of the setting time for slow injection in soils with fine. Based on laboratory tests performed in this research, the effect of colloidal silica on the strength parameters and the short-term behaviour of silty sand was examined. For characterizing the soil stabilized by colloidal silica, the silty sand samples with different silt values, in both unstabilized and stabilized conditions, were prepared with different concentrations of the stabilizer. 45 Uniaxial tests and 75 unconsolidated- undrained compressional triaxial tests were conducted. An increase in the undrained cohesion of all samples was observed. On the other hand, two different trends were observed in the alteration of the undrained internal friction angle of soils with low and high fines content.

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.

A potential use of a hydrophilic polymeric material to enhance durability properties of pavement materials

With the increasing demands for stable and high quality materials in road construction, the need for opening new gravel borrow pits is increasing, which compromises the ability of future generations to meet their own needs. Therefore, stabilizing existing or low quality materials to meet the desired performance criteria is needed. Polymer stabilizing additives have been shown to enhance strength and durability characteristics of soils in addition to their advantage of lower carbon footprints compared to traditional stabilizing ones. An extensive laboratory investigation has been carried out to assess the potential use of polymeric stabilization in improving engineering properties of three soil types for use in foundation layers of flexible pavements. A synthetic hydrophilic polyacrylamide-based (PAM) additive has been used to stabilize the soils. The strength characteristics of PAM-treated soils have been assessed by conducting unconfined compressive strength (UCS) tests and their durability characteristics have been evaluated by conducting hydraulic conductivity tests. Erosion and abrasion tests have been also performed to characterize the durability of the treated materials when subjected to traffic abrasion and water erosion. Additionally, microstructure analysis has been performed by conducting Scanning Electron Microscopy (SEM) test. The tests have shown that treating soils with PAM results in significant improvements in their strengths however, those with high content of fines are associated with low UCS values. The tests results have also shown that PAM-treated soils have considerable reductions in their permeability, dramatic improvements in their erosion resistance and significant improvements in abrasion resistance.

Transformation models for effective friction angle and relative density calibrated based on generic database of coarse-grained soils

This study compiles a generic database of seven parameters, including relative density and friction angle, for coarse-grained soils from 176 studies, covering a wide range of reconstituted and in situ coarse-grained soils. This database, labeled as “SAND/7/2794”, is dominated by data from laboratory reconstituted soils such as Erksak, Hokksund, Monterey, Ottawa, Sacramento River, Ticino, and Tonegawa sands. About 15% of the data points in the database are in situ samples obtained from tube sampling, block sampling, or ground freezing techniques. The correlation behavior among some parameters in the database is consistent with existing transformation models in the literature. Mine tailings, volcanic soils, railroad ballast, gravelly soils with significant cobble or boulder content, and soils with high fines contents are removed from the database because they exhibit inconsistent behavior. Soils subjected to very high effective stresses are also removed from the database. The generic database is adopted to calibrate the bias and variability of existing transformation models. Transformation uncertainties are characterized based on their bias, variability, and the range of applicability.

Assessment of hydrocyclone operation in gravity induced stirred mill circuits

The performance data of hydrocyclones in circuits containing a gravity induced mill (hereafter referred to as a stirred mill) were evaluated to understand their performance in the circuits and the current operational practices. There are many studies conducted to understand and evaluate the hydrocyclone performances in the semi-autogenous mill (SAG) and ball mill circuits. The literature on hydrocyclone operation in stirred milling circuits is still limited. A database consisting of various hydrocyclone sizes, operating conditions, classification duties, and commodities was developed based on extensive circuit surveys. The database was used to evaluate the hydrocyclone performance. Among the key operational issues observed were poor circuit control strategies, improper hydrocyclone sizing and operation in the roping condition. Analysis of long-term operational data indicated that hydrocyclone feed solid density is an essential operating variable that needs to be controlled to maintain the cut size. An increase in hydrocyclone feed density leads to an increase in cut size. Almost 50% of the hydrocyclones (in the database) were operating in the roping condition. Besides the hydrocyclone feed solid density, high amounts of fine particles (−25μm) in the hydrocyclone feed also caused the roping condition. Further research is required to operate the hydrocyclone in a spraying condition when the feed has high solid-density and a high content of fines. Plitt’s cut size model was fitted to the data set to evaluate its capability to be used in the stirred mill’s hydrocyclone. The analysis shows the Plitt’s model can predict the cut size when the hydrocyclone is in spraying mode. This result indicates that Plitt’s model can be used for the regrind duty hydrocyclones. An empirical model was developed relating the hydrocyclone feed density and the Plitt onset roping hydrocyclone underflow density. This model can be used to predict the roping condition. Finally, the impact of hydrocyclone performance on circuit performance was compared through the size specific energy of the mill. High size specific energy values were observed when the hydrocyclone is operating in the roping condition. These findings are based on the real operating condition, and it shows the importance of operating the hydrocyclone optimally to achieve overall circuit efficiency.

Experimental measurement and numerical simulation of frost heave in saturated coarse-grained soil

A series of 1-D freezing experiments were conducted to simulate frost heave in saturated coarse-grained soil (CGS) with variable fines content. Visible frost heave occurred in CGS that contained a considerable fraction of fines when supplied by an external water source. Near the beginning of the experiments, a small amount of water was expelled, likely due to consolidation of the thawed portion of the sample. As time elapsed, the total amount of frost heave was proportional to the intake of water. Furthermore, frost heave increased linearly as the fines content increased. At higher fines content, frost heave occurred mainly due to water migration and segregated ice lensing. Finally, a simple finite element model that combined thermal and mechanical analyses based on Takashi's equation was developed. The model accurately reproduced experimental results and therefore can be used to simulate and predict frost heave in CGS.

Laboratory testing and numerical modelling on bearing capacity of geotextile-reinforced granular soils

This paper summarises the details of an experimental work and numerical simulation on the bearing capacity of geotextile-reinforced granular soils with different fine grain contents (10 and 15%) which are mostly used in pavement design. The effects of position and number of geotextile layer(s) on the bearing capacity of reinforced specimens were investigated. The standard laboratory California Bearing Ratio (CBR) test was conducted to investigate the load-penetration behaviour of the unreinforced granular soils as well as reinforced ones with nonwoven geotextile layer(s). The reinforcements have been placed in samples in seven different scenarios (one, two and/or three layers of reinforcement in the bottom, middle and/or top compacted soil layers). The results indicated an increase in bearing capacity for most of the scenarios due to placing the geotextile layer(s); however, it was seen that increasing the number of reinforcement layers will not necessarily increase the reinforced soil mass bearing capacity. Also it was found that the efficiency of placing the reinforcement layers in order to increase the bearing capacity is higher for the soil mass with higher fine content in compare to the soil mass with lower fine content; even in some scenarios for the soil with lower fine content, the geotextile would decrease the bearing in compare to the unreinforced sample. Besides this laboratory testing, Finite Element (FE) software was used to simulate the CBR tests. The FE analysis results showed that the ratio of predicted to measured CBR value is varied between the range of 1.06–1.20 for the soil with lower fine content and 0.86–1.086 for the soil with higher fine content. After the FE model was validated, it was tried by changing the properties of the nonwoven geotextile with a woven one in software to make a comparison between two reinforcement types.

Soil wind erosion in ecological olive trees in the Tabernas desert (southeastern Spain): a wind tunnel experiment

Abstract. Wind erosion is a key component of the soil degradation processes. The purpose of this study is to find out the influence of material loss from wind on soil properties for different soil types and changes in soil properties in olive groves when they are tilled. The study area is located in the north of the Tabernas Desert, in the province of Almería, southeastern Spain. It is one of the driest areas in Europe, with a semiarid thermo-Mediterranean type of climate. We used a new wind tunnel model over three different soil types (olive-cropped Calcisol, Cambisol and Luvisol) and studied micro-plot losses and deposits detected by an integrated laser scanner. We also studied the image processing possibilities for examining the particles attached to collector plates located at the end of the tunnel to determine their characteristics and whether they were applicable to the setup. Samples collected in the traps at the end of the tunnel were analyzed. We paid special attention to the influence of organic carbon, carbonate and clay contents because of their special impact on soil crusting and the wind-erodible fraction. A principal components analysis (PCA) was carried out to find any relations on generated dust properties and the intensity and behavior of those relationships. Component 1 separated data with high N and OC contents from samples high in fine silt, CO3= and available K content. Component 2 separated data with high coarse silt and clay contents from data with high fine sand content. Component 3 was an indicator of available P2O5 content. Analysis of variance (ANOVA) was carried out to analyze the effect of soil type and sampling height on different properties of trapped dust. Calculations based on tunnel data showed overestimation of erosion in soil types and calculation of the fraction of soil erodible by wind done by other authors for Spanish soils. As the highest loss was found in Cambisols, mainly due to the effect on soil crusting and the wind-erodible fraction aggregation of CaCO3, a Stevia rebaudiana cover crop was planted between the rows in this soil type and this favored retention of particles in vegetation.

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.

Soda Pulp Properties from Corn Stalk as Raw Material

ABSTRACT Corn stalk is the lignocellulosic biomass, which remain as leftover after harvesting. To use the corn stalk as raw material for paper industry, soda pulping was applied. In chemical compositional analysis, extractive contents of corn stalk (45.1%) was higher than hard-wood. With corn stalk pith, soda pulp yield was 25.3% at 10.6 Kappa number, but 39.5% yield with 14.8 Kappa number for corn stalk rind. Higher extractives content in pith is one of the reason for lower pulp yield than rind. Pith pulp fibers had higher fines content than rind pulp. Pith parenchyma cell was removed as fines during pulping or washing process, which caused the lower yield. To use the corn stalks as a raw material for paper making, de-pith process is essential for higher pulp yield and longer pulp length.Keywords: Corn stalk, soda pulp, Kappa number, morphological properties http://dx.doi.org/10.7584/ktappi.2015.47.6.073Journal of Korea TAPPIVol. 47. No. 6, 2015, 73-80pISSN (Print): 0253-3200Printed in Korea

The influence of water content on the Dynamic Cone Penetration Index of a lateritic soil stabilized with various percentages of a quarry by-product

Laterites and lateritic soils have been a source of good pavement material in tropical countries for a long time. However, increasingly it is becoming difficult to find lateritic material that meets the required specification within economic haulage distances of roads under construction. This has necessitated, among other things, the need for stabilization of lateritic soils of high fines content with quarry by-products. The use of such marginal material however requires that they be properly compacted in order to improve their engineering properties. For low volume roads there is the need for simple, rapid and economical methods of compaction quality control. This study builds upon previous ones on using the Dynamic Cone Penetrometer (DCP) for compaction verification and seeks to account for post-compaction water content changes. The use of the DCP for compaction verification starts with the establishment of a correlation between the Dynamic Cone Penetration Index (DPI) and the relative level of compaction. However, the DPI is sensitive to water content changes even at constant dry density. The objective of this study is to investigate how the DPI of a lateritic soil determined at the optimum moisture content changes when the water content varies and the fines content reduces. The results show that small changes in water content can lead to significant effects on DPI.

High-Angle Frac-Pack Completions in Shallow Sands: A Case Study

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper IPTC 18220, “High-Angle Frac-Pack Completions in Shallow Sands: A Case Study on Program Learnings and Operational Improvements,” by Azhar Ibrahim, Edgar Romero, and Chiu Chee Yang, ExxonMobil, and Woon Geok Cheen, Halliburton, prepared for the 2014 International Petroleum Technology Conference, Kuala Lumpur, 10–12 December. The paper has not been peer reviewed. Telok is a gasfield development in the Malay basin offshore Terengganu, Malaysia. This paper discusses the program learnings and operational improvements captured while completing eight new wells in 2012 and 2013. The primary reservoirs targeted in the field require sand control, specifically frac-pack technology, because of high fines content. Introduction Telok field is a faulted, east/west-trending anticline in the Formation A reservoir. The major reservoir in Telok is Formation A sands, containing dry nonassociated gas (NAG). The Formation A reservoir is located at approximately 700- to 800-m true vertical depth subsea (TVDSS) and is laterally extensive across the Telok, Tabu, and Guntong fields. Minor NAG reservoirs are the Formation B group and Formation C group sandstones. Formation B and C reservoirs are located between 1100- and 1900-m TVDSS. Sand control was performed for the Formation A and B-1 reservoirs on the basis of the offset well’s performance and sand-screening evaluation completed on the basis of data from a Telok exploration well. Sieve analysis conducted on core material collected from the exploration wells, together with sand-strength-modeling work, confirmed that the Formation A sand is friable and would produce sand on initial completion with a high percentage of fines. Mechanical properties of the formation and fluid flow were evaluated and in-house sand-control experts were consulted before adopting the frac-pack option as the sand-control method.

Comparing CPT and Vs Liquefaction Triggering Methods

Significant developments have taken place over the past 20 years to evaluate the liquefaction potential of soils using in situ tests. The cone penetration test (CPT) is now commonly used to evaluate liquefaction potential in soils. There have also been significant developments to evaluate liquefaction potential based on in situ shear wave velocity (Vs) measurements. Liquefaction methods base on shear wave velocity have the advantage that they are essentially independent of soil characteristics, such as fines content, but often lack the stratigraphic detail obtained using the CPT. Liquefaction methods based on the CPT have the advantage of continuous, repeatable measurements but require corrections based on soil characteristics that can be significant in soils with high fines content. Comparing the most recent Vs-based method with a CPT-based method provides an independent evaluation of the associated corrections applied to the CPT-based method. This paper compares the current Vs-based method with a specific CPT-based method from the literature to evaluate the associated CPT-based corrections. The paper also examines the advantage of using both CPT and Vs measurements (e.g., using the seismic CPT) to evaluate liquefaction potential.

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.

Power consumed by a crusher rotor in overcoming atmospheric drag

Analytical formulas are developed for assessment of the influence of dusty air on the energy consumption in a hammer-type crusher applied to coal batch with a high content of fines. Analytical and experimental approaches are adopted. The ≤3 mm class present in the coal batch supplied for crushing forms a dust–air suspension, which is not crushed by hammer impact but significantly increases the drag on the rotor, with consequent increase in energy consumption. In overcoming the drag of the dust–air suspension, the energy consumption in the crusher may be 40% above the rated value. In that case, the removal of the ≤3 mm class from the feed to the crusher is necessary.

Effects of water and fines contents on the resilient modulus of the interlayer soil of railway substructure

This paper deals with the resilient behavior of the interlayer soil which is created mainly by the interpenetration of ballast and subgrade soils. The interlayer soil studied was taken from a site in the southeast of France. Large-scale cyclic triaxial tests were carried out at three water contents (w = 4, 6 and 12 %) and three fines contents corresponding to 5, 10 % subgrade added to the natural interlayer soil and 10 % fine particles (<80 μm) removed from the natural interlayer soil. Soil specimens underwent various deviator stresses, and for each deviator stress, a large number of cycles was applied. The effects of deviator stress, number of cycles, water content and fines content on the resilient modulus (M r) were analyzed. It appears that the effects of water content and fines content must be analyzed together because the two effects are closely linked. Under unsaturated conditions, the soil containing high fines content has higher resilient modulus due to the contribution of suction. When the soil approaches the saturated state, it loses its mechanical enhancement with a sharp decrease in resilient modulus.

Model for Seasonal Variation of Resilient Modulus in Silty Sand Subgrade Soil: Evaluation with Falling Weight Deflectometer

One of the main input parameters in the mechanistic design and analysis of pavement systems, the stiffness of unbound pavement material usually is moisture dependent. As a result, most unbound pavement layers exhibit seasonal variations in stiffness as the pavement moisture content changes over the year. Any realistic pavement design should take this variation into account. In unbound material with a high fines content, a change in moisture content can change the stress state because of suction effects. An enhanced predictive resilient modulus model is presented to account for seasonal variation by means of suction measurement. A silty sand subgrade soil was tested with a modified repeated load triaxial system under different moisture (suction) conditions, and a set of resilient modulus model regression parameters was determined. The capability of the model to capture seasonal variation in moisture content was evaluated further with field data. A series of falling weight deflectometer (FWD) tests with multilevel loads was conducted on an instrumented pavement structure in which the moisture content of the subgrade was changed by manipulating the pavement drainage condition. The resilient modulus values obtained from the model were compared with backcalculated stiffness data obtained from FWD tests conducted under different moisture conditions. Overall, agreement was good between the laboratory-based resilient modulus values and the backcalculated stiffness. The resilient modulus–suction model could efficiently capture the moisture content effects.

Fines-content effects on liquefaction hazard evaluation for infrastructure in Christchurch, New Zealand

To assess soil liquefaction hazards for civil infrastructure, several competing liquefaction evaluation procedures (LEPs) are used to estimate the potential for liquefaction triggering, often for use in a liquefaction potential index (LPI) framework. However, due to the relatively uncertain effects of fines-content (FC) on liquefaction behavior, LPI hazard assessments may be less accurate at sites with high FC. Accordingly, this study investigates “fines-content effects” on the accuracy of LPI hazard assessment during the 2010–2011 Canterbury Earthquake Sequence (CES). These effects are resolved into: (1) criteria based on the soil-behavior-type index (Ic) for identifying liquefaction-susceptible soils; (2) FC-corrections inherent to each LEP, used to adjust liquefaction resistance for the presence of fines; and (3) the potential for non-liquefied, high-FC soils to inhibit liquefaction manifestation. This investigation is performed using 7000 liquefaction case studies from the CES, wherein LPI hazard assessments computed with the Robertson and Wride [50], Moss et al. [41], and Idriss and Boulanger [30] LEPs are compared to field observations. For the assessed dataset, LPI hazard assessments were significantly and uniformly less accurate at sites with silty and clayey soil mixtures. For these sites, the existing LPI framework has inherent limitations, such that all LEPs produce erroneous hazard assessments. In particular, the capacity of plastic soils to inhibit liquefaction manifestation by affecting pore pressure development and redistribution should be further evaluated.