Characterization of surface topography of sand Caracteristiques de surface de sables

This study was conducted to investigate surface characteristics of sand particles. Surface topography of sand particles was determined in 3-D using a commercially available optical profiler. Measurements were made on areas that had side dimensions on the order of 0.1 mm at a lateral resolution of 0.3 Ilm and height resolution of less than 6 nm. The 3-D representation of a surface obtained using the measurement system is analyzed to determine 3-D as well as 2-D surface texture parameters. The parameters included amplitude, spacing, hybrid (amplitude and spacing), and functional (performance related) parameters. Tests were conducted on two silica sands: one rounded and one angular. The tests were conducted in 2 sets, initially single measurements were made on multiple particles and then multiple measurements were made on a single sand particle. Results of the analysis indicated that surface texture parameters were statistically dissimilar for the rounded and angular sands. In addition, single measurements can be used to investigate surface texture characteristics of sands. RESUME Cette etude a ete effectuee pour examiner les caracteristiques de surface de particules de sable. Les caracteristiques de surface des par­ ticules de sable ont ete determinees a I'aide d'un systeme de balayage optique en 3 D commercialement disponible dans Ie marche. Les mesures ont ete faites sur les surfaces qui ont des dimensions laterales de l'ordre de 0, I mm aune resolution laterale de 0,3 Ilm et une resolution verticale de moins de 6 nm. La representation en 3 D d'une surface obtenue utilisant Ie systeme de mesure est analysee pour determiner les parametres de texture de surface aussi bien en 3 D qu'en 2 D. Les parametres pris en consideration sont I'ampli­ tude, l'espacement, une variable hybride constituee a la fois de l'amplitude et de l'espacement, et un parametre fonctionnel, soit la per­ formance de I' essai. Les tests ont ete effectues selon deux groupes de sables siliceux : un arrondi et un angulaire. Les essais ont ete menes sur deux (2) series; initialement les mesures optiques sont effectuees d'abord par I'examen individuel des grains sur un en­ semble constitue d'une multitude de particules et ensuite les mesures ont ete effectuees grain par grain. Les resultats de I' etude ont in­ dique que ces parametres de texture de surface etaient statistiquement dissemblables pour les sables arrondis et angulaires. Enfin, les mesures individuelles peuvent etre utilisees pour examiner les caracteristiques de texture de surface de sables. INTRODUCTION variably interact with different soil surfaces. This phenomenon has implications for contaminant transport as well as remedia­ Size, shape, and surface characteristics of soil particles can tion analyses (Sharma and Reddy, 2004). have significant effects on the engineering properties and be­ Even though the effects of surface characteristics of soils on havior of soil masses. The interaction between adjacent parti­ the engineering behavior of soil masses are recognized, surface cles and in tum, the overall fabric, is affected by texture due to texture characteristics have generally been represented using the contacts made at the asperities present on the surface of simplistic, qualitative analysis or texture characteristics have soils. Surface texture of soil particles can affect both mechani­ been lumped into generalized empirical terms that describe the cal and transport properties of granular soils. Specific surface of effects of these parameters on soil behavior (Mitchell, 1993). soils depends on surface roughness. The contact area and re­ The main reason for this trend has been the difficulty of accu­ sulting contact stresses affect shearing resistance and deforma­ rate and representative determination of surface texture charac­ tion characteristics of coarse-grained soils (Mitchell, 1993). teristics of soil particles. Recent developments in image and Both peak shear strength and void ratio range for sands were microscopy analyses methods allow for detailed quantitative experimentally determined to be functions of surface roughness analysis of surface texture of soils. This study was conducted to (Oda et aI., 1971 as referenced by Matsushima and Konagai, determine the surface texture characteristics of sands using opti­ 2001). Similarly, Matsushima and Konagai (2001) determined cal profilometry. that peak shear strength increased with surface roughness using numerical analysis. Koplik et al. (1984) stated "a long-standing problem in the physics of random media is the calculation of 2 SURFACE TEXTURE ANALYSIS transport coefficients in terms of the medium's microscopic ge­ ometry." Conduction through soils (hydraulic, chemical, ther­ Texture parameters that are commonly used in surface metrol­ mal, electrical) is affected by surface characteristics due to tex­ ogy analysis include amplitude, spatial, hybrid, and functional ture effects on contact between particles as well as texture parameters (Whitehouse, 2002; Cohen, 2004). These parame­ effects on void structure and void size distribution. In hydraulic ters may be determined on raw (unfiltered) profiles (referred to analyses, saturated hydraulic conductivity of granular soils has as preliminary profiles) directly or on filtered profiles at rough­ been described as a function of pore shapes and tortuosity fac­ ness, waviness, or form scales. Roughness scale is used com­ tors in addition to void ratio, which are all affected by surface monly in the surface metrology discipline and is also adopted in roughness. Wetting characteristics of soils are also affected by this study. Use of notation Rj describes parameter "i" deter­ surface texture. Solid matter present in pore liquids can have mined at the roughness scale. 2-D parameters are provided in this section for simplicity. Similar concepts are applicable to the determination of these parameters in 3-D. The common amplitude parameters include average rough­ ness (R,); RMS roughness (~); second and third moments of height distribution: skewness (Rsk) and kurtosis (Rku), respec­ tively; maximum peak-to-valley height (R,); average height of high peaks (Rpm); average depth of low valleys (Rvm); and aver­ age peak-to-valley height (Rz). R, is determined as: