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This paper examines the specific role and interdependencies between soil density, particle size, particle shape, and gradation on the water entry pressure of hydrophobized sands. The tested granular materials include quartz sands of three size ranges, glass beads, and crushed glass. All granular materials were initially silanized with polydimethylsiloxane (PDMS) coatings to achieve the same intrinsic hydrophobicity. The water-ponding method was adopted to measure the water entry pressure in a comprehensive parametric study that consisted of 96 tests. Despite an acute sensitivity of the water entry pressure to relative density, the results revealed a more dominant effect of particle size. The largest water entry pressure (hydrophobized fine sand) was 14 times that of the lowest (hydrophobized coarse sand). Relatively higher water entry pressures were recorded with sands having larger coefficients of uniformity. A comparison between hydrophobized glass beads and crushed glass also revealed that rounded particles were less effective in retarding water infiltration in a dense state. A relationship, based on Jurin's law, was proposed for dense sands whereby the water entry pressure is obtained from the coefficient of uniformity, mean particle size, and particle shape. Key words: hydrophobized sand, hydrophobicity, water entry pressure, gradation, particle shape, relative density Cet article examine le role specifique et les interdependances entre la densite du sol, la taille des particules, la forme des particules et la gradation sur la pression d'entree d'eau des sables hydrophobises. Les materiaux granulaires testes comprennent des sables de quartz de trois gammes de taille, des billes de verre et du verre concasse. Tous les materiaux granulaires ont ete initialement silanises avec des revetements en polydimethylsiloxane (PDMS) pour obtenir la meme hydrophobie intrinseque. La methode de l'etang d'eau a ete adoptee pour mesurer la pression d'entree de l'eau dans une etude parametrique complete qui comprenait 96 tests. Malgre une sensibilite aigue de la pression d'entree de l'eau a la densite relative, les resultats ont revele un effet plus dominant de la taille des particules. La pression d'entree d'eau la plus importante (sable fin hydrophobise) etait 14 fois superieure a celle de la plus faible (sable grossier hydrophobise). Des pressions d'entree d'eau relativement plus elevees ont ete enregistrees avec les sables ayant des coefficients d'uniformite plus importants. Une comparaison entre les billes de verre hydrophobisees et le verre concasse a egalement revele que les particules arrondies etaient moins efficaces pour retarder l'infiltration d'eau a l'etat dense. Une relation, basee sur la loi de Jurin, a ete proposee pour les sables denses, dans laquelle la pression d'entree de l'eau est obtenue a partir du coefficient d'uniformite, de la taille moyenne des particules et de leur forme. [Traduit par la Redaction] Mots-cles : sable hydrophobise, hydrophobie, pression d'entree de l'eau, gradation, forme des particules, densite relative, 1. Introduction Soil hydrophobicity retards water infiltration, influencing water movement and evaporation (Fink et al. 1980; Ritsema and Dekker 1994; Hall et al. 2010; Wallach 2010; Bardet et al. 2014; [...]

An increase in the operation speed of high-speed trains often leads to an increase in the loading frequency on subgrade soil. Hence, the long-term dynamic behavior of the subgrade and the service performance of high-speed tracks are affected. To determine the stress-strain characteristics of granular soil under high-frequency loading, a triaxial test setup was modified to investigate the effects of loading acceleration and duration, water content, vibration frequency, cell pressure, and initial soil density. The experimental results indicate that there are reductions in axial stress and volumetric strain during high-frequency loading. The reduction in axial stress is as high as 40%, and that of volumetric strain, which is permanent, could approach 0.1%. The stress reduction, strain compression, and excess pore pressure are found to vary linearly with vibration acceleration when a/g > 0.02, where a is vertical vibration acceleration and g is gravitational acceleration. The reduction in strength and strains are found to depend on the loading acceleration and effective cell pressure, but independent of the loading duration, water content, frequency, and initial density. A threshold acceleration a = 0.02g is observed, below which the changes in the shear strength and volumetric strain induced by vibration are negligible. At high vibration acceleration, the strain amplitude could increase, eventually leading to a collapse of the specimen. Key words: granular soil, critical state, fluidization, deviatoric stress, volumetric strain. L'augmentation de la vitesse d'exploitation des trains a grande vitesse entraine souvent une augmentation de la frequence de chargement du sol de la plate-forme. Le comportement dynamique a long terme de la plate-forme et les performances de service des voies a grande vitesse sont donc affectes. Afin de determiner les caracteristiques de contraintedeformation du sol granulaire sous un chargement a haute frequence, un montage d'essai triaxial a ete modifie pour etudier les effets de l'acceleration et de la duree du chargement, de la teneur en eau, de la frequence de vibration, de la pression des cellules et de la densite initiale du sol. Les resultats experimentaux indiquent qu'il y a des reductions de la contrainte axiale et de la deformation volumetrique pendant le chargement a haute frequence. La reduction de la contrainte axiale peut atteindre 40% et celle de la deformation volumetrique, qui est permanente, peut approcher 0,1%. La reduction des contraintes, la compression des deformations et l'exces de pression interstitielle varient lineairement avec l'acceleration des vibrations lorsque a/g > 0,02 ou a est l'acceleration de vibration verticale et g est l'acceleration gravitationnelle. La reduction de la resistance et des deformations depend de l'acceleration de la charge et de la pression effective des cellules, mais est independante de la duree de la charge, de la teneur en eau, de la frequence et de la densite initiale. Un seuil d'acceleration a = 0.02g est observe, en dessous duquel les changements de la resistance au cisaillement et de la deformation volumetrique induits par la vibration sont negligeables. En cas d'acceleration elevee, l'amplitude de la deformation peut augmenter et conduire a l'effondrement du specimen. [Traduit par la Redaction] Mots-cles: sol granulaire, etat critique, fluidization, contrainte deviatorique, deformation volumetrique., 1. Introduction Vibrations induced by high-speed trains frequently lead to long-term settlement of the track owing to the permanent compression of the subgrade. When the speed of a high-speed train [...]

Vertosols are widely used for cotton production globally. One main advantage of this soil type is its capacity to improve its structure gradually due to natural processes over time. However, Vertosols are highly susceptible to compaction, especially under wet soil conditions. This study investigated the change in characteristics of Australian Vertosols due to the impact of rainfall, seasonal variability, and John Deere 7760 cotton picker traffic. Soil cores were collected between October 2016 and May 2017. Measurements of soil physical properties (soil water content, dry bulk density, and soil penetration resistance) were carried out in the 0-80 cm depth profile during the study period. Increasing soil water content due to rainfall caused the Vertosol to swell, providing some degree of natural compaction alleviation and decreasing the dry bulk density and soil penetration resistance. Increased temperatures from October 2016 to January 2017 resulted in increased moisture evapotranspiration. This led to shrinkage of the Vertosol and resulted in increased dry bulk density and soil penetration resistance, particularly in the top 0-30 cm of soil. Traffic from the JD7760 cotton picker induced significant compaction throughout the depth profile. These findings have important implications for farmers intending to grow crops in Vertosols and managing the issue of soil compaction. Keywords: compaction, cotton picker, soil density, Vertosols., Introduction Vertosols are a collection of soils dominated by cracking clay soil (black earths and grey and brown clays) with clay texture (Eswaran et al. 1988; McKenzie 1998). Vertosols exist [...]

Cohesive horizons are widespread along the Brazilian coastal tablelands and, despite their importance to soil management under intensive cultivation, their genesis remains, in many aspects, controversial. Studies diverge and indicate the participation of different mechanisms in the formation of these soil horizons. Although clay illuviation has been considered as one of the processes determining the formation of this soil attribute, recent studies suggest a limited participation of this soil process. The aim of the present study was to evaluate the relative contribution of argilluviation and sorting of sand to the genesis of cohesive horizons in an Ultisol toposequence from a toposequence from north-east Brazil. Soil samples were collected from cohesive and non-cohesive horizons from four soil profiles. We determined bulk soil density (BD), penetration resistance (PR), particle size distribution and the percentage of different sand fractions. The sand fractionation data were treated statistically to obtain different grain size parameters, such as mean grain size, sorting and kurtosis. An additional micromorphological study was performed on cohesive and non-cohesive horizons. The lowest BD and PR were recorded in non-cohesive horizons (1.53 Mg [m.sup.-3] and 0.74 MPa, respectively), whereas significantly higher values of BD (1.66-1.80 Mg [m.sup.-3]) and PR (2.61-7.71 MPa) were observed in cohesive horizons. Thin sections of cohesive soil horizons showed a significant reduction in void sizes and interconnecting pores compared with non-cohesive soil horizons. The higher values of BD and PR observed in the cohesive horizons are apparently related to this poorly interconnected void network. Textural pedofeatures observable with optical microscopy, which indicate argilluviation, were only found in one cohesive horizon. Sand fractionation showed a predominance of medium and fine sand fractions and indicated the dominance of poorly selected sand in cohesive horizons, probably causing the higher BD and PR values. However, the presence of textural pedofeatures (clay coatings) in one of the cohesive horizons studied may indicate a combined contribution of sand heterogeneity and argilluviation in the genesis of these horizons. Overall, the results of the present study showed that subtle variations in the distribution of basic soil components (i.e. particle size fractions) may determine the formation of cohesive horizons and thus must be taken into account in future studies aiming to predict their spatial distribution and to establish more efficient management strategies. Additional keywords: hard-setting soils, micromorphology, pedogenesis, soil physical properties, tropical soils. Received 27 June 2013, accepted 10 September 2014, published online 1 December 2014, Introduction The Coastal Tablelands represent a geomorphological unit of great social and economic importance in Brazil, extending from Rio de Janeiro to the Amazon (Amapa state) of Brazil. These coastal [...]

Grass is recognized as being beneficial in reducing rainfall infiltration in some kinds of surface cover systems such as landfill cover, because rainwater discharges as surface runoff due to reduced water permeability caused by evapotranspiration-induced soil suction as well as foliage interception. However, the distributions of grass-induced suction in various compacted soils during rainfall are rarely reported. Moreover, it is not straightforward to determine an optimum soil dry density for minimizing rainfall infiltration and at the same time encouraging plant growth. This is because there are conflicting requirements for vegetated cover systems, i.e., compacted soil should not be too dense as to impede root growth, while on the other hand to minimize infiltration. This study thus aims to investigate, quantify, and compare grass-induced suction distributions in silty sand compacted at different densities when subjected to artificial rainfall in the laboratory. A grass species, Cynodon dactylon, which is common in many parts of Asia, was selected for testing. Compacted soil with and without a growing grass patch was tested at three relative compactions (RCs) of 70%, 80%, and 95%, in six test boxes. Test results reveal that at an RC of 95%, suction (40 kPa) retained in vegetated soil after rainfall is 100% higher than that (20 kPa) in bare soil. Among the vegetated soil compacted at the three RCs, suction retained was the highest at an RC of 95% (40 kPa), whereas suction decreased to 0 kPa at an RC of 70% after rainfall. As the average depth of grass roots decreased by 36% due to an increase in RC from 70% to 95%, the depth of influence of suction for vegetated soil at an RC of 95% reduced to less than half of root depth, which was the shallowest among the three compacted soil specimens. Key words: vegetation, suction, Cynodon dactylon, density, rainfall infiltration. L'herbe est reconnue comme etant benefique pour reduire l'infiltration de l'eau de pluie dans le cas de certains types de systeme de recouvrements de surface, comme les couvertures sur les sites d'enfouissement. En effet, l'eau de pluie s'ecoule a la surface en raison de la faible permeabilite a l'eau, qui est causee par la succion du sol induite par l'evapotranspiration et par l'interception de l'eau par les feuillages. Cependant, les distributions de la succion induite par l'herbe dans differents sols compactes durant les precipitations sont rarement rapportees. De plus, il n'est pas evident de determiner une densite seche optimale du sol pour minimiser l'infiltration de l'eau de pluie et en meme temps favoriser la croissance des plantes, puisque les criteres pour les couvertures de vegetation ne sont pas les memes, c'est-a-dire que le sol compacte ne devrait pas etre trop dense pour empecher la croissance des racines mais devrait tout de meme minimiser les infiltrations. Cette etude vise a investiguer, quantifier et comparer les distributions des succions induites par les plantes dans un sable silteux compacte a differentes densites lorsque soumis a des precipitations artificielles en laboratoire. Une espece d'herbe, Cynodon dactylon, qui est commune dans plusieurs parties de l'Asie, a ete selectionnee pour les essais. Le sol compacte avec et sans plante a ete teste a trois niveaux de compaction relative (CR), soit de 70, 80 et 95%, dans six boites d'essais. Les resultats des essais revelent qu'a une CR de 95%, la succion (40 kPa) retenue dans le sol vegete apres la pluie est 100% plus elevee que celle retenue dans le sol nu (20 kPa). Parmi les sols vegetes compactes aux trois CR, la succion retenue etait la plus elevee a une CR de 95% (40 kPa), tandis que la succion etait reduite a 0 kPa a une CR de 70% apres la pluie. La profondeur d'influence de la succion pour un sol vegete ayant une CR de 95% est reduite jusqu'a moins de la moitie de la profondeur des racines, ce qui represente le moins profond des trois echantillons de sol compactes, puisque la profondeur moyenne des racines de l'herbe ont diminue de 36% avec une augmentation de la CR de 70 a 95%. [Traduit par la Redaction] Mots-cles: vegetation, succion, Cynodon dactylon, densite, infiltration de l'eau de pluie., Introduction On most surface cover systems such as landfill covers, vegetation including grass often exists and is considered to be a sustainable and environmentally friendly alternative for minimizing rainfall infiltration, [...]

The capacity of a commercially available miniature pressure sensor for measuring stress evolutions in a partially saturated soil under quasi-static loads is studied, in view of its later application in laboratory-scale physical models. An extensive calibration program is first performed on a triaxial cell under isotropic loadings. These calibration tests provide useful data for assessing the uncertainty in stress measurements, especially in the case of partially saturated granular materials. Notably, influences of soil density, water content, and average grain size on stress measurements are quantified. Following these tests, an example of stress measurements on an original reduced- scale model of 'earth pressure balance shield' (EPBS) is presented, which involves three-dimensional arching effects developing around the shield during excavation. Key words: soil stress measurement, soil stress sensor, calibration test, granular material, partially saturated soil, physical modeling, tunneling, soft ground, arching effect. Les capacites d'un capteur de pression miniature disponible dans le commerce a mesurer les evolutions des contraintes dans les sols partiellement satures sous chargements quasistatiques sont etudiees, en vue de leur utilisation sur des modeles reduits de laboratoires. Dans un premier temps, une campagne d'etalonnage exhaustive est realisee sous chargement isotrope dans une cellule triaxiale. Ces etalonnages permettent d'evaluer l'incertitude regnant sur les mesures de contraintes effectuees, en particulier dans le cas des sols partiellement satures. Les influences de l'indice des vides, de la teneur en eau et de la taille moyenne des grains sur les mesures de contraintes sont notamment quantifiees. A la suite de ces etalonnages, un exemple de mesures de contraintes sur un modele reduit de laboratoire original de tunnelier a pression de terre (EPBS) est presente. Les mesures effectuees permettent la mise en evidence des effets de voute tridimensionnels se developpant autour du bouclier au cours de l'excavation. Mots-cles : mesure des contraintes dans les sols, capteur de contrainte, etalonnages, materiaux granulaires, sols partiellement satures, modelisation physique, creusement de tunnels, terrains meubles, effets de voute., Introduction A reliable estimate of the stress state of soil in the vicinity of a geotechnical structure and knowledge of its evolution with time subjected to external loads are essential [...]

Large scale environmental impact studies typically involve the use of simulation models and require a variety of inputs, some of which may need to be estimated in absence of adequate measured data. An important input, soil bulk density ([D.sub.b]) affects conditions for soil aeration, solute transport, and storage as well as the outcome of soil C stock calculations. Correct representation of [D.sub.b] in simulation studies is essential since any bias or uncertainty will propagate through a variety of processes and time steps. We used the U.S.-wide NRCS National Soil Survey Characterization (NSSC) database of point measurements and the 'k-nearest neighbor' (k-NN) pattern recognition algorithm combined with random resampling without replacement to estimate [D.sub.b] and its uncertainty. Soil particle-size distribution and organic C content were utilized as inputs and soil taxonomy classification, sample depth, and soil horizon notation were tested as optional grouping and limiting factors to the calibration (reference) data. We obtained an overall root-mean-squared error (RMSE) of 0.17 g [cm.sup.-3] and mean error (ME) of 0.01 g [cm .sup.-3]. Grouping samples by taxonomic classification proved to be advantageous, while limiting samples by depth helped avoid depth-specific bias in the estimations. Grouping samples by horizon notation did not yield significant improvement due to the great variability of bulk density within horizons of the same notation. Varying the proportion of data used in the resampled data subsets can be used to establish greater or lesser degree of confidence in mean estimates without affecting those mean estimates. Simulation based environmental impact and risk assessment studies can be direct beneficiaries of data with characterized uncertainty. doi: 10.2136/sssaj2009.0370

The density of soil is crucial in engineering, construction, and research. Standard methods to determine density use procedures, equipment or expendable materials that limit their effectiveness in challenging field conditions. Some methods require burdensome logistics or have time requirements that limit their use or the number of tests that can be executed. A test method, similar to the sand-cone method, was developed that uses steel shot as the material to which a volume of soil is compared to calculate soil density. Steel shot is easily recovered and reused, eliminating the need for specialty sand and calibrated cones or containers, and allows rapid determination of the volume of displaced soil. Excavated soil also provides measurements of total mass and moisture content. Volume, mass, and moisture content are applied in simple calculations to determine wet and dry densities and unit weight of the soil. Proficiency in performing the test can be achieved with minimal training, and the required kit can be assembled for a reasonable cost. Field uses of the method in dry environments in a variety of soil types demonstrated that the method can produce repeatable results within 2% of the values of soil density determined by traditional methods, with advantages in logistics. Key words: soil density, soil moisture, in situ soil testing, soil properties. La densite d'un sol est un parametre cle en ingenierie, construction et recherche. Les meethodes usuelles utilisees pour determiner la densite comportent des procedures, des eequipements ou des mateeriaux consommables qui limitent l'efficacite de ces methodes dans des conditions de terrain difficiles. Certaines meethodes neecessitent une logistique compliqueee, ou ont une duree longue, qui affectent soit leur utilisation ou le nombre d'essais qui peuvent etre effectues. Une nouvelle methode, similaire a la methode du c Mots-cles: densite du sol, humiditee du sol, essai in-situ, proprietes du sol. [Traduit par la Redaction], Introduction and previous work The density of soil is a property that is important in many applications, such as agriculture, engineering, construction, and research. Measurement of soil density can be [...]

The paper brings out the influence of relative density of foundation soil on performance improvement of geocell reinforcement; through model load tests on geocell-reinforced and unreinforced sand beds. Tests were carried out for five different relative densities of sand (30, 40, 50, 60, and 70%). The test results indicate that the beneficial effect of geocell reinforcement, in terms of increase in stiffness, bearing capacity, and load dispersion angle of the foundation bed, is present over a wide range of relative density; however, it is higher for dense condition of foundation soil. With geocell reinforcement offering three-dimensional confinement, the dilation induced benefit is substantially high for dense soil fill. Therefore, for effective utilization of geocell reinforcement, the foundation soil should be compacted to higher density. DOI: 10.1061/(ASCE)MT.1943-5533.0000040 CE Database subject headings: Foundations; Soil stabilization; Reinforcement; Model studies; Relative density; Sand, soil type. Author keywords: Foundation bed; Reinforced soil; Geocell reinforcement; Relative density; Model studies.

Soil bulk density ([p.sub.b]) is required to estimate, evaluate, and calculate many physical soil properties and processes and is essential to convert data from weight-based to volume- and area-related data. One of the dominating factors changing [p.sub.b] is the soil's organic matter (SOM) concentration that alters the soil's compressibility; [p.sub.b] is an important soil structure attribute. Currently, no parameter for characterizing soil compactness giving directly comparable values for all soils is available. Therefore, our aim was to develop a general approach to calculate the effect of SOM concentration on [p.sub.b] that would be universally valid for soils different in their genesis, compaction, and type of land use. To describe the effect of SOM on [p.sub.b] mathematically, we used a nonlinear regression model that was parameterized and validated using published data from experiments where SOM concentration was the main [p.sub.b]--affecting factor (long-term fertilization and proctor experiments, wetlands, reclaimed soils, and volcanic soils). To obtain a standardized parameter describing the present compaction status of a site, we introduced the standardized bulk density [sp.sub.b]. Mathematically, [sp.sub.b] is the intercept parameter of the used nonlinear regression model, and ranged between 0.7 and 2.1 Mg [m.sup.-3] and was very simple to estimate. Another distinct advantage of this novel concept is that only one representative pair of [p.sub.b] and SOM has to be known to calculate [sp.sub.b] as well as the bulk densities corresponding to other SOM concentrations measured on the site. This concept might also be helpful for identifying similar universal approaches to standardize the effect of other [p.sub.b] affecting parameters (e.g., texture, soil depth, tillage regime), however, reassessed from the SOM effect. Abbreviations: OM, organic matter; [p.sub.b], bulk density; RMSE, root-mean-square error; RC, relative compaction; SD, standard deviation; SE, standard error; SOC, soil organic carbon; SOM, soil organic matter; [sp.sub.b], standardized bulk density.

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jenvman.2008.09.003 Byline: Su-Hsia Lin (a), Ruey-Shin Juang (b)(c) Abbreviations: A, Redlich-Peterson constant (L/g); AC, activated carbon; B, Redlich-Peterson constant (L/mg.sup.(1 .sup.- .sup.1/A)); C.sub.e, equilibrium concentration of solute in liquid-phase (mg/L); BDNP, 2-sec-butyl-4,6-dinitrophenol; BFA, bagasse fly ash; CDs, cyclodextrins; CEC, cation exchange capacity; CFA, coal fly ash; CNTs, carbon nanotubes; CP, chlorophenol; CPB, n-cetylpyridinium bromide; CTAB, cetyltrimethylammonium bromide; DCP, dichlorophenol; DMP, dimethylphenol; DNBP, dinitrobutyl phenol; DNP, dinitrophenol; DVB, divinylbenzene; GAC, granular activated carbon; HDTMAB, hexadecyltrimethyl ammonium bromide; K.sub.d, distribution coefficient (L/kg); K.sub.F, Freundlich constant (mg/g) (L/g).sup.n ; K.sub.L, Langmuir constant (L/mg); MAAP, methacrylamidoantipyrine; MP, methylphenol; n, Freundlich exponent; NP, nitrophenol; OTMAC, octodecyl trimethylammonium chloride; PAC, powdered activated carbon; PHEMA, poly(2-hydroxyethyl methacrylate); q.sub.e, equilibrium amount of solute adsorbed (mg/g); SDS, sodium dodecyl sulfate; TCP, trichlorophenol; [beta], exponent lying between 0 and 1 Abstract: In this article, the technical feasibility of the use of activated carbon, synthetic resins, and various low-cost natural adsorbents for the removal of phenol and its derivatives from contaminated water has been reviewed. Instead of using commercial activated carbon and synthetic resins, researchers have worked on inexpensive materials such as coal fly ash, sludge, biomass, zeolites, and other adsorbents, which have high adsorption capacity and are locally available. The comparison of their removal performance with that of activated carbon and synthetic resins is presented in this study. From our survey of about 100 papers, low-cost adsorbents have demonstrated outstanding removal capabilities for phenol and its derivatives compared to activated carbons. Adsorbents that stand out for high adsorption capacities are coal-reject, residual coal treated with H.sub.3PO.sub.4, dried activated sludge, red mud, and cetyltrimethylammonium bromide-modified montmorillonite. Of these synthetic resins, HiSiv 1000 and IRA-420 display high adsorption capacity of phenol and XAD-4 has good adsorption capability for 2-nitrophenol. These polymeric adsorbents are suitable for industrial effluents containing phenol and its derivatives as mentioned previously. It should be noted that the adsorption capacities of the adsorbents presented here vary significantly depending on the characteristics of the individual adsorbent, the extent of chemical modifications, and the concentrations of solutes. Author Affiliation: (a) Department of Chemical and Materials Engineering, Nanya Institute of Technology, Chung-Li 320, Taiwan (b) Department of Chemical Engineering and Materials Science, Yuan Ze University, Chung-Li 32003, Taiwan (c) Fuel Cell Center, Yuan Ze University, Chung-Li 32003, Taiwan Article History: Received 19 June 2008; Revised 26 August 2008; Accepted 19 September 2008

Biodegradable polymer blends consisting of poly (L-lactic acid) (PLLA) and poly(butylene succinate) (PBS) were prepared in the presence of dicumyl peroxide (DCP). The effects of DCP content on the mechanical properties, thermal and rheological behavior, phase morphology as well as the toughening mechanism of the blends were investigated. The notched lzod impact strength of PLLA/PBS (80/20) blend significantly increased after the addition of 0.05-0.2 phr DCP, but the strength and modulus monotonically decreased with increasing DCP content. PBS acted as a nucleating agent at the environmental temperature below its melting temperature and accelerate the crystallization rate of PLLA but had little effect on its final degree of crystallinity. The degree of crystallinity of PBS and the cold crystallization ability of PLLA gradually reduced with increasing DCP content. The addition of DCP induced as well as finer dispersion of PBS particles and better interfacial adhesion between PLLA and PBS, indicating the in situ compatibilization occurred between the two components. The optical clarity of PLLA/PBS blends was significantly improved after of addition of DCP, which was in accordance with the crystallization behavior and phase structure of the blends. POLYM. ENG. SCI., 49:26-33, 2009, (C) 2008 Society of Plastics Engineers, INTRODUCTION In recent years, biodegradable polymers such as poly ([epicilon]-caprolactoen) (PCL) (1), (2), poly(lactic adicd) (PLA) (3), (6), polyhydroxyalknoates (PHAs) (7), and poly (butylene succinate) (PBS) (8), (9) have been [...]

This technical note defines an 'effective soil density' that controls the velocity of small strain shear waves in saturated soil. Biot theory indicates that the ratio of effective density to saturated density will generally range from 0.75 to 1.0 and is a function of specific gravity of solids, porosity, hydraulic conductivity, and shear wave frequency. For many geotechnical applications, effective density will be equal to saturated density for low hydraulic conductivity soils (clays and silts) and may be less than saturated density for high hydraulic conductivity soils (clean sands and gravels). The findings are relevant to applications involving the propagation of small strain shear waves through saturated soil, and in particular for laboratory and field tests in which shear modulus is back-calculated from measured shear-wave velocity. CE Database subject headings: Soil properties; Density; Saturated soils; Shear modulus; Wave velocity; Hydraulic conductivity; Wave propagation.

To evaluate compaction meter value and machine drive power roller-integrated compaction technologies, a field study was conducted with 30-m test strips using five granular materials. The test strips were compacted using a prototype CS-533E vibratory smooth drum roller and tested for various compaction parameters using in situ test methods (e.g., nuclear moisture density, dynamic cone penetrometer, plate load tests, etc.). To characterize the roller machine-ground interaction, soil testing focused on measuring soil compaction parameters of the compaction layer, to a depth not exceeding 300 mm. The experimental testing of five test strips provided roller data and in situ measurements for several stages of compaction that were used in performing statistical regression analyses. The relationships between data from the roller-integrated compaction technologies were investigated with special consideration for the relative variation that was observed for each measurement system. Statistical averaging mitigated measurement variability and revealed statistically significant ([R.sup.2] > 0.9) relationships between in situ and roller-integrated compaction measurements. This research demonstrates statistical analysis techniques for which calibration procedures using roller-integrated compaction technologies may be developed. CE Database subject headings: Soil compaction; Monitoring; Statistics; Earthwork; Quality control; Granular materials.

The results from a laboratory experimental study on silty sand are presented. Undrained triaxial compression tests were performed on Nevada sand containing nonplastic silt. All specimens underwent monotonic loading after isotropic consolidation to 25 kPa. Various depositional techniques were used to create specimens to compare their stress-strain behavior within three separate density ranges and three different silt contents. As density increased, the effect of the depositional method on the undrained behavior decreased. The influence of the depositional method on specimen behavior also was found to increase with silt content, particularly at lower densities. These findings therefore are of special interest with regard to laboratory testing for the purpose of characterizing liquefaction potential, where loose, silty sands may be encountered. A description and analysis of five different depositional techniques is provided. These methods include: dry funnel deposition, water sedimentation, slurry deposition, mixed dry deposition, and air pluviation. The results of the undrained testing are analyzed using void ratio after consolidation and silt content as the bases of comparison. Key words: density, deposition, depositional method, fines, liquefaction, sand, silt, specimen reconstitution, stress-strain, undrained testing. On presente les resultats d'une etude experimentale en laboratoire sur un sable silteux. Des essais de compression triaxiale non drainee ont ete realises sur le sable du Nevada contenant un silt non plastique. Tous les specimens ont ete soumis a un chargement monotonique apres une consolidation isotrope sous 25 kPa. Diverses techniques de deposition ont ete utilisees pour creer des specimens dans le but de comparer leur comportement contrainte-deformation a l'interieur de trois plages separees de densite et de trois teneurs en silt. Lorsque la densite croit, l'effet de la methode de deposition sur le comportement non draine decroit. On a aussi trouve que l'influence de la methode de deposition sur le comportement du specimen croit avec la teneur en silt, particulierement aux faibles densites. Par consequent, ces resultats presentent un interet special pour les essais en laboratoire dans le but de caracteriser le potentiel de liquefaction, dans le cas ou des sables silteux meubles peuvent etre rencontres. On fournit une description et une analyse de cinq differentes techniques de deposition. Ces methodes comprennent: une deposition a sec avec entonnoir, une sedimentation dans l'eau, une deposition en boue, une deposition seche melangee, et une deposition a l'air en pluie artificielle. Les resultats des essais non draines sont analyses au moyen de l'indice des vides apres consolidation et la teneur en silt comme bases de comparaison. Mots-cles: densite, deposition, methode de deposition, fines, liquefaction, sable, silt, specimen, reconstitution, contraintedeformation, essais non draines., [Traduit par la Redaction] Introduction Past research has debated the effect of nonplastic silt content on the liquefaction behavior of sand. Many studies suggest that liquefaction resistance increases with increasing [...]

Measurements of soil bulk density profiles combined with thin-section analysis have been suggested to assess the structural seedbed degradation caused by rainfall. The effects of water table elevation and rainfall duration on surface sealing and seedbed slumping were studied on a repacked silt loam soil. Two initial water table elevations (0.3 and 0.7 m below the soil surface) and three simulated rainfall durations (15, 30, and 40 min at 30.5 mm [h.sup.-1] followed by 180 min at 7 mm [h.sup.-1]) were used. Seedbed bulk density profiles were generated using x-radiography of resin-impregnated soil slices. Macroporosity measurements using image analysis and thin-section observations showed that infilling of eroded particles in interaggregate voids and compaction of the infilled particles were the main sealing processes. Below the seal, the seedbed exhibited coalescence and welding of aggregates into larger units, which affected mainly macroporosity. A model of sealing, exponential decrease in bulk density with depth, and slumping, linear increase in bulk density with depth, adequately reproduced the measured bulk density profiles (regression RMSE range 0.057-0.106 Mg [m.sup.-3]). The change in surface bulk density increased with rainfall duration, whereas this factor did not significantly affect slumping. The highest initial water table elevation led to the highest soil surface and internal seedbed bulk densities. It was suggested that high values of soil water content led to a decrease in aggregate cohesion. Moreover, the number of wetting and drying cycles and the water content during these cycles were shown to increase the magnitude of slumping. Abbreviations: HWT, high water table; LWT, low water table; RI, roughness index; UV, ultraviolet.

Abstract: Two contrasting populations of seabuckthorn (Hippophae rhamnoides L.) from western China were employed to study their differences in adaptive responses to drought. The Daofu population was from a wetter [...]

ABSTRACT: Scioto Marsh in Hardin County, OH, was a 16,000-acre wetland area that was drained in the mid-1800s by channelizing the Scioto River to create farmland. The resulting soils are [...]

This study aimed to evaluate the effects of Eucalyptus grandis root growth on localised soil compaction and fracturing. Undisturbed soil (Kandiustox) samples subjected to root growth pressure were used, employing 2 methods to study the phenomenon: (i) micromorphological analysis of thin sections of soil samples compacted by roots of 0.3, 0.9, 1.3, 2.8, 3.5, 6.4, 8.0, 9.0, and 10.2 cm diameter, carried out in the zone under direct root influence, up to l cm from the root soil surface, compared with a reference area at a distance of 3 cm from the contact surface; (ii) a Iocalised infiltration test to assess the time taken to infiltrate one drop of water into the surface of root-compacted soils, compared with the time taken in a reference sample without root compaction. The soil compaction was greater around root diameters > 3.5 cm, and this effect was accompanied by reduced water infiltration in the soil surface at the root contact. Presence of chiseling fractures at an approximate 45° angle to the soil surface suggested helicoidal growth of the E. grandis root, causing both soil compression and shearing. At microscopic level the soil-root contact showed clay-oriented features, microfractures, fungi coatings, and micro-slickensides. The lower infiltration rate in the compacted soil-root surface is associated with both physical (compaction) and chemical (possibly hydrophobicity) mechanisms. The use of micromorphological techniques and image analysis allowed the observation and quantification of soil porosity in the vicinity of roots. Additional keywords: tree roots, rhizosphere, chiseling fractures, slickensides., Introduction Plant growth and development depend on many environmental factors including soil compaction. The harmful effect of compaction encompasses decreases in soil porosity, structure, and permeability to air and water, [...]

Compaction caused by some intensive forest management practices can reduce tree growth, but growth reduction is the result of complex interactions between soil properties and tree physiological processes, which may differ by species. We used a 7 by 7 factorial greenhouse experiment to create a matrix of bulk density ([rho]b) and volumetric water content ([[theta].sub.v],) to better understand soil compaction effects on seedling growth of: (i) ponderosa pine (Pinus ponderosa var. ponderosa Dougl. ex Laws) grown on Dome and Cohasset soils: (ii) shortleaf pine (Pinus echinata Mill.) on a Clarksville soil; and (iii) loblolly pine (Pinus taeda L.) on an Argent soil. Models of root length density (RLD) were developed using multiple regression. The general model of RLD = [b.sub.0] + [b.sub.1][[theta].sub.v + [b.sub.2] [rho]b + [b.sub.3][[theta].sup.2.sub.v] described rooting response for the Clarksville-shortleaf and Argent-loblolly soil-species combinations (p = 0.005). However, the ponderosa pine RLD response on Cohasset soil was linear and there was an interaction between [[theta].sub.v] and [rho]b in the Dome soil. Shoot mass of seedlings growing within the least limiting water range (LLWR) was greater than those growing outside the range for all soil-species combinations except the Argent-loblolly pine (p = 0.05). The loblolly pines had greater shoot mass at [[theta].sub.v] above the upper LLWR limits (aeration limiting). Least limiting water range has potential as a soil quality indicator, but seedling response was not always associated with LLWR. Root length density (RLD) response surface models in conjunction with seasonal site water data have potential for determining compaction-induced soil limitations for tree growth, but need to be field tested and calibrated for both soil and species.

Characterization of plant uptake of soil water at different points in time and space are important in evaluating seasonal water use as well as rotational dryland cropping strategies. The objective of this study was to characterize root length density (RLD) and soil water depletion patterns of cowpea [Vigna unguiculata (L.) Walp.], grain sorghum [Sorghum bicolor (L.) Moench], and sunflower (Halianthus annuns (L.)] under no tillage (NT) and stubble mulch tillage (SMT) systems in a Torrertie Paleustoll. Root length density of crops was measured from scanned images of washed root samples obtained from soil cores extracted several times during each of two growing seasons. Soil water contents were measured with a neutron moisture meter to a depth of 2.3 in at weekly intervals throughout each growing season. The RLDs of sorghum and sunflower near the soil surface increased rapidly after planting but thereafter declined whereas subsoil RLD increased throughout the growing season. Residual water contents at harvest were 28 to 93 mm greater (P < 0.05) under cowpea as compared to sorghum. As compared to the other crops, most of the additional residual water under cowpea was confined to soil depths between 0.5 and 1.7 m. Soil depths of 1.0 to 1.8 m were the most important source of stored water for sorghum and sunflower towards the end of the season. Deeper rooting and greater soil water extraction below 1.2 m depth were observed for NT as compared to SMT (P < 0.05). Results suggest that a rotation of cowpea with sorghum or sunflower would permit the stratified use of soil water and that the storage and crop use of water deep in the profile would be optimized under NT.

Many soil physical properties and crop yield are affected by compaction. The effects of compaction of two axle loads resulting from wheel traffic on soil bulk density and crop growth were investigated. Subsoiling as a method to alleviate or reduce effects of soil compaction was evaluated. As a result of compacting loads in 2000, corn (Zea mays L.) yield was reduced by 26.8 and 14.5% in 2000 and 2001. Even two years after compaction, soil bulk density was 1.6 to 6.1% greater than the zero-load from 10- to 50-cm depths by 8- and 19-Mg axle loads. Plants in compacted plots had a greater concentration of roots near the base of the plant compared with the plants in the zero-load plots. Plants in the subsoiled plots had fewer roots concentrated near the base of the plant compared with the plants in the nonsubsoiled plots for each load. Plant height was also significantly reduced by compaction. Compaction affected plant and soil properties, but subsoiling removed the compaction effect and improved soil properties, growth, and yield.

This paper presents experimental data of earth pressure acting against a vertical rigid wall, which moved toward a mass of dry sand. The backfill had been placed in lifts to achieve relative densities of 38, 63, and 80%. The instrumented retaining-wall facility at National Chiao Tung University in Taiwan was used to investigate the effects of soil density on the development of earth pressure. Based on the experimental data, it has been found that the Coulomb and Terzaghi solutions calculated with the peak internal friction angle significantly overestimated the ultimate passive thrust for the retaining wall filled with dense sand. As the wall movement S exceeded 12% of the wall height H, the passive earth thrust would reach a constant value, regardless of the initial density of backfill. Under such a large wall movement, soils along the rupture surface had reached the critical state, and the shearing strength on the surface could be properly represented with the residual internal-friction angle. The ultimate passive earth pressure was successfully estimated by adopting the critical state concept to either Terzaghi or Coulomb theory. CE Database keywords: Passive pressure; Earth pressure; Sand; Vertical angles. DOI: 10.1061/(ASCE) 1090-0241 (2002) 128:8(651)